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This is to certify that the
dissertation entitled

Evaluation of Orchard Floor Management Systems for apple
orchards under organic protocol: effect on soil organic matter and
nitrogen, nematode community, root architecture and development,

and rootstock performance.

presented by

Dan'o Stefanelli

has been accepted towards fulﬁllment
of the requirements for the

Ph.D degree in Horticulture

 

 

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EVALUATION OF ORCHARD FLOOR MANAGEMENT SYSTEMS FOR APPLE
UNDER ORGANIC PROTOCOL: EFFECT ON SOIL ORGANIC MATTER AND
NITROGEN, NEMATODE COMMUNITY, ROOT ARCHITECTURE AND
DEVELOPMENT, AND ROOTSTOCK PERFORMANCE.

By

Dario Stefanelli

A DISSERTATION
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
Department of Horticulture

2006

Abstract
Evaluation of Orchard Floor Management Systems for apple orchards under
organic protocol: effect on soil organic matter and nitrogen, nematode community, root
architecture and development, and rootstock performance.
By Dario Stefanelli

Orchard ﬂoor managements systems (OFMS) play the fundamental role in
establishing the soil conditions for tree growth. Organic growers rely on the soil food
web to provide nutrient availability for the plant. A change in soil biology by changing or
modifying OFMS could reﬂect on the food web, the plant root responses, and ultimately
the tree production.

With this experiment we evaluated the effect of three different OFMS on soil
nitrogen, food web structure, tree root dynamics and architecture, and responses of three
rootstocks. The experiment was conducted in an organically certified (Organic Crop
Improvement Agency - OCIA) orchard of “Paciﬁc Gala”. Three rootstocks were
evaluated: M.9 NAKB 337 (dwarﬁng), M.9 RN 29 (semi-dwarﬁng), and Supporter 4
(semi-vigorous). Three OFMS were used: Mulch of alfalfa hay (MU), propane Flaming
(FL), and strip tilling at each side of the tree row while natural vegetation was allowed to
grow undisturbed on the tree row (Swiss Sandwich System, SS). The effect of OFMS was
evaluated by measuring SOM and N content at 2 depths (0—10 and 0-30 cm). The effect
on soil biology structure was measured by the relative percentage of the populations
categorized by feeding habit. Root infections by mycorrhizae and number of root feeders’
nematodes in the roots were also measured. Fine root responses to the soil conditions

were measured by minirhizotrons only in MU and SS, while the response of the root

distribution was measured by trenching in the soil proﬁle in all the treatments. These last
two measurements were performed only on M.9 NAKB 337 rootstock.

The Mulch treatment had the highest values of SOM and N with no differences
between the SS and FL treatments. These parameters are still growing in MU while they
seem stabilized in FL and SS. This had an effect on the structure of the soil biology.
Mulch presented the highest number of bacterial feeding nematodes (85% against 60% of
SS and FL) with continued increases. Swiss Sandwich and FL had higher fungal feeders,
which play an important role in nutrient release in depleted soils and higher root feeding
nematodes, both in soil and in roots, but the trees did not suffer. Flame and SS presented
the highest number of mycorrhizal infection in roots. A positive linear correlation
between root infection % and number of spores in the soil was found.

Supporter 4 had the highest values in all the growth parameters. M.9 RN 29
showed the highest values of production parameters both in FL and SS where there was
less N content.

Root architecture was affected by the OFMS. Mulch and FL had almost the same
root frequency along the soil proﬁle, with the majority of the roots localized closer to the
surface and to the tree trunk inside the weed free area of the treatments. Swiss Sandwich
had a more expanded root system both vertically and horizontally. Fine root development
was also affected by the OFMS. Swiss Sandwich had a higher ﬁne root lifespan (50-60
day against 30 of MU) possibly related to the lower N content in the soil and a higher %
of very ﬁne roots (0.2-0.4 mm) deeper in the soil proﬁle.

Overall, SS seemed to be a better balanced OFMS and if coupled with M.9 RN 29

it could help organic apple growers in Michigan.

Copyright by
DARIO STEFANELLI

2006

AKNOWLEDGEMENTS

I would like to acknowledge the members of my Guidance Committee for their
time dedicated, advice, and the excellent relationship that developed.

I want to especially thank my major professor, Dr. Ron Perry for giving me the
wonderful opportunity to come to Michigan State University and start this work. He gave
me continuous advice and directions during my work, as well as support, both at
professional and personal level. I want to thank him and his family for the ﬁ'iendship
showed, they made me part of their family and they are true friends. I also want to thank
Dr. Jim Flore for the ideas and advice that he gave continuously and also for his
friendship; Dr. Franco Weibel, for his support and experience in the horticultural aspect
of the project, without his development of the Swiss Sandwich System this work would
have not been done; Dr. George Bird for his advice and experience in the soil biological
aspect of the project; Dr. John Biembaum for his advice in sustainability.

An important support was received in the form of friendship, discussion,
suggestion, and idea sharing from numerous students and colleagues. Special thanks go to
Dr. Roberto Zoppolo with which I shared a good friendship as well as hard ﬁeld and
laboratory work; to Paolo Sabbatini, Costanza Zavalloni, Mauricio Canoles, Marlene
Ayala, Daniele Trebbi, Adriana NiKoloudi, Steve Berkheimer, Michael Jost, and Randy
Vos for their friendship.

Special recognition and appreciation to the staff and personnel at Clarksville
Horticultural research Station, especially to Jerry Skeltis, Gail Byler, and Denise

Ruswerma for their prompt support and efﬁciency in the different activities related to my

ﬁeld work; also to the summer students that helped me collect the data in the ﬁeld, Sara
Byler, Aaron Perry, Brian, and Aaron Manshaim and all the numerous others.

Special recognition goes to Jon Dahl and the stuff of the MSU Soil and Plant
Nutrient Laboratory, as well as Fred Warner of the MSU Nematode Diagnostic
Laboratory, for their work.

A special thank to Sasha Cravchenko for her advice in the statistical aspect of my
project.

A very kind thought goes to all the Italian friends present at MSU that helped me
feel a bit more at home and lessened the loneliness of being in a foreign Country.

A special recognition goes to my parents, Vittore e Silvia, my grand parents,
Emma and Delio, my brother Enrico and his wife Francesca, for their constant support,
without them I could have not made it to MSU.

Finally I would like to acknowledge Project Green, SARE, and INIA for the

economical support of this project.

vi

TABLE OF CONTENTS

LITERATURE REVIEW ............................................................................................... 1
CHAPTER 1. Soil nitrogen, organic matter and nematode communities as affected

by ground ﬂoor management in apple orchard under organic protocol. ........................ 12
Abstract ........................................................................................................................... 12
Introduction .................................................................................................................... 14
Materials and Methods ................................................................................................... 18
Results ............................................................................................................................ 25
Discussion ....................................................................................................................... 29
Conclusion ...................................................................................................................... 34
Literature cited ................................................................................................................ 36
Figures ............................................................................................................................ 40

CHAPTER 2. The Response of “Paciﬁc Gala” on three Rootstocks to three Orchard

Floor Management Systems under Organic Protocol ..................................................... 47
Abstract ........................................................................................................................... 49
Introduction .................................................................................................................... 50
Materials and Methods ................................................................................................... 53
Results ............................................................................................................................ 60
Discussion ....................................................................................................................... 63
Conclusion ...................................................................................................................... 66
Literature cited ................................................................................................................ 68
Figures ............................................................................................................................ 71

CHAPTER 3. Effect of Orchard Floor Management Systems on Root

Architecture of “Paciﬁc Gala” on M.9 NAKB 337 under Organic Protocol ................. 78
Abstract ........................................................................................................................... 78
Introduction .................................................................................................................... 80
Materials and Methods ................................................................................................... 82
Results ............................................................................................................................ 88
Discussion ....................................................................................................................... 92
Conclusion ...................................................................................................................... 95
Literature cited ................................................................................................................ 96
Figures ............................................................................................................................ 98

vii

CHAPTER 4. Root Development of Apple as Affected by Orchard Floor

Management Systems under Organic Protocol. ...................................... 104
Abstract ........................................................................................................................... 104
Introduction .................................................................................................................... 106
Materials and Methods ................................................................................................... 110
Results ............................................................................................................................ 116
Discussion ....................................................................................................................... 119
Conclusion ...................................................................................................................... 122
Literature cited ................................................................................................................ 123
Figures ............................................................................................................................ 126
CONCLUSION .............................................................................................................. 137
LITERATURE CITED ................................................................................................... 143

viii

LITERATURE REVIEW

Organic agriculture focuses on soil management systems and a common phrase
used to characterize organic growing is, “Feed the soil, not the plant”. Organic matter
plays a central role in the building of a healthy and productive soil (Magdoff and van Es,
2000). In organic fruit production, in contrast to conventional production that relies on
regular fertilization, one of the main goals is to build organic matter in the soil (Bloksma,
2000). Organic matter is also an indicator of carbon sequestered in the soil (Stevenson,
1994).

A goal in organic agriculture is the development and implementation of an
integrated approach to agriculture that considers potential impacts on the environment
and the soil (FAOa). Consideration of biological, chemical and physical implications of
land use and management practices and of ecological principles will allow agricultural
productivity to be sustained in low and high input agricultural systems. Effective soil
biology management will provide opportunities for enhancing productivity and for the
restoration of degraded soils (FAOb). Orchard ﬂoor management systems in orchards are
the main tool to implement these concepts.

Orchard ﬂoor management systems available to organic growers are limited.
Unlike herbaceous crops, limitations exist in woody perennial crops that restrict the
incorporation of soil amendments. Also in organic fruit production there is the need for a
more sustainable approach to weed management that is compatible with organic

protocols and also provides careful utilization instead of suppression (Sooby, 1999).

Orchard ﬂoor management systems (OFMS) affect soil conditions and
consequently nutrient availability, tree growth and yield (Yao et a1, 2005). Organic
growers have to rely on the soil food web to obtain the nutrient availability for the plants,
since the N release varies with the quantity and quality of the amendments and the soil
environment (Myers et al., 1997; Wardle and Lavelle, 1997; Magdoff and van Es, 2000;
Brady and Wei], 2002). OFMS will change the microbial composition of the soil (Yao et
a1, 2005). There have been several studies on the effects of soil management systems on
soil microbes and the structure of the soil food web (Mader et al., 2002; Ferris et al.,
2004; Yao et al., 2005). Most of these studies were on herbaceous crops (Ferris et al.,
1996; Robertson et al., 1997) and very few on apples (Forge et al., 2003; Yao et al,
2005). Rhizosphere microorganisms may affect the hormonal balance and competitive
ability of the plant, which will modify the rhizosphere community and the ecosystem (El-
Shatnawi and Makhadmeh, 2001). Factors that are more likely to enhance stability of the
soil microbial biomass are more likely to enhance nutrient conservation in the soil
(Wardle and Nicholson, 1996). Alleviating stress on the microbial community has
stabilizing effects (Wardle, 1998). Factors that stabilize the microbial biomass reduce
turnover, and are likely to have important consequences for soil nutrient dynamics and
ultimately plant growth and ecosystem productivity (Wardle, 1998).

The more active microorganisms in the organic system control the release of
available nitrogen to the trees in the soil (Forge et al., 2003). OFMS provide organic
forms of C and N which are quickly metabolized to inorganic nitrogen and other
nutrients, primarily by bacteria and fungi (Ferris et al., 1998). N is also mineralized as

predators of bacteria and fungi, such as protozoa and microbivorous ("microorganism

eating") nematodes, graze on prey which contain more N than required by the predators
(Ferris et al., 1998). Although more research attention is given to the plant parasitic
nematodes, microbivorous organisms make up a large portion of the nematode
community. Excess N generated by grazing is released to the soil and becomes available
for plant uptake (Ferris et al., 1998). Nematodes feeding types play an overall positive
contribution to soil and thus ecosystem processes (Yeates, 1987; Bongers and Ferris,
1999; Bardgett et al., 1999). Nematodes can be used as indicators of soil ﬁmctional and
biodiversity aspects (Yeates, 2003) since they reﬂect the soil and ecological processes
(Yeates, 1999). Most of the studies on the beneﬁts of nematodes on nutrient release and
availability in the soil have been done on the bacterial and fungal feeder nematodes.
Bacterial feeders are responsible for a higher release of N when soil conditions are closer
to optimal (Ferris et al., 1996; Ferris et a1, 1997; Laakso et al., 2000; Forge et al., 2003)
while ﬁrngal feeders have a greater effect when soil conditions are not optimal (Ingham et
al., 1985; Ferris et al., 1998; Ferris and Chen, 1999; Ferris et al., 2004). Most of the
current ecological research agrees that a food web becomes more beneﬁcial with
increased structure and diversiﬁcation (Power, 1992; Paine, 1996; Sugihara et al., 1997;
Garlaschelli, 2004).

The interaction between the OFMS and soil food web will have an impact on
edaphic conditions and nutrient availability. The degree to which kinetics of nutrient
uptake or other potential adjustments are expressed would ultimately depend on soil
nutrient availability and soil factors that determine nutrient transport to the root surface

(Bassirirad, 2000). The retention of nutrients within an ecosystem depends on temporal

and spatial synchrony between nutrient availability and nutrient uptake (Tierney et al.,
2001).

Plant root systems have the ability to adjust nutrient acquisition capacity to meet
variation in shoot demand caused by environmental changes (Chapin, 1980; Clarkson and
Hanson 1980; Clarkson 1985). Plant roots can alter water and nutrient absorption by
adjusting physiological longevity, morphological and/or architectural characteristics to
meet changes in shoot nutrient demand (Chapin, 1980; Clarkson and Hanson 1980;
Clarkson 1985). It becomes important then, to evaluate the usefulness of root parameters,
such as lifespan and turnover, as indicators of growth potential of the plant and its actual
nutrient acquisition (Bakker, 1999).

Roots, and ﬁne roots in particular, play a central role (Schulze et al., 1997) in soil
chemical (pH, 02, C02 and other chemicals), physical (moisture and aeration), and
biological (soil pathogens, beneﬁcial microorganisms and allelopathy) composition
(Makhadmeh and El-Shatnawi, 2001) with important consequences for plant growth and
productivity, plant competition, biological activity, and carbon and nutrient cycling at an
ecosystem scale by releasing in the soil a wide variety of exudates (Makhadmeh and El-
Shatnavvi, 2001; Bertin et al., 2003; Walker et al., 2003). Plants expend a substantial
proportion of photosynthate below ground in the annual production of ﬁne roots
(Eissenstat et al., 2000) and release of exudates (Walker et al., 2003). In many cases,
more than 50% of annual net primary production is allocated below ground, and the
return of nutrient to the soil by tree ﬁne root death may exceed that of the above ground
litterfall (Kasuya N., 1997). Tree root turnover may return four to ﬁve times more carbon

to the soil than above ground litter (Zech and Lehrmann, 1998). Consequently there is a

need to include the effects of root turnover in models of carbon and nutrient cycling (Cox
et al., 1978; Vogt et al., 1986; Hendricks et al., 1993; Jackson et al., 1997; Norby and
Jackson, 2000).

Moreover, through the exudation of a wide variety of compounds, roots regulate
the soil microbial community in their immediate vicinity, cope with herbivores, and
encourage beneﬁcial symbioses (Nardi et al., 2000, Walker et al., 2003).

Assessing root turnover is very important as an indicator of plant productivity and
a measurement of carbon return to the soil. In the last decade the most common technique
to measure ﬁne root turnover is by minirhizotrons installed in the ground. They can be
used to characterize ﬁne root production, phenology, growth, mortality and lifespan, and
are useful in developing ecosystem carbon budgets (Hendrick and Pregitzer, 1996; Majdi,
1996). Data reliability depends on the accuracy of assessing physiological status of the
roots (alive or dead) (Wang et al, 1995; Tingey et al, 2000) mostly based on color
(Hendrick and Pregitzer 1992a, b; Comas et al, 2000).

However, the determination of ﬁne root physiological status is a common
problem (Comas et al., 2000). Also there is a certain inconsistency in the deﬁnition of the
proper diameter for ﬁne roots. Lately, several authors reported that, for woody perennials,
ﬁne roots should be 2 1 mm in diameter (McCrady and Comerford, 1998; Eissenstat et al,
2000; Comas and Eissenstat 2001).

Processes and responses vary not only with root diameter, but with other root
characteristics as well (Norby and Jackson, 2000). It is necessary to couple the total size
of the root system with physiological information on the response of root speciﬁc nutrient

uptake efﬁciency (Norby and Jackson, 2000). The size of the root system and its

efﬁciency to deploy roots at the time and place nutrients are present (Fitter et al., 1991),
as well as the efficiency by which a particular root segment can take up a nutrient from
the soil solution (Norby and Jackson, 2000), are fundamental for the plant uptake
capacity (Tjeerd et al., 2001). The degree to which kinetics of nutrient uptake or other
potential adjustments are expressed would ultimately depend on the availability of soil
nutrients (Tjeerd et al., 2001) and soil factors that determine transportation of nutrients to
the root surface (Bassirirad, 2000). The retention of nutrients within an ecosystem
depends on temporal and spatial synchrony between nutrient availability and nutrient
uptake. Disruption of ﬁne root processes can have dramatic impacts on nutrient retention
(Tierney et al., 2001).

In general, increased N concentrations in the soil decrease ﬁne root turnover
because of increased root lifespan (Pregitzer et al., 1993; Ostonen et al., 1999; Burton et
al., 2000; Hendricks et al., 2000; King et al., 2002), allowing the plant to reduce carbon
costs. However, several authors report that with increased N concentration in soil, root
turnover rates accelerate reducing ﬁne root lifespan (Aber et a1, 1985; Nadelhoffer et al.,
1985; Persson and Ahlstrom, 2002). Burton et a1. (2000), in an experiment on ﬁne root
(<1 mm) dynamics within and across forest species related to different ranges in N
availability, found that root lifespan decreases with increasing N availability, while
within species there is the opposite trend. Tjeerd et a1. (2001) found that citrus ﬁne root
life span was diminished in P depleted soils.

In any case all the authors agree on the importance of the interaction between N

availability and ﬁne root dynamics, especially for the effects on organic matter

(McClaugherty et al, 1982), on the organic N pool in the soil (Ehrenfeld et al., 1997) and
on the control of the substrate quality (Hendricks et al., 2000).

Root turnover has been extensively studied in grassland and forest ecosystems,
but there is not much literature on fruit trees and none in organic tree production.

The ability of trees to adapt their roots dynamics to different soil conditions is not
limited only to life span, turnover and nutrient uptake, but is extended to entire root
system architecture.

Plants tend to expand their root system (both vertically and horizontally) in
response to drought conditions (Schenk and Jackson, 2002). This ﬁnding is also
conﬁrmed in fruit trees in response to irrigation and drought stress (Perry et al., 1983;
Layne et al., 1986; Bassoi et al., 1998; Smart et al., 2006). Soil type also affects root
distribution. Soil properties, such as the presence of soil proﬁles impermeable to root
penetration, stoniness, and presence of gravel lenses, have a greater inﬂuence on depth
distributions than does genotype, even in deep fertile soils (Smart et al., 2006). Higher
fertility tends to increase root density, induce a more superﬁcial root system and/or
encourage localized rooting in the more fertile area (Lyons et al., 1962; Smith, 1965).
Root architecture also responds to competition from other species, which reduces the
amount of roots in the competitive area and expands it both horizontally and vertically as
a result (Atkinson and White, 1976; Glen and Welker, 1989; Parker, 1993; Merwin and
Stile, 1994; Merwin et al., 1995).

Ground ﬂoor management practices, in regards to perennial woody species, which
can reduce nutrient uptake competition by inﬂuencing root morphology, have great value

in conventional and sustainable systems. It is important to develop OFMS that will

optimize productivity without disrupting soil-food web-root processes. It is a goal not
easily achieved, given the restriction of the organic protocols, which create different
edaphic conditions than conventional management. Therefore, an OF MS needs to be
implemented which will create the best environment for tree growth allowing the
maximization of its performance (Weibel, 2002).

Another form of management that growers can use is the selection of beneﬁcial
herbaceous species that can coexist with woody perennials. In the case of fruit trees,
rootstocks can be selected that vary in reaction to ﬂora competition, edaphic conditions,
disease resistance, and vigor and production characteristics that they induce on the scion
(Ferree and Carlson, 1987). There are extensive research programs that focus on
rootstock evaluation for the above mentioned characteristics, but managed with
conventional practices, and often under optimal growing conditions. This factor alone
reduces the utility of the rootstock outside of those conditions. Thus inducing the growers
to adapt their orchard conditions to the optimal in which the rootstocks were tried.
Environmental factors seem to be more inﬂuential on the uptake of nitrogen and
phosphorus than the rootstock genotype (Kennedy et al., 1980), but not enough is known
on the subject. There is a strong relationship between genetic (vigor) and environmental
factors in determining the adaptability of the root system, and consequently its capability
of nutrient uptake and tree performance under adverse conditions.

In this study we decided to evaluate different organic OFMS that present different
practical and rationale approaches to management. We avoided a comparison that allows

the entire ground ﬂoor area inhabited by competitive indigenous herbaceous ﬂora as a

treatment. Numerous studies have been conducted over many years demonstrating the
detrimental effect of this practice (Merwin and Ray, 1997; Giovannini et al., 1998).

Mulching keeps the soil free from weed competition, keeps soil moisture and
temperature constant, increases organic matter through its decomposition, releases
nutrients to the soil, and improves the soil environment, enhancing the microbial activity
(Merwin and Stiles, 1994; Merwin et al., 1995; Marsh et al., 1996; Lloyd et al, 2000).

Tillage of the entire orchard ﬂoor also keeps the soil free from weed competition
but encourages soil compaction, reduces internal soil water drainage, accelerates
superﬁcial organic matter losses (Merwin and Stiles, 1994) and disrupts and injures
surface roots by mechanical cultivation (Cockroft and Wallbrink, 1996). Tillage is still
widely used in the world even if it is expensive, requires specialized machinery, and
encourages risks of water run-off.

Recently a modiﬁed tilling system has been implemented in Switzerland, called
the Swiss Sandwich System. It consists of a strip where spontaneous vegetation is
allowed to grow on the tree row and two shallow tilled narrow strips at each side of the
tree row. This system permits predator insects to complete their cycle in the volunteer
weeds that grow on the tree row, becoming more efﬁcient in controlling pests and
diseases, and increasing biodiversity (Luna and Jepson, 1998; Horton, 1999; Schmid and
Weibel, 2000; Galoach, 2002). The resulting weeds in the tree row can be considered as
cover crops by contributing to the prevention of soil erosion, increasing soil organic
matter, assisting to the recycling of soil nutrients, and helping in reducing the amount of
nitrate runoff and leaching from the soil (Miles and Chen, 2001). This system also

simpliﬁes management, since there is no need to reach under the tree canopy to mow

weeds or till (Schmid and Weibel, 2000; Schmid et al.; 2001; Weibel, 2002; Weibel and
Haseli, 2003). There is less chance for harm to tree trunks by passing implements. The
two strips of shallow tilled bare soil reduce weed competition for water and nutrients
(Merwin and Ray, 1997) and increase yield and fruit size of apples (Schupp and McCue,
1996).

Flaming of herbaceous weeds is another practice used by organic growers (Gourd,
2002; Robinson, 2003). The impacts of this system are relatively unknown. Some
drawbacks include initiation of spontaneous ﬁres, damage to the trees, encouragement of
rodents (Zoppolo, 2004), need of special equipment, and usage of valuable energy source
(propane).

Since organic OFMS do create environmental conditions and stresses that are
different from the conventional ones under which rootstocks are normally evaluated,
perhaps differences in rootstock vigor can compensate for different conditions.

We therefore hypothesize that the different soil conditions that OFMS creates will
have an impact on all factors involved in soil processes, including plant roots (both ﬁne
and at system level). Eventually, the best OFMS should create a balanced and self
sustaining edaphic condition. We also hypothesize that the right rootstock, with different
vigor, can compensate for stresses imposed by an organic OF MS, thus improving above
ground performance.

The objectives of this research were: 1) to determine the effect of OFMS on soil
nutrition and SOM; 2) to estimate the effect of OFMS on the soil food web; 3) to
determine the effect of OFMS on ﬁne root development; 4) to estimate the effect on root

architecture; 5) to evaluate rootstock performance related to the soil condition established

10

by OFMS treatments. The overall objectives are to determine the best OFMS for the

growers coupled with the ideal rootstock to maximize production.

11

Abstract
CHAPTER 1. Soil Nitrogen, Organic Matter and Nematode Communities as Affected
from Orchard Floor Management Systems in Apple under Organic Protocol.
By Dario Stefanelli

A common phrase used to characterize organic growing is “Feed the soil, not the
plant”. In organic agriculture the consideration of biological, chemical and physical
implications of land use and management practices and of ecological principles will
allow agricultural productivity to be sustained in low and high productive environments.
Organic growers can implement these concepts by using different Orchard Floor
Management Systems (OF MS) that provide organic forms of C and N, which are quickly
metabolized primarily by bacteria and fungi. Nitrogen is also mineralized by predators of
bacteria and fungi; for this reason nematode feeding types play an overall positive
contribution to soil and thus ecosystem processes. Nematodes can be used as indicators of
soil functional and biodiversity aspects since they reﬂect the status of soil and ecological
processes. Fungal feeders have a higher effect in water and nutrient depleted soils.
Orchard ﬂoor management systems will change the microbial composition of the soil.
The objectives of this experiment were: 1) to determine the effect of the OFMS on the
nutritional status of the soil; 2) to evaluate the different structures of the food web; 3) to
determine which system would create a more suitable environment to maximize tree
pcrformance.The experiment was conducted in an organic certiﬁed orchard of apple
cultivar “Paciﬁc Gala”. Three OFMS treatments were implemented: mulch of alfalfa hay
(MU), propane ﬂaming (FL), and strip tilling at each side of the tree row where natural

vegetation was allowed to grow undisturbed in the tree row (Swiss Sandwich System,

12

SS). We evaluated the effect of the treatment on soil nutrition by measuring SOM and N
concentration at 2 depths (0-10 and 0-30 cm) for 4 years. The effect on food web
structure was measured, 4 times in 2 years at ﬁxed intervals, by the relative percentage of
the populations divided by feeding habit. We also measured root infection by
mycorrhizae and root feeder nematodes in the roots. The mulch treatment had the highest
values of SOM, and nitrogen in the soil at both sampling depths, but had the least
structured food web with the majority of the populations represented by bacteria feeding
nematodes. One positive factor was that it showed the lowest percentage of herbivore
nematode species. Soil organic matter and mineral nitrogen was lowest in SS. Soil
organic matter is progressively decreasing at 0-10 cm depth in the tilled area and
increasing at the deeper sampling (due to tilling), while mineral N is decreasing in the
vegetated area at 0-10 cm depth (due to higher competition). The food web structure is
more balanced in SS than MU, with the vegetated area having highest values of herbivore
nematodes and root mycorrhizal infection, while the tilled area has the highest value of
fungivores with a similar percentage to MU of root mycorrhizal infection. Flaming
produced similar soil conditions as the Swiss sandwich, having a reduction in SOM at 0-
10 cm. Soil food web structure and percentage of feeding habit nematode populations
was similar for FL and SS suggesting that the two treatments have less SOM and N than
MU, but they are coping through a shift in microbial populations. Based on this study
there is a high correlation between the amount of mycorrhizal spores in the soil and the
percentage of infection in the apple roots. Overall, tree performance and soil microbial
conditions for SS compare similarly with FL, where all weeds are suppressed. Data

supports further study of this system for organic apple growers in Michigan.

13

Introduction

Organic agriculture focuses on soil management systems and a common phrase
used to characterize organic growing is, “Feed the soil, not the plant”. Organic matter
plays a central role in the building of a healthy and productive soil (Magdoff and van Es,
2000). In organic fruit production, in contrast to conventional production that relies on
regular fertilization, one of the main goals is to build organic matter in the soil (Bloksma,
2000). Organic matter is also an indicator of carbon sequestered in the soil (Stevenson,
1994)

A goal in organic agriculture is the development and implementation of an
integrated approach to agriculture that considers potential impacts on the environment
and the soil (FAOa). Consideration of biological, chemical and physical implications of
land use and management practices and of ecological principles will allow agricultural
productivity to be sustained in low and high input agricultural systems. Effective soil
biological management will provide opportunities for enhancing productivity and for the
restoration of degraded soils (FAOb). Orchard ﬂoor management systems are the main
tool to implement these concepts.

Unlike herbaceous crops, limitations exist in woody perennial crops that restrict
the incorporation of soil amendments. Also, in organic fruit production there is the need
for a more sustainable approach to weed management compatible with organic protocols
that provides careful utilization instead of suppression (Sooby, 1999).

Orchard ﬂoor management systems (OF MS) affect soil conditions and

consequently nutrient availability, tree growth and yield (Yao et al, 2005). Organic

14

growers have to rely on the soil food web to obtain the nutrient availability for the plants
since the N release from different sources varies with the quantity and quality of the
material used and the soil environment (Myers et al., 1997; Wardle and Lavelle, 1997;
Magdoff and van Es, 2000; Brady and Wei], 2002). Orchard ﬂoor management systems
will change the microbial composition of the soil (Yao et al, 2005).

There have been several studies on the effects of soil management systems on soil
microbes and the structure of the soil food web (Mader et al., 2002; Ferris et al., 2004;
Yao et al., 2005). Most of these studies were on herbaceous crops (Ferris et al., 1996;
Robertson et al., 1997) and very few on apples (Forge et al., 2003; Yao et al, 2005).

Rhizosphere microorganisms may affect the hormonal balance and competitive
ability of the plant, which will modify the soil biology community and the soil ecosystem
(El-Shatnawi and Makhadmeh, 2001). Factors that are more likely to enhance stability of
the soil microbial biomass are more likely to enhance nutrient conservation in the soil
(Wardle and Nicholson, 1996). Alleviating stress on the microbial community has
stabilizing effects (Wardle, 1998). Factors which stabilize the microbial biomass reduce
turnover, and are likely to have important consequences for soil nutrient dynamics and
ultimately plant growth and ecosystem productivity (Wardle, 1998).

The microorganism activity in the organic system inﬂuences the release of
available nitrogen to the trees in the soil (Forge et al., 2003). Orchard ﬂoor management
systems can provide organic forms of C and N which are quickly metabolized to
inorganic nitrogen and other nutrients, primarily by bacteria and fungi (Ferris et al.,
1998). Nitrogen is also mineralized as predators of bacteria and fungi, such as protozoa

and microbivorous ("microorganism eating") nematodes, graze on prey which contain

15

more N than required by the predators (Ferris et al., 1998). Although more research
attention is given to the plant parasitic nematodes, microbivorous organisms make up a
large portion of the nematode community. Excess N generated by grazing is released to
the soil and becomes available for plant uptake (Ferris et al., 1998). Nematodes feeding
types play an overall positive contribution to soil and thus ecosystem processes (Yeates,
1987; Bongers and Ferris, 1999; Bardgett et al., 1999). Nematodes can be used as
indicators of soil functional and biodiversity aspects (Yeates, 2003) since they reﬂect the
soil and ecological processes (Yeates, 1999). Most of the studies on the beneﬁts of
nematodes on nutrient release and availability in the soil have been done on the bacterial
and fungal feeder nematodes. Bacterial feeders are responsible for a greater release of N
when soil conditions are closer to optimal (Ferris et al., 1996; Ferris et al, 1997; Laakso
et al., 2000; Forge et al., 2003) while fungal feeders have a higher effect when soil
conditions are not optimal (Ingham et al., 1985; Ferris et al., 1998; Ferris and Chen,
1999; Ferris et al., 2004). A food web becomes more beneﬁcial with increased structure
and diversiﬁcation (Power, 1992; Paine, 1996; Sugihara et al., 1997; Garlaschelli, 2004).
The interaction between the OFMS and the soil food web has an impact on
edaphic conditions and nutrient availability. The degree to which kinetics of nutrient
uptake or other potential adjustments are expressed would ultimately depend on soil
nutrient availability and soil factors that determine nutrient transport to the root surface
(Bassirirad, 2000). The retention of nutrients within an ecosystem depend on temporal

and spatial synchrony between nutrient availability and nutrient uptake (Tierney et al.,

2001).

16

Orchard ﬂoor management systems that support the most diversiﬁed food web
will be able to reach a balance in time with an increased probability of a self sustainable
environment, thus increasing the long term productivity of the plants.

In this experiment we evaluated three different OFMS for their rationale and input
of organic material to the soil. One has a constant addition of N containing organic
material (alfalfa hay mulch added twice yearly), another has the constant destruction of
organic material on the soil surface (ﬂaming), and the last one is a combination between
modiﬁed cover crop (natural vegetation never mowed) and tillage.

We hypothesize that these differences in management will have an impact on the
soil N concentration and organic matter content and therefore will impact the soil food
web structure and diversity.

Our objectives were: 1) to determine the effect of the OFMS on the nutritional
status of the soil; 2) to evaluate the structure of the soil food web; 3) to determine which

system would create a more suitable environment to maximize tree production.

17

Material and Methods.

The experiment was conducted in an orchard of cultivar “Paciﬁc Gala” (Malus x
domestica Borkh.) apple established in April 2000 at the Clarksville Horticultural
Experiment Station. The orchard was certiﬁed organic by the Organic Crop Improvement
Association (OCIA) in 2003 and 2004 and Organic Grower of Michigan (OGM) in 2005.

The site was previously farmed with conventional soybean-com-corn-alfalfa rotation for
two cycles until 1998. Subsequent soil preparation consisted of sowing of buckwheat and
chicken compost (1250 kg/ha) and lime (2250 kg/ha) application in 1999 on the entire
surface. At plantation (April 2000) a mixture of red mammoth clover and endophytic rye
was sown in the alleys.

The predominant soil type of the orchard is Kalamazoo sandy clay loam (Typic
Hapludalfs) with 53.1% sand, 23.1% silt, and 23.8% clay. The orchard presents mild
slopes (less than 3%).

Drip irrigation with drippers of 2.3 L/h every 0.6 m was installed in May 2001 and
suspended from the lowest wire of the trellis on the tree row. All orchard ﬂoor
management systems received equal irrigation throughout the season. Soil moisture was
measured by time domain reﬂectometry (TDR) using a Mini Trase 6050X3 (Soilmoisture
Equipment Corp., Goleta, CA) with 45 cm long stainless steel rods permanently installed
in the tree rows in 2001, halfway between two trees and in the middle of the tilled strip in
2002. Measurements were taken for each of the 6 plots per treatment weekly in 2002 and

every other week in 2003-2005.

18

The three orchard ﬂoor management systems (OFMS) under study were established in
the beginning of the second growing season (2001) and maintained for the entire study.
The treatments consisted of mulch (MU) of alfalfa hay, the Sandwich System (SS) and
Flaming (FL) with a propane burner. The alfalfa hay mulch was laid underneath the tree
canopy in a strip of 1 m on each side of the tree and kept 15-20 cm thick. 105 round
alfalfa bales/ha were used with a C:N ratio of 15:1. The treatment was hand-applied
every spring and fall to keep the thickness of the mulch constant in order to provide a
shading effect for weed suppression, and to maintain soil moisture.

The ﬂaming treatment consists of the burning of weeds underneath the tree canopy and 1
m on each side of the tree with propane gas (estimated 56 L/ha). A custom engineered
burner, consisting of 4 burners (200000 BTU/burner) in a row, and covered with a metal
protective shield to concentrate the heat and to prevent its escaping and damaging the
canopy. On the back of the shield was also mounted a sprinkler system to extinguish
eventual ﬁres occurring during the burning. To reach the weeds underneath the canopy on
the tree row, a hand burner (150000 BTU) was used. The burner was mounted on the side
of a tractor on a hydraulic arm to better control the application of the treatment. The
treatment was applied ﬁve to six times during the year, starting at the end of April -
beginning of May and ending at the end of August. The treatment was repeated every
time the weeds would reach 10 cm high. Tractor speed was kept between 1.6 and 3.2
km/h depending on the density of the weeds to be controlled.

The Sandwich System is an adaptation of the Swiss system (Weibel, 2002) and consists
of an area 25-30 cm on each side of the tree, underneath the canopy, where spontaneous

vegetation is allowed to grow undisturbed (SVA). On each side of this vegetated area,

19

two strips of soil were kept free of vegetation (STS) by shallow tilling (5-10 cm deep).
The strips were 70 cm wide from tree planting till 2003 and expanded to 90 cm wide in
2004. Timing of the treatment application was the same as the ﬂaming treatment. The
tilling was accomplished from 2001 through 2004 with a spring-tooth (three teeth 2001-
2003, S teeth 2004) harrow mounted on a side-bar of a tractor. To improve tillage
effectiveness, a modiﬁed notch-disk tiller, mounted on the tractor side-bar, was deployed
during the 2005 growing season.

The alley consisted of an equal mixture of endophytic rye and mammoth clover
established soon after planting the orchard in 2000. Clover was also reseeded in 2005 to
keep the proportion constant. The alleys were managed equally in all treatments by
periodical mowing (3-4 times year).

Soil samples, from which the effect of OFMS on soil conditions and microbial
communities were measured, were collected for the three OFMS by mixing 20 soil core
sub-samples from the tree row. Soil samples from the alleys and the tilled strip of the SS
were obtained by mixing 10 soil core sub-samples from each side of the tree row. Soil
samples were collected four times per year (from April till November) at 0-10 and 0-30
cm depth starting from April 2001 till November 2005 to measure the temporal effect on
the soil conditions. The two depths have been chosen to represent the surface soil, where
most of the microbial processes take place (0-10 cm), and the most frequently explored
part of soil by roots (0-30 cm). The two depths also provided an indication of the effect of
depth on the soil conditions. Soil samples were stored at 4°C until the analyses were
performed.

The effects of the OFMS on the soil conditions were monitored through:

20

Soil nitrate (No3), from 2001 till 2005, and ammonium (NHJ), from 2003 till 2005,
concentration (ppm) in the soil, to check the immediate available nitrogen released
from the treatments available to the trees. The addition of the two forms of nitrogen
gave us the total available mineral nitrogen concentration. Soil samples were air dried
at 105°C for 24 hrs. Nitrates and ammonium concentration was extracted from the
soil by 100 ml of KCl 1 M on 10 g of dried soil, placed for 1 hour on a shaker and
then ﬁltered with ﬁlter paper. The extraction liquid was sent to the MSU soil lab for
the analysis of NH4+ and N03' following the procedure described by (Kenney, 1982)
using a Lachat automated colorimetric analyzer (Lachat Instruments Inc. Milwaukee,
WI).

Soil organic matter content, from 2002 till 2005, was measured by loss on ignition of
3g of dry soil, from the above described soil samples, at 400 °C for 8 hours in a
mufﬂe fumace.

Soil carbon content was calculated from the organic matter values and divided by
1.724. This value is based on the organic matter containing 58% carbon (Stevenson
1994). Values obtained from the organic matter were corrected for the relative surface
covered from each segment of the treatments (alley, tree row, and in case of the
sandwich, vegetated area and tilled strip) and reported as the treatments were
covering the entire surface of an orchard. Corrected values were then related to the
volume of soil, respectively at 0-10 and 0-30 cm depth, contained in a hectare and
showed as t/ha. Data were reported for the year 2005 and as average of the period

2002-2005 for both sampling depths (0-10 and 0-30 cm).

21

The effects of OFMS on microbial communities were measured two times during the
growing season (April and November) starting from November 2003 until] April 2005.
Nematode populations’ composition were utilized as indicators of soil functional and
biodiversity aspects (Yeates, 2003) since they reﬂect the soil and ecological processes
(Yeates, 1999). To better understand these effects, apple and grass roots were examined
for mycorrhizal infection (November 2004) and root lesion nematodes inside the roots
(August 2005). Mycorrhizae spores in the soil were correlated with mycorrhizal root
infection to determine eventual relationship between the two.

After collection, soil samples were transported to the soil nematode analysis facility of Dr
George Bird at Michigan State University in East Lansing, MI. The extraction of
nematodes and mycorrhizal spores from the soil was performed by the centrifugal-
ﬂotation (Jenkens, 1964). Nematodes were then sequentially sieved into a counting plate,
and identiﬁed at 50x magniﬁcation to families, genera and trophic group levels.
Nematode communities’ composition was calculated as percentage of each group feeding
behavior on the total number of nematodes in the soil (Bird personal communication,
2006).

Apple roots from the four treatment positions (mulch row, ﬂame row, sandwich vegetated
area, and sandwich tilled strip), as well as a composite sample of weed roots from the
vegetated area in the sandwich tree row, were collected in November 2004 were sent to
the Dr. Amarantus lab (Grant Pass, Or) to determine the percent of endomycorrhizal
infection. The percent of endomycorrhizal colonization was determined using a grid
intercept method. This method includes examination for the development of spores,

vesicles, arbuscules and fungal hyphae along the sample roots. Sampled roots are placed

22

in capsules in a 10% KOH solution in a water bath at low heat for 24 hours. The KOH is
poured off and capsules rinsed in three complete changes of tap water. Capsules are
placed in a 1% HCL mixture for 30 minutes then immediately transferred into a water
bath of Tri Pan blue for 3 hours and repeatedly rinsed. Roots from each capsule are
rinsed and chopped in segments. Segments from each capsule are examined and tallied
for percent colonization and presence of arbuscular spores of mycorrhizal fungi using a
dissecting microscope. Roots are examined on a graduated Petri dish and each root
intersection tallied as mycorrhizal or non mycorrhizal at 100 grid line crossings. Apple
roots from the four treatment positions (mulch row, ﬂame row, sandwich row, and
sandwich tilled strip) were collected in August 2005 to determine the number of root
lesion nematodes in the roots. Root lesion nematodes were extracted with the shake
method (Bird 1971) from 1 g of roots and then counted with a counting plate at 50x
magniﬁcation.

Statistical analysis was performed with SAS (Version 8, SAS Institute, Cary, NC, USA).
Analysis of variance was performed using the MIXED procedure to detect treatment
effects. In case of signiﬁcance, means were separated using the Least-square means test
(LSMEAN S) with p_<_0.05. All the soil data statistical analysis was considered separately
(to determine the effect on microbial populations) as well as repeated measures (to
determine the overall effect on microbial dynamics). Repeated measures were preformed

using block*OMFS as the subject.

23

The following timetable explains the history of the plot, sampling and measurements for

the duration of the experiment.

 

 

 

 

 

 

 

 

 

Prior Conventional soybean-com-com-alfalfa rotation (2 cycles). Last crop was com.
tol998 Minimal tillage.
1999 Spring: tillage sowing of soybean, Chicken compost (lZSOkg/ha), lime (2250 kg/ha).
Fall: tillage, sowing of Buckwheat
2000 April: tillage, tree planting. August: sowing of red mammoth clover and endophytic rye
in the alleys.
2001 May: April, June, TCA, TCAI, shoot growth, canopy
implementation of August, November: volume, leafN 0/0, SPAD
the 3 orchard ﬂoor soil sampling for
management N03"
systems.
2002 Maintenance of the April, June, TCA, TCAI, shoot growth, canopy
OFMS and tree August, November: volume, leafN 0/0, SPAD
training soil sampling for
SOM and N03'
2003 Same as above April, June, TCA, TCAI, November: soil sampling
August, November: shoot growth, for Food web
soil sampling for canopy
SON} N03- and volume, leaf
NH4 N %, SPAD,
yield
2004 Same as above Same as above Same as April and November:
above soil sampling for food
web. November: root
sampling for
Mycorrhizal infection
2005 Same as above Same as above Same as April: soil sampling for
above food web. August: root

 

 

 

 

sampling for root lesion
nematodes counting.

 

24

 

Results

Effect on soil organic matter and carbon content.

The soil organic matter content was similar between the plots prior to the
establishment of the treatments. Over the duration of the experiment the treatments did
have an effect on organic matter content. Within each year soil organic matter (SOM)
content was always signiﬁcantly higher in the alfalfa hay Mulch (MU) than in the other
treatments, except in 2002 where it was similar to the Swiss Sandwich tilled strip (STS)
for the depth of 0-10 cm (Figure 1A). Soil organic matter increased during the years in
MU, remained constant in the Swiss Sandwich vegetated area (SVA) and decreased in
Flame (FL) and in STS. For the deeper sampling (0-30 cm) there is no difference between
treatments within the year, however SOM increases during the years in MU and STS
while it remains constant in FL and SWA (Fig. 1B). No treatment effect occurred in the
alleys at any depth during the experiment period.

Carbon sequestered in the soil was different between the treatments at 0-10 cm
depth with MU showing the highest value, FL the lowest and sandwich not differing
between the two both in 2005 and as average during the evaluation period (2002-2005)
(Table 1). The amount of carbon sequestered in 2005 was not different from the average
of the evaluation period at 0-10 cm depth (Table 1). For the deeper sampling (0-30 cm)
FL presented the lowest value of carbon sequestered with no differences between the
other two treatments in the year 2005. No differences were measured in the average
2002-2005 between the treatments (Table 1). However both mulch and sandwich
treatments presented an increase in carbon sequestered during 2005 when compared with

the average 2002-2005 (Table 1).

25

Effect on soil Nitrogen concentration.

Since the implementation of the treatments the N03' - N, at both depths,
concentration in the soil of the MU treatment was signiﬁcantly higher than the other two
treatments. Between the years, only SVA shows a decrease in N03' concentration at both
depths (Figure 2 A-B). The total mineral N follows the same pattern of NO;', with MU
showing the highest concentration between the treatments for the duration of the
experiment at both depths (Figure 3 A-B). However all the treatments show a signiﬁcant
increase in 2005, mostly due to the high concentration of NH4+ (data not shown).

Effect on NeLamde community structure.

Nematode community structure was affected by the treatments during the 18
months of the duration of the experiment (November 2003 — April 2005). MU presented
the highest number of total nematodes between the treatments. Bacterivores represented
the highest percentage in the community structure in all the treatments followed by the
fungivores, except for the vegetated area of the Swiss Sandwich where herbivores
presented the same percentage as the fungivores (Table 2). However, between the
treatments some differences in the structure composition were noted. While MU
presented the highest percentage of bacterivores between the treatments, FL and STS
presented the highest percentage of fungivores and omnivores, and SWA presented the
highest percentage of herbivores (Table 2). No differences were noted between
treatments for the carnivores. Mulch presented the lowest percentage of herbivores. This
result was conﬁrmed from the number of lesion nematodes in the apple roots where MU

presented the lowest with no differences between the other treatments (Figures 5).

26

A direct correlation was found between the amount of mycorrhizal spores in the
soil and the percentage of roots colonized from arbuscular mycorrhizae with an r2 value
of 0.7059 (Figure 6). However, the percentage of root colonization from arbuscular
mycorrhizae was higher in SVA and FL, followed by MU and STS. The weeds present in
the vegetated area of the Swiss Sandwich treatment presented the lowest percentage of
infected roots (Figure 7).

Temporal effect on the nematode community structure.

Inside of each collecting date the nematode community structure followed the
general structure presented in Table 2. With some exceptions, Swiss Sandwich vegetated
area always presented the highest number of herbivores during the experiment period
(Figure 8). Mulch had the lowest percentage of fungivores in November 2003 and April
2005 and the highest percentage of bacterivores (entire period) (Figure 8).

There was a temporal effect on the community structure inside of each treatment.
In all the treatments the total number of nematodes increased in time, except for STS,
where it remained constant (Table 3). All the treatments presented an increase in
bacterivores during the duration of the experiment, except for STS where there is a
decrease (Figure 9). However the feeding groups that compensate this increase in
bacterivores vary between treatments (Figure 9). In ﬂame the herbivores diminished, in
mulch, herbivores and fungivores, and in SVA there is not a clear variation (Figure 9). In
STS, at the diminishing of the bacterivores, there is an increase of fungivores (Figure 9).
Omnivores and carnivores did not seem affected by temporal variation during the

experiment period (Figure 9).

27

Soil water content.

Measurements performed with TDR (Figure 10) demonstrated that most of the
time there were no differences between OFMS. When some difference was present MU
had always the highest values while the SVA had the lowest. Flame and the STS did not

differ from the other two.

28

Discussion

In our study, Orchard Floor Management Systems (OFMS) did have an impact on
soil organic matter (SOM), even if it is largely believed that the process should take
several years unless large quantities of organic matter are added. The greatest impact
occurred under the mulch treatment near the surface (0-10 cm), where it increased during
the experiment. Similar results were reported by Merwin et a1. (1994), Sanchez et al.
(2003) and Zoppolo (2004). At the deeper sampling (0-30 cm), the SOM increased but to
a lesser degree, this is probably caused from the fact that the alfalfa mulch was layered on
the soil surface without disturbance. Soil organic matter was the highest for the entire
duration of the experiment under the mulch treatment. When differences occurred, water
content in the soil was also the highest under alfalfa mulch.

The SOM varied in the sandwich treatment depending on the position in the
orchard. In the vegetated area SOM content remained constant during the experiment at
both sampling depths, while in the tilled area SOM decreased at 0-10 cm depth but
increased at 0-30 cm depth. This result is normal for tilled soils where the increased
aeration provoked by ﬁlling initiates loss of organic matter (Brady and Weil 2002). When
differences occurred, water content in the soil was the lowest in the vegetated area due to
weed competition.

In the ﬂame treatment, SOM decreased only at the shallow depth, probably due to
the constant burning of the vegetation leaving only ashes on the soil surface.

In the alleys, where vegetation was mowed regularly and left on the soil, SOM

remained more or less constant during the experiment.

29

Organic matter in the soil is mostly responsible for the carbon sequestration in the
soil (Stevenson 1994). It is interesting to notice that when we consider the treatments as if
applied to the entire surface of an orchard, taking into consideration the relative surface
covered from each segment of the treatments (alley, tree row, and in case of the sandwich
weeded area and tilled strip), we did not ﬁnd the same differences reported for the SOM
in each single segment. At 0-10 cm depth, mulch is still sequestering the highest amount
of carbon/ha, ﬂame the least and sandwich is in the middle, and the values are remaining
constant during the years. At 0-30 cm depth, mulch and sandwich sequestered the same,
and highest, amount of carbon and it increased during the experiment, while for ﬂame it
decreased. If we consider the fact that mulch is the only treatment with continuous
addition of external sources of carbon, it appears that the sandwich system is the
treatment with the highest potential of sequestering more carbon in the soil.

The effect of the treatments on the SOM correlated with soil nitrogen
concentration (Powlson and Jenkinson, 1990; Diaz Rossello, 1992b; Bloksma, 2000) to a
certain degree. The highest soil nitrogen concentration (almost double), for both nitrates
and total mineral concentration was in the mulch treatment, while ammonium was the
same between treatments. Nitrate concentration ﬂuctuated during the years under the
mulch treatment ending up being more or less constant compared with the beginning of
the experiment. Only the vegetated area of the sandwich had a decrease in N03'
concentration. The NH4+ concentration increased for all treatments, especially in 2005,
resulting in a general increase in total mineral nitrogen concentration. This shows that the
treatments reached a sort of equilibrium because even if there was not an increase in

SOM (treatments ﬂame and sandwich), there was an increase in nitrogen concentration.

30

Organic ﬂoor management systems change the microbial composition (Yao et al,
2005) that is responsible for the nutrient availability in the soil (Forge et al., 2003; Yao et
al, 2005).

Our experiment supports previous studies (Mader et al., 2002; Ferris et al., 2004;
Yao et al., 2005) afﬁrming that OF MS has an impact on the soil biology composition that
we represented by the relative abundance (% on the total) of nematode populations (Ritz
and Trudgil, 1999; Ferris et al., 2001; Yeates, 2003; Zoppolo, 2004) with different
feeding habits .

The total number of nematodes was highest in mulch treatment followed by the
vegetated area of the Swiss Sandwich (SVA). The difference between these two and the
others is probably caused by the continuous decomposition of the vegetative material on
the soil (Cookson et al., 2002).

In all the treatments, the bacterivores dominated the nematode population, which
was highest in mulch treatment and had no differences between the other treatments. The
composition of the remaining nematode p0pulations varied depending on the treatment.
According to Ingham et a1. (1985) the more stressful the environment, lacking in
nutrients (N and P) and/or water, the higher will be the amount of fungal feeding
nematodes. This was corroborated in our experiment, where ﬂame and Sandwich Tilled
Area (STA) showed the highest number of fungal feeding nematodes, followed by SVA
and mulch.

The number of herbivore nematodes (root feeding) in the soil is very important
because it could create damage to the crops (Merwin and Stiles, 1989). The percentage of

this nematode feeding population in the soil was affected by the OFMS. In fact, the SVA

31

had the highest percentage followed by ﬂame, STA and mulch. This result was not
however, conﬁrmed from the number of root feeding nematodes inside the roots where
ﬂame, STA, and SVA presented the same number, with mulch showing the lowest. It is
not clear if the difference in percentage in the soil and the number inside the roots is due
to the fact that the herbivore nematodes measured in the soil are a more expanse
composition of populations than those in the roots. Another factor could be that the
highest values measured in SVA could be due to the higher number of weed roots present
in the treatment, since we did not measure the root feeding nematodes in the weeds.

Most of the current ecological research agrees that the most beneﬁcial food webs
are those which are highly structural and diversiﬁed (Power, 1992; Paine, 1996; Sugihara
et al., 1997; Garlaschelli, 2004). Based on trends, oveé’lime, in this study we suggest an
impact, and through the evolution of the populations’ diversiﬁcation, on structure.
Populations ﬂuctuated according to treatments. Bacterial feeder nematodes increased in
ﬂame treatment to the detriment of herbivores. In contrast there was a decrease in
herbivore nematodes in mulch with no clear tendency in other populations. The
ﬂuctuation was high in SVA of all the populations and STA showed an increase in fungal
feeder nematodes with no clear tendency of which population was decreasing. If we
consider the last sampling date (April 2005) as an indicator of the treatments to reach a
balance in their structure it appears that mulch has the highest percentage of bacterivores,
STA the highest of fungivores with mulch the lowest, and that SVA has the highest
percentage of herbivores.

To have a better comprehension of the food web structure we measured the

amount of endomycorrhizal spores in the soil as well as the percentage of infection from

32

said mycorrhizae in the roots. It is established that mycorrhizae are of extreme
importance in aiding the plant to absorb nutrients from the soil in low N conditions
(Miller et al., 1985; Grange et al., 1994; Newsharn et al., 1995). There is a clear
correlation between the amount of spores in the soil and the percentage of infection in the
roots indicating that the amount of spores in the soil could be utilized as an indicator of
infection. Additionally, mycorrhizal infection in the roots was highest in SVA and ﬂame,
with the weeds in the SVA showing the lowest (probably due to a species-host issue).
Mulch and STA presented the same percentage of infection in between the other
treatments. This could be due to mulch associated with a high nutritional status of the soil
and for STA to the disturbance generated from tillage.

All of these results suggest that the mulch treatment has the lowest diversiﬁed soil

biology among the treatments.

33

Conclusions

Our study demonstrates that Orchard Floor Management Systems have an impact
on the soil conditions such as SOM, carbon sequestration, nitrogen concentration and
food web.

The mulch treatment presented the highest values of SOM, carbon sequestered,
and nitrogen in the soil at both sampling depths, but had the least structured food web
with the majority of the populations represented by bacteria feeding nematodes. One
positive outcome is that there appears to be less herbivore nematodes associated with this
treatment. The high amount of nitrogen could have potential to leach in the soil proﬁle.
Also, the continuous addition of external carbon (alfalfa hay) to the system undermines
the capability to sequester high level of carbon.

The sandwich treatment presented lower values of SOM and nitrogen than alfalfa
mulch. SOM is decreasing at 0-10 cm depth in the tilled area and increasing at the deeper
sampling (due to the tillage), while nitrogen is decreasing in the vegetated area at 0-10
cm depth (due to higher competition). The treatment had the same amount of carbon
sequestered as mulch, without external additions, creating a higher potential for carbon
sequestration. Sandwich presented a more balanced food web structure than mulch with
the weeded area having highest values of herbivore nematodes and root mycorrhizal
infection, while the tilled area has the highest value of fungivores with a similar
percentage for mulch of root mycorrhizal infection. It is not clear if the tillage is one of
the factors responsible for the increase in fungivores and reduction of mycorrhizae, since

the nutritional soil status between the two positions inside this treatment are similar.

34

The ﬂame treatment has similar soil conditions as the sandwich, showing a
reduction in SOM at 0-10 cm probably due to the continuous burning of the vegetation.
The practice also shows similar food web structure and repartition inside the populations
as the sandwich suggesting that the two treatments have more stressful soil conditions
than mulch (lower SOM, N and in case of the sandwich vegetated area, water content),
but they are coping through a shift in microbial populations. As expected, this treatment
provided for the lowest carbon sequestered.

In this study there was a high correlation between the amount of mycorrhizal
spores in the soil and the percentage of infection in the apple roots in Michigan
conditions.

Overall, organic apple growers should consider the use of the sandwich as a
suitable choice of orchard ﬂoor management in Michigan. More research is still
necessary, especially coupling the structure of the food web with the effect of the tillage
and the nutritional status in the soil through fertilization trials and use of growing

legumes.

35

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39

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letters represent statistical difference (LSMEANS with P S 0.05) between years inside of

the duration of the experiment (2002-2005) at 0-10 (A) and 0-30 (B) cm depth. Different
each treatment and should be read separately. Bars represent standard errors.

Fig. 1: Effect of the treatments on percentage of organic matter content in the soil during

37

 

  
 
 
 

   
  
   
 
 

 

 
 

      
 
  
   
       
      
 
    
 

  

   

  
 

 

  

 

  
  
     

    

  

 

 

   

   

 

 

 

 

 

 

  
 
   

 
 
      
     

      
  

 

     

 

   

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Fig. 2: Effect of the treatments on N-NO3' content in the soil during the duration of the
experiment (2001-2005) at 0-10 (A) and 0-30 (B) cm depth. Different letters represent
statistical difference (LSMEANS with P S 0.05) between years inside of each treatment
and should be read separately. Bars represent standard errors.

38

Total mineral N (ppm)

 

 

 

Flame Mulch Sandwich Row Sandwich Strip
Treatment

 

2003 2004 2005

 

60

Total mineral N (ppm)

 

 

 

Flame Mulch Sandwich Row Sandwich Strip
Treatment

 

2003 2004 2005 l

 

Fig. 3: Effect of the treatments on Total mineral N (N-NO3' + N-NH4+) content in the
soil during the duration of the experiment (2003-2005) at 0-10 (A) and 0-30 (B) cm
depth. Different letters represent statistical difference (LSMEANS with P S 0.05)
between years inside of each treatment and should be read separately. Bars represent
standard errors.

39

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Fig. 4: Effect of the treatments on N-NHX content in the soil during the duration of the
experiment (2003-2005) at 0-10 (A) and 0-30 (B) cm depth. Different letters represent
statistical difference (LSMEANS with P S 0.05) between years inside of each treatment
and should be read separately. Bars represent standard errors.

40

Table 1: Tons of carbon sequestered in one hectare of soil considered as entirely covered
from each treatment in 2005 and as average of the period 2002-2005. Different small
letters represent statistical difference (LSMEAN S with P S 0.05) between the treatments
inside of the years (letters should be read vertically). Different capital letters represent
statistical difference (from orthogonal contrasts at p S 0.05) between the years inside of
the each treatment (letters should be read horizontally).

0-10 cm 0-30 cm
2005 2002-2005 2005 2002-2005
Flame 18bA 18bA 46bA 44aA
Mulch 22aA 21aA 51aA 47aB
Sandwich 20 ab A 19 ab A 51 a A 45 a B

 

 

 

 

 

 

 

 

 

 

 

 

Table 2: Nematode community structure during the 18 months of the experiment
(November 2003-April 2005) at 0-30 cm depth. Feeding behaviors are the percentage of
each group based on the absolute nematode density (total nematodes number). Different
letters represent statistical difference (LSMEANS with P S 0.05) between the treatments
inside of each nematode feeding behavior and should be read horizontally.

 

 

 

 

 

 

 

 

Treatment
Sandwich Sandwich

Feeding Vegetated tilled
Behavior (%) Flame Mulch area Strip
Herbivores 8 b 3 c 14 a 5 be
Fungivores 18 a 9 c 14 b 21 a
Omnivores 5 a 3 b 4 ab 5 a
Carnivores 1 a 1 a 1 a 1 a
Bacterivores 68 b 84 a 67 b 68 b
Absolute

Density 471 c 1246 a 754 b 343 c

 

 

 

 

 

 

 

Table 3: Total number of nematodes during the 18 months of the experiment (November
2003-April 2005) at 0-30 cm depth. Different letters represent statistical difference
(LSMEANS with P S 0.05) between the dates of collection inside of treatment and should
be read vertically.

 

 

 

 

 

 

 

 

 

 

 

Treatment
Date of Sandwich Sandwich Tilled
collection Flame Mulch Vegetated area Strip
November 03 169 b 226 c 225 c 179 a
April 04 264 b 405 c 356 c 235 a
November 04 882 a 1123 b 1356 a 611 a
April 05 572 ab 3231 a 1081 b 345 a

 

 

41

 

 

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Treatments

Figure 5: Number of root lesion nematodes in l g of apple roots in collected in August
2005. Different letters represent statistical difference (LSMEAN S with P S 0.05) between
the treatments. Bars represent standard errors.

42

#ofnyoonhlmlsporasinthesoil

200 -

150 - ~

50—

 

T ”9 Eiiccéx + 3211' 11
R2 = 0.7059

9

 

 

I 1

60 80

% mycorrhizal colonization in the roots

Figure 6: Correlation between percentage of arbuscular mycorrhizal colonization in the
roots and number of mycorrhizal spores in the soil (November 2004). (Proc REG Pr > F
<0.001)

% Infected Roots

50 —
45 -
4o - i
35 —
30
25 —~
20 —
15 -
1o -
5 _

 

 

 

 

 

 

 

 

0

Flame Row

1

Mulch Row Sandwich Row Sandwich Strip

Sandwich
Weeds

Treatment

Figure 7: Percentage of roots colonized from arbuscular mycorrhizae (November 2004).
Different letters represent statistical difference (LSMEANS with P S 0.05) between the

treatments. Bars represent standard errors.

Figure 8: Temporal effect on the Nematode community structure (0-30 cm) during the 18
months of the experiment (November 2003-April 2005). Feeding behaviors (expressed in
the legend) are the percentage of each group based on the absolute nematode density
(total nematodes numbers). Different letters represent statistical difference (LSMEANS
with P S 0.05) between treatments inside each collection date. If there are no letters
means no statistical difference.

 

sandwich strip

sandwich row

I!)

flame

:3 E3.

sandwich strip

W h e
m kuc m
m m n
m
d
n
a
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r U
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0%

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IE1 herbivores fung

44

Figure 9: Temporal effect on the Nematode community structure (0-30 cm) during the 18
months of the experiment (November 2003-April 2005). Feeding behaviors (expressed in
the legend) are the percentage of each group based on the absolute nematode density
(total nematodes numbers). Different letters represent statistical difference (LSMEANS
with P S 0.05) between collection dates inside of each treatment. If there are no letters
means no statistical difference.

 

E3 bacterivore;

camlvores

'52

APRIL
NOVEMBER 04

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IE herbivores fungivores omnivores

APRIL 04

NOVEMBER 03

cm Esaaam

APRIL 05

NOVEMBER 04

APRIL 04

sows—5am

NOVEMBER 03

93

APRIL 05

NOVEMBER 04

APRIL 04

NOVEMBER 03

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NOVEMBER 04

 

APRIL 04
NOVEMBER 03

20% 40% 60% 80% 100%

{a
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45

Soll Molsture (% vlv)

301

 

 

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5 4 - 0 - Mulch
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0100] ”V 2 (0090500!- 03040300000: “('0 QPQNSOQ NOFNIOCOONIOSQ

eééaééaa‘” a
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2002 2003 2004 2005
Date

Figure 10: Volumetric soil moisture content (as %) measured with TDR for the average
0-45 cm depth, for the different treatments during 2002-2005.

46

Abstract
CHAPTER 2. The Response of “Paciﬁc Gala” on three Rootstocks to three Orchard
Floor Management Systems under Organic Protocol.

By Dario Stefanelli

In organic apple production, orchard ﬂoor management is of greatest importance
since it determines weed management and fertility. In this experiment we evaluated the
response of the cultivar “Paciﬁc Gala” on three rootstocks of different vigor: M.9 NAKB
337, M.9 RN 29, and Supporter 4 (in respective order of vigor from dwarﬁng to semi-
vigorous). The three rootstocks were also evaluated for the response to three orchard
ﬂoor management systems: mulching (alfalfa hay), ﬂaming, and strip tillage on each side
of the row with natural vegetation allowed to grow on the tree row (Swiss Sandwich
System). The experiment was conducted in an orchard planted in 2001 and certiﬁed
organic since 2003.

The three treatments did change the soil conditions with mulch showing higher
concentrations of SOM and N creating different growing conditions for the rootstocks.
The OFMS treatments did not have an effect on the tree growth parameters measured
except for foliar nitrogen concentration that was higher with alfalfa mulch. Trees on
Supporter 4 were most vigorous, as anticipated. There was an interaction between
treatments and rootstocks with M.9 RN 29 showing the highest yield and “yield
efﬁciency” per tree in ﬂame and sandwich while no differences were noticed between the
rootstocks in mulch despite its better growing conditions. This suggests that M.9 RN 29

is a rootstock that adapts well to more stressful conditions (lower SOM and N, and in

47

case of the Sandwich vegetated area, water content) posed by sandwich and ﬂame
treatments. Cumulative yield/ha was highest in mulch and sandwich and lowest in the
ﬂame treatment.

The ﬂame treatment appeared less desirable related to management regarding
low SOM, N, ﬁre risk, risk of injures to branches, and irrigation plastic system. On a
positive side the ﬂame was economical at an annual expense of $278 in our experimental
orchard. Drawbacks to the alfalfa hay mulch system included; expensive ($788), high
maintenance (to keep it thick), high risk of rodents damage, and risk of leaching. The
sandwich system provided a less suitable growing conditions (lower SOM, N
concentration and water content in the vegetated area), it was however, easy to deploy
and manage, it did not damage the tree, it was low cost at $98, and it requires only an
easily modiﬁed notch disk tiller.

Overall, considering the sandwich system coupled with the M.9 RN 29 rootstock
seems to be a suitable choice for growers that want to grow Paciﬁc Gala under organic
protocol in Michigan and similar climates. More research is still necessary especially to

conﬁrm these results in a longer term study.

48

Introduction

Organic horticulture is becoming one of the fastest growing sectors in the
agriculture economy (Dimitri, 2002). There is a worldwide growing interest in the
development of sustainable production systems for food production (Yusseﬁ, 2004).

Organic agriculture limits the inputs used to those considered environmentally
and economically sustainable when compared with conventional methods. It becomes
then, a challenge to overcome issues such as pest, weed control, and fertilization.

There is the need to identify management systems that are productive under these
constrains. In organic production the soil is considered the most important part in
sustaining production and plant health. A common phrase used to characterize organic
growing is “Feed the soil, not the plant”.

In tree fruit production, Orchard Floor Management Systems (OF MS) are
developed to create the best environment for tree growth allowing the maximization of its
performance (Weibel, 2002). A successful OF MS needs to increase soil fertility, physical
and biological properties, to supply nutrients to the trees, while suppressing the
competitive effects of weeds without the use of traditional herbicides, and minimizing
insect and disease pressure.

Orchard ﬂoor management practices have been developed and adopted by
commercial fruit growers to satisfy practical needs. Mulching (with organic or inorganic
material) keeps the soil free from vegetation competition, conserves soil moisture, keeps
temperature constant, increases organic matter through its decomposition (in the case of

organic mulches), releases nutrients to the soil, and improves the soil environment

49

enhancing the microbial activity (Merwin and Stiles, 1994; Merwin etal., 1995; Marsh et
al., 1996; Lloyd et a1, 2000).

Tillage also keeps the soil free from vegetation competition but can impede
internal water drainage, cause surface organic matter losses (Merwin and Stiles, 1994)
and disrupt surface roots. (Cockroft and Wallbrink, 1996). Additionally, tillage can cause
surface water run-off and soil erosion. It is still widely used globally even if it is
expensive, uses precious petrol fuel and requires specialized machinery.

Recently a modiﬁed tilling system has been implemented in Switzerland, called
the Swiss Sandwich System. It consists of a strip where spontaneous vegetation is
allowed to grow on the tree row and two shallow tilled strips at each side of the tree row.
This system encourages predator insects to complete their cycle in the volunteer
vegetation that grow on the tree row, becoming more efﬁcient in limiting pests and
diseases, and increasing biodiversity (Luna and Jepson, 1998; Horton, 1999; Schmid and
Weibel, 2000; Galoach, 2002). The resulting vegetation in the tree row can be considered
as cover crops, contributing to the system their signiﬁcant beneﬁts to organic production
systems aiding in the prevention of soil erosion, increased soil organic matter, facilitation
in the recycling of soil nutrients, and reduction in the amount of nitrate runoff and
leaching from the soil (Miles and Chen, 2001). The Swiss system is easy to manage since
there is no need to reach under the tree canopy to mow weeds or till (Schmid and Weibel,
2000; Weibel, 2002; Weibel and Haseli, 2003). The two strips of shallow tilled bare soil
have the effect of reducing vegetation competition for water and nutrients (Merwin and

Ray, 1997).

50

Flaming is another effective practice in use by organic growers (Gourd, 2002;
Robinson, 2003), with relative little known regarding the effects of this system, besides
vegetation suppression. It has, however, drawbacks associated with its practice, such as
ﬁres, damage to the trees (Zoppolo, 2004) and the need of special equipment.

All of these systems achieve the goal to keep a certain amount of soil surface free
from competitive vegetation which can have a negative impact on tree growth (Parker,
1990; Welker and Glenn, 1991; Merwin and Ray, 1997). Without the use of herbicides,
vegetation management requires more thought and management skills by growers in
organic production (Webster, 2000).

It is clear, that all of these OFMS have a different approach and will have
different results, since they are difﬁcult to standardize or compare, even if they somewhat
achieve the same results. It will then be left to the trees to overcome eventual stressful
situations created in the soil from the OFMS.

Another form of management that growers can usee to overcome this problem is
the selection of appropriate rootstock, irrigation and nutrient management. There is a
wide variety of speciﬁcally selected apple rootstocks that have been developed and
released over many years. Each rootstock differs in its ability to adapt to soil conditions
(Ferree and Carlson, 1987), disease resistance, and inﬂuenced vigor and production
characteristics of the scion. There are extensive research programs that center on
rootstock evaluation for the above mentioned characteristics. The evaluation is performed
with conventional practices and under optimal growing conditions unless different
conditions are strictly required. This factor alone reduces the utility of the rootstock

outside of those conditions, thus inducing the growers to adapt their orchard conditions to

51

the optimal one in which the rootstocks were tested. Environmental factors seem to be
more inﬂuential on the uptake of nitrogen and phosphorus than the rootstock genotype
(Kennedy et al., 1980) but not enough is known on the subject. There is a strong
relationship between genetic (vigor) and environmental factors in determining the
adaptability of the root system and consequently its capability of nutrient uptake and tree
performance under adverse conditions.

Since organic OFMS do create environmental conditions that are different from
the conventional practices in which rootstocks are evaluated, perhaps rootstock selection
can compensate and overcome these differences.

It will then be of great value to obtain information on rootstock performance as a
response to OFMS. In this study we evaluated three rootstocks of different vigor
managed with three different organic OFMS (mulching, ﬂaming and the new Swiss
sandwich system).

The objectives of this work were to evaluate the responses of rootstocks to the
different growing conditions present in the OFMS; to asses the effective impact of OFMS

on the soil conditions; to determine the suitability for growers of the OFMS.

52

Materials and Methods.

An orchard of “Paciﬁc Gala” (Malus x domestica Borkh.) was planted in May 2001 at the
Clarksville Horticulture Research Station in Clarksville, MI. The orchard has been
certiﬁed organic in 2003 and 2004 by Organic Crop Improvement Association (OCIA),
and in 2005 by Organic Growers of Michigan (OGM).

The orchard consists of 468 trees graﬁed on three rootstocks depending on their vigor.
The rootstocks under evaluation are the dwarﬁng M9. NAKB 337 (40% of the size of a
seedling. Marini et al., 2000), the semi-dwarﬁng M9. RN 29 (Perry, 2000a), and
Supporter 4 (semi-vigorous) (Perry, 2000b).

Spacing between the trees is dependant of the rootstock vigor (Perry, 2002) and are 4.6 x
1.4 m for M9. NAKB 337, 4.6 x 1.7 m for M9. RN 29, and 4.6 x 2.0 m for Supporter 4.
Trees were trained to a vertical axe system. Rubber bands and clothes pin were used to
bend branches in early years (Perry, 2000c). Minimal pruning was applied to allow the
tree to grow as natural as possible mainly singularizing the leader or main branches. A
two wire trellis with galvanized metal poles was installed as support system. Drip
irrigation with drippers of 2.3 L/h every 0.6 m was installed in May 2001 and suspended
from the lowest wire of the trellis on the tree row. All orchard ﬂoor management systems
received equal irrigation throughout the season.

Soil moisture was measured by time domain reﬂectometry (TDR) using a Mini Trase
6050X3 (Soilmoisture Equipment Corp, Goleta, CA) with 45 cm long stainless steel rods

permanently installed in the tree rows, halfway between two trees and in the middle of

53

the tilled strip in 2002. Measurements were taken for each of the 6 plots per treatment
weekly in 2002 and every other week in 2003-2005.

The predominant soil type of the orchard is Kalamazoo sandy clay loam (Typic
Hapludalfs) with 53.1% sand, 23.1% silt, and 23.8% clay. The orchard presents mild
slopes (less than 3%).

The site was previously farmed with conventional soybean-com-corn-alfalfa rotation for
two cycles until 1998. Subsequent soil preparation consisted of sowing of buckwheat and
chicken compost (1250 kg/ha) and lime (2250 kg/ha) application in 1999 on the entire
surface. At plantation (April 2000) a mixture of red mammoth clover and endophytic rye
was sown in the alleys.

The orchard ﬂoor management systems (OFMS) have been applied since the plantation
of the orchard. The treatments consist of Mulch of alfalfa hay, the Sandwich System (SS)
and Flaming (FL) with a propane burner. The objective of the treatments is the weed
management of the orchard.

The mulch treatment consists of alfalfa hay laid underneath the tree canopy in a strip of 1
m on each side of the tree and kept 15-20 cm thick. 105 round alfalfa bales/ha were used
with a C:N ratio of 15:1. The mulch was hand-applied every spring and fall to keep the
thickness constant in order to provide a shading effect for weed suppression, and to
maintain soil moisture.

The ﬂaming treatment consists of the burning of weeds underneath the tree canopy and l
m each side of the tree with propane gas (estimated 56 L/ha). A custom engineered
burner, consisting of 4 burners (200000 BTU) in a row, comprehensive of a metal

protective shield to concentrate the heat and to prevent its escaping and damaging the

54

canopy. On the back of the shield was also mounted a sprinkler system to extinguish
eventual ﬁres occurring during the burning. To reach the weeds underneath the canopy on
the tree row a hand burner (150000 BTU) was used. The burner was mounted on the side
of a tractor on a hydraulic arm to better control the application of the treatment. The
treatment was applied ﬁve to six times during the year, starting at the end of April -
beginning of May and ending at the end of August. The treatment was repeated every
time the weeds would reach 10 cm high. Tractor speed was kept between 1.6 and 3.2
km/h depending on the density of the weeds to be controlled.

The Sandwich System is an adaptation of the Swiss system (Weibel, 2002) and consists
of an area of 25-30 cm on each side of the tree, underneath the canopy, where
spontaneous vegetation is allowed to grow undisturbed. On each side of this weeded area
two strips of soil were kept free of vegetation by shallow tilling (5-10 cm deep). The
strips were 70 cm wide from plantation till 2003 and 90 cm wide from 2004. The width
of the strip has been changed to follow the growth of the trees. Timing of the treatment
application was the same of the Flaming treatment. The tilling was applied by a three
tooth arrow tiller mounted on the side of a tractor on a hydraulic harm till 2003, a ﬁve
tooth arrow tiller during 2004, and a modiﬁed notch disk tiller during 2005. The notch
disk tiller was modiﬁed to reach on the side of the tractor (Picture 1 and 2).

The alley consisted of an equal mixture of endophytic rye and mammoth clover seeded at
the orchard plantation. Clover was also reseeded in 2005 to keep the proportion constant.
The alleys were managed equally in all treatments by periodical mowing (3-4 times year)

and the remains were left on site according to best management farming practices.

55

Rootstock performances were measured by growth, production, and nutritional status

parameters of the trees while OFMS effect on the soil was measured by periodically

checking the soil conditions.

Growth parameters measured were:

Trunk cross sectional area (TCA) at dormancy as well as its differential since
establishment (TCAI) during the years. This methodology has been proven to be
highly correlated with the tree growth (Westwood and Roberts, 1970).

Shoot growth (extension) was measured every week on three representative shoots
plus the leader during all the vegetative season to measure the growth rate. Shoots
were selected to represent the bottom, middle and top part of the tree. Selected shoots
were comparable in size and insertion angle at the time of selection.

Canopy volume was calculated measuring the total height as well as two orthogonal

diameters of the canopy at 0.7 m from the soil.

Production parameters measured were:

Yield (kg/tree) and number of fruits to obtain the average fruit weight (g), as well as
cumulative yield during the years. Values were also corrected to the actual number of
trees to obtain productions/ha.

“Yield efﬁciency” (kg/cmz), or ratio of fruit yield to trunk vigor (TCA) was
calculated by dividing the yield of the year by the TCA of the previous year, as well
as the cumulative yield efﬁciency (kg/cmz) calculated by dividing the cumulative

yield by the TCAI of the current year.

56

Tree nutritional status parameters measured were:

Relative chlorophyll content of a composite sample of 10 leaves per data tree
collected from the middle portion of one year old branches. Relative chlorophyll
content was measured using a SPAD-502 meter (Spectrum Technologies Inc,
Plainﬁeld IL) in early August.

Mineral nitrogen concentration of the previously described composite sample of
leaves. Leaves were rinsed with distilled water, air dried at 60°C for 48 hrs, ground

and sent to the MSU soil and plant nutrition lab to be analyzed for N concentration.

Soil conditions measured were:

Soil nitrate (NO3') and ammonium (NH4I) concentration in the soil, to check the
immediate available nitrogen released from the treatments available to the trees. Soil
samples were obtained for the three OFMS by mixing 20 soil core sub-samples from
the tree row. Soil samples from the Alleys and the tilled strip of the SS were obtained
by mixing 10 soil core sub-samples from each side of the tree row. Soil samples were
collected every two months starting in April until November at 0-10 and 0-30 cm
depth each year. The two depths have been chosen to represent the soil surface, where
most of the microbial and root activity is greatest. Soil samples were air dried at
105°C for 24 hrs. Nitrates and ammonium were extracted from the soil with 100 ml of
KC] 1 M on 10 g of dried soil, placed for 1 hour on a shaker and then ﬁltered with

ﬁlter paper. The extracted liquid was sent to the MSU soil lab for the analysis

57

following the procedure described by (Kenney, 1982) using a Lachat automated
colorimetric analyzer (Lachat Instruments Inc. Milwaukee, WI).
0 Soil organic matter content was measured by loss on ignition of 3g of dry soil, from

the above described soil samples, at 400 °C for 8 hours in a muffle furnace.

We also performed a limited maintenance cost comparison of the systems deployed for
the 2005 growing season utilizing our experimental plot as unit.

The treatments were applied in a complete randomized split plot design with OFMS as
main plots and the rootstocks as sub-plots with 6 replicates. Four trees for each rootstock
were planted in each sub-plot. Only the two central trees for each rootstock were utilized
as data trees for a total of 84 trees under evaluation. Each data row was alternated with
buffer rows consisting of trees of same rootstocks and distances arranged in single rows.
Statistical analysis was performed with SAS (Version 8, SAS Institute, Cary, NC, USA).
Analysis of variance was performed using the MIXED procedure to detect treatment
effects. When signiﬁcant, mean separation was conducted by Least-square means test
(LSMEANS) with pS0.05. All the soil data statistical analysis was considered as repeated

measures using OMFS*rootstock as the subject.

58

The following timetable explains the history of the plot, sampling and measurements for

the duration of the experiment.

 

 

 

 

 

 

 

Prior to Conventional soybean-corn-com-alfalfa rotation (2 cycles). Last crop was com.
1998 Minimal tillage.
1999 Spring: tillage sowing of soybean, Chicken compost (lZSOkg/ha), lime (2250 kg/ha).
Fall: tillage, sowing of Buckwheat
2000 April: tillage, tree planting. August: sowing of red mammoth clover and endophytic
rye in the alleys.
2001 May: implementation of April, June, August, TCA, TCAI, shoot
the 3 orchard ﬂoor November: soil sampling growth, canopy volume,
management systems. for NO; leafN %, SP AD
2002-05 Maintenance of the April, June, August, TCA, TCAI, shoot
OF MS and tree training November: soil sampling growth, canopy volume,
for SOM and NO; leafN %’ 31) AD

 

 

 

59

 

Results

The orchard ﬂoor management systems (OF MS) treatments impacted the soil
organic matter (SOM) and Nitrogen (N) concentration of the soil, effectively changing
the grth conditions for the rootstocks. Within each year, SOM content was always
higher in the Mulch (MU) than in the other treatments, except in 2002 where it was
similar to the tilled strip in the Sandwich (STS) for the depth of 0-10 cm (Fig. 1A). Soil
organic matter increased during the years in MU, remained constant in the Sandwich
vegetated area (SVA) and decreased in Flame (FL) and in STS. For the deeper sampling
(0-30 cm) there is no difference between treatments within the year. However, SOM
increased during the years in MU and STS while it remained constant in FL and SWA
(Fig. 18). No treatment effect was measured in the alleys at any depth during the
experiment period.

Since 2003, at both depths, total mineral nitrogen (NO3' - N + NH: - N)
concentration in the soil of the MU treatment was signiﬁcantly higher than the other two
treatments (Figure 2 A-B), however all the treatments had a signiﬁcant increase in 2005.

In 2005, for all the growth parameters considered, there was no effect of the
treatments and no interaction between the treatments and rootstocks (Figure 3; Table 1).
Only during training years (2001-2003) did the treatments present some effect on branch
growth, trunk cross sectional area (TCA) and its increase (TCAI) with mulch (MU)
showing the highest values (Zoppolo, 2004). However, since the trees entered in full

production (2004) the treatment effect has ceased to be noticeable.

60

Among rootstocks, Supporter 4 had the highest values in most of the grth
parameters considered, presenting the same trend as Figures 3, with no differences
between the other two rootstocks (M.9 RN 29 and M.9 NAKB 337) except for branch
grth in 2004 (data not shown) and 2005 where no differences were noticed. Branch
growth in 2005 ranged between 38 cm (M.9 RN 29 in mulch) and 43 cm (M.9 NAKB
337 and Supporter 4 in sandwich).

Rootstock did not inﬂuence the nitrogen status of the leaves. Since 2003 MU
presented the highest values in leaf nitrogen concentration (Table 2).

Cropping was not inﬂuenced by OFMS but differences among rootstock exist
(Table 3). Rootstock did not impact cropping in mulch treatment, while M.9 RN 29 was
most productive (with no differences between the other two rootstocks) in both of the
other treatments (Figure 4). Yield efﬁciency, as the ratio of fruit yield to trunk vigor,
presented the same trend as the yield values (Figure 4).

The same production parameters behaved differently when corrected for the
number of trees to obtain values per hectare. There was still no inﬂuence of the
treatments on any of the parameters, but there was an inﬂuence from the rootstocks and
their interaction with the treatments (Table 3). All the parameters considered had the
same trend as the cumulative yield (t/ha) in which there was no difference between the
rootstocks in the treatments ﬂame (Figure 5). Supporter 4 presented the lowest
production in both mulch and sandwich while M.9 NAKB 337 had the highest yield/ha in

mulch and M.9 RN 29 in sandwich (Figure 5).

61

The cost evaluation for the applications of the Orchard ﬂoor management systems
suggested that sandwich was the least expensive (8 91), followed by the ﬂame ($ 218)
and mulch ($ 788), (Table 4).

Soil wgter content.

Measurements performed with TDR (Figure 6) demonstrated that most of the time
there were no differences between OFMS. When some difference was present MU had
always the highest values while the SVA had the lowest. Flame and the tilled strip in the

sandwich did not differ from the other two.

62

Discussion

During the experiment the orchard ﬂoor management systems did have an impact
on the soil conditions. Mulch increased the percentage of soil organic matter (SOM) at
both measured depths (from 2.7 to 3.3 % at 0-10 cm and from 2.0 to 2.4 % at 0-30 cm)
and it was higher than the other two treatments. This is due to the continuous break down
(Cookson et al., 2002) of the mulch itself by the microorganisms in the soil and its
continuous addition (twice yearly) for the duration of the experiment (Merwin et al.,
1994; Sanchez et al., 2003, Zoppolo, 2004). Differences between the two measured
depths are probably due to the fact that the alfalfa mulch was layered on the soil surface
without disturbance. Also, when differences occurred, mulch had the highest soil water
content.

On the vegetated area of the sandwich system the constant level of SOM was
probably kept from the decaying dry matter produced by the dead vegetation laying on
the soil. When differences occurred, mulch had the lowest soil water content. In the tilled
strip however, we noticed a decrease in SOM at the soil surface (0-10 em) but an increase
deeper in the soil proﬁle (0-30 cm). This behavior has been reported as normal since
tilling increases aeration and loss in organic matter (Brady and Weil, 2002).In the ﬂame
treatment, the superﬁcial loss in SOM is likely associated with the constant burning of
the vegetation that leaves only ashes on the soil surface.

The effect of the treatments the SOM reﬂected on the effects of nitrogen
concentration in the soil (Powlson and Jenkinson, 1990; Diaz Rossello, 1992b; Bloksma,

2000). In fact, MU, especially at 0-10 cm depth, generated almost double the amount of

63

total mineral nitrogen when compared with the other two treatments, as expected from its
high protein concentration (Donahue et al., 1970; Sarrantonio, 2003). It seems however,
that the different systems are reaching a sort of balance, since the amount of N in the soil
is increasing during the years (especially evident in 2005).

The mulch treatment created the most favorable soil conditions for the tree growth
having higher concentration of SOM, N and water in the soil while the other two
treatments had similar soil conditions. This was reﬂected in the foliar N concentration, as
has been reported by Nielsen and Hogue (1985), and Merwin and Stiles (1994). It is not
clear which is the optimal N concentration in the leaves to determine eventual deﬁciency,
since it has not been measured for each available variety but only in general. In our study,
in fact, branch growth, TCA, TCAI and canopy volume have not been affected from the
OFMS treatments, suggesting that foliar N was still sufﬁcient.

Despite the effect of the treatments on the soil conditions, they did not have an
effect on any of the growth parameters measured (TCA, TCAI, branch growth, and
canopy volume) except in early years (2001-2003) where sandwich presented the least
growth probably due to the vegetation competition exerted by the vegetated area
underneath the canopy (Welker and Glenn, 1989; Parker 1990; Merwin and Ray, 1997;
Giovannini et al., 1998; Zoppolo, 2004). An expansion of the width of the tilled strip
from 2004 probably compensated and reduced vegetation competition.

Trees on Supporter 4 were more vigorous than the M.9 clones used in the
experiment, as noted in previous studies (Marini, 2000).

While there has been no effect of OFMS on the vigor, there is an interaction

between treatments and rootstocks regarding cropping. In the mulch, which had the most

64

favorable growing conditions, there were no differences measured between the rootstocks
while in both ﬂame and sandwich M.9 RN 29 was the rootstock with the highest yield
and “yield efficiency”, with no differences between the other two rootstocks. Generally,
trees on vigorous rootstocks are less precocious than less vigorous rootstocks. M.9 RN 29
appears to be a rootstock that adapts better to the less favorable growing conditions
presented by SS and FL (lower SOM, N, and water content in the vegetated area of the
sandwich) as expressed from the higher “yield efﬁciency” measured in these two
treatments when compared with MU.

When we consider cropping per hectare, we have to adapt the results to relative
tree density. The lowest cumulative yield per hectare is the ﬂame treatment with no
differences among the rootstocks. Yield and Yield efﬁciency per tree as well as the
cumulative production per hectare (even if somewhat diminished by the reduced number
of trees) make M.9 RN 29 and the low cost sandwich system a very interesting
combination that should be considered by growers that wish to plant Paciﬁc Gala under

organic protocol in Michigan and related climates.

65

Conclusion

The orchard ﬂoor managements systems implemented had an impact on the soil
conditions. Soil organic matter and nitrogen was highest in the mulch treatment. Flame
and sandwich systems provided lower but similar nitrogen and SOM content. The effect
of the treatments was more noticeable at 0-10 cm depth where a reduction of SOM was
measured in both ﬂame (due to the continuous burning of the vegetation) and the tilled
strip in the sandwich system (due to tillage). The increase in nitrogen concentration,
especially in 2005, suggests that the treatments are reaching a sort of equilibrium in
sustainability. However, more research is needed to balance each system with plant
nutrition needs and soil reactions. For example it appears that nitrogen is excessive with
the alfalfa mulch.

The treatments did not have an effect on the growth, but leaf nitrogen
concentration was lowest in sandwich and ﬂame. Plant vigor appears adequate in this
trial, but leaf nitrogen values are approaching the lowest acceptable range for Michigan
apple orchards (Hanson, 2000).

Among the rootstocks, Supporter 4 was the most vigorous as expected. There was
an interaction between treatment and rootstock regarding yield and yield efﬁciency with
Gala on M.9 RN 29 being the highest per tree in ﬂame and sandwich while no differences
were noticed between the rootstocks in mulch despite its better growing conditions. This
suggests that M.9 RN 29 is a rootstock that is better adapted to the conditions that the
sandwich and ﬂame treatments generate. This is probably due to its comparative greater

vigor than M.9 NAKB 337 and its inﬂuence on earlier bearing than Supporter 4.

66

When considering the values per hectare and especially the cumulative
production, the ﬂame treatment was least productive having no differences between the
rootstocks. This ﬁnding is surprising considering that this treatment maintained a
signiﬁcant weed-free zone over the years. The ﬂame system also had a low SOM and N
concentration and with the various management concerns, this OFMS appears to be the
least desirable for organic growers. The mulch and sandwich treatments presented similar
cumulative production per hectare with Supporter 4 having the lowest values with no
differences between the other two rootstocks.

The mulch and sandwich OFMS also have some drawbacks. Alfalfa hay mulch is
expensive and difﬁcult to apply, and it poses a high risk of damage by rodents. Soil in the
sandwich system appears more nitrogen and water stressed with less favorable growing
conditions (lower SOM and water content on the vegetated area) than mulch. Also the
desirable width of the tilled strip needs more deﬁnition especially for different soil types.
The sandwich system is relatively easy to implement, avoids tree-trunk injury, is
relatively inexpensive to establish and maintain, and it requires only an easily modiﬁed
notch disk tiller.

Overall, the sandwich system coupled with the M.9 RN 29 rootstock seems to be
a suitable choice for growers that want to grow Paciﬁc Gala under organic protocol in
Michigan and similar climate and soil conditions. More research is still necessary
especially to conﬁrm these results in a longer term study with other disease resistant

rootstocks.

67

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69

Perry, R.L. (2000c). Keys to maintaining productive vertical axe trees. CAT, Fruit Ed.
MSU Extension, 15(2):2-3.

Robertson T. (2003). Insect Management and fruit thinning in commercial organic apple
production systems in New York. ORFR Project, Awarded spring 2000.

Sanchez, J. E., C. E. Edson, G. W. Bird, M. E. Whalon, R. R. Harwood, K. Kizilkaya, J.
E. Nugent, W. Klein, A. Middleton, T. L. Loudon, D. R. Mutch and J. Scrimger
(2003). Orchard ﬂoor and nitrogen management inﬂuences soil and water quality
and tart cherry yields. J. Amer. Soc. Hort. Sci. 128(2): 277-284.

Sarrantonio, M. (2003). Soil response to surface-applied residues of varying carbon-
nitrogen ratios. Biol. Fertil. Soils 37: 175-183.

Schmid A. and F. Weibel (2000). “Das Sandwich-System —ein Verfahren zur
herbizidfreien Baumstreifenbe- wirtschaftung?” Obstbau 25: 214-217.B

Webster T. (2000). Apple and pear scion varieties and rootstocks for organic tree fruit
production. Conference ‘Organic fruit opportunities and challenges’, Ashford,
Great Britain.

Weibel F. (2002). Soil management and in-row weed control in organic apple production.
The Compact Fruit Tree 35: 118-121.

Weibel, F. and A. Haseli (2003). Organic Apple Production - With Emphasis on
European Systems (2003). In: The CABI Apple Book, D. C. Ferree und 1. J.
Warrington (eds), CABI Publishing, Wallingford Oxon., approx. 40 pp,
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Weibel, F. and A. Haseli (2003). Organic Apple Production - With Emphasis on
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Warrington (eds), CABI Publishing, Wallingford Oxon., approx. 40 pp,
submitted.

Welker W.V. and D.M. Glenn (1989). Sod proximity inﬂuences the growth and yield of
young peach trees. J. Amer. Soc. Hort. Sci. 114(6): 856-859.

Yusseﬁ, M. (2004). Development and state of organic agriculture worldwide. The world
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167.

Zoppolo R.J. (2004). Orchard ﬂoor management systems and rootstock performance of
organically managed apples (Malus x domestica Borkh.). Ph.D. Dissertation
thesis, Michigan State University.

70

 

Picture 1: Modiﬁed notch disk tiller for the implementation and maintenance of the
Sandwich tilled strip.

 

Picture 2: Particular of the modiﬁcation in the disk set up for the notch disk tiller.

71

 

, afﬂgmmi

 

 

3.. .83: 2:qu

andwich Strip

S

Sandwich Row

Treatment

Mulch

F lame

2003 2004 2005 ]

 

l a 2002

 

 

 

ilanl
Atrium

c\\\\\\\\\\\\\\\\

\\\ﬁ\uwi§l:. r

 

 

 

3.5 -*

g .852 £590

 

andwich Strip

S

Sa
Treatment

Mulch

Flame

2003 a 2004 2005 [

 

E3 2002

I

Fig. 1: Effect of the treatments on Percentage of Organic Matter content in the soil during

the duration of the experiment (2002

 

2005) at 0-10 (A) and 0-30 (B) cm depth. Different

letters represent statistical difference (LSMEANS with P S 0.05) between years inside of

each treatment and should be read separately. Bars represent standard error.

72

Total mineral N (ppm)

Total mineral N (ppm)

Fig. 2: Effect of the treatments on Total mineral N (N-NO3' + N-NH4+) content in the soil
during the duration of the experiment (2003-2005) at 0-10 (A) and 0-30 (B) cm depth.
Different letters represent statistical difference (LSMEANS with P S 0.05) between years

 

 

 

 

 

 

 

 

 

Mulch
Treatment

 

in 2003 2004 2005

 

 

70 —ﬁ
60 - i¥ﬁ—

 

 

Mulch
Treatment

 

 

2003 2004 20057

 

inside of each treatment and should be read separately. Bars represent standard error.

73

Table 1: Pr >F values for the tree growth parameters measured during 2005

 

 

 

 

 

 

 

 

 

:mruszk Trunk cross
. sectional area Branch
sectronal Volume .
area Increase extensron
(2005) (2000-2005)
Treatment 0.5273 0.9780 0.5305 0.7672
Rootstock <0.0001 0.0010 <0.0001 0.4368
Tretament“ Rootstock 0.4069 0.3494 0.4069 0.6592

 

 

Table 2: Nitrogen content (ppm) in leaves from 2001 till 2005. Different letters represent
statistical difference (LSMEANS with P S 0.05).

 

 

 

 

 

 

 

 

 

2001 2002 2003 2004 2005
Mulch 2.1 2.4 a 2.7 a 2.2 a 2.1 a
Sandwich 2.1 2.2 b 2.2 c 1.8 b 1.8 b
Flame 2.] 2.4 a 2.4 b 1.9 b 1.8 b

 

 

 

Table 3: Pr > F values for the production parameters measured during 2005. Cumulative
parameters represent data 2003-2005.

 

 

 

 

 

 

 

 

 

 

 

 

 

Avg. . . Cumulative .
Fruit Yield Cl’mu'a‘m “dd. Yield Yield cu‘I‘ma‘”
Weight (kg/tree) (lg/'3“) 5:12:20; efﬁciency (t/ha) iii/:5“
(g) (kg/cmz)
Treatment 0.0652 0.9688 0.6813 0.7572 0.4304 0.9370 0.6014
Rootstock 0.1078 0.0001 0.0007 <0.0001 <0.0001 <0.0001 <0.0001
Tretament“
Rootstock 0.4360 0.0304 0.0454 0.0474 0.0414 0.0303 0.0414

 

74

 

r/I/I/n ~ , 7

TCAI 2000-2005 (cmz)

 

 

(I’ll/ll

 

 

 

Treatment Rootstock

Figure 3: Trunk Cross Sectional Area Increase (TCAI) from 2000 till 2005 for both
Treatments and Rootstocks. Different letters represent statistical difference (LSMEANS
with P S 0.05), n.s. means no statistical difference. Bars represent standard error.

Yield +Yle|d Eff.

Yield (kgltnae)
Yield Efﬁciency (kg/cm’)

 

 

 

Flame Mulch Sandwich

Figure 4: Rootstock productivity (kg/tree), expressed by the columns, and yield
efﬁciency (kg/cmz), expressed by the line, in 2005 divided in treatments and rootstocks.
Different letters represent statistical difference (LSMEANS with P S 0.05), n.s. means no
statistical difference. Same letters apply to both yield and yield efﬁciency. Bars represent
standard error.

75

Yield (tlha)

30
25
20

 

15
10

 

  

 

 

 

0

 

56‘
’0
xi.
0'0

Flame Mulch Sandwlch

Figure 5: Cumulative yield (t/ha) 2003-2005 divided in treatments and rootstocks.
Different letters represent statistical difference at (LSMEANS with P S 0.05). Bars
represent standard error.

Soll Moisture (% VIV)

 

30-

 

 

+ Flame
5 7 - 0 - Mulch
--0 - . SandwichStripi
— 0 - SandwiehRow

 

 

 

 

o I T—V 1 T Y | 17 l l l l V V I I I I l l l l l I V I V 1 I I I I Y I I l l I I V l ﬁf' V T I' I I

ixix“ tn" oo ‘— ix 02"" Six "" co‘o‘ 86" ixQ 8‘" 070')“

Rkkggga amt—.— eaS‘S 335$ a§ g3” ERBBgm $3 5% an: ;§ §
2002 2003 2004 2005

Date

Figure 6: Volumetric soil moisture content (as %) measured with TDR for the average 0-
45 cm depth, for the different treatments during 2002-2005.

76

Table 4: Cost evaluation of the application of the different ground ﬂoor management

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

systems during 2005.
Mulch Cost $
14 round bales of alfalfa 420
labor for application by hand 30 hrs
" $ 12.25/hr 367.5
Total 788
Flame
30 gal LPG * $1 .33/gal 39.9
labor 9hr 45' * $12.25/hr 119.44
tractor 25 hp 9hr 45' * $6.0 hr 58.5
Total 218
Sandwich
labor 4hr 05' * $12.25/hr 50
tractor 55hp 4hr 05' * $10/hr 40.83
Total 91

 

 

 

 

77

Abstract
CHAPTER 3. Effect of Orchard Floor Management Systems on Root
Architecture of “Paciﬁc Gala” on M.9 NAKB 337 under Organic Protocol.
By Dario Stefanelli

Plant root systems have a high plasticity, mostly due to their short life span, when
compared with the canopy. This continuous growth and mortality of roots allow the
plants to change their root architecture, probing the soil proﬁle for favorable conditions.
Fruit growers can change the soil conditions by using different orchard ﬂoor management
systems. It is important to implement sustainable systems that will provide proﬁtable
productivity without disrupting soil-root processes. The objective of the experiment was
to evaluate apple root distribution in response to three orchard ﬂoor management systems
(OFMS) under organic protocol by trench proﬁle mapping.

The experiment was conducted in an organically certiﬁed orchard of apple
“Paciﬁc Gala” on M.9 NAKB 337 (dwarﬁng) established in 2001. The three OFMS used
were mulch of alfalfa hay (MU), propane ﬂaming (FL), and strip tilling at each side of
the tree row while natural vegetation was allowed to grow undisturbed on the tree row
(Swiss Sandwich System, SS). We measured SOM and N concentration at 2 depths (0-10
and 0-30 cm) for 4 years. Root architecture was assessed after growing season and
harvest 2005 with the trench proﬁle mapping method. Trenches, 50 cm wide were dug 45
cm from the trunk perpendicular to the tree row in each OFMS. Trenches were
approximately 336 cm long and 132 cm deep. A 158 cm by 130 cm metal frame divided

by strings into 28 cm by 22 cm grid was placed against the proﬁle faces to facilitate the

78

counting and mapping of the rooting frequency. Roots on each proﬁle face were counted
and recorded in two diameter size classes: small (5 2 mm) and large (> 2 mm).

Orchard floor management systems did have an impact on root number and
distribution both vertically and horizontally. More roots were found in mulch than the
other two systems without showing any difference in the above ground part of the tree
suggesting that there was a greater allocation of carbohydrates in the roots. Mulch and
ﬂame showed a higher concentration of roots closer to the soil surface and mostly
restricted to the weed free area created by the treatments. Roots in the sandwich system
were found to be greatly extended through the soil proﬁle both vertically and
horizontally. Suggestions are made in this report as to the signiﬁcance of these ﬁndings

regarding the growing and managing of apples in an organic system.

79

Introduction

Plant root systems have a high plasticity, mostly due to their short life span, when
compared with the canopy (DeWitt et al., 1998). This continuous growth and mortality of
roots allow the plants to change their root architecture probing the soil proﬁle for
favorable conditions (Andrews and Newman, 1970). They respond differently to most of
the factors that inﬂuence soil conditions, both imposed (Beckenbach and Gourley, 1932)
or natural (Atkinson D. and Holloway, 1976a), by changing their life span or their entire
root system architecture, expanding/contracting it vertically and/or horizontally
depending on the soil conditions.

Plants tend to expand their root system (both vertically and horizontally) in
response to drought conditions, (Schenk and Jackson, 2002). This ﬁnding is also
conﬁrmed in fruit trees on which research has been done on the response to irrigation and
drought stress (Perry et al., 1983; Layne et al., 1986; Bassoi et al., 1998; Smart et al.,
2006). Soil type also affects root distribution. Fruit trees tend to have deeper root systems
in coarse soils. However, if there is an impermeable layer in soils, roots will not be able
to pass it (Smart et al., 2006). Higher soil fertility tends to induce a more superﬁcial root
system and/or concentrated in the more fertile area (Lyons et al., 1962; Smith, 1965).
Root architecture also responds to competition from other species, reducing the amount
of roots in the competitive area expanding it both horizontally and vertically (Atkinson

and White, 1976b; Glen and Welker, 1989; Parker, 1993; Merwin and Stiles, 1994;

Merwin et al., 1995).

80

It is clear that the root system, as a whole, is able to interact and to respond to soil
conditions (Ryser and Eek, 2000). Fruit growers can change the soil conditions by using
different ground ﬂoor management systems. It is important to develop systems that will
provide proﬁtable productivity based on soil-food web-root processes.

Efforts have then been put in developing OFMS that will create the best
environment for tree growth, allowing the maximization of its performance with minimal
external inputs (Weibel, 2002).

It therefore becomes necessary in organic production to assess the responses of
the root system to the OFMS implemented. In organic production it is necessary to
achieve a balance between above and below ground processes while implementing
OF MS, since growers can rely primarily on soil processes to make nutrient available for
the plants (Yao et al., 2005). If we know the root system response to certain OFMS, it
could be a great step toward a better understanding and utilization of the system, thus
beneﬁting the growers.

The objective of the experiment was to evaluate apple root distribution in

response to three GFMS under organic protocol by trench proﬁle mapping.

81

Materials and Methods

The experiment was conducted at the Clarksville Horticultural Experiment Station of
Michigan State University, MI. An orchard of “Paciﬁc Gala” (Malus x domestica Borkh.)
was established in May 2001. The orchard was certiﬁed organic by the Organic Crop
Improvement Association (OCIA) in 2003 and 2004 and Organic Grower of Michigan
(OGM) in 2005. The trees are grafted on three rootstocks, but for this experiment we
considered only those on M.9 NAKB 337 with 4.6 x 1.4 m spacing between the trees.
Trees were trained to a vertical axe system with relatively little pruning over the years
(Perry, 2000). Minimal pruning was applied to allow trees to grow as natural as possible
maintaining a single leader. A two wire trellis with galvanized metal poles was installed
as a support system. A drip irrigation with drippers of 2.3 L/h every 0.6 m was installed
in May 2001 and suspended from the lowest wire of the trellis on the tree row. All
orchard ﬂoor management systems received equal irrigation throughout the season.

Soil moisture was measured by time domain reﬂectometry (TDR) using a Mini Trase
6050X3 (Soilmoisture Equipment Corp., Goleta, CA) with 45 cm long stainless steel rods
permanently installed in the tree rows, halfway between two trees and in the middle of
the tilled strip in 2002. Measurements were taken for each of the 6 plots per treatment
weekly in 2002 and every other week in 2003-2005.

The site was previously farmed with conventional soybean-com-com-alfalfa rotation for
two cycles until 1998. Subsequent soil preparation consisted of sowing of buckwheat and

chicken compost ( 1250 kg/ha) and lime (2250 kg/ha) application in 1999 on the entire

82

surface. At plantation (April 2000) a mixture of red mammoth clover and endophytic rye
was sown in the alleys.

Three orchard ﬂoor management systems (OF MS) were established in the beginning of
the second growing season (2001) and maintained for the entire study. The treatments
consist of mulch of alfalfa hay (MU), the Sandwich System (SS) and Flaming (FL) with a
propane burner. The alfalfa hay mulch was laid underneath the tree canopy in a strip of 1
m on each side of the tree and kept 15-20 cm thick. 105 round alfalfa bales/ha were used
with a C:N ratio of 15:1. The treatment was hand-applied every spring and fall to keep
the thickness of the mulch constant in order to provide a shading effect for weed
suppression, and to maintain soil moisture.

The ﬂaming treatment consists of the burning of weeds underneath the tree canopy and 1
m on each side of the tree with propane gas (estimated 56 L/ha). A custom engineered
burner, consisting of 4 burners (200000 BTU/burner) in a row, and covered with a metal
protective shield to concentrate the heat and to prevent its escaping and damaging the
canopy. On the back of the shield was also mounted a sprinkler system to extinguish
eventual ﬁres occurring during the burning. The burner was mounted on the side of a
tractor on a hydraulic arm to better control the application of the treatment. To reach the
vegetation underneath the canopy on the tree row, a hand burner (150000 BTU) was
used. The treatment was applied ﬁve to six times during the year, starting at the end of
April - beginning of May and ending at the end of August. The treatment was repeated
every time the weeds would reach 10 cm high. Tractor speed was kept between 1.6 and

3.2 km/h depending on the density of the weeds to be controlled.

83

The Sandwich System is an adaptation of the Swiss system (Weibel, 2002) and consists
of an area 25-30 cm on each side of the tree, underneath the canopy, where spontaneous
vegetation is allowed to grow undisturbed. On each side of this weeded area two strips of
soil were kept free of vegetation by shallow tilling (5-10 cm deep). The strips were 70 cm
wide from planting till 2003 and expanded to 90 cm wide in 2004. Timing of the
treatment application was the same as the ﬂaming treatment. The tilling was
accomplished from 2001 through 2004 with a spring-tooth (three teeth 2001-2003, 5 teeth
2004) harrow mounted on a side-bar of a tractor. To improve tillage effectiveness, a
modiﬁed notch-disk tiller, mounted on the tractor side-bar, was deployed during the 2005
growing season.

The alley consisted of an equal mixture of endophytic rye and mammoth clover
established soon after planting the orchard in 2000. Clover was also reseeded in 2005 to
keep the proportion constant. The alleys were managed equally in all treatments by
periodical mowing (3-4 times year).

Tree growth parameters (TCA at dormancy, shoot growth, and canopy volume) and ﬁ'uit
production (Yield and average fruit weight) were measured to monitor the effect of the
OFMS on the above ground part of the tree.

The effect of the OFMS on the soil conditions were monitored through:

0 Soil organic matter concentration was measured by loss on ignition of 3g of dry soil,

from the above described soil samples, at 400 °C for 8 hours in a mufﬂe furnace.

84

The predominant soil type of the orchard is Kalamazoo sandy clay loam (Typic
Hapludalfs) with 53.1% sand, 23.1% silt, and 23.8% clay. The orchard presents mild
slopes (less than 3%).

Root architecture was assessed at the end of the sixth growing season and after harvest
2005 with the proﬁle wall method described by Bohm (1979). Trenches 50 cm wide were
dug in the middle between two trees (45 cm from the trunk) for each GFMS. Trenches
were approximately 336 cm long and 132 cm deep (Fig 1A and 1B) perpendicular to the
tree row. Trenches were dug with a backhoe. The distance from the surface of each soil
proﬁle was also measured.

A 158 cm by 130 cm metal frame divided by strings into 28 cm by 22 cm grid was placed
against the proﬁle faces to facilitate the counting and mapping of the root distribution.
Roots on each proﬁle face were counted and sub-divided in smaller than 2 mm diameter
and larger than 2 mm. The number of roots in each grid was transformed in percentage of
the visible root system and also represented as # roots / dm2 of soil.

The OP MS were applied in a complete randomized block design with six replicates. The
trenches were dug between the two central trees under evaluation for a total of twelve
proﬁle faces for each ground ﬂoor.

Statistical analysis was performed with SAS (Version 8, SAS Institute, Cary, NC, USA).
Distances from the trunk and depth in the soil proﬁle (determined from the string
positions) were considered as continuous components to determine the statistical
differences between the GFMS through polynomial analysis at the desired distance and
depth. The Least-square means test (LSMEANS) with pS0.05 was utilized to determine

statistical differences between the treatments after the polinomium was constructed.

85

The following timetable explains the history of the plot, sampling and measurements for

the duration of the experiment (conducted Sept-Oct 2005).

 

 

 

 

 

 

 

 

 

 

 

Prior to Conventional soybean-com—corn-alfalfa rotation (2 cycles). Last crop was com.
1993 Minimal tillage.
1999 Spring: tillage sowing of soybean, Chicken compost (1250kg/ha), lime (2250 kg/ha).
Fall: tillage, sowing of Buckwheat
2000 April: tillage, tree planting. August: sowing of red mammoth clover and endophytic
rye in the alleys.
2001 May: implementation of April, June, August, TCA, TCAI, shoot
the 3 orchard ﬂoor November: soil sampling growth, canopy volume,
management systems. for N03' leafN %’ 3}) AD
2002 Maintenance of the April, June, August, TCA, TCAI, shoot
OFMS and Tree training November: soil sampling growth, canopy volume,
for SOM and N03' leafN %, SP AD
2003-05 Maintenance of the April, June, August, TCA, TCAI, shoot
OFMS November: soil sampling growth, canopy volume,
for SOM, N02' and NH4 leafN %, SPAD, yield
1 *— Mulch area —""—’ I
l 0 i All
6
Alley : Tree : y
I I
: 45 cm :
l l
l l
l l
I I
l l
: 50 cm :
J 1
i i
I l
: 45 cm :
I I
l I
:< :
' 100 cm Tree ‘

Fig 1A. Top view diagram of trench location for apple tree root distribution study in the

 

 

 

mulch treatment.

86

 

Vegetated

: area

 

 

 

 

 

: n—n I
l l 50cm l l
: : Tree : :
I I l - I
Tilled Alle
Alley : Tilled : O : area : y
I area : I: I I
. I —T'45°“‘ I
i i r l l
l l i l
. l I I
l I l 50 cm I
l l l I
i I I I
l I l I
' I I I
l‘L >1 ——I‘45 cm I
I I v I I
: 90 cm : l"————’|90 cm I
' I O l I
Tree

Fig 1B. Top view diagram of trench location for apple tree root distribution study in the

sandwich treatment.

87

Results

There was no difference between treatments in the percentage of soil organic
matter (SOM) in the soil at either of the depths under evaluation (0-10 and 0-30 cm).
However, if we consider the position inside of each treatment, . we notice some
differences, except for the treatment mulch (MU) at 0-10 cm depth. For the treatments
ﬂame (FL) and Sandwich System (SS) the percentage of SOM in the alley was always
higher than where the treatments were applied (Tablel). We did not ﬁnd any difference
in SOM percentage neither between treatments, nor between positions inside of the
treatment at 0-30 cm depth (Table 2).

Tree vigor and cropping of Gala on M.9 NAKB 337 were not signiﬁcant among
treatments (data not shown).

The separation between the A and B horizon in the soil occurred at approximately
20 cm depth, thus the data representing the effects of depth on the root distribution are
expressed in 20 cm increments. Since there was no statistical signiﬁcance on the
interaction between the horizon and the treatments we evaluated the rooting only based
on the depth in the soil proﬁle discarding the horizon effect.

The mulch treatment had a higher total number of small (52 mm) roots/dm2 (6.9)
compared with the treatment ﬂame and sandwich (5.7 and 5.6). No difference was
determined between treatments regarding total number of large (>2 mm) roots/dm2

(Table 3).

88

Effect of depth on number of roots
Rooting frequency of small roots was greatest under the mulch system and for
large roots, under MU and FL at the shallow depth. (Table 4 and 6). Rooting

progressively declined in depth within each OF MS (Table 5 and 7).

Effect of distance from the tree trunk on number of roots.

Distances from the tree trunk were evaluated every 20 cm. Every distance
discussed below represents each side of the tree trunk. Between 0 and 20 cm from the
tree trunk treatment MU presented the highest number of small (<2 mm) roots/dm2
(1.18), followed by FL (1.0) and SS (0.8). Between 20 and 60 cm from the trunk MU
again had the highest number of small roots, SS presented the smallest and FL was in the
middle not differing from either of the other treatments (Tab. 8). Between 60 and 100 cm
from the trunk no difference between the treatments was found. Between 100 and 160 cm
from the trunk the treatment SS had the highest number of small roots/dm2 while no
differences were found between the other two treatments (Tab. 8).

When we consider the effect of distance from the tree trunk inside of each
treatment we can see slightly different results. In the MU treatment we noticed a
signiﬁcant steady decrease in the number of small roots/dm2 from 0 to 100 cm from the
trunk (the area where the mulch was applied) (Tab. 9). Flame treatment also presented a
similar decrease at the same distances, but differences were not as accentuated (Tab. 9).
Farther than 100 cm, where the alley is situated (100-160), no difference in number of
small roots was noticed in MU or FL treatments. In the SS treatment the decrease in

number of small roots, depending on the distance from the trunk, is even less accentuated

89

than the other two treatments. Sandwich system still had that the highest number of small
roots is closer to the tree trunk (0-40 cm); however the decrease is more gradual. In fact,
between 20 and 100 cm from the trunk (most of the tilled strip) the number of small roots
is the same, as well as between 80 and 160 cm from the trunk (Tab. 9).

The distance from the tree trunk did not have any effect on large (>2 mm) roots
among the treatments (Tab. 10). The number of large roots steadily and signiﬁcantly
decreased in each treatment between 0 and 80 cm from the trunk. No differences were
found in any of the treatments greater in distance than 80 cm from the tree trunk (80 to

160 cm) (Tab. 11).

Percentage of rootiﬂz

Percentage of rooting is another method to represent the distribution of the roots
in the face wall of the soil proﬁle. It represents the percentage of roots present at each
distance from the trunk and at each depth on the total amount of roots present. From Fig.
1&2 we can see that MU and FL show the same percentages along the soil proﬁle both in
distance from the trunk and in depth in the soil proﬁle. For these two treatments,
percentage of rooting steadily decreases along the depth of the soil proﬁle till 80 cm, with
the highest percentages closer to the soil surface, below that it is similar. They also show
a steady decrease in rooting percentage the farther from the trunk till 100cm distance,
which is the area covered from the treatment and weed free, with the highest percentage
closer to the trunk. Farther than 100 cm the percentage of rooting is similar. In treatment
SS (Figure 3) percentage of rooting is more evenly distributed along the soil proﬁle both

in distance from the trunk and in depth in the soil proﬁle. It still shows a decrease in

90

rooting percentage the farther we move from the trunk but it is less pronounced, in fact
from 0 to 40 cm from the trunk SS shows the same percentages as well as from 40 to 100
cm. Farther than 100 cm (100-160 cm) the percentages are similar. While MU and FL
presented the highest percentages closer to the soil surface rapidly declining along the
entire proﬁle (Figure 1), SS shows the same percentage of rooting at 60 cm deep and then
it starts decreasing (Figure 1). The depth, at which the percentage of roots starts
decreasing, increases with the distance from the trunk (Figure 1). The sandwich system
practically promotes rooting deeper and farther from the trunk compared with FL and
MU where the roots are shallower and closer to the trunk. The same pattern described for
small roots was noticed for the large roots as well (Figures 2).

If we consider the treatments in their weed free areas, we notice that there are
differences in percentages of small roots between the treatments. The mulch and FL
treatments had 90.1% and 89.9% of the roots respectively are in the weed free area (0-
100cm from the trunk), having only more or less 10% of the small roots that reache in the
alley. The sandwich system instead, had 20.9% of the small roots in the weeded area
underneath the canopy, 63.6% in the tilled area and 15.5% that reache in the alley.

Soil water content.

Measurements performed with TDR (Figure 3) demonstrated that most of the time
there were no differences between OFMS. When some difference was present MU had
always the highest values while the SVA had the lowest. Flame and the tilled strip in the

sandwich did not differ from the other two.

91

Discussion

The treatments had an effect on the soil organic matter concentration only in the
superﬁcial sampling (0-10 cm) with mulch showing the highest numbers. This is
probably due to the continuous addition and consequent decomposition during the season
and years of alfalfa hay. The fact that only the superﬁcial layer was affected is probably
due to the fact that the mulch was added on top of the previous one and left undisturbed.
The different concentrations of SOM will reﬂect on the available nitrogen in the soil as
well (Powlson and Jenkinson, 1990; Diaz Rossello, 1992b; Bloksma, 2000). However,
considering that the deepest sampling we tested was 30 cm, it is difﬁcult to assess if there
were different concentrations of SOM in deeper soil proﬁles and consequently if they
exerted any effect on deeper root distribution. This factor should probably be better
investigated. When a difference occurred, MU had the highest soil water content.

The different soil composition of the B horizon did have an effect on the number
of roots as reported by Fernandez et al. (1995), but since there was no interaction
between treatments and soil type it was discarded from the analysis as inconsequential in
this investigation.

We measured no differences in tree vigor and cropping between the treatments,
however the mulch treatment had a higher number of roots/dm2 than the other two
treatments. Mulch also presented the highest number of roots/dm2 closer to the soil
surface where the treatment was able to exert some effect on the soil conditions (higher
SOM and nitrogen concentration). Morlat and Jacquet (1993) did in fact ﬁnd a higher

number of roots in soil with higher organic matter concentration for grapevine. The

92

consideration of these two factors suggests that there is a higher carbon allocation in the
root system under mulch than in the other two treatments (Lakso et al., 1999 and Comas
et al., 2005). However, several other factors could be responsible, besides the carbon
allocation, for the different response that the Orchard ﬂoor management systems had on
root number and distribution.

In general the treatments responded as reported from Cowart (1938), Lyons and
Krezdom (1962), and Parker (1993) who demonstrated a decrease in root number with
the increase of depth and/or distance from the trunk. However, the pattern of this
decrease was different depending on the treatments. In fact, when considering the root
frequency (as % of root in a particular position on the total number of roots in the wall
proﬁle), we noticed that mulch and ﬂame had the same distribution while sandwich was
different. Sandwich had a lower concentration of roots closer to the surface and at the
same time a more extensive root system that reached well into the alley. In contrast to
Cockroft and Wallbrink (1966), and Parker (1993) in peaches, there was a greater
concentration of roots deeper in the soil proﬁle. As expected, there were more roots in the
weed free zones (mulch and ﬂame) compared with vegetated areas as reported from
Atkinson and White (1976), Glen and Welker (1989) and Parker (1993). This was
relatively true for SS as well. It still had higher root percentage closer to the trunk than in
the weed free area. This could be caused from the position of the irrigation that was
established on the tree row. If we had the irrigation on the tilled strip it would have
probably have shown higher percentage than what we found in that area. When
differences occurred, the vegetated area had the lowest water content, while the tilled

area had similar water content to MU and FL. This factor should be probably investigated

93

more deeply. Bechenbach and Gourley (1932), Cockroft and Wallbrink (1966), and
Richards (1983) reported that mulching encourages rooting in the mulch and in the soil
surface for apple, peach, pear, and grapes. However, the expansion of the sandwich root
system into the alley zone was not expected. This could be due to the combination of
greater competition underneath the tree canopy (Schenk and Jackson, 2002) coupled with
the effect of the tillage in the weed free area that prompted the sandwich root system to
expand both vertically and horizontally. It is, in fact, known that tilling disturbs and
reduces roots closer to the soil surface (Cockroft and Wallbrink, 1966; Richards, 1983).
The same pattern of distribution was observed for both small (<2 mm) and large (>2 mm)

I'OOtS .

94

Conclusion

Orchard ﬂoor management systems did have an impact on root number and
distribution along the soil wall both vertically and horizontally. Mulch presented a higher
number of roots compared with the other two systems without showing any difference in
the above ground part of the tree leading to a higher allocation of carbohydrates in the
roots.

Mulch and ﬂame had a higher concentration of roots closer to the soil surface and
mostly restricted to the weed free area created by the treatments. The sandwich root
system was prompted by the treatment to explore more soil extending both vertically and
horizontally. Considering the higher difﬁculties that organic horticulture encounters in
creating more balanced soil conditions for the tree uptake (mostly through fertilization), a
more expanded root system is beneﬁcial to the tree because it encourages greater probing,
helping in the uptake of nutrients and water. It will also reduce eventual leaching since

the root free area will be lower in the soil proﬁle than a more superﬁcial root system.

95

Literature cited

Andrews RE. and KC. Newman (1970). Root density and competition for nutrients.
Ecologia plant. (5): 319-334.

Atkinson D. and R.I.C. Holloway (1976a). Weed competition and the performance of
established apple trees. Proc. 1976 British Crop. Conf. Weeds (1): 299-304.

Atkinson D., G.C. White, E.R. Mercer, M.G. Johnson and D. Mattam (1976b). The
distribution of roots and the uptake of nitrogen by established apple trees grown
in grass with herbicide strip. Rpt East Malling Res Sta, p.183-185.

Beckenbach J. and J .H. Gourley (1932). Some effect of different cultural practices upon
root distribution of apple trees. Amer. Soc. Hort. Sci. Proc. (29): 202-204.

Bassoi, L. H. ; Jorge, L. A. C. ; Crestana, S. (1998). Root distribution analysis of irrigated
grapevines in Northeastern Brazil by digital image processing. In: World
Congress of Soil Science, Montpellier.

DeWitt T.J., A. Sih and D.S. Wilson (1998). Costs and limits of phenotypic plasticity.
Tree 13(2): February 1998.

Glenn D.M. and W.V. Welker (1989). Peach root development and tree hydraulic
resistance under tall fescue sod. HortScience 24(1): 117-119.

Lyons C.G. Jr. and AH. Krezdom (1962). Distribution of peach roots in Lakeland ﬁne
sand and the inﬂuence of fertility levels. Proc. Florida State Hort. Soc. (75): 371-
377.

Merwin LA. and WC. Stiles (1994). “Orchard ground cover management impacts on
apple tree grth and yield, and nutrient availability and uptake”. Journal of
American Society of Horticultural Science. 119(2): 209-215.

Merwin I.A., D.A. Rosenberger, C.A. Engle, D.L. Rist and M. Fargione (1995).
Comparing mulches, herbicides, and cultivation as orchard groundcover
management systems. HortTechnology 5(2): 151-158.

Morlat R. and A. Jacquet (1993). The soil effects on grapevine root system in several
vineyards of the Loire valley (France). Vitis, Suebeldingen, 32(1): 35-42.

Parker M.L., J. Hull and R.L. Perry (1993). Orchard ﬂoor management affects peach

rooting. J oumal-of-the-American-Society-for-Horticultural-Science. l 993;
118(6): 714-718

96

Perry R.L., S.D. Lyda and H.H. Bowen (1983). Root distribution of four Vitis cultivars.
Plant and soil (71): 63-74.

Richards D. (1983). The grape root system. Horticultural review, (5): 127-168.

Ryser P. and L. Eek (2000). Consequences of phenotypic plasticity vs. interspeciﬁc
differences in leaf and root traits for acquisition of aboveground and belowground
resources. American Journal of Botany 87(3): 402-411.

Schenk H]. and RB. Jakcson (2002). Rooting depths, lateral root spread and below-
ground/above-ground allometries of plants in water-limited ecosystems. Journal
of Ecology (90): 480-494.

Smart D.R., E. Schwass,A. Lakso and L. Morano (2006). Grapevine rooting patterns: A
comprehensive analysis and a review. Am. J. Enol. Vitic. 57(1): 89-104.

Smith PF. (1965). Effect of nitrogen source and placement on the root development of
Valencia orange trees. Proc. Fla. State. Hort. Soc. (78) 55-59.

Van Zyl J.L. (1988). The grapevine root and its environment. Pretoria: Department of
Agriculture and Water Supply. (Technical communication 215).

Yao S., LA. Merwin, G.W.Bird, G.S. Abawi and J.E. Thies (2005). Orchard ﬂoor
management practices that maintain vegetative or biomass groundcover stimulate

soil microbial activity and alter soil microbial community composition. Plant and
soil (2005) 271 :377-389.

97

Table 1: Percentage of Organic Matter in the soil in the treatments at 0-10 cm depth.

 

 

 

 

 

 

Treatments
Position Flame Mulch Sandwich
Alley 2.7 a 3.5 a 3.0 a
Tree row 1.8 b 3.1 a 2.1 b
Tilled strip 1.9 b

 

 

 

 

Different letters represent statistical differences (LSMEANS with P5005).

Table 2: Percentage of Organic Matter in the soil in the treatments at 0-30 cm depth.

 

 

 

 

 

 

Treatments
Position F lame Mulch Sandwich
Alley 2.2 a 2.3 a 2.5 a
Tree row 1.9 a 2.0 a 1.9 a
Tilled strip 1.9 a

 

 

 

 

 

Different letters represent statistical differences (LSMEANS with P5005).

Table 3: Total number of roots/dm2 in each treatment.

 

 

 

 

 

Treatments Small roots (52 mm) Large roots (>2 mm)
Mulch 6.9 a 0.09 a
Flame 5.7 b 0.07 a
Sandwich 5.6 b 0.07 a

 

 

 

 

Different letters represent statistical differences (LSMEANS with P5005).

Table 4: Number of small (52 mm) roots/dm2 at each depth in the soil proﬁle depending

 

 

 

on the treatments.
De 0th in the soil proﬁle (cm)
Treatments 0-20 20-40 40-60 60-80 80-100 100-120
Flame 0.78 b 0.59 a 0.45 a 0.35 a 0.27 a 0.20 a
Mulch 1.00 a 0.71 a 0.50 a 0.37 a 0.24 a 0.16 a
Sandwich 0.66 b 0.65 a 0.59 a 0.51 a 0.38 a 0.22 a

 

 

 

 

 

 

 

 

 

Different letters represent statistical differences (LSMEANS with P5005) between

treatments at each depth in the soil proﬁle.

97

 

Table 5: Number of small (52 mm) roots/dm2 for each treatment depending on the depths
in the soil proﬁle (cm).

 

 

Depth in the soil

proﬁle (cm _) Flame Sign. Mulch Sign'. Sandwich Sigi
0-20 0.78 a 1.00 a 0.66 a
20.40 0.59 b 0.71 b 0.65 a
40-60 0.45 be 0.50 c 0.59 a
60-80 0.35 cd 037 cd 0.51 ab
80-100 0.27 d 0.24 de 0.38 be
100120 0.20 d 0.16 e 0.22 c

 

 

 

 

 

 

IDifferent letters represent statistical differences (LSMEAN S with P5005) between
depths in the soil proﬁle inside each treatment.

Table 6: Number of large (>2 mm) roots/dm2 at each depth in the soil proﬁle depending

on the treatments.

 

De 0th in the soil proﬁle (cm)

 

 

 

 

 

 

 

 

 

Treatments 0-20 20-40 40-60 60-80 80-100 100-120
Flame 0.16 a 0.09 a 0.05 a 0.02 a 0.01 a 0.00 a
Mulch 0.18 a 0.10 a 0.05 a 0.02 a 0.01 a 0.00 a
Sandwich 0.11 b 0.09 a 0.06 a 0.04 a 0.02 a 0.00 a

 

 

Different letters represent statistical differences (LSMEAN S with P5005) between
treatments at each depth in the soil proﬁle.

Table 7: Number of large (>2 mm) roots/dm2 for each treatment depending on the depths
in the soil proﬁle (cm).

 

 

 

 

 

 

Depth in the soil

proﬁle (cm_) Flame Signl. Mulch Sign'. Sandwich Sign].
0-20 0.16 a 0.18 a 0.11 a
20-40 0.09 b 0.10 b 0.09 ab
40-60 0.05 c 0.05 c 0.06 bc
60-80 0.02 cd 0.02 d 0.04 cd
80-100 0.01 d 0.01 d 0.02 (1
100-120 0.00 d 0.00 d 0.00 d

 

 

lDifferent letters represent statistical differences (LSMEANS with P5005) between
depths in the soil proﬁle inside each treatment.

98

Table 8: Number of small (52 mm) roots/dm2 at different distances from the tree trunk

 

 

 

 

 

 

 

 

 

 

 

 

depending on the treatments.

Distances from the trunk Em)
Treatments 0-20 20-40 40-60 60-80 80-100 100-120 120-140 140-160
Flame 1.00 b 0.81 ab 0.65 ab 0.49 a 0.32 a 0.18 b 0.07 b 0.01 b
Mulch 1.18 a 0.97 a 0.77 a 0.53 a 0.32 a 0.18 b 0.04 b 0.00 b
Sandwich 0.80 c 0.68 b 0.58 b 0.49 a 0.42 a 0.37 a 0.34 a 0.33 a

 

Different letters represent statistical differences (LSMEANS with P5005) between
treatments at each distance from the tree trunk.

Table 9: Number of small (52 mm) roots/dm2 for each treatment depending on the
distance from the tree trunk (cm).

 

 

 

 

Distance from

the trunk (cm) Flame Sign]. Mulch Signl. Sandwich Sign .
0-20 1.00 a 1.18 a 0.80 a
20-40 0.81 ab 0.97 b 0.68 ab
40-60 0.65 bc 0.77 c 0.58 b
60-80 0.49 c 0.53 d 0.49 bc
80-100 0.32 d 0.32 e 0.42 bc
100-120 0.18 de 0.18 ef 0.37 c
120-140 0.07 e 0.04 f 0.34 c
140-160 0.01 e 0.00 f 0.33 c

 

 

 

 

1Different letters represent statistical differences (LSMEANS with P5005) between
distances from the tree trunk inside each treatment.

Table 10: Number of large (>2 mm) roots/dm2 at different distances from the tree trunk
depending on the treatments.

 

 

 

 

 

Distances from the trunk (cm)
Treatments 0-20 20-40 40—60 60-80 80-100 100-120 120-140 140-160
Flame 0.16 0.11 0.08 0.05 0.03 0.01 0.01 0.00
Mulch 0.17 0.12 0.09 0.06 0.04 0.02 0.01 0.00
Sandwich 0.16 0.1 1 0.08 0.05 0.02 0.00 0.00 0.00

 

 

 

 

 

 

 

 

 

No differences were found between treatments (LSMEANS with P5005).

99

 

Table 11: Number of large (>2 mm) roots/dm2 for each treatment depending on the
distance from the tree trunk (cm).

 

 

 

 

 

 

Distance

from the

trunk (cm) Flame Signl. Mulch Sign'. Sandwich Sign].
0-20 0.16 a 0.17 a 0.16 a
20-40 0.11 b 0.12 b 0.11 b
40-60 0.08 c 0.09 c 0.08 c
60-80 0.05 cd 0.06 cd 0.05 d
80-100 0.03 d 0.04 d 0.02 de
100-120 0.01 d 0.02 d 0.00 e
120-140 0.01 d 0.01 d 0.00 e
140-160 0.00 d 0.00 d 0.00 e

 

 

IDifferent letters represent statistical differences (LSMEANS with P5005) between
distances from the tree trunk inside each treatment.

100

Figure 1: Frequency (% on the total number of roots) of small roots (5 2 mm in diameter)
related to the distance from the trunk and depth in the soil proﬁle.

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103

Abstract
CHAPTER 4. Root Development of Apple as Affected by Orchard
Floor Management Systems under Organic Protocol.
By Dario Stefanelli

One of the major challenges in organic fruit production is the implementation of a
successful orchard ﬂoor management system (OFMS) to maintain productivity. Many
plant root systems can adjust nutrient uptake capacity to meet variation in shoot demand
caused by environmental changes. Root turnover is an important indicator of plant
productivity and a measurement of carbon return to the soil. In general, an increased N
concentration in soil accelerates the process of ﬁne root turnover. It becomes then,
important to determine root response to the different conditions that an OF MS will create.
In adverse soil conditions, negative impact on root development and generation could be
detrimental for tree production, thus making that OFMS less suitable.

The aim of this experiment was to evaluate ﬁne root development as affected by
two different OF MS using the minirhizotron technique.

The experiment was conducted in an orchard of “Paciﬁc Gala” (Malus x
domestica Borkh.) on M.9 NAKB 337, planted in May 2001. The OFMS used were
mulch of alfalfa hay (MU) and strip tilling at each side of the tree row while natural
vegetation was allowed to grow undisturbed on the tree row (Swiss Sandwich System,
SS). We measured SOM and N concentration at 2 depths (0-10 and 0-30 cm) for 4 years.
Root development was monitored by minirhizotrons. Root characteristics (number,
length, diameter, area, volume, number of branches, and angle of branch insertion) were

monitored and measured utilizing a custom software program.

104

Orchard ﬂoor management systems did have an effect on ﬁne root development.
The different soil conditions created from the systems (higher N concentration in mulch)
were likely responsible for the increase in ﬁne root life span measured in the sandwich
system (50-60 days against 30 for the mulch). Fine root production initiated earlier in SS

vegetated area than MU and more ﬁne roots were found in SS vegetated area than MU.

105

Introduction

One of the major challenges in organic fruit production is the implementation of
successful orchard ﬂoor management systems (OFMS). The lack of herbicides in organic
horticulture requires OFMS that limit or restrict ground cover competition so tree
performance does not suffer.

Whichever the OFMS selected, organic growers rely primarily on soil microbial
processes to obtain the nutrients for plants; thus, OFMS are extremely important because
they have an effect on soil conditions and consequently on nutrient availability, tree
growth and yield (Yao et al, 2005). Orchard ﬂoor management systems will change the
microbial composition and food web of the soil (Yao et al, 2005). The absorption of
nutrients within an ecosystem depends on temporal and spatial synchrony between
nutrient availability and nutrient uptake (Bassirirad, 2000; Tierney et al., 2001).

Plant roots can alter their water and nutrient acquisition capacity by adjusting
their physiological longevity, morphological and/or architectural characteristic to meet
changes in shoot nutrient demand (Chapin, 1980; Clarkson and Hanson 1980; Clarkson
1985). Therefore, it is useful to evaluate root characteristics that play a role such as
lifespan and turnover, as indicators of grth potential of the plant and its actual nutrient
acquisition (Bakker, 1999).

Roots, and ﬁne roots in particular, play a central role (Schulze et al., 1997) in soil
chemicals (pH, 02, C02 and other ions), physical (moisture and aeration), and biological
(soil pathogens, beneﬁcial microorganisms and allelopathy) composition (El-Shatnawi

and Makhadmeh, 2001) with important consequences for plant growth and productivity,

106

plant competition, biological activity, and carbon and nutrient cycling at an ecosystem
scale by releasing in the soil a wide variety of exudates (Makhadmeh and El-Shatnawi,
2001; Bertin et al., 2003; Walker et al., 2003). Plants expend a substantial proportion of
photosynthate below ground in the annual production of ﬁne roots (Eissenstat et al.,
2000) and release of exudates (Walker et al., 2003). In many cases, more than 50% of
annual net primary production (N PP) is allocated below ground, and nutrient return to the
soil by tree ﬁne root death may exceed that by the above ground litterfall (Kasuya N.,
1997). Tree root turnover may return four to ﬁve times more carbon to the soil than
above ground litter (Zech and Lehrmann, 1998). Consequently there is a need to include
the effects of root turnover in models of carbon and nutrient cycling (Cox et al., 1978;
Vogt et al., 1986; Hendricks et al., 1993; Jackson et al., 1997; Norby and Jackson, 2000).

Moreover, through the exudation of a wide variety of compounds, roots regulate
the soil microbial community in their immediate vicinity, cope with herbivores, and
encourage beneﬁcial symbioses (Nardi et al., 2000, Walker et al., 2003).

Assessing root turnover becomes then, very important as an indicator of plant
productivity and a measurement of carbon return to the soil. In the last decade the most
common technique to measure ﬁne root turnover is by minirhizotrons installed in the
ground. They can be used to characterize ﬁne root production, phenology, growth,
mortality and lifespan, and are useful in developing ecosystem carbon budgets (Hendrick
and Pregitzer, 1996; Majdi, 1996). Their reliability depends on the accuracy of assessing
physiological status of the roots (alive or dead) (Wang et al, 1995; Tingey et al, 2000)

mostly based on color (Hendrick and Pregitzer 1992a, b; Comas et al, 2000).

107

However, the determination of ﬁne root physiological status is a common
problem (Comas et al., 2000). Also, there is a certain inconsistency in the deﬁnition of
the proper diameter for ﬁne roots. Several authors reported that ﬁne roots, for woody
perennials, should be 5 1 mm in diameter (McCrady and Comerford, 1998; Eissenstat et
al, 2000; Comas and Eissenstat 2001).

Processes and responses vary not only with root diameter but with other root
characteristics as well (Norby and Jackson, 2000). It is necessary to couple the total size
of the root system with physiological information on the response of root speciﬁc nutrient
uptake efficiency (Norby and Jackson, 2000). The size of the root system and its
efficiency to deploy roots at the time and place nutrients are present (Fitter et al., 1991),
as well as the efﬁciency by which a particular root segment can take up a nutrient from
the soil solution (Norby and Jackson, 2000), are fundamental for the plant uptake
capacity (Tjeerd et al., 2001). The degree to which kinetics of nutrient uptake or other
potential adjustments are expressed would ultimately depend on soil nutrient availability
(Tjeerd et al., 2001) and soil factors that determine transport to the root surface
(Bassirirad, 2000). Nutrient adsorption, and eventually absorption within an ecosystem,
depend on temporal and spatial synchrony between nutrient availability and nutrient
uptake, and disruption of ﬁne root development (Tierney et al., 2001).

In general, increased N concentrations in the soil decrease ﬁne root turnover
because of their increased lifespan (Pregitzer et al., 1993; Ostonen et al., 1999; Burton et
al., 2000; Hendricks et al., 2000; King et al., 2002) allowing the plant to reduce carbon
costs. However, several authors reported that with increased N concentration in soil, root

turnover rates increase, reducing ﬁne root lifespan (Aber et al, 1985; Nadelhoffer et al.,

108

1985; Persson and Ahlstrdm, 2002). Burton et a1. (2000), in an experiment on ﬁne roots
(<1 mm) dynamics within and across forest species with different N availability, found
that, across species root lifespan decreases with increased N availability, while within
species there is the opposite trend. Tjeerd et a1. (2001) found that in P depleted soils
citrus ﬁne roots life span was diminished.

In any case, all the authors agree on the importance of the interaction between N
availability and ﬁne root dynamics, especially for the effects on organic matter
(McClaugherty et al, 1982), on the organic N pool in the soil (Ehrenfeld et al., 1997), and
on the control of the substrate quality (Hendricks et al., 2000).

Root turnover has been extensively studied in grasslands and forests ecosystems
but there is not much literature on fruit trees and none in organic tree production.

The established interaction between OF MS, food web, and root processes could
create a different response from the roots that needs to be studied and compared between
conventional and sustainable conditions.

The aim of this experiment was to evaluate ﬁne root development as affected by

two organic OFMS utilizing the minirhizotron technique.

109

Materials and Methods.

The experiment was conducted in an orchard of “Paciﬁc Gala” (Malus x domestica
Borkh.) on M.9 NAKB 337, planted in May 2001 at the Clarksville Horticultural
Extension Station at a spacing of 4.6 x 1.4 m between the trees. The orchard has been
certiﬁed organic in 2003 and 2004 by Organic Crop Improvement Association (OCIA),
and in 2005 by Organic Growers of Michigan (OGM). Trees were trained to a vertical
axe system with relatively little pruning over the years (Perry, 2000). Minimal pruning
was applied to allow the tree to grow as natural as possible maintaining a single leader. A
two wire trellis with galvanized metal poles was installed as support system. Drip
irrigation with drippers of 2.3 L/h every 0.6 m was installed in May 2001 and suspended
from the lowest wire of the trellis on the tree row. All orchard ﬂoor management systems
received equal irrigation throughout the season.

Soil moisture was measured by time domain reﬂectometry (TDR) using a Mini
Trase 6050X3 (Soilmoisture Equipment Corp., Goleta, CA) with 45 cm long stainless
steel rods permanently installed in the tree rows, halfway between two trees and in the
middle of the tilled strip in 2002. Measurements were taken for each of the 6 plots per
treatment weekly in 2002 and every other week in 2003-2005.
The site was previously farmed with conventional soybean-com-com-alfalfa rotation for
two cycles until 1998. Subsequent soil preparation consisted of sowing of buckwheat and
chicken compost (1250 kg/ha) and lime (2250 kg/ha) application in 1999 on the entire
surface. At plantation (April 2000) a mixture of red mammoth clover and endophytic rye

was sown in the alleys.

110

The two orchard ﬂoor management systems (OF MS) under study were
established in a complete randomized block design at the beginning of the second
growing season (2001) and maintained for the entire study. The treatments consist of
mulch of alfalfa hay (MU), the Sandwich System (SS). The alfalfa hay mulch was laid
underneath the tree canopy in a strip of 1 m on each side of the tree and kept 15-20 cm
thick. 105 round alfalfa bales/ha were used with a C:N ratio of 15:1. The treatment was
hand-applied every spring and fall to keep the thickness of the mulch constant to provide
a shading effect for weed suppression, and to maintain soil moisture. The Sandwich
System is an adaptation of the one reported by Weibel (2002) and consists of an area 25-
30 cm on each side of the tree, underneath the canopy, where spontaneous vegetation is
allowed to grow undisturbed. On each side of this vegetated area two strips of soil were
kept free of vegetation by shallow tilling (5-10 cm deep). The strips were 70 cm wide
from planting till 2003 and expanded to 90 cm wide in 2004. Timing of the treatment
application was the same as the ﬂaming treatment. The tilling was accomplished from
2001 through 2004 with a spring-tooth (three teeth 2001-2003, 5 teeth 2004) harrow
mounted on a side-bar of a tractor. To improve tillage effectiveness, a modiﬁed notch-
disk tiller, mounted on the tractor side-bar, was deployed during the 2005 growing
season.

The alley consisted of an equal mixture of endophytic rye and mammoth clover
established soon after planting the orchard in 2000. Clover was also reseeded in 2005 to
keep the proportion constant. The alleys were managed equally in all treatments by

periodical mowing (3-4 times year).

111

The predominant soil type of the orchard is Kalamazoo sandy clay loam (Typic
Hapludalfs) with 53.1% sand, 23.1% silt, and 23.8% clay. The orchard presents mild
slopes (less than 3%).

Tree grth parameters (TCA at dormancy, shoot growth, and canopy volume)
and fruit production (Yield and average fruit weight) were measured to monitor the effect
of the OFMS on the above ground part of the tree.

The effect of the OF MS on the soil conditions were monitored:

0 Soil nitrate (NO3') and ammonium (NIH) concentration in the soil, to
check the immediate available nitrogen released from the treatments available to the
trees. Soil samples were obtained for the two OFMS by mixing 20 soil core sub-
sarnples from the tree row. Soil samples from the Alleys and the tilled strip of the SS
were obtained by mixing 10 soil core sub-samples from each side of the tree row. Soil
samples were collected every two months starting in April until November at 0-30 cm
depth each year. The 0-30 cm depths have been chosen to represent the most
frequently explored part of soil from roots. Soil samples were air dried at 105°C for
24 hrs. Nitrates and ammonium concentration was measured by extraction with 100
ml of KCl 1 M on 10 g of dried soil, placed for 1 hour on a shaker and then ﬁltered
with ﬁlter paper. The extraction liquid was sent to the MSU soil lab for the analysis
following the procedure described by (Kenney, 1982) using a Lachat automated
colorimetric analyzer (Lachat Instruments Inc. Milwaukee, WI).

0 Soil organic matter (SOM) concentration was measured by loss on ignition
of 3g of dry soil, from the above described soil samples, at 400 °C for 8 hours in a

mufﬂe furnace.

112

Root development was monitored using minirhizotrons installed during summer
2002. Minirhizotrons consisted of clear butyrate plastic tubes 13 cm in diameter and 182
cm long. Four tubes for each tree in trial were installed at a 45° angle facing the tree at 40
cm from the tree trunk parallel to the tree row, and 122 cm deep. To evaluate the effect of
the OFMS on root development the tubes were installed at the same ﬁxed intervals from
the tree trunk in each treatment (2 at 13 cm on each side the tree trunk perpendicular to
the tree row, 1 at 53 cm, and the last one at 68 cm) (Fig. 1 A and 1 B). Two trees for each
treatment were utilized in the experiment with four replicates for a total of 32 tubes for
each treatment.

Images of roots were recorded at ﬁxed time intervals (2-3 weeks) during the
growing season with a digital camera developed by Bartz Technology Corp., CA.
Thirteen images were collected for each tube and recorded every 10 cm along the length
of the tube starting at 10 cm depth. Data were collected in 2003 and 2004.

Root parameters (number, length, diameter, area, volume, number of branches,
and angle of branch insertion) were measured through a software program especially
designed from our department. The software utilizes an algorithm (claimed in US. Patent
Number 6,690,816 which has been assigned to the University of North Carolina at
Chapel Hill. Used with permission) speciﬁcally modiﬁed for root studies. The program is
copyrighted by the MSU Board of Trustees, and is currently not commercially available.

Root data from each image was segregated into four classes (0-30 cm, 30-60 cm,
60-90 cm, and below 90 cm) to evaluate development within the soil horizons. Distances
from the tree trunk were kept separated to evaluate the effect of distance on root

development.

113

Data were log transformed to maintain homogeneity. Statistical analysis was

performed with SAS (Version 8, SAS Institute, Cary, NC, USA). Analysis of variance

was performed using the MIXED procedure to detect treatment, distance from the trunk,

and depth in the soil proﬁle effects, as well as their interactions. Where appropriate,

means were separated using the Least-square means test (LSMEANS) with p5005.

The following timetable explains the history of the plot, sampling and

measurements for the duration of the experiment (conducted May-Sept 2004 & 2005).

 

 

 

 

 

 

 

 

 

 

Prior to Conventional soybean-com-com-alfalfa rotation (2 cycles). Last crop was com.

1998 Minimal tillage.

1999 Spring: tillage sowing of soybean, Chicken compost (1250kg/ha), lime (2250 kg/ha).
Fall: tillage, sowing of Buckwheat

2000 April: tillage, tree planting. August: sowing of red mammoth clover and endophytic
rye in the alleys.

2001 May: April, June, TCA, TCAI, shoot growth, canopy
implementation of August, November: volume, leafN %, SPAD
the 3 orchard ﬂoor soil sampling for
management NO3'
systems.

2002 Maintenance of the April, June, TCA, TCAI, shoot July-August:
OFMS and tree August, November: growth, canopy installment of
training 50" sampling for volume, leaf N %, minirhizotrons

SOM and N03. SP AD

2003 Same as above April, June, TCA, TCAI, shoot growth, canopy
August, November: volume, leaf N %, SPAD and yield
soil sampling for
SOM, NO; and
NHa+

2004 Same as above Same as above Same as above

2005 Same as above Same as above TCA, TCAI, shoot growth, canopy

 

 

 

volume, leaf N %, SPAD and yield,

 

114

 

A
V

.-—-_——-——ﬂﬂﬁ_-—-—----_

Mulch area

Alle
Alley y

40 cm

llli Ull
llﬁ ﬁll

40
cm 68 cm

<——>

< 53 cm
100 cm

 

V

 

13cm

Fig 1A. Minirhizotron location for apple tree root development study in the mulch

 

 

treatment.
Weeded

I l area I I
I I <———> I I
| ' 50 cm "< 71
' ' ' 90 cm '
. I I I
I

I I I - I

T 11 d All
Alley : Tilled ' l l e : ey

I h3 cm ' area I
I area I 40 cm I
I I I I
I I I I
I I I I
I l I I
l I I I
I I i I
I I I I
l I I I
I I I i
I I I I
I A J I I
l V 'l l l
I 40 cm I 68 cm I
l 90 cm 1 e_I__. l
' l ' 53 cm I

I
Fig 1B. Minirhizotrons location for apple tree root development study in the Swiss

Sandwich treatment.

115

Results

The treatments did have an impact on the organic matter (SOM) and nitrogen
concentration, effectively changing the chemical, physical and biological conditions of
the soil (Chapter 1). We did not notice any effect of SOM or N on any of the ﬁne root
parameter measured (data not shown).

In general there were no differences between the two years of observation (2003-
2004) in any of the ﬁne root parameters measured. Also, the only ﬁne root parameters
that were affected from the treatments were the ﬁne root numbers, area, and the rate of
growth.

Effect on ﬁne root number

There were more ﬁne roots per image in SS than MU in both years (Figure 2).
Fine root number in SS declined during the growing season and approached values of
MU towards the beginning of July and then no differences were measured between the
treatments for the rest of the measurements (Figure 2).

Fine root number was not affected by depth in the soil proﬁle but was affected by
distance from the trunk in SS, which had a higher number of ﬁne apple roots closer to the
trunk in the vegetated area than MU (Figure 3).

When the ﬁne root number was segregated by classes of diameter and checked for
their frequency (expressed as the percentage of ﬁne roots in each diameter class), there
was signiﬁcant difference among the diameter classes, with a greater proportion of apple
roots being 0.4 to 0.8 mm (Figure 4). Orchard ﬂoor management systems did not affect

root diameters. Roots generated near the trunk (13 cm) are larger in MU than SS (Figure

116

5). Sandwich presented the opposite in the middle position that is closer to the transition
between the vegetated area and the tilled strip, and a much higher percentage of very ﬁne
roots (02-04 mm) farther from the trunk (corresponding to the middle of the tilled strip)
(Figure 5).

Larger roots were found developing deeper in the soil proﬁle in MU (Figure 6).

Effect on ﬁne root area

 

The amount of ﬁne root area for both treatments varied, depending on the distance
from the trunk and soil depth. Closer to the surface (0-30 cm) SS presented a higher ﬁne
root area closer to the trunk (in the vegetated area) than mulch for most of the duration of
the experiment, both in 2003 and 2004 (Figure 7). No differences were measured
between the treatments in any other position in both years.

Below 30 cm there was a lot of variation during the experiment that nulliﬁed
differences between positions inside of the treatments and between them in both years
(Figure 8). Differences did not exist deeper in the soil proﬁle (below 60 cm) (Figure 9;

10).

Effect on growth rate

The growth rate (expressed as number of roots/day ") was different between the
two treatments. In the literature, root length is normally used to establish root turnover
rates and life span. According to Tracey et a1. (2003), root number can be substituted for

root length if there is a direct correlation between the two. The correlation found in this

117

experiment allowed us to use root number as an indicator of ﬁne root turnover and
lifespan (Figure 11).

There was a decline in ﬁne root number greater for SS than MU. The amount of
re-growth was similar between the treatments, but SS always had a higher ﬁne root
reduction than MU (Figure 12). Additionally, the turnover rate was greater in SS than
MU when expressed as ﬁne root mortality (Figure 12) following the methodology
utilized by Joslin et a1. (2000). The amount of time between active grth and ﬁne root
disappearance was used as an estimation of ﬁne root life span. Sandwich had an
estimated lifespan of around 30 days compared with the 50-60 for mulch (Figure 12).

Growth rate was not affected by the depth in the soil proﬁle or by the distance
from the trunk; also, there were no interactions with the treatments.

The different classes of ﬁne root diameter considered did not differ in growth rate.

Soil water content.

 

Measurements performed with TDR (Figure 13) demonstrated that most of the
time there were no differences between OFMS. When some difference was present MU
had always the highest values while the SVA had the lowest. Flame and the tilled strip in

the sandwich did not differ from the other two.

118

Discussion

The orchard ﬂoor managements under evaluation did have an impact on the soil
conditions. Mulch increased the percentage of soil organic matter (SOM) in the soil and it
was higher than sandwich. This is due to the continuous break down of the mulch itself
by the microorganisms in the soil and its continuous addition (twice yearly) for the
duration of the experiment, as most of the work done on similar conditions attests
(Merwin et al., 1993; Sanchez et al., 2003).

We did not ﬁnd a clear correlation between ﬁne root parameters and amount of
nitrogen present in the soil, except for the ﬁne root lifespan and turnover. The literature
present is contradictory regarding the effect of nitrogen on ﬁne roots. Some authors
report that with increased N concentration in soil, root production and length, as well as
their life span increases (Aber et al, 1985; Nadelhoffer et al., 1985; Persson and
Ahlstrtim, 2002) while others (Pregitzer et al., 1993; Ostonen et al., 1999; Burton et al.,
2000; Hendricks et al., 2000; King et al., 2002) reported the opposite. Our work aligns
with the correlation of higher N concentration and increased life span, thus reducing
carbon costs of the root system (N adelhoffer and Raich, 1992).

In any case, all the authors agree on the importance of the interaction between N
availability and ﬁne root dynamics especially for the effects on organic matter
(McClaugherty et a1, 1982), on the organic N pool in the soil (Ehrenfeld et al., 1997), and

on the control of the substrate quality (Hendricks et al., 2000).

119

McClaugherty et a1 (1982) reported that increased organic matter in the soil
increased root lifespan while we found the opposite. The difference in SOM in our
experiment was probably not enough to exert an effect.

The 30 days of root lifespan found in the mulch treatment is similar to the ﬁnding
by Bouma et a1. (2001) for apples. The same author also states that nutrient depleted
systems increase not only the ﬁne root lifespan but also their nutrient efﬁciency uptake,
thus implying that the sandwich system is more efﬁcient.

This theory also explains the higher number of ﬁne roots measured in SS
compared with MU early in the season when the trees are in higher demand. It also
explains the higher amount of ﬁne roots and area found closer to the trunk in the ﬁrst 30
cm of soil in the sandwich system. The higher competition for nutrients and water exerted
from the vegetation present in this area of the SS is probably responsible for this ﬁnding,
since it will increase the system nutrient depletion (Schenk and Jackson, 2002).

It is not clear which factors are responsible for the lack of response in ﬁne root
area in the other positions and depths between the treatments.

Wells and Eissenstat (2001), reported that 55-60 % of apple roots in their study
have a diameter of 0.5-1.1 mm and 30 % of 03-05 mm. Our ﬁndings, even if the
division in classes of diameter are slightly different, support their observation. We did
not, however, ﬁnd an association between root diameter and mortality, as found in their
report.

We did instead ﬁnd an interaction between the diameter class frequency and both
depth in the soil proﬁle and distance. This interaction was different for the two

treatments. It is not clear which factors are responsible for these results. Closer to the

120

trunk (the vegetated area in the sandwich), MU tends to show a higher frequency of
larger diameters than SS, especially both, near to and the farthest distance to the trunk.
Sandwich presented the opposite in the middle position that is closer to the transition
between the vegetated area and the tilled strip, and a much higher percentage of very ﬁne
roots (0.2-0.4 mm) farther from the trunk (corresponding to the middle of the tilled strip).
A similar tendency was noticed for soil proﬁle depth. Mulch tends to have higher
frequency of larger root classes deeper in the soil proﬁle, even if the most represented
classes are still the two mid size roots in both treatments.

The reason why SS tends to show a higher frequency of very ﬁne roots farther
from the trunk and deeper in the soil proﬁle than MU could be explained by lower carbon
cost for very ﬁne root, thus reducing the demand of the root system and allowing SS to be
equally productive as MU.

More research should be done trying to link root diameters with efﬁciency of

nutrient absorption, response to water content, SOM, and carbon cost of their production.

121

Conclusion

With this experiment we did demonstrate that ﬁne root development was affected
by the ground ﬂoor management systems implemented. The different soil conditions
created from the systems (higher N concentration in mulch) were responsible for the
increase in ﬁne root life span measured in the sandwich system (50-60 days against 30 of
the mulch). This treatment also had a higher ﬁne root number early in the season than
mulch.

The vegetated area underneath the canopy of the sandwich system was probably
responsible for the higher ﬁne root area found in this position compared to mulch.

We also found unique data that linked the treatment diameter class of ﬁne roots
with the depth in the soil proﬁle and distance from the trunk. The Sandwich system had
higher frequency of very ﬁne roots (0.2-0.4 mm) closer and farthest from the trunk, as
well as deeper in the soil proﬁle when compared with mulch.

Even if we did not measure them, from the results of this study, it is possible to
suggest that the sandwich system is able to implement a root system that is both more
efﬁcient in the uptake and less costly on the carbon demand. More research should be

done to assess this point.

122

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Burton A.J., Pregitzer KS. and Hendrick R.L., (2000). Relationships between ﬁne root
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125

 

 

 

 

2.5 - a
2 n a
1.5 . a

1 _
b b b ' L
b - . . l ‘4‘.

0.5 7

Avg. # Rootsllmage

 

 

0 ’ I 7 l I l l I
8-May 28-May 17-Jun 7-Jul 27-Jul 16-Aug 5-Sep 25—Sep

Dates of picture collection

 

 

-o— mulch —-— sandwich

 

 

 

 

 

 

 

Avg. # Roots/Image

 

 

 

 

 

O 2 I I I 1 I I I 1
8-May 28-May 17-Jun 7-Jul 27-Jul 16—Aug 5-Sep 25-Sep 15—Oct 4-Nov

Dates of picture collection

 

—o— mulch + sandwich

 

 

 

Figure 2: Average root number/image during 2003 (A) and 2004 (B) for the two
treatments. Different letters represent statistical signiﬁcance (LSMEANS with P5005).
Bars represent standard error.

126

 

—<>— mulch + sandwich

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4 _
3.5 .
8
g 3‘
E 2.5 i
8 2 -
n:
it 1’5l
2"
< 1 ‘
0.5 ~
0 1 I— 1 j
0 20 4O 60 80
Distance from the tree (cm)
—<>— mulch +sandwich
3.5 —
a 3 ‘ a
g 2.5 —
'5
o 2 I
o
n: 1.5 -
‘f
in 1 1 b
0.5 l
O I i I I
0 20 40 60 80

Distance from the tree (cm)
Figure 3: Average root number/image as affected from distance from the trunk (cm) for

2003 (A) and 2004 (B). Different letters represent statistical signiﬁcance (LSMEANS
with P5005). Bars represent standard error.

127

 

 

EZI mulch sandwich

 

 

 

 

 

 

 

 

 

 

(I!
O

 

 

A
O

 

 

 

 

 

Percentage
00
O

 

 

N
O

 

 

.3
O

 

 

 

 

 

 

 

 

 

04-06 0.6-0.8 0.8-1.0 1.2-1.4
Root class diameter (mm)
Figure 4: Frequency of roots (percentage on the total number of roots) in each root class

diameter (mm) for the two treatments. Bars represent standard error (LSMEANS with
P5005).

128

 

El Mulch Sandwich 1

 

0.6-0.8

68 cm

0.8-1.0

1.2-1.4

02-04

0.4-0.6

0.6-0.8

53 cm

0.8-1.0

1 .2-1.4

 

02-04

0.4-0.6

0.6-0.8

13cm

0.8-1.0

1.2-1.4

 

 

70

Percentage

Figure 5: Effect of the distance from the trunk (cm) on the frequency (percentage on the
total number of roots) of roots in each class diameter (mm) for the two treatments. Bars
represent standard error.

129

 

t3 Mulch Sandwich

 

 

 

 

 

 

Below 90 cm

 

90 cm

 

 

 

 

 

 

 

60 cm

 

 

 

 

30 cm

 

 

 

Percentage

Figure 6: Effect of depth in the soil proﬁle (cm) on the frequency (percentage on the total
number of roots) of roots in each class diameter (mm) for the two treatments. Bars
represent standard error.

130

2.4 a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1.9 n A
"5
v 1.4 ~
I!
2
<
‘6 0.9 ‘ ‘ 40
° ‘ b V
m 0
0-4 4 a. ,‘gﬁ;=32_4:hg2«_ ., _ _
'O'bliilay 28-May 17-Jun 7-Jul 27-Jul 16-Aug 5-Sep 25-Sep
Dates of picture collection
—o-— Mach 13cm -A— Mulch 53cm -I:I— Mach 68cm
+Sandwich13cm +Sandwich 53cm +Sandwich 68cm
2.5 .
B
A 2 ‘1
"a
1i
i. 1.5 -
2
<
a 1 i
o
It
0 5 d e . e - e e
O I 1 T I T— 1 l 1 1
8-May 28-May 17-Jun 7-Jul 27-Jul 16-Aug 5-Sep 25-Sep 15-Oct 4-Nov

Dates of picture collection

 

-o— Mulch 13cm + Mulch 530m —i:I— Mach 680m
-e— Sandwich 13cm + Sandwich 53cm + Sandwich 68cm

 

 

 

Figure 7: Root area dynamics depending on the distance from the trunk for both
treatments at 0-30 cm depth in the soil proﬁle during 2003 (A) and 2004 (B). Bars
represent standard errors for signiﬁcance (LSMEANS with P5005).

131

 

 

 

 

 

 

Root Area (cmz)

 

 

 

I I I I

8-May 28-May 17-Jun 7-Jul 27-Jul 16-Aug 5-Sep 25—Sep
Dates of picture collection

 

—o— Mulch 13cm —¢— Mulch 53cm —-0— Mulch 680m
+ Sandwich 13cm + Sandwich 53cm + Sandwich 68cm

 

 

 

 

 

 

 

1-

0.8 7

m2)

0.6 7
0.4 7

Root Area (c

 

 

0.2 7

 

 

 

 

0 1 I l l I T 1 T 1
8-May 28-May 17-Jun 7-Jul 27-Jul 16—Aug 5-Sep 25—Sep 15-Oct 4-Nov

Dates of picture collection

—0— Mulch 13cm -A- Mulch 53cm —I:I— Mulch 68cm
+ Sandwich 13cm + Sandwich 530m + Sandwich 68cm

 

 

 

 

Figure 8: Root area dynamics depending on the distance from the trunk for both
treatments at 30-60 cm depth in the soil proﬁle during 2003 (A) and 2004 (B). Bars in
ﬁgure A represent standard errors for signiﬁcance (LSMEAN S with P5005). There was
no difference between treatments in ﬁgure B.

132

Root Area (cmz)

Root Area (cmz)

 

 

 

 

 

 

 

 

 

.0 .0 .o .0 T" T‘ .“
O N ~5- 0) m -‘ N -§ 0)
J l 1 1 l l 1 41

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

‘I
"i\. A... 5.
5% V
' :‘ > 5.
8-May 28-May 17-Jun 7-Jul 27-Jul 16—Aug 5-Sep 25-Sep
Dates of picture collection
—0— Mulch 13cm —A— Mach 53cm —0- Mulch 68cm
+ Sandwich 13cm + Sandwich 53cm + Sandwich 68cm
1.6 —
1.4 1 B
1.2 7 q "
1 ~ 1_
0.8 7
0-6 ‘ ‘5 ‘
.lL - ‘
0-4 ‘ -- , A 4"
0.2 - C— 7 ’ \-
o f ﬂ . . T . . . .
8—May 28-May 17-Jun 7-Jul 27-Jul 16-Aug 5-Sep 25-Sep 15-Oct 4—Nov

Dates of picture collection

 

 

—o— Mulch 130m -A— Mach 53cm -CI— Mulch 68cm
+ Sandwich 13cm + Sandwich 53cm —I— Sandwich 68cm

 

 

Figure 9: Root area dynamics depending on the distance from the trunk for both
treatments at 60-90 cm depth in the soil proﬁle during 2003 (A) and 2004 (B). Bars
represent standard errors for signiﬁcance (LSMEAN S with P5005).

133

 

 

 

 

1.8 . -- i"
1.6 —
1.4 —
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0 r u A- l I T I i r U l
8-May 28-May 17-Jun 7-Jul 27-Jul 16-Aug 5—Sep 25-Sep
Dates of picture collection
-0— Mulch 13cm + Mach 53cm —i:l— Mulch 68cm
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Dates of picture collection

 

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-0— Sandwich 13cm + Sandwich 53cm -I— Sandwich 68cm

 

 

 

Figure 10: Root area dynamics depending on the distance from the trunk for both
treatments at below 90 cm depth in the soil proﬁle during 2003 (A) and 2004 (B). Bars in
ﬁgure A represent standard errors for signiﬁcance (LSMEANS with P5005). There was
no difference between treatments in ﬁgure B.

134

 

 

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Tot. # Roots

Figure 1 1: Correlation between root number and root length (cm).

 

 

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Figure 12: Root growth rate (number of roots day 'l) for treatment mulch and sandwich
during 2004. Measurement starts at the second collection date. Bars represent standard
errors for signiﬁcance (LSMEAN S with P5005).

135

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Figure 13: Volumetric soil moisture content (as %) measured with TDR for the average
0-45 cm depth, for the different treatments during 2002-2005.

136

CONCLUSION

With this dissertation we asserted that the Orchard Floor Management Systems
(OF MS) under evaluation were able to change the soil conditions regarding organic
matter, carbon sequestration and nitrogen concentration.

The highest soil organic matter (SOM) concentration was found in the mulch
treatment (MU), which increased over the duration of the experiment, especially near the
soil surface where litter was added twice yearly. Soil organic matter decreased near the
soil surface for ﬂame (FL) and the tilled strip of the sandwich system (SS) where there
was continuous burning of the vegetation (in the ﬂame treatment) and the effect of tillage
(in the tilled strip of the sandwich, STA). Soil organic matter in the vegetated area of the
sandwich system (SVA) remained constant for the duration of the experiment due to the
continuous degradation of the on site vegetation. Soil organic matter was less signiﬁcant
deeper in the soil proﬁle (0-30 cm), where MU increased overtime and was the highest in
soil organic matter. The tilled strip of the sandwich also increased in SOM. There was no
change at this depth over time for the other systems/positions sampled.

A very similar trend was found for all treatments regarding Nitrogen (N)
concentration in the soil.

When some difference was present MU had always the highest water content
values in the soil while the SVA had the lowest. Flame and the tilled strip in the sandwich

did not differ from the other two.

137

The trend for carbon sequestration per hectare at orchard level was inverse in
relation to SOM for the systems. The greatest potential for carbon sequestration was at O-
30 cm depth, for MU and SS.

The different nematode populations present in the soil were changed by the
OF MS. There were more bacteria feeding nematodes (84%) in the mulch system which
accelerated over time and eventually dominated nematode populations. In contrast,
bacteria feeding nematodes stabilized (around 60%) in SS and FL, while the fungal
feeding populations strengthened. Fungal feeding nematodes usually develop in depleted
soil conditions but at the same time have an enhanced effect on nitrogen release in the
soil. This may have occurred here where there was a measured increase in nitrogen
concentration in the soil, even with decreasing or stable SOM. Also, a higher percentage
of roots were infected by mycorrhizae in FL and SS, which is commonly associated with
poor soil conditions. These results suggest that these two treatments found a balance to
overcome the lower SOM concentration, thus increasing their efﬁciency. Mycorrhizal
infection enhances root lifespan in woody roots (Hooker et al., 1992).

There were less root feeding nematodes in the soil in MU than FL and SS. Levels
in FL and SS were similar but below damage threshold.

There was a direct correlation between mycorrhizal spores in the soil and
percentage of roots infected by mycorrhizae.

It appears that trees managed in all system treatments were equally efﬁcient
regarding plant growth and development (TCA, TCAI, canopy volume, and shoot
growth). Perhaps the different performances of plants under the OFMS improved root

system efﬁciency. This was demonstrated when we measured the ﬁne root development

138

under MU and SS by minirhizotrons. Fine root turnover life span was increased under SS
(from 30 days of MU to 50-60 days), suggesting an improved efﬁciency of nutrient
uptake and reducing the carbon cost of new root production. The adaptation of the root
system to the OFMS was not conﬁned only to a physiological but also to a physical one.

Weed presence inﬂuenced root architecture measured by trench soil proﬁle.
Apple roots were conﬁned to the weed free area in MU and FL and relatively closer to
the soil surface. In contrast, very few roots were found in SS closer to the trunk
(vegetated area), and more were found extended into the tilled strip (vegetation free), and
reached farther into the alley. It was also found to have a greater frequency of roots
deeper in the soil proﬁle. The lower water content found in the vegetated area of the
sandwich could have also played a role in the root distribution.

In total, there were more roots found in MU than the other two treatments. This
fact coupled with the fact that no differences were measured in the tree grth
parameters suggests that there is a better carbon allocation for trees in FL and SS.

The trench proﬁle data contradicts the spatial results from the minirhizotrons
regarding between MU and SS. The soil and root interface sampling in the minirhizotrons
is very limited and thus data is not applicable in assessing spatial distribution. This
technique is reliable in monitoring root growth development. With the trenches, a
selected part of the root system is measured and it is assumed representative of the
totality. The general trends of the results should still be considered valid.

During the minirhizotron experiment we found some unique results that linked the
treatment diameter class of ﬁne roots with the depth in the soil proﬁle and distance from

the trunk. The Sandwich system had higher frequency of very ﬁne roots (0.2-0.4 mm)

139

closer and farthest from the trunk, as well as deeper in the soil proﬁle when compared
with mulch. The reason of this ﬁnding is not clear and more research should be done on
the subject.

As part of the OFMS evaluation we also measured the performance of three
rootstocks (the dwarﬁng M.9 NAKB 337, the semi-dwarﬁng M.9 RN 29, and the semi-
vigorous Supporter 4) to the different conditions created.

The OFMS treatments did not have an effect on tree growth, but nitrogen
concentration of leaves was lowest in sandwich and ﬂame. This suggests that the growing
conditions were still sufficient but should still be monitored because the values were in
the lowest acceptable range.

As expected, trees on Supporter 4 rootstock were most vigorous.

There was an interaction between treatments and rootstocks regarding the crop
yield with M.9 RN 29 having the highest yield and yield efficiency per tree in ﬂame and
sandwich while no differences were noticed between the rootstocks in mulch despite its
better growing conditions. This suggests that M.9 RN 29 is a rootstock that is better
adapted to the more stressful conditions imposed by sandwich and ﬂame treatments
(lower SOM, N and in case of the sandwich vegetated area less water content). This is
probably due to RN 29 being slightly more vigorous than NAKB 337 and more
precocious than Supporter 4. It could also depend on its higher efﬁciency in nutrient and
water absorption.

When considering the values per hectare and especially the cumulative yield, the

ﬂame treatment cropped least with no differences between the rootstocks. Mulch and

140

sandwich treatments had similar cumulative production per hectare with Supporter 4
having the lowest values with no differences between the other two rootstocks.

The low production per hectare in FL, despite its higher “yield efﬁciency” per
tree, and the low level of nitrogen in the leaves, suggests that this OFMS could not be
sufﬁcient anymore without implementation of fertilization. This is interesting since this
system is equivalent to conventional orchards where a weed free zone is maintained with
herbicides.

Implementation of each of these OF MS is quite different and should be
considered during the selection and implementation for the growers.

The ﬂame system presents high risk of ﬁres, damage to the lowest branches due
to heat convection, and requires specialized equipment. It is however, relatively
inexpensive to maintain ($218). In my opinion, this treatment is not particularly desirable
to organic growers.

The mulch is expensive ($788), difﬁcult to apply, requires multiple redressing to
maintain adequate thickness, subject to rodent damage and wild ﬁres during the summer.
In my opinion this treatment is slightly more desirable to organic growers than ﬂame.
More research should be done on the kind of mulching material to use, in relation to
SOM and soil food web.

The sandwich system is easy to implement, it does not damage tree trunks, it is
less expensive to manage ($91), and it requires only an easily modiﬁed notch disk tiller.
The drawback of this system is that vegetation competes with tree grth and soils are

lower in SOM and N concentration than mulch. Therefore, irrigation and soil fertility

141

must be monitored. Also the ideal width of the tilled strip requires more research for
various soil types.

Overall, the sandwich system coupled with the M.9 RN 29 rootstock appears to be
a suitable choice for growers that want to grow Paciﬁc Gala under organic protocol in
Michigan and similar climates. More research is still necessary, especially to conﬁrm

these results in a longer term study and under commercial orchard operations.

142

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