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This is to certify that the
thesis entitled
Conservation Tillage Effects on
Soil Properties and Corn Yields

in Central Michigan

presented by
Michael James Staton

has been accepted towards fulfillment

of the requirements for
Crop and Soil

Master of Science degreein Sciences

gym MW

Majoé! @[Ofessor

 

Date @MMv/é/L / ?X<f

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

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CONSERVATION TILLAGE EFFECTS ON SOIL PROPERTIES
AND CORN YIELDS IN CENTRAL MICHIGAN

By

Michael James Staton

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of crop and soil sciences

1988

ml p,

l

2.4 V

ABSTRACT

CONSERVATION TILLAGE EFFECTS ON SOIL PROPERTIES
AND CORN YIELDS IN CENTRAL MICHIGAN

By

Michael James Staton

No-tillage alters soil properties, sometimes inhibiting crop growth.
The effects of plowing on no-tillage soil properties were evaluated.
No-tillage plots were plowed after five and six years.

Plowing improved the physical and chemical condition of the no-till
soil. Bulk density was decreased, while porosity and saturated
hydraulic conductivity were increased. Acidic and high nutrient layers
were mixed throughout the plow layer.

Zone tillage is increasing in Michigan. The effects of zone tillage
on soil physical properties and corn yields were evaluated. Plots were
subsoiled in the row and then planted as no-tillage for one and two
years with controlled traffic to determine any residual tillage
effects.

Zone tillage improved soil physical properties but not corn yields.
Bulk density and soil strength were reduced while porosity and
saturated hydraulic conductivity increased. The bulk density and total

porosity effects of zone tillage persisted for two years.

ACKNOWLEDGEMENTS

I wish to express my sincerest gratitude to my major professor Dr.
Francis J. Pierce for his support and guidance in this degree program.
Appreciation is extended to Drs. A. E. Erickson and R. Wilkinson for
their service as committee members. I am indebted to Dr. A. E.
Erickson who initiated the no-tillage experiment I evaluated and
provided field and laboratory equipment essential to the completion of
this project.

B. Long and D. Reinert were invaluable in ensuring the accuracy and
timeliness of field operations and data collection. Appreciation is
extended to Drs. C. Cress and C. W. Rice for their availability and
expert consultations. I am grateful for the laboratory assistance
provided by R. Deatrick, S. Rice, M. Seitz and M. Zwiernik. D. Knezek
provided valuable computer information continually throughout this
project. B. Johnson, J. Dahl, R. Deason, and R. Cabrera also
contributed significantly to this work. I am grateful for the moral
support given by C. Burpee and M. Fortin.

Finally, I wish to express my deepest appreciation to A. R. and M. L.
Staton who were responsible for helping me overcome the setbacks and

hardships encountered while pursuing this degree.

iii

TABLE OF CONTENTS

List of tables .
List of figures
INTRODUCTION

Chapter 1: LITERATURE REVIEW .
Soil compaction . . . . .
Definition of soil compaction .
Causes of soil compaction . . . .
Compaction effects on soil properties .
Compaction effects on plant growth
Alleviation of soil compaction .
Subsoiling effects on plant and soil properties
Comparison of soil properties of no- tillage and
conventional tillage . . . . . . . . . . . . . .
Summary .
List of references (Introduction and Chapter 1)

Chapter 2: CHANGES IN SOIL PHYSICAL AND CHEMICAL PROPERTIES
ASSOCIATED WITH PERIODIC PLOWING IN NO-TILL SOILS
Introduction . . . . . . . . . . . . . . . . . . . . . .
Materials and methods
Results and discussion . . . . . . . . . . .
Physical properties . .
Tire traffic effects on soil physical properties .
Chemical properties . . . . . . . . .
Plant responses and yields .
Conclusions .
List of references .

Chapter 3: IMMEDIATE AND RESIDUAL EFFECTS OF ZONE TILLAGE 0N
SOIL PHYSICAL PROPERTIES AND CORN YIELDS
Introduction . . . . . . . . . . . . . . . . .
Materials and methods
Results and discussion . . . .
Immediate effects of zone tillage . . .
Residual effects of zone tillage .
Zone tillage effects on soil properties compared over time
Plant responses and yields . . . . . . . . . . . . .
Conclusions . . . . . . . . . .
List of references

SUMMARY AND CONCLUSIONS .
Recommendations .

iv

. vi

. viii

Hmflbwwww

O
O
H

. 13
. 19
. 20

. 24
. 26
. 31
. 31

. 56
. 65
. 70
. 72

. 75
. 76
. 80
. 80
. 9O

. 104
. 112
. 119
. 121

. 123
. 124

APPENDIXFIGURES.........................126
APPENDIXTABLES..........................127

LIST OF TABLES

Chapter 2:
Table 1. Descriptions of the tillage treatments.

Table 2. Total porosity and saturated hydraulic conductivity
(Ksat) from 6/21/86 and 9/16/86. . . . . . . . .

Table 3. Total porosity and saturated hydraulic conductivity
(Ksat) from 7/14/87. . . . . . . . . . . .

Table 4. Total porosity and saturated hydraulic conductivity
(Ksat) from 6/21/86 compared between tire tracks and
non-tire tracks. . . . . . . . . . . . . . . . .

Table 5. Total porosity and saturated hydraulic conductivity
(Ksat) from 9/16/86 compared between tire tracks and
non-tire tracks. . . . . . . . . . . . . . . . .

Table 6. Soil pH, phosphorus content, and potassium content from

4/10/87.
Table 7. Emergence data from 1986.
Table 8. Emergence data from 1987.

Table 9. Total nitrogen contents in ear leaf, stover and grain
from 1986.

Table 10. Yield data from 1986 and 1987.
Chapter 3:

Table 11. Immediate effects of tillage on total porosity and
saturated hydraulic conductivity (Ksat) from 1987.

Table 12. Residual effects of zone tillage on bulk density after
one year 0 O O O O O O O O I O O O O O O O O O O O O 0

Table 13. Residual effects of zone tillage on bulk density after
two years. . . . . . . . . . . . . . . . . . . . .

Table 14. Residual effects of zone tillage on total porosity and

saturated hydraulic conductivity (Ksat) after one year.

vi

. 27

. 47

. 48

. 57

. 58

. 63

. 66

. 66

. 67

. 69

. 89

. 92

. 94

103

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

15.

16.

17.

18.

19.

20.

21.

22.

Residual effects of zone tillage on total porosity and

saturated hydraulic conductivity (Ksat) after two years.

Residual effects of zone tillage on bulk density
compared over time. . . . . . . . . . . . . . .

Residual effects of zone tillage on total porosity and
saturated hydraulic conductivity compared over time.

Immediate tillage effects on seedling emergence from
1986. . . . . . . . . . . . . . . . . . . .

Immediate tillage effects on seedling emergence from
1987. . . . . . . . . . . . . . . . . . . . . .

Plant tissue nitrogen contents from 1986.
Yield data from 1986.
Yield data from 1987.

APPENDIX TABLES

Soil volumetric moisture contents at the time of
subsoiling from 1986 and 1987.

Soil volumetric moisture contents at the time of

penetrometer sampling of tillage treatments implemented
in 1985, 1986, and 1987. . . . . . . . . . . . . . .

vii

105

. 106

. 111

. 114

. 114

. 116

. 117

. 118

. 127

. 128

Chapter 2:

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

1.

10.

11.

12.

LIST OF FIGURES

Tillage effects on soil bulk density from 6/21/86 (a)
and 9/16/86 (b). . . . . . . . . . . . . . . . . . .

Tillage effects on soil bulk density from 7/14/87.

Tillage effects on the pore size distribution from
6/21/86. . . . . . . . . . . . .

Tillage effects on the pore size distribution from
9/16/860 0 o o o o o o o o o o o o o o o o o o

Tillage effects on the pore size distribution from
7/14/87. 0 O O O O O O O O O O O O O O I O O O

The effects of tillage on moisture retention (a) and
air‘filled porosity (b) at the 0 to 7. 5 cm depth from
6/21/86. . . . . . . . . . . . . . . . . . . .

The effects of tillage on moisture retention (a) and
air- filled porosity (b) at the 7. 5 to 15 cm depth
from 6/21/86. . . . . . . . . . . . . . . . . . .

The effects of tillage on moisture retention (a) and
air- -filled porosity (b) at the 0 to 7. 5 cm depth
from 9/16/86. . . . . . . . . . . . . . . . . . .

The effects of tillage on moisture retention (a) and
air- filled porosity (b) at the 7. 5 to 15 cm depth
from 9/16/86. . . . . . . . . . . . . . . . . .

Tillage effects on moisture retention (a) and air-
filled porosity (b) at the 0 to 7.5 cm depth from
7/14/870 0 o o o o o o o o o o o o o o o o o o o

Tillage effects on moisture retention (a) and air-
filled porosity (b) at the 7.5 to 15 cm depth from
7/14/87. 0 O O O O O O O O C O O O O O 0 O O O 0

Tire traffic effcts on bulk density at the 0 to 7. 5

cm depth (a) and the 7. 5 to 15 cm depth (b) from
6/21/86. . . . . . . . . . . . . . . . .

viii

. 32

. 33

. 3S

. 36

. 37

. 39

. 4O

. 41

. 42

. 43

. 44

. SO

Figure

Figure

Figure

Figure

Figure

Figure

Figure

13.

14.

15.

16.

17.

18.

19.

Chapter 3:

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

20.

21.

22.

23.

24.

25.

26.

27.

28.

Tire traffic effects on bulk density at the 0 to 7.5
cm depth (a) and the 7. 5 to 15 cm depth (b) from
9/16/86. . . . . . . . . . . . . . . . .

Tire traffic effects on the pore size distribution at
the 0 to 7.5 cm depth from 6/21/86.

Tire traffic effects on the pore size distribution at
the 7.5 to 15 cm depth from 6/21/86.

Tire traffic effects on the pore size distribution at
the 0 to 7.5 cm depth from 9/16/86. . . .

Tire traffic effects on the pore size distribution at
the 7.5 to 15 cm depth from 9/16/86. . . . .

Inorganic nitrogen content at three depths as
affected by tillage from 1987.

Organic carbon content at four depths as affected by
tillage from 4/10/87.

Immediate effects of tillage on soil bulk density.

Immediate effects of tillage on pore size
distribution at 0 to 7.5 cm (a), 7.5 to 15 cm (b),
and 22.5 to 30 cm (c). . . . . . . . . . . . .

Immediate tillage effects on moisture retention (a)
and air-filled porosity (b) at the 0 to 7.5 cm depth.

Immediate tillage effects on soil moisture retention
(a) and air- -filled porosity (b) at the 7. 5 to 15 cm
depth. . . . . . . . . .

Immediate tillage effects on soil moisture retention
(a) and air- -filled porosity (b) at the 22. 5 to 30 cm
depth. . . . . . . . . . . .

Immediate tillage effects on cone index.

Residual effects of zone tillage after one year on
soil pore size distribution at the 7.5 to 15 cm (a)
and 22.5 to-30 mm (b) depths. . . . .

Residual effects of zone tillage after two years on
soil pore size distribution at the 7.5 to 15 cm (a)
and 22.5 to 30 cm.(b) depths. . . . . . . . .

Residual effects of zone tillage after one year on
soil moisture retention (a) and air-filled porosity
(b) at the 7.5 to 15 cm depth.

ix

. 51

. 52

. 53

. 54

. 55

. 59

. 61

. 81

. 82

. 84

. 85

. 86

. 91

. 9S

. 97

. 98

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

29.

30.

31.

32.

33.

34.

35.

Residual effects of zone tillage after one year on
soil moisture retention (a) and air- -filled porosity
(b) at the 22. 5 to 30 cm depth. . . . . . . . .

Residual effects of zone tillage after two years on
soil moisture retention (a) and air-filled porosity
(b) at the 7.5 to 15 cm depth.

Residual effects of zone tillage after two years on
soil moisture retention (a) and air-filled porosity
(b) at the 22.5 to 30 cm depth. .

Zone tillage effects on soil moisture retention (a)
and air-filled porosity (b) compared over time at the
0 to 7.5 cm depth. . . . . . . . . . . . .

Zone tillage effects on soil moisture retention (a)
and air-filled porosity (b) compared over time at the
7.5 to 15 cm depth. . . . . . . . . . . . . . . . .
Zone tillage effects on soil moisture retention (a)
and air-filled porosity (b) compared over time at the
22.5 to 30 cm depth. . . . . . . . . . . . . . . .
Residual tillage effects on cone index.

APPENDIX FIGURES

Inorganic nitrogen contents at three depths as
affected by tillage from 1986.

. 99

. 100

. 101

. 108

. 109

. 110

. 113

. 126

INTRODUCTION

No-tillage corn production has been increasing in the United States
in recent years. No-tillage planting systems involve chemical weed
control and planters which can place seed directly into an untilled
soil. This system is well suited for soils that have no physical
limitations to crop growth. Soane and Pidgeon (1975) state that when
soil physical properties are not limiting to crop growth, tillage is
required for seed placement only.

Soil physical and chemical properties are known to change under no-
tillage. No-till has been shown to increase soil bulk density (Gantzer
and Blake, 1978), increase soil strength (Van Ouwerkerk and Boone,
1970; and Hill et al., 1985a), and alter the soil's pore size
distribution (Van Ouwerkerk and Boone, 1970; and Hill et al., 1985b).
Acidic surface layers develop (Shear and Moschler, 1969: Blevins et
al., 1977; and Dick, 1983) and nutrients become stratified (Triplett
and Van Doren, 1969; Shear and Moschler, 1969; Fink and Wesley, 1974;
Juo and Lal, 1979: and Hargrove, 1985) under no-tillage. These soil
properties can inhibit crop production. Periodic plowing has been
implemented to alleviate some of these undesirable soil properties of
no-till.

Soil compaction is a widespread phenomenon in the United States
(Voorhees, 1977a). Cohron (1971) states that vehicle traffic is the
largest single source of compaction in agricultural soils. Compaction

from agricultural vehicles can extend down to 30 cm (Voorhees, 1978).

2
Soil compaction at depth can increase soil strength, decrease air-
filled porosity (Grable, 1971), and restrict water flow (Warkinten,
1971). Russell and 0085 (1974) showed that soil strengths of 20 kPa
caused barley root elongation to be reduced by 50 percent. Vomocil and
Flocker (1961) stated that when air-filled porosity falls below 10
percent, no gas exchange occurs between the soil and the atmosphere.
Soil compaction can reduce soil-water recharge which can cause moisture
stress to occur when rainfall is limiting.

Subsoiling has been shown to alleviate soil compaction below the
normal depth of plowing (Campbell et al., 1974). Zone tillage (under-
the-row subsoiling) is used extensively on the coastal plain soils and
is increasing in Michigan.

Normally, subsoiling should be performed when the soil is dry in
order to achieve the maximum loosening (Spoor and Godwin, 1978). This
condition rarely occurs in Michigan. Zone tillage is a costly
Operation and doesn't always increase yields.

The objectives of this study were to: 1) quantify changes in soil
physical and chemical properties when no-till soils are periodically
plowed; 2) determine the impact of wheel traffic on soil physical
properties of no-tillage and conventional tillage; 3) determine the
plant responses to the soil physical and chemical changes which occur
following plowing; 4) determine if satisfactory soil loosening can be
achieved by spring subsoiling operations; 5) determine if the loosened
zone created by subsoiling will persist for one or two years after the
initial subsoiling operation was performed; and 6) measure the effects

of zone tillage on corn production and yields.

Chapter 1
LITERATURE REVIEW

Soil physical and chemical properties affect crop growth and yield.
These soil properties can be manipulated by tillage to create a more
favorable growing environment. Soil properties and how tillage can
improve them to favor plant growth will be the subjects of this review.

Soil Compaction

Definition

Soil compaction is defined as the compression of an unsaturated soil
which results in a reduction of the air-filled volume (Hillel, 1982).
This phenomenon is so widespread in American agriculture that it can be
considered a natural resource (Voorhees, 1977a). This review will
discuss the causes and effects of compaction on soil properties and
plant growth as well as its alleviation.
gauge

The forces which cause compaction can be divided into two catagories:
internal and external (Cohron, 1971). Internal forces can be thought
of as natural forces which occur within the soil. External forces are
.those which are applied externally to the soil. This review will
concentrate on the external forces.

Three external forces are responsible for the compaction of
agricultural soils: raindrop impact, vehicle traffic, and tillage
operations. Each of these forces creates a distinct compact layer in

the soil (Warkentin, 1971).

4

Raindrop impact applies a compressional force directly on the soil
surface. This force causes aggregates to break down into their primary
particles. These particles are rearranged and packed so that fine
particles fill in the voids between larger particles. When the soil
dries, it forms a surface crust.

Vehicle traffic is by far the largest single source of compressional
forces in agricultural soils (Cohron, 1971). Soane et al. (1975)
reported that 90 percent of the soil surface is compacted by wheel
traffic during the preparation of a conventional seed bed for a cereal
crop. Soil compaction from wheel traffic extends deeper into the soil
profile than the surface crusting caused by raindrop impact. Voorhees
(1978) found that wheel traffic compaction extended down to a depth of
30 cm in a Minnesota soil.

Tillage implements compress the soil as they pass through. The
primary areas of compression occur just ahead of the tool and below the
tool. Just as in the case of traffic-induced compaction, tilling the
soil when it is too wet increases the severity of the compaction. Even
subsoiling operations which are aimed at loosening a compacted layer
can cause further compaction if the critical depth of the tool is
exceeded or if conditions are too wet (Spoor and Godwin, 1978).
Coppaction Effects on Soil Properties

Compaction reduces the total porosity of a soil (Voorhees, 1977a) and
alters the size distribution of the pores in the soil (Warkentin,
1971). Hillel (1982) stated that the volume of soil occupied by large
pores is reduced while the volume of small pores is increased by
compaction. Russell (1973), as cited by Cannell and Jackson (1981),

found that pores smaller than 60-30 um will remain filled with water at

5
the soil's field capacity. It is pores of this size and smaller which
predominate in a compacted soil. This alteration of the pore size
distribution alters the 5011's hydraulic, aeration, and strength
properties.

Water is retained in the soil at field capacity by capillary and
adsorptive forces exerted by the soil matrix. These combined forces
make up the matric potential of the soil water. Capillarity is due to
the water's surface tension and its contact angle with the solid
particles (Hillel, 1982). This force is most important when matric
suctions are less than one bar and adsorptive forces predominate when
matric suctions exceed one bar (Hillel, 1982). In the capillary rise
equation, the matric suction and the radius of pores which will retain
water against this suction are related. This is an inverse
relationship -- as suction increases, the pore radius decreases. Based
on this equation, a compacted soil will retain less water at low matric
suctions and more water at high matric suctions.

Compaction in the form of a surface crust will inhibit infiltration
of surface water into the soil. A compacted soil layer at depth will
restrict internal drainage of the overlying layers. These two
conditions affect water transmission throughout the soil differently.
Warkentin (1971) proposed the following theoretical explanations of how
the location of the impermeable layer in the profile affects continuous
water flow. When a compacted layer exists below a permeable layer,
saturated flow will occur throughout the profile. When a surface crust
forms over a more permeable layer, unsaturated flow can occur in the
transition zone between the two layers. Warkentin (1971) stated that

compaction reduces air-filled porosity and vapor movement.

6

Gaseous exchange between the soil and the atmosphere (aeration)
occurs primarily in the air-filled pores (Grable, 1971). This process
is accomplished primarily by diffusion. Diffusion is driven by partial
pressure gradients. At an air-filled porosity of about 10 percent,
this partial pressure gradient has been shown to be zero (Vomocil and
Flocker, 1961). When the partial pressure gradient is zero, no gas
exchange occurs between the soil and the atmosphere.

Vomocil and Flocker (1961) and Voorhees (1977a) state that compacting
a soil leads to a larger volume of the soil comprised of small pores.
These pores retain water at field capacity and restrict the diffusion
of gases (Grable, 1971). Therefore, compaction inhibits aeration of
the soil because of the altered pore size distribution of the compacted
soil.

Chancellor (1971) defines soil strength as a measure of the
resistance which must be exceeded in order to physically deform a soil.
Soil strength is the property in soil which resists compaction. This
property is affected by other soil properties: porosity, water
content, soil texture, and number of particle-to-particle contacts. A
soil is the most susceptable to compaction at high water contents.
Water has a lubricating effect on the soil and reduces the friction in
inter-particle contacts.

Soils which have a wide range of primary particle sizes are more
susceptable to compaction than a soil with a uniform size of primary
particles (Chancellor, 1971).

Compaction increases soil strength by decreasing porosity and by

increasing the particle-to-particle contacts.

7

Voorhees (1977a) states that the cloddy surface created by plowing up
a compacted soil can reduce wind and water erosion from harvest to
planting. This is accomplished by improving infiltration, trapping
wind-blown particles, and resisting raindrop impact. However, wheel
tracks in the growing season reduce infiltration and increase surface
runoff.

Coppaction Effects on Plant Growth

Compaction alters the soil environment which in turn alters root
growth. Specifically, it is the increase in soil strength and decrease
in aeration which reduce root growth. The decrease of water recharge
and storage associated with a compacted soil also contribute to reduced
root growth.

The increased soil strength associated with soil compaction impedes
root growth. This mechanical constrainment of the growing plant by the
soil is termed mechanical impedance (Bowen, 1981).

Taylor and Burnett (1964) showed that root growth was prevented when
the soil strength reached 25-30 bars (Critical Strength). Gerard et
a1. (1982) found that the critical strength was a function of clay
content. They showed that critical strengths were as high as 70 bars
for a coarse sand but dropped to 25 bars for a clay soil.

Wiersum (1957) showed that in a rigid system, plant roots were only
able to enter pores that are of greater diameter than that of the root.
The author also demonstrated that roots/could move soil particles aside
and enter pores smaller in diameter if the soil strength was low. Soil
compaction mechanically impedes root growth by reducing pore size and

by increasing soil strength.

8

When a surface crust forms on a bare soil surface after planting but
before emergence, plant stands will be reduced (Bowen, 1981). Bowen
(1981) cites work he did in 1966 to quantify the soil strength limits
on cotton seedling emergence. He found that there was no mechanical
impedance when crust strength was 70 kPa. But when strength increased
above 75 kPa, the percentage of seedlings that emerged was reduced. At
strengths of 200 kPa, no emergence occurred.

The metabolic energy required by roots is provided primarily by
respiration. Root respiration consumes oxygen and produces carbon
dioxide. In order for this process to occur at metabolic rates, the
soil atmosphere must be constantly replenished with oxygen, and carbon
dioxide must be free to escape out of the soil and back into the
atmosphere. Aeration refers to the process of gaseous exchange between
the atmosphere and the soil. This process occurs primarily in the air-
filled pores of the soil. Compaction reduces aeration by reducing the
air-filled pore volume of the soil.

Letey et al. (1962) created low oxygen conditions in the root zone of
green beans, sunflower, and cotton seedlings by flushing the soil with
nitrogen gas. They found that low oxygen is the most damaging in the
early growth stages following germination; that roots stop growing at
low oxygen concentrations; and that there is a lag time in the recovery
of root growth when oxygen has been replenished.

Alleviation of Soil Compaction

Tillage operations are often employed to alleviate soil compaction.
Tillage is defined as the act of mechanically manipulating the soil to
improve soil conditions which affect crop growth (Hillel, 1982). The

historical objectives of tillage are to move the soil for seed

9
placement, manage crop residues, modify the physical properties of the
soil, add and mix soil amendments, and control weeds. The control of
weeds has been the primary reason for tillage operations. Chemical
weed control can be so thorough that there is no longer need to till
the soil for weed control.

Soane and Pidgeon (1975) realized that with chemical weed control and
planters which can insert seed into an untilled soil, it is the
physical properties of a soil which determine the tillage requirement.
They state that tillage affects soil strength, soil aeration, water
status, and soil temperature. Letey (1985) states that these same soil
physical properties affect crop growth. In a soil where these
prOperties are limiting to crop growth, tillage would be required.

Soil below 30 cm is usually loosened by subsoiling operations which
consist of shattering the soil using high draft rigid-tined implements
referred to as subsoilers and deep chisels. These implements have a
critical working depth where soil is displaced forwards, sideways, and
upwards (crescent failure) (Spoor and Godwin, 1978). When the critical
depth is exceeded, the soil is displaced only laterally and forwards
(lateral failure) causing compaction to occur beneath the base of the
tine. The soil is fractured at a 45-degree angle from the surface of
the soil to a point above the base of the tine. This forms a "Y"-
shaped cross section of loosened soil.

Subsoiling when the soil is dry has been recommended to achieve the
maximum soil shattering. Spoor and Godwin (1978) support this view,
saying that as the soil becomes more plastic, the critical depth
becomes shallower, resulting in less disturbance of the soil at the

same operating depth.

10

Cooper (1971) disagrees, reporting that a very compact soil will
fracture equally well at soil moisture contents from field capacity to
the wilting point.

Because of the localized loosening of the soil and the cost of
subsoiling, zone tillage -- planting crop rows directly over the
loosened area -- has become widely practiced. Zone tillage is also
referred to in the literature as under-the-row subsoiling. Zone
tillage is used extensively on the coastal plain soils in the
southeastern United States. The soils here are coarse textured and
contain a dense A2 horizon which restricts root elongation and water
movement. Rainfall is limiting and poorly distributed throughout the
growing season (Campbell et al., 1974).

Conventional tillage systems consist of primary tillage, commonly
moldboard plowing the soil in either the spring or the fall of each
cropping season. Moldboard plowing loosens the soil by shearing,
lateral movement, and inversion. The surface of the soil is left free
of plant residues. Secondary tillage is then performed in the spring
to create a uniform seed bed, to increase seed-soil contact, and to
break up large clods (Soane and Pidgeon, 1975). This system requires
large time, labor, and fuel inputs and offers no protection against
wind and water erosion.

'When the physical properties of the soil are not limiting to plant
growth, tillage is not required and seeds can be placed directly into '
the untilled soil. The only tillage operation is opening the slit for
seed placement; This system leaves the soil surface covered with
residues. The no-tillage system is attractive to producers for several

economic reasons. Because residues are left intact on the soil

11
surface, soil erosion hazards are significantly reduced. This allows
crops to be grown on land previously considered unsuitable because of
high erosion hazards. Time, labor, and fuel inputs are all reduced
under the no-till system.

The location of the compacted layer in the soil profile dictates what
type of tillage implement is used. Surface crusts can be broken up
with a rotary hoe. Compaction occurring in the plow layer can be
alleviated by moldboard plowing. Compaction occurring beneath the plow
layer is the most difficult to alleviate. It is the loosening of this
type of soil compaction which will be addressed in this review.
Subsoiling effects on Plant and Soil Properties

Subsoiling has been shown to reduce the strength of compacted soils.
Busscher et al. (1986) conducted research on a loamy sand soil in South
Carolina in order to determine the residual effects of subsoiling on
soil strength. They found that deep chiseling significantly reduced
the soil strength immediately following tillage. However, after one
year, the strength returned to a level where roots were restricted.

Chaudhary et al. (1985) measured a loamy sand soil in India. They
found that subsoiling significantly decreased soil strength. However,
the bulk density of the soil was not significantly affected. This was
attributed to the fact that in coarse textured soils, strength is due
to inter-particle friction and not due to the density of the soil.
Subsoiling relieved this inter-particle friction on these soils.

Compaction at depth causes poor internal drainage of the soil. This
creates a perched water table above the compact layer and restricts
subsoil recharge. This can cause flooding of young plants early in the

season and drought stress to occur in plants later in the season.

12

Trouse (1983) conducted research comparing underéthe-row subsoiling
with conventional tillage for 15 years on coastal plain soils. He
found that shattering the compacted layer increased water availability
by two mechanisms. First, roots were able to penetrate deeper and
extract subsoil moisture. Secondly, moisture could enter the subsoil
via the loosened areas and recharge the soil supply.

Mukhtar et al. (1985) measured infiltration rates as affected by
subsoiling. The experiment was conducted in Iowa on two soils -- a
silty clay loam and a silt loam. A double ring infiltrometer was used
to measure one-minute and 30-minute cumulative infiltration. The
subsoiled treatment had significantly higher one-minute and 30-minute
cumulative infiltration rates than conventional tillage or no-tillage.

When a root-restricting layer such as that found in the A2 of the
coastal plain soils is shattered, root growth is increased (Campbell et
al., 1974: Trouse, 1983; and Box and Langdale, 1984). This increased
root growth allows a larger volume of soil to be explored for water and
nutrients. Chaudhary et al. (1985) found that in coarse textured soils
in India, subsoiling increased both rooting depth and rooting density.

Grain yields are increased in areas where a root restricting-layer
exists and the rainfall is limiting (Trouse, 1983; and Box at al.,
1984). Therefore, the effect subsoiling has on crop yields is a
function of the soil's hydraulic properties and the climatic conditions
which occur during the growing season (Trouse, 1983).

- Sene et al.(1985) measured soil physical properties to determine the
yield response to subsoiling. They found that when aggregate mean
weight diameter was greater than one mm, aggregation and texture were

correlated to relative yield increases. When peds were not less than

13
one mm, the fraction of very coarse sand became very important and was
highly correlated to relative increases.

Comparison of Conventional and No-tillage Soil Properties
No-tillage crop production methods are increasing in use where soil
physical properties are not limiting to crop growth. Soil physical and
chemical properties have been shown to change under no-till due to the
lack of plowing. There has been much concern about how these changes
in soil physical and chemical properties will affect crop growth. Many
studies have been conducted to measure these changes in soil properties
and their effects on crop growth. The results of which will be
reported in this review.

The bulk density of a soil is the ratio of the mass of the oven dried
soil to its total volume (Hillel, 1982). Many researchers found that
no differences in bulk density occurred between no-till and
conventional tillage soils (Shear and Moschler, 1969, Blevins et al.,
1983 and Hill and Cruze, 1985). However, there are some reports that
bulk density is increased under no-tillage (Gantzer and Blake, 1978).
Soane and Pidgeon (1975) reported that a dense soil layer develops
around 12 cm deep in no-till soils.

Based on the capillary model, the pore size distribution of a soil
determines the percentage of the total porosity which will retain water
at field capacity. _Thus, aeration and soil water status are determined
largely by the soil's pore size distribution.

Hill et al. (1985b) conducted experiments in Iowa on loam and clay
loam soils to determine tillage effects on soil water retention and
pore size distribution. They reported that no-till soils had a

different pore size distribution than that of a conventional tillage

14
soil. Conventional tillage had a larger amount of its pore volume in
pores larger than 15 um while no-tillage had a larger amount of its
pore volume in pores smaller than 15 um. Van Ouwerkerk and Boone
(1970) reported that on medium textured soils in the Netherlands, no-
tillage produced a more uniform pore size distribution than
conventional tillage.

Blevins et al. (1971) researched the effects of no-tillage on soil
moisture in Kentucky. The authors found that no-tillage had
significantly higher volumetric water contents than conventional
tillage at the zero to eight cm depth. No-tillage consistently had
higher volumetric moisture contents to a depth of 45 cm. Gantzer and
Blake (1978) reported similar results on a clay loam soil in Minnesota.

This trend for no-tillage soils to have higher water contents is
primarily due to the residue cover on the soil surface. The residues
trap surface waters, reducing runoff and increasing infiltration. They
.also reduce the radiant energy at the soil's surface which reduces
water losses due to evaporation. No-till soils have a greater ability
to store water against loss by deep percolation because of the increase
in the volume occupied by small pores (Blevins, 1971).

Saturated hydraulic conductivity (Ksat) measures the soil's ability
to conduct water when fully saturated. Gantzer and Blake (1978) found
that conventional tillage had higher Ksat values than no-till when
measured in the spring. Blevins et al. (1983) reported that on a silt
loam soil in Kentucky, Ksat was not significantly different between no-
till and conventional tillage.

Research has shown that soil strength is significantly increased by

no-tillage (Van Ouwerkerk and Boone, 1970 and Hill et al., 1985a).

15
However, Hill et al. (1985a) showed that the cone index values were low
and should not inhibit root growth.

No-tillage has been shown to lead to a reduction in the volume of
soil occupied by air-filled pores (Van Ouwerkerk and Boone, 1970;
Gantzer and Blake, 1978; and Bauder et al., 1981). Because gas
exchange occurs primarily in the air~filled pores, aeration is reduced
in no-till soils at field capacity.

Soil pH is defined as the negative log of the H+ ion activity in the
soil. Soil pH has been shown to be significantly lower at the surface
of no-till soils when compared to conventional tillage (Shear and
Moschler, 1969; Blevins et al., 1977; and Dick, 1983). This difference
is primarily attributed to the surface broadcasting of acidifying
nitrogen fertilizers (Blevins et al., 1977; and Letaw et al., 1984).
Dick (1983) studied a silty clay loam soil and a silt loam soil in
Ohio. He found that the no-till soil had the lowest pH throughout the
plow layer. He also concluded that acidic surface conditions can be
alleviated by broadcast applications of lime, but acidity at depth
cannot.

Tillage affects volumetric moisture content, temperature, aeration,
and placement of microbial substrates. These factors regulate the
types of microorganisms which predominate in the soil environment. The
numbers, types, and activities of microorganisms are important because
of their regulatory effects on soil carbon and nitrogen levels.

Microbial populations under no-tillage and conventional tillage were
compared by Linn and Doran (1984) at five locations in 1980 and six
locations in 1981 across the United States. They found that no-till

soils had larger populations of both aerobic and anaerobic

16
microorganisms in the 0 to 7.5 cm depth. At the 7.5 to 15 cm and 15 to
30 cm depths, conventional tillage had the higher microbial
populations. In the 7.5 to 30 cm depth, anaerobic microbes comprised a
larger percentage of the total population in no-tillage than in
conventional tillage. Aerobic microorganisms predominated in
conventional tillage soils due to the existence of a smaller volume of
water-filled pores.

Organic carbon content is higher in the surface of no-till soils
compared to conventional tillage soils (Blevins et al., 1977; Juo and
Lal, 1979; and Dick, 1983). This buildup of organic carbon results
from crop residues accumulating on the soil surface. Dick (1983)
discusses three mechanisms which contribute to organic carbon buildup
at the surface of no-till soils. He states that the absense of plowing
decreases the soil-residue interaction, reduces soil erosion, and
decreases the rate of biological oxidation.

It has been reported that no-tillage yields were lower than
conventional tillage when nitrogen (N) fertilizers are applied at low
rates. Blevins et al. (1977) reported lower N plant uptake for no-
tillage at zero or low rates of N fertilizer application. This reduced
efficiency of N fertilizer in no-tillage has been attributed to higher
rates of denitrification, increased leaching, increased microbial
immobilization, and reduced mineralization.

Denitrification is the biochemical conversion of nitrates and
nitrites to nitrogen gas (Tisdale and Nelson, 1985). This conversion
is carried out by anaerobic bacteria when oxygen is limiting in the

soil.

17

Denitrification rates were found to be consistently and significantly
higher in no-till soils by Rice and Smith (1982). Their experiment was
conducted on a Maury silt loam (well-drained soil) in Kentucky. The
authors stated that higher moisture contents under no-tillage cause
anaerobic conditions to persist. Linn and Doran (1984) showed that at
7.5 to 30 cm, no-till soils contained a higher percentage of
facultative and total anaerobes than conventional tillage.

Microbial immobilization of soil N occurs when a high C/N ratio is
present. The microbial populations increase due to the high
concentration of carbohydrates. Nitrogen is used to build the new
cells of the microbes and becomes unavailable to plants.

Rice and Smith (1984) studied three silt loam textured soils in
Kentucky in order to measure short-term immobilization under no-tillage
and conventional tillage. They found that on two of the three soils,
no-tillage had twice as much immobilization after seven days. These
findings resulted from the higher C/N ratio occurring in no-till soils.
The authors reported that immobilization plays a larger role in the
availability of fertilizer N then leaching or denitrification in no-
till soils.

Mineralization of soil N is the opposite of immobilization. It is
the conversion of organic N to mineral N which is available to plants.
Rice et al. (1986) measured the soil N availability after long-term.no-
tillage and conventional tillage corn production on a silt loam soil in
Kentucky. They found that conventional tillage led to greater N
mineralization in the initial years. However, after five to 10 years
of cropping, no-tillage mineralization rates were equal to those of

conventional tillage. Plowing accelerates decomposition of crop

18
residues by increasing soil-residue interaction and soil aeration.
This decomposition of crop residues enhances N mineralization. After
five to 10 years, many of the microbial substrates have been depleted
in conventional tillage while they have been accumulating in no-
tillage.

Nitrification is the last step in the process of mineralization.

This step involves the conversion of ammonium to nitrate by aerobic
bacteria collectively referred to as the nitrobacterial Rice and Smith
(1983) showed that nitrification was reduced in no-till soils. Tisdale
and Nelson (1985) list six factors which affect nitrification: supply
of ammonium, population of nitrobacteria, soil pH, soil aeration, soil
moisture, and temperature. No-tillage has been shown to affect each
one of these factors.

Both phosphorus (P) and potassium (K) are immobile nutrients in the
soil. When these nutrients are broadcast applied, they accumulate in
the surface five cm of no-till soils (Shear and Moschler, 1969:
Triplett and Van Doren, 1969; Fink and Wesley, 1974; Juo and Lal, 1979;
and Hargrove, 1985). Eckert and Johnson (1985) found that P
accumulated at the surface of no-tillage plots which received no P
fertilizer applications. Plant roots extracted P from deeper in the
soil and deposited it on the surface as plant residues.

Hargrove (1985) conducted research to determine the influence of
tillage on nutrient uptake and yield of corn on a sandy loam soil in
Georgia. He reported that P and K did accumulate at the surface of no-
tillage. However, he found that P and K concentrations in the ear leaf
and above ground whole plants were equal or greater for no-tillage.

Rubidium (Rb) was used to determine the activity of the roots in the

19
different tillage systems. It was concluded that plant roots under no-
tillage had the highest Rb uptake.

Triplett and Van Doren (1969) found that on a silt loam soil in Ohio,
P and K uptake were equal or higher in no-tillage. Plant uptake of P
and K in no-till soils is a function of the increased root growth in
this nutrient-rich layer. Grain yields were higher under no-till for
all six years of the experiment.

Eckert and Johnson (1985) conducted research in Ohio to compare crop
and soil response to placement of P fertilizer. Equal rates of P
fertilizer were applied by surface broadcasting and by subsurface
banding. The authors reported that banding increased yields and
fertilizer use efficiency while reducing the accumulation of P in the
soil surface.

Summary

When soil physical properties are limiting to crop growth, tillage is
required to improve these properties. Tillage can alleviate soil
compaction whether at the soil surface or as deep as 45 cm.

If soil properties are not limiting to crop growth, then tillage is
not required. No-tillage crop production methods on such soils have
produced good results. However, no-till -- when practiced over long
periods of time -- does alter the soil's physical and chemical
properties. Some of these changes produce a soil environment that is
less than ideal for plant growth. Periodic plowing of no-till soils

becomes necessary to improve conditions for plant growth.

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Blevins, R.L., G.W. Thomas, P.L. Cornelius. 1977. Influence of
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20

21

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22

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on the root-growth habits of plants. Soil Sci. 98:174-180.

23

Tisdale, S.L., W.L. Nelson, and J.D. Beeton. 1985. Soil
fertility and fertilizers. Macmillan Publishing Co., New
York, NY.

Triplett, G.B.Jr., and D.M. Van Doren Jr. 1969. Nitrogen,
phophorus, and potassium fertilization of non-tilled maize.
Agron. J. 61:637-639.

Trouse, A.B.Jr. 1983. Observations on under-the-row subsoiling
after conventional tillage. Soil & Tillage Research. 3:67-
81.

Van Ouwerkerk, C., and P.R. Boone. 1970. Soil physical aspects
of zero-tillage experiments. Neth. J. Agric. Sci. 18:247-
261.

Vomocil, J.A., and W.J. Flocker. 1961. Effect of soil
compaction storage and movement of soil air and water.
Trans. ASAE. 4:242-246.

Voorhees, W.B. 1977a. Soil compaction: our newest natural
resource. Crops Soils. 29:13-15.

Voorhees, W.B. 1977b. Soil compaction: how it influences
moisture, temperature, yield, and root growth. Crops Soils.
29:7-10.

Voorhees, W.B., Senst, and W.W. Nelson. 1978. Compaction and
soil structure modification by wheel traffic in the northern
corn belt. Soil Sci. Soc. Am. J. 42:344-349.

Warkentin, B.P. 1971. Effects of compaction on content and
transmission of water in soils. p. 126-153. In K.K. Barnes
et al. Compaction of agricultural soils. Am. Soc. Agric.
Eng., St. Joseph, MI.

Wiersum, L.K. 1957, The relationship of the size and structural

rigidity of pores to their penetration by roots. Plant and
soil. 9:78-85.

Chapter 2

Changes in Soil Physical and Chemical Properties
Associated with Periodic Plowing in No-till Corn

INTRODUCTION

No-tillage crop production is increasing throughout the United
States. Optimistic estimates indicate that 60 to 80 percent of the
total crop acreage will be planted to no-till in the next 20 years. No-
till significantly reduces soil erosion on sloping fields. No-till
also reduces time, labor, and fuel inputs required for seed bed
preparation.

The absense of plowing causes a unique soil environment to form under
no-tillage. These changes in soil physical and chemical properties
have been well documented and there is concern about how these
properties will affect plant growth.

No-till has been shown to affect soil physical properties. Gantzer
and Blake (1978) showed that soil bulk density was higher under no-
till. Hill et al. (1985b) reported that no-till increased the volume
of soil occupied by pores smaller than 15 um. Van Ouwerkerk and Boone
(1970) found that no-till produced a more uniform pore size
distribution than conventional tillage. Blevins (1971) and Gantzer and
Blake (1978) found that volumetric water contents were higher under no-
till. Saturated hydraulic conductivities were shown to be‘
significantly lower for no-till by Gantzer and Blake (1978). Air-
filled porosity was found to be reduced in no-till soils (Van Ouwerkerk
and Boone, 1970; Gantzer and Blake, 1978; and Bauder et al., 1981).

24

25
Because gas exchange occurs in the air-filled pores, the process of
aeration can be inhibited in no-till soils. Hill et al. (1985a) and
Van Ouwerkerk and Boone (1970) found that soil strength was increased
by no-till. However, Hill et al. (19853) showed that the cone index
values were low and should not inhibit root growth.

Tire traffic is the leading cause of soil compaction in agricultural
soils (Cohron, 1971). Compaction has been shown to inhibit root growth
through mechanical impedance and aeration stress (Taylor and Burnett,
1964; and Letey et al., 1962). Wheel traffic-induced compaction could
be a problem in no-till soils due to the absence of annual soil
loosening provided by plowing.

Extended periods of no-tillage can lead to significant changes in
soil chemical properties. Acidic surface conditions have been shown to
develop in no-till soils (Shear and Moschler, 1969; Blevins, et al.,
1977: and Dick, 1983). Blevins et al. (1977) attributes this process
to the broadcast application of acidifying nitrogen fertilizers.
Blevins et a1. (1977), Juo and Lal (1979), and Dick (1983) reported
accumulated organic carbon at the surface of no-till soils. Nitrogen
(N) cycling has been shown to be affected by no-tillage. At low
application rates, fertilizer N availability was found to be reduced in
no-till by Blevins et al. (1977). Rice and Smith (1982) found that no-
till had consistently higher rates of denitrification. Microbial
immobilization was also found to be higher in no-till (Rice and Smith,
1984). Rice et al. (1986) showed that N mineralization was higher for
conventional tillage in the initial years (five to 10 years). After
this time, mineralization rates were similar between no-tillage and

conventional tillage. Phosphorus (P) and potassium (K) have been shown

26
to accumulate near the surface of no-till soils when surface broadcast
(Shear and Moschler, 1969; Triplett and Van Doren, 1969; Fink and
Wesley, 1974; Juo and Lal, 1979; and Hargrove, 1985).

Periodic plowing has been recommended to alleviate some of the
adverse conditions which develop under no-till. Plowing mixes the
stratified nutrients and organic carbon into the plow layer. Woody
perennial weeds can be controlled better by plowing. Acidic surface
conditions can also be alleviated by plowing.

The objectives of this research were to: 1) quantify changes in soil
physical and chemical properties when no-till soils are periodically
plowed; 2) determine the impact of wheel traffic on the soil physical
properties of no-tillage and conventional tillage: and 3) determine the
plant responses to the soil physical and chemical changes which occur
following plowing.

MATERIALS AND METHODS

The experiment was originally initiated in 1981 to assess the effect
of rye cover management in no-tillage compared to conventional tillage.
The site was located at the Michigan State University experimental
farms in East Lansing, Michigan. The soil at this site was a Conover
loam (Fine-loamy, Mixed, Mesic, Udollic Ochraqualf). This soil is
somewhat poorly drained. However, this site was tile drained.

There were four tillage treatments from 1981 to 1985 (Table 1): 1)
fall plowed and spring secondary tillage in each year (CT); 2) no-till
with 90 percent rye cover killed at planting except three to four
inches between rows (NTRl); 3) no-till with 90 percent of the rye cover
crop killed at planting (NTR2); and 4) no-till with 100 percent rye

cover crop killed at planting (NT). In the spring of 1986, the NTR2

27

 

 

Table 1. Descriptions of the tillage treatments.
Tillage Code Tillage Treatments
---------------- Year -----------------
1981-1985 1986 1987
CT CT CT CT
NTP6 NTRl NT CT
NTPS NTR2 CT NT

NT NT NT NT

 

28
treatment was plowed (NTPS) in addition to the CT treatment. The NTRl
and NT treatments were no-tilled.in 1986. In the fall of 1986, the CT
treatment and the NTRl treatment were plowed (NTP6). The NTPS
treatment was returned to no-tillage for the 1987 field season as was
the NT treatment from 1986. In 1986, soil measurements were made only
on the CT, NTPS, and NT treatments. In 1987, measurements were made on
CT, NTPS, NTP6, and NT.

Due to a wet fall in 1985, CT and NTPS were spring plowed on April 18
for the 1986 field season. The CT and NTP6 treatments were plowed in
the fall of 1986 for the 1987 field season. The depth of plowing was
20 cm for both years. Secondary tillage was performed in the spring
and consisted of one pass of a disk and one pass of a spring-tined
field cultivator.

In 1986, pioneer 3744 variety seed corn was planted on May 3. In
1987, pioneer variety 3737 was planted on April 28. In both years
planting was done with a Buffalo no-till planter seeded to an intended
population of 65,000 seeds per hectare.

Fertilizers and rates were the same in 1986 and 1987. A liquid
starter fertilizer of 13 kg N ha'1 and 19 kg P ha'1 as ammonium
polyphosphate was banded near the row at planting. Fertilizer N at a
rate of 168 kg N ha'1 was broadcast as ammonium nitrate prior to
seedling emergence.

Weed control in 1986 was achieved by broadcasting 4.7 liter alchlor
he'l, 2.3 liter atrazine he'l, and 2.3 liter cyanazine he'l. In 1987,
the alachlor and cyanazine were increased by 1.17 liter he'l. In 1986
and 1987, 2.3 liter he"1 of paraquat were broadcast applied to the no-

till plots.

29

Plant emergence was monitored by counting the number of plants
emerged in 40 feet of row.

Ear leaf samples were taken in 1986 when half of the plants were
silking. Fifteen leaves located opposite and below the ear were chosen
at random to form a composite sample. The leaves were washed in sodium
lauryl sulfate, rinsed in distilled deionized water, dried, and ground
for N analysis.

Grain was harvested by hand from two 30-foot rows from each plot.

The grain was subsampled for moisture and N analysis. Grain moisture
was determined using a moisture meter. Stover from 20 random plants
was chopped and weighed from each plot in 1986 and subsampled for
moisture and N analysis. In 1987, all the plants from the harvest area
were chopped, weighed, and subsampled for moisture and N analysis.

Ear leaf, grain, and stover tissue samples were digested using a
Kjeldahl procedure (Bremner and Mulvaney, 1982). The N in the digest
was determined analytically on the Lachet flow injection analyzer.

Inorganic nitrogen content was determined from composite samples,
taken in the spring prior to fertilizer applications. In 1986, the
sampling depths were 0 to S cm, 5 to 15 cm, and 15 to 30 cm. Six punch
probe cores made up a composite sample. The soils were sampled on six
dates: 4/14, 4/22, 4/24, 4/27, 5/1, and 5/5. In 1987, the sampling
depths were 0 to S cm, 5 to 10 cm, and 10 to 20 cm. Eight punch probe
cores made up a composite sample. The sampling was performed on six
dates: 4/10, 4/13, 4/17, 4/20, 4/23, and 4/30.

Soil samples were frozen after sampling. The samples were thawed,
sieved, and mixed thoroughly. Ten grams of moist soil were combined

with 100 ml of 1.0 N KCl and shaken for one hour (Keeney and Nelson,

30
1982). The extract was then filtered through Whatmen #2 filter paper.
The filtrate was analyzed colorimetrically for N03" and NH4+ on the
Lachet flow injection analyzer. Duplicate extractions were performed
on each sample and blanks were included to determine the filter paper's
contribution of NO3'. The blanks were averaged and subtracted from the
samples.

Soil pH, organic carbon, phosphorus, and potassium were determined
from composite samples taken on April 10, 1987. The sampling depths
were 0 to 5 cm, 5 to 10 cm, 10 to 15 cm, and 15 to 20 cm. Soil pH was
determined using a glass electrode and a 1:1 soil-water slurry.

Organic carbon was determined using the method of Snyder and Trofmow
(1984). Phosphorus was extracted with Bray extract and analyzed on a
Brinkmen PC 800 Fiberoptic probe calorimeter. Potassium was extracted
using 1.0 N NHAOAc and extracted K was determined by atomic absorption.

Soil physical properties (bulk density, total porosity, pore size
distribution, moisture characteristic curve and saturated hydraulic
conductivity) were determined on 7.6 cm x 7.6 cm intact soil cores.
Soil cores were taken at two depths: 0 to 7.5 and 7.5 to 15 cm. In
1986, both the wheel-tracked and non-wheel-tracked areas were sampled.
In 1987, only the non-trafficed area was sampled on July 14. Cores!
were taken on two dates in 1986: June 21 and September 16.

The cores were saturated from the bottom for 48 hours. Saturated
hydraulic conductivity (Ksat) was determined using the constant head
method of Klute (1965). The cores were then resaturated and weighed.
Moisture retention for 1, 2, 3, 4, and 6 kPa of metric suction were
determined by the blotter paper method (Leamer and Shaw, 1941). The

water retention at 10, 33.3, and 100 kPa of metric suction were

31
determined using pressure plates (Richards, 1965). The pore size
distribution was calculated by applying the capillary model to the
moisture characteristic curve (Vomocil, 1965). Bulk density was
determined on a mass per volume basis after oven drying the cores for
48 hours at 105 degrees C.

In 1986, the experimental design for the core samplings was a split
plot with tillage as the main plots and tire traffic as the sub-plots.
In 1987, the experimental design for the core samplings was a
randomized complete block. The treatments were replicated four times
in all years of the experiment. Analysis of variance was employed to
detect significant differences between treatment means. Duncan's
Multiple Range Test was used to separate and rank the treatment means.

RESULTS AND DISCUSSION
Physical Properties

The bulk density data from 6/21/86 and 9/16/86 are presented in
Figure 1. The NT treatment had the highest bulk density (Db) values of
all treatments at both the 0 to 7.5 cm depth and the 7.5 to 15 cm
depth. At the 0 to 7.5 cm depth, Db values for NT were 1.43 g cm“3 on
6/21 and 9/16. At the 7.5 to 15 cm depth, Db values for NT ranged from
1.48 g cm'3 on 6/21 to 1.55 g cm'3 on 9/16. Plowing a no-till
treatment (NTPS) decreased these values by .20 g cm'3.

The 1987 bulk density data is presented in Figure 2. Again, the NT
treatment had the highest Db at both the 0 to 7.5 cm depth and the 7.5
to 15 cm sampling depth. At the surface, all four bulk density
treatment means were significantly different from each other. These
means were ranked in the following order: NT) NTPS) CT) NTP6. At the

7.5 to 15 cm depth, NT and NTPS (the two no-till treatments in 1987)

BULK DENSITY (g cm")

BULK DENSITY (g cm")

32

1.70

 

l [2221 CT 0
1.60- I: NTP5

i - NT LSD (.05) I
1.504 I

1.40-
1.30-

1.20-

 

   

 

 

W

 

 

 

 

1’1 0 0-7.5 7.5-15

SAMPLING DEPTH (cm)

1.70

 

. m CT b
[:1 NTP5 LSD (.05) I

1.60-

- NT

1.50— I
1.40-1
1.30-

1.20-

W
V////A

 

   

 

 

 

 

1.10

 

 

 

 

0-7.5 7.5-15
SAMPLING DEPTH (cm)

Figure 1. Tillage effects on soil bulk density from between the
tire tracks on 6/21/86 (a) and 9/16/86 (b).

33

.em\ea\e echo suamame sang show no moomoow mmmaaae .m magmas

98V Emma
mplmfi

 

OZ_n_n:2<m

 

s m

 

 

 

  

 

 

63 am;

 

 

 

were ,
V

 

 

hz .NNN.
mmpz I
mnfiz U
.5 a

0.:
wow;
ion;
10¢; .
tom.—

tom;

 

 

on;

(c-wv 5) AllSNI-lCl M108

34.

were significantly greater than those of the NTP6 and CT treatments
(the two plowed treatments in 1987). The Db values for the NT
treatment at the 0 to 7.5 cm depth and the 7.5 to 15 cm depth were 1.43
g cm"3 and 1.50 g cm‘3 respectively. Plowing reduced these values to
1.16 g cm'3 and 1.22 g cm"3 for the 0 to 7.5 cm depth and the 7.5 to 15
cm depth respectively in the NTP6 treatment.

The pore size distribution of the no-tillage soil was significantly
affected by plowing in 1986 and 1987. The data from 6/21/86 and
9/16/86 are presented in figures 3 and 4 respectively. At both
sampling depths, plowing increased the volume of soil occupied by pores
whose radii were greater than 146 um by a factor of at least 1.5 for
the three sampling dates. The volume of soil occupied by pores with
radii between 146 and 24 um in the NTP5 treatment was double that of
the NT treatment in 1986. This was true at the 0 to 7.5 cm depth and
the 7.5 to 15 cm depth. In 1987 (Figure 5), the volume of pores in the
size interval 146 to 24 um was increased 1.7 times by plowing (NTP6)
when compared to continuous no-till (NT). With the exception of the
7.5 to 15 cm depth of the June 1986 sampling, plowing significantly
decreased the volume of soil occupied by pores with radii less than 24
um compared to the NT treatment.

The pore size distribution of the no-tilled Conover loam was
significantly affected by plowing. Plowing increased the volume of
soil occupied by pores with radii greater than 24 um and decreased the
volume occupied by pores with radii less than 24 um. This change in
pore size distribution can in turn affect other soil properties: water

retention and air-filled porosity.

PORE VOLUME (cm3 cm'i)

PORE VOLUME (cm’ cm")

0.50

35

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[222! CT
'1 E NTP5 0-7.5 cm
0.401 - NT I
0.50 7
0.20% /
. a
0.10% LSD (.05) I I g
/
1 A
0’00 >146 246-24 <24 '
PORE RADIUS INTERVALS (pm)
0.50
J [222! or
:3 mp5 7.5-15 cm
0.401 - NT I
I
0.50J ‘ ‘
0.20- /
LSD (.05) I %
0.10- 1 %
am @1 fl 2
>146 146-24 <24

PORE RADIUS INTERVALS (pm)

Figure 3. Tillage effects on the pore size distribution from

6/21/86.

PORE VOLUME (cm’ cm")

PORE VOLUME (cm’ cm")

0.50

36

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[222! cr
‘ E NTP5 0-7.5 cm
0.40~ - NT I
0.50-I .
. 7
0.20-1 %
LSD (.05) 1 1 g
0.10- ‘
I 21 m 6
0'00 >146 146-24 <24
PORE RADIUS INTERVALS' (pm)
0.50
[222 CT
‘ E NTP5 7.5-15 cm
0.40- - NT
I I
0.301 . fl
7
0.20- g
1 L80 .05
0.10~ ( ) I 3 Z
+ ‘ /
0'00 . >146 . 146-24 ' <2'4-

PORE RADIUS INTERVALS (I...)

Figure 4. Tillage effects on the pore size distribution from

9/16/86.

PORE VOLUME (cm’ cm”)

PORE VOLUME (cm’ cm")

0.50

37

 

 

 

 

 

 

 

      

 

 

 

 

 

 

 

 

 

 

 

 

 

 

j 153:: 07
0.40.1 E :1.ng O-7.5 cm I
4 1221 NT ,
0.30% Q
0.20- _ §
.~ LSD (.05) 1 I
0.00 W I K N A
>146 146—24 <24
PORE RADIUS INTERVALS (pm)
0.50
. m or
0.40.. E 2:: 7.5-15 cm I
. 1222: NT
0.304 Q
A
LSD (.05) I I §
0.10- §
0 00 M M \ /
° >146 146-24 <24

PORE RADIUS INTERVALS (1.4m)

Figure 5. Tillage effects on the pore size distribution from

7/14/87.

38

The volume of water which drains at a given matric suction
corresponds to the volume of soil occupied by pores with radii greater
than those which will retain water by capillarity at that suction
(Vomocil, 1965). In 1986, water retention curves were determined from
intact soil cores at metric potentials of -1, -2, -3, -4, -6, -10,
-33.3, and -100 kPa. The 6/21/86 data for the 0 to 7.5 cm and the 7.5
to 15 cm depths are presented in Figures 6 and 7 respectively. The
9/16/86 water retention curves for the 0 to 7.5 cm and the 7.5 to 15 cm
depths are shown at the top of Figures 8 and 9 respectively. At both
depths in 1986, the NTP5 and CT treatments had higher volumetric water
contents at low metric suctions and lower volumetric water contents at
high metric suctions than the NT treatment.

In 1987, the water retention curves were determined at matric
potentials of -1, -2, -4, -6, and -33.3 kPa. The water retention
curves for the 0 to 7.5 cm depth and the 7.5 to 15 cm depth are
presented at the top of Figures 10 and 11 respectively. The CT, NTP5,
and NTP6 treatments had higher volumetric water contents at high matric
potentials and lower volumetric water contents at low matric potentials
than the NT treatment.

The air-filled porosity (fa) of the soil is a function of the pore
size distribution also. Pores whose radii are from 30 to 60 um will
remain filled with water at the soil's field capacity which occurs at a
metric potential from -5 to -10 kPa (Cannell and Jackson, 1981). Foth
(1978) states that the field capacity for medium and coarse textured
soils corresponds to a metric potential of -6 kPa. Therefore,
particular attention will be focused on the air-filled porosity of the

tillage treatments at -6 kPa of metric potential.

6 (cm3 cm")

f. (cm3 cm")

39

 

0.55
0.50-

0.45- ‘

0.40-
0.351
0.30-

0.251

 

 

0.20

UIUUI

U r rTTT

 

0.30

0.25-

 

 

 

Figure 6. The effects of tillage on moisture retention (3)
and air-filled porosity (b) at the 0 to 7.5 cm

depth from 6/21/86.

 

 

9 (cm3 cm")

f. (cm3 cm”)

40

 

 

 

 

 

0.55 -_
I LSD (.05) ° 0
0.50-
0.45- I
0.404 .. I I
0.354 \\
7“:====:\\ I I
0.50- ' -
a—a NT ’
0.25- H NTP5
0.20 H97. .., . L W...“ . . .....,
0.50
0—9 CT I) I
H NTP5
0.25- H NT I

0A20-4 ‘ I 1: 1

 

 

 

0°15“ LSD (.05) I

0.10-

0.054 /

0.00 f I fit I I ‘0' t D t ti 5‘1] 0 I r U I 'TTr
— 0.1 — 1.0 - 10.0 —100.0

Figure 7. The effects of tillage on moisture retention (a)
and air-filled porosity (b) at the 7.5 to 15 cm
depth from 6/21/86.

6 (cm3 cm“)

f. (cm’ cm")

41

 

 

 

 

 

 

 

 

 

0.55
I LSD (.05) a
0050-:
Ou45w-
‘ I
0.40- I
< - I I I
0.55- - _ I I
?\\ I
OJBOH-
a—e NT 7
CLZEL- Ehda hflTflS
e—o or
0.20 . . .m, . ......, e .. . .,
0.30
ehqa cn' b :I
0254 e—a NTP5 I .
° a—e NT I I
I
0.20-I , =
0.15-1
0.1CL4
0.05-
0.00 . ...... . . new, - Inrm,
-O.1 —l.0 -l0.0 —100.0
‘Irm (kPa)

Figure 8. The effects of tillage on moisture retention (a)

and air-filled porosity (b) at the 0 to 7.5 cm
depth from 9/16/86.

6 (cm’ cm")

f. (cm3 cm”)

42

 

0.555

0.50-11 LSD (.05)
0.45- “

0.40- _

0335-
ONSCL-
OJ25-

 

 

 

OJZO

 

 

ONSC)

OJZS-H

OMZCL-

0.15-

0.10-4

OJJS-w

 

CLCNJ

-(DJI

LSD (.05) I j = '*

 

 

r rrth'I r I fUrIIUI I U YTTrUU

—1.o —1o.o -1ob.o

Figure 9. The effects of tillage on moisture retention (3)

and air-filled porosity (b) at the 7.5 to 15 cm
depth from 9/16/86.

6 (cm3 cm")

fa (cm3 cm")

43

 

 

 

 

 

 

    
 

 

 

0.60
055-11 LSD (.05) a
0.50-
0.45- p I I
0.40— \\ I I
0435-- \\§§§ I
0.30- H NT °
A—A NTP5
025“ a—a NTP6
0.20 H 9 1 MT r r r I r u
0.30
a—a NTP6
0'25 a—a NTP5 I
020 H NT I /
o -‘ I a/,:
0'15“ L50 (.05) I ‘
0.10-‘
0435-
o.oo e e ,, T m, e r r m
-O.1 -1.0 -10.0 -100.0
{rm (kPa)

Figure 10. Tillage effects on moisture retention (a) and air-
filled porosity (b) at the 0 to 7.5 cm depth from
7/14/87.

0 (cm’ cm")

fCl (cm3 cm“)

44

 

 

 

 

 

 

   

 

 

0.60
0.55-I LSD (.05) °
0.50-
0.45J I
0.40- :\ I I
‘\§i. I
0.35- \\ I
:\
0°30.— H NT \5\
H NTP5 . 3
025‘ a—a NTP6
0.20 H537. r. I , . n r
0.30
¢}-6 (Tr I b
a—a NTP6
W 11 :
abet h“' g
0.20- I/
0.15- LSD (.05) I ‘
0.10- ' -
0.05-
0.00 1 hum, . ”WWW . mm,
—0.1 —1.0 —10.0 —100.0
‘Ifm (kPa)

Figure 11. Tillage effects on moisture retention (a) and air-

filled porosity (b) at the 7.5 to 15 cm depth from
7/14/87.

45

The air-filled porosity data is presented in figures 6, 7, 8, 9, 10,
and 11. On all dates and at all depths, plowing significantly
increased the air-filled porosity over all matric potentials compared
to the NT treatment.

In 1987, after returning to no-till for one year, the NTP5 treatment
had a higher percentage of air-filled pores than the NT treatment. At
the 0 to 7.5 cm depth, the NTP5, NTP6, and CT treatments were not
significantly different. At the 7.5 to 15 cm depth, the NTP5 treatment
had a significantly lower percentage of air-filled pores than the NTP6
treatment.

In 1986, the NT treatment contained fewer than 10 percent air-filled
pores at both depths for the -6 kPa matric potential. When air-filled
porosity is less than 10 percent, gas exchange and plant growth can be
reduced (Vomocil and Flocker, 1961). The NTP5 treatment doubled the
volume of air-filled pores at the -6 kPa matric potential over that of
the NT treatment. This was true for both sampling depths.

In 1987, the NT treatment contained fewer than 10 percent air-filled
pores only at the 7.5 to 15 cm depth for the -6 kPa matric potential.
The volume of air-filled pores at -6 kPa was increased in the NTP6
treatment by a factor of 1.8 at the 0 to 7.5 cm depth and by a factor
of 2.5 at the 7.5 to 15 cm depth over that of the NT treatment.

Plowing significantly increased the air-filled porosity over that of
the continuous no-till (NT). But most importantly, it increased the
volume of air-filled pores at the soil's field capacity. This would
indicate that plowing may reduce the frequency and duration of aeration

Stresses .

46

The total porosity data for 1986 and 1987 are presented in tables 2
and 3 respectively. In 1986, the NTP5 treatment contained
significantly more total pore volume than the NT treatment at the 0 to
7.5 cm and the 7.5 to 15 cm depths.

In 1987, the NTP6 treatment contained the highest percentage of pore
space at both depths. However, at the 0 to 7.5 cm depth, the NTP6,
NTP5, and CT treatments were similar and significantly higher than the
NT treatment. At the 7.5 to 15 cm depth, NTP6 contained significantly
more total pore volume than NTP5 and NT but not CT. However, NTP5
contained significantly more pore space than NT: .46 cm3 cm"3 and .42
cm3 cm.‘3 respectively.

Saturated hydraulic conductivity (Ksat) is a measure of the soil's
ability to transmit water under saturated conditions. The 1986 data is
presented in Table 2 and the 1987 data can be found in Table 3. The
Ksat values were not significantly different between tillage treatments
in the June 1986 sampling. However, plowing significantly increased
the Ksat in the NTP5 treatment in September of 1986 over those of the
NT and CT treatments at the 0 to 7.5 cm depth. In the 0 to 7.5 cm
depth the Ksat values were 9.00 cm hr'1 for the NT treatment and 46.50
cm hr'1 for the NTP5 treatment. At the 7.5 to 15 cm depth, Ksat was
1.95 cm hr'1 and 9.60 cm hr'l for NT and NTP5 respectively. These were
significantly different. In 1987, the NTP5 treatment had significantly
higher Ksat values than the NT treatment at the Ofito 7.5 cm depth but'
not at the 7.5 to 15 cm,depth.

Ksat is correlated with the size of the soil pores. Large pores
conduct more water under saturated conditions than small pores. Ksat

is also a function of the continuity and tortuosity of the pores.

47

Table 2. Total porosity and saturated hydraulic conductivity
(Ksat) from 6/21/86 and 9/16/86.

 

 

 

 

 

Tillage Depth Total Porosity Ksat
(cm) (cm3 cm'3) (cm hr’l)
--------------------- 6/21/86 ----------------------
0-7.5
CT .48 ab 3.93 a
NTP5 .49 a 5.88 a
NT .46 b 3.98 a
LSD (.05) .03 2.36
7.5-15
CT .47 b 4.08 a
NTP5 .50 a 8.26 a
NT .42 c 8.70 a
LSD (.05) .03 7.91
---------------------- 9/16/86 ----------------------
0-7.5
CT .48 a 20.85 b
NTP5 .49 a 46.50 a
NT .44 b 9.00 b
LSD (.05) .02 17.10
7.5-15
CT .46 a 16.35 a
NTP5 .46 a 9.60 a
NT .39 b 1.95 b
LSD (.05) .02 7.05

 

Means in each column which are not followed by the same letter
are not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

48

Table 3. Total porosity and saturated hydraulic conductivity
(Ksat) from 7/14/87.

 

 

 

 

Tillage Depth Total porosity Ksat
(cm) (cm cm' ) (cm hr'l)
0-7.5
CT .48 a 26.2 ab
NTP6 .50 a 32.0 a
NTP5 .48 a 20.4 b
NT .45 b 7.3 c
LSD (.05) .03 8.4
7.5-15
CT .49 ab 30.7 a
NTP6 .52 a 32.7 a
NTP5 .46 b 17.0 ab
NT .42 c 3.4 b
LSD (.05) .033 16.3

 

Means in each column which are not followed by the same letter
are not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

49

During a rain or an irrigation event, the surface of the soil becomes
saturated. The ability of water to infiltrate through this saturated
soil layer is largely controlled by the Ksat of the soil. Plowing
significantly increased the Ksat values compared to those of the
continuous no-till.
Tire Traffic Effects on Soil Physical Properties

Wheel traffic significantly increased the bulk density of the plowed
treatments at the 0 to 7.5 cm and the 7.5 to 15 cm depths (Figures 12
and 13). However, the bulk density of the NT treatment was not
significantly affected by wheel traffic. Tire traffic increased Db in
the plowed treatments by at least .15 g cm.3 at all sampling dates and
depths, with the exception of the 7.5 to 15 cm depth on 9/16/86 where
the increase was .07 g cm'3.

Pore size distribution was significantly altered by wheel traffic in
the CT and NTP5 treatments. The NT treatment was not significantly
affected by wheel traffic at either depth or sampling time or for any
pore class. These trends are demonstrated by Figures 14 through 17.
The volume of soil occupied by pores with radii greater than 146 um was
cut in half in the CT and the NTP5 treatments at all sampling times and
for both sampling depths. With the exception of the 0 to 7.5 cm depth
of the 9/16/86 sampling, the pore volume occupied by pores with radii
in the range from 146 to 24 um was.significantly reduced in the CT and
.NTPS treatments. 'This reduction was on the order of 25 percent. At
both sampling depths, the volume of soil occupied by pores with radii
less than 24 um was increased by wheel traffic in the CT and NTP5
treatments. Wheel traffic decreased the volume of soil occupied by

pores larger than 24 um and increased the volume of soil occupied by

Anucco 0v trcmzmo v33m ATEU 0» \rtmzuc v. :E

BULK DENSITY (g cm")

BULK DENSITY (g cm")

50

1.70

 

. 1:1 BETWEEN TIRES o
1.60“ 12221 TIRE TRACK

L
H

1'50“ LSD (.05) I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

. w
”"1 —%
1::1 4 “4 4
1:352:53? 14 b
4 ‘4
‘4 4 4
If? 4 4 4

TILLAGE TREATMENT

Figure 12. Tire traffic effects on bulk density at the 0 to 7.5
cm depth (a) and the 7.5 to 15 cm depth (b) from
6/21/86.

BULK DENSITY (g cm")

BULK DENSITY (g cm")

51

 

1.70
1.604
1.501
1.40:
1.2.01

1.20~

 

1.10

. 1:] BETWEEN TIRES

12221 TIRE TRACK

 

 

 

 

 

 

 

 

 

 

1.70

LSD (.05) I I I ,
4 ‘4
4 4
0% NTP5/A é

TILLAGE TREATMENT

 

1.601
1.50;
1.40;
1.30-

1.20-

 

1.10

E BETWEEN TIRES
m TIRE TRACK

 

\

 

 

 

 

 

 

m

 

 

4

 

.. J +
”W

NTP5 NT
TILLAGE TREATMENT

Figure 13. Tire traffic effects on bulk density at the 0 to

7.5 cm depth (a) and the 7.5 to 15 cm depth (b)
from 9/16/86.

 

 

FORE VOLUME (cm’ cm")

0.50

52

 

 

. E BETWEEN TIRES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.40.. IZZZI TIRE TRACK >146 “
0.30J
0.204
' LSD (.05) 1: I
0.10"I ——W ‘— I
0.00 m m
0.50 I
[:1 BETWEEN TIRES _
0.40.4 [ZZZ] TIRE TRACK 14a 2‘ "
0.304
0.20-
0.10; LSD (.05) x x
‘ —T ' _-WI 1
0.00 W cm
0.50
. = 3013.213 »
0.40- m x a: x LSD (.05)
0.30~ ‘ y/ ‘ g/
0.20- % %
0.10-1 4% %
0.00‘ //7 4 /
CT NTP5 NT

TILLAGE TREATMENT

Figure 14. Tire traffic effects on the pore size distribution
at the 0 to 7.5 cm depth from 6/21/86.

 

 

 

PORE VOLUME (cm’ cm")

0.5CI

53

 

 

. C223 BETWEETITNRES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.40- 1222 TIRE TRACK >146 "
0.30-1
0.20-

‘ LSD (.05) I I
0.1(1- » ‘—"1 I

1 —17m *

0.00 m
0.50
. I:I BETWEEN TIRES __
Q40- Izzz TIRE TRACK '46 24 "
0.304

1
0.204
010- LSD (.05) 1 , I I
000 m [—1772
0.50

. E:I BETWEEN TIRES
0.40- m TIRE TRACK <24 “

J I , I , , I LSD (.05)
0.30- ‘ /7 /?/ /%
0.20~ % ‘ % %
0.104 % / %
0.00 ‘ / j /

CT NTP5 NT

TILLAGE TREATMENT

Figure 15. Tire traffic effects on the pore size distribution
at the 7.5 to 15 cm depth from 6/21/86.

 

 

 

FORE VOLUME (cm3 cm")

54

 

0.50

 

:3 BETWEEN TIRES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.404 2221 TIRE TRACK >146 "
0.30-
0.20-
LSD (.05) 3 a:
0.10- "'—‘ *—* x
0.00 m E Em
0.50
. I: BETWEEN TIRES _
0.40- Izzz TIRE TRACK ”'6 24 "
0.30-
.I
0.204
L LSD .05 I I
0.10fl ( ) , fl 4 I
0.00 W4 V/Z rm
0.50
. 1:1 BETWEEN TIRES <24 p
0.40. m TIRE TRACIK I I LSD (.05)
0.30- . % __/// y
I / /
0.204 / / /
0.10- / /
CT NTP5 NT

TILLAGE TREATMENT

Figure 16. Tire traffic effects on the pore size distribution
at the 0 to 7.5 cm depth from 9/16/86.

 

 

 

PORE VOLUME (cm: cm”)

0.50

55

 

 

E: BETWEEN TIRES

 

 

 

 

 

 

0.40; 12221 TIRE TRACK >146 "
0.30-I
0.20-

‘ LSD (.05) I I
0.10- .—

.. _—I I
0.00 m m l m
0.50

0.4(W1
0.30.4
0.20-

0.10-

 

0.00

. 1:: BETWEEN TIRES

TZZZI TIRE TRACK

LSD (.05) :

 

 

S

146-24 [3

 

 

0.50

 

0.401

.1
0.30‘
0.20-

0.10-

 

1:: BETWEEN TIRES

IZZZI TIRE TRACK
I

 

 

 

<24 3

\\\\\\\\\N

 

 

 

 

1 LSD (.05)

 

4

 

0.00

T§.\\\\\\\\N

C

NTP5

NT

 

 

 

TILLAGE TREATMENT

Figure 17. Tire traffic effects on the pore size distribution

at the 7.5 to 15 cm depth from 9/16/86.

56
pores with radii less than 24 um in the plowed treatments. However,
the NT treatment was not significantly affected by wheel traffic.

Wheel traffic significantly reduced the total pore volume of the CT
and the NTP5 treatments, but had no effect on the NT treatment (Tables
4 and 5). This was true for both sampling dates and both sampling
depths. The reduction ranged from .03 cm3 cm.3 to .05 cm3 cm'3.

Ksat was significantly affected by wheel traffic in the CT and NTP5
treatments, but not in the NT treatment (Tables 4 and 5). At the 0 to
7.5 cm depth, Ksat was significantly reduced by wheel traffic for the
CT and NTP5 treatments. At the 7.5 to 15 cm depth, wheel traffic
significantly reduced the Ksat values of the CT treatment from the
9/16/86 sampling only. Wheel traffic compaction decreased the Ksat
values of the plowed treatments at the soil surface. This could cause
reduced infiltration and increased surface runoff.

Chemical Properties

In 1986, no significant differences were found in nitrogen
mineralization between tillage treatments (see Appendix Figure 1).
However in 1987, tillage did significantly affect nitrogen
mineralization in the spring as illustrated in Figure 18. At the 0 to
5 cm sampling depth, NTP5 consistantly had the lowest inorganic N
content. This was in contrast to the N mineralization pattern observed
in 1986 (see Appendix Figure 1). Plowing significantly increased the
inorganic N content of the NTP6 treatment over that of the NT on the
last four sampling dates. The difference between NTP6 and NT ranged
from 6.6 ug g"1 on 4/17 to 13.2 ug g'1 on 4/30.. At the 5 to 10 cm .
depth, the NTP6 treatment had the highest inorganic N content on all

six sampling dates. NTP6 was significantly higher than NT on 4/17 and

57

Table 4. Total porosity and saturated hydraulic conductivity
(Ksat) from 6/21/86 compared between tire tracks and
non-tire tracks.

 

 

 

 

Tillage Depth (cm) Between tires Tire track
0-7.5 Total porosity
.......... cm3 cm-3 -------_-_
CT .48 a .45 b
NTP5 .49 a 45 b
NT .46 a 45 a

 

7 5-15
.......... cm3 cm’3 ----------
CT .47 a 43 b
NTP5 .50 a 45 b
NT .42 a 41 a
1Lsn (.05) .029
0-7.5 Ksat
----------- cm hr’1 ----------
CT 3.93 a 1.28 b
NTP5 5.88 a .95 b
NT 3.98 a 2.88 a
1LSD (.05) 2.63
7.5-15
----------- cm hr"1 ----------
CT 4.08 a 3.38 a
NTP5 8.26 a 2.70 a
NT 8 70 a 5.03 a

1LSD (.05) 8.32

 

Means in each row which are followed by the same letter are not
significantly different at the indicated alpha level by Duncan's
Multiple Range Test. 1LSD for comparing two location means at
the same level of tillage.

58

Table 5. Total porosity and saturated hydraulic conductivity
(Ksat) from 9/16/86 compared between tire tracks and
non-tire tracks.

 

 

 

Tillage Depth (cm) Between tires Tire track
0-7.5 Total porosity
.......... cm3 cm’3 -------_--
CT .48 a 45 b
NTP5 .49 a 44 b
NT .44 a 43 a

 

 

 

7.5-15
.......... cm3 cm'3 ----------
CT .46 a 41 b
NTP5 .46 a 43 b
NT .39 a 40 a
1LSD (.05) .014
0-7 5 Ksat
----------- cm hr"1 ----------
CT 20.85 a 5.40 b
NTP5 46.50 a 5.55 b
NT 9.00 a 5.70 a
1LSD (.05) 15.29
7.5-15
----------- cm hr'1 ----------
CT 16.35 a 4.80 b
NTP5 9.60 a 4.35 a
NT 1.95 a 1.95 a

1LSD (.05) 8.32

 

Means in each row which are followed by the same letter are not
significantly different at the indicated alpha level by Duncan's
Multiple Range Test. 1LSD for comparing two location means at
the same level of tillage.

INORGANIC N (pg 9“)

59

 

   

 

 

 

 

 

 

 

 

 

 

 

e—o CT ' _
35‘aII—IIINTFIB-   , 95"“ - . I.
30- H NTP5 ‘ ’ I
25_ a—e NT
20‘ L80 (.05)I
15-
10-
5..
0 l r’ l r r r l r l I
40
o—o CT _ '
35- H NTP6 5 10 cm
30- H NTP5
25 H NT LSD (.05) I
20-
15-
10‘
5.4
0 l . T r I l r I
40
35_ H CT 10—20 cm
H NTP6
30- H NTP5
H NT
:3‘ LSD (.05) I I
15-
IO-
5-
O f

 

 

 

4/ "lI/Ic'I' VII/153 fl U26 ' ' II/zé ' ' U36 ' ' 5/4
SAMPLING DATE

Figure 18. Inorganic nitrogen content at three depths as
affected by tillage from 1987.

60
4/23. The minimum difference was 6.5 ug g'l. At the 10 to 20 cm
depth, the inorganic N content was the highest for the NTP6 treatment
on the last five sampling dates. NTP6 was significantly higher than NT
on 4/13, 4/17, 4/23, and 4/30. The difference between NTP6 and NT
ranged from 2.7 ug g"1 on 4/13 to 8.15 ug g"1 on 4/23.

No-tillage can reduce N mineralization by decreasing the availability
of organic N (Phillips and Phillips, 1984). Plowing increases the
soil-residue contact which increases the availability of organic N.
Plowing increases the soil aeration which leads to an increase in the
population of the aerobic nitrifiers. The bare surface of the plowed
soil allows the temperature to increase more rapidly than on a no-till
soil. This can cause higher N mineralization rates particularly in
temperate climates.

Therefore more N is mineralized from the soil reserves when no-till
is plowed. This could potentially reduce the application rate of N
fertilizer after plowing of a no-till field.

The organic carbon contents of the tillage treatments were determined
in the spring of 1987 and are presented in Figure 19. At the 0 to S cm
sampling depth, NT had significantly more organic carbon than the other
treatments. NT was 3 g kg'1 higher than NTP6 and 5 g kg'1 higher than
CT. This agrees with other reports of organic carbon accumulations at
the surface of no-till soils (Blevins et al., 1977; Juo and Lal, 1979;
and Dick, 1983). Dick (1983) stated that the reduced soil-residue
contact, reduced soil erosion, and reduced biological oxidation found
in no-tillage soils led to this accumulation of organic carbon on the
surface. At the 5 to 10 cm depth, no significant differences occurred.

However, the NTP6 and NTP5 treatments had the highest organic carbon

61

.>m\oa\v Eoum mmmHHHu >3 cmuommwm mm msumwn “so“ no mucmucoo conumo oacmwuo .ma musmflm

AEOV :Ema oz_._n§<m .
m—IOF owlm mlo

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0min,
/ N / N o,
/ / / ,
w w w W , w
/ _ / / / o
M y W W W
W k. / 7 m
. w
_ mom mm
H H H 7898.. \im/
92 NH. mm m.
B a .on

62

contents. At the 10 to 15 cm depth, NTP6 contained significantly
higher amounts of organic carbon than CT. Both the NTP6 and NTP5
treatments contained more organic carbon than NT. At the 15 to 20 cm
depth, NTP6 and NTP5 contained the most organic carbon. However, the
difference was not significant at the five percent probability level.

Plowing tended to mix the organic carbon-rich surface layer found in
the NT treatment throughout the plow layer. This process is
demonstrated by the data in Figure 19. Organic carbon is important in
maintaining good soil structure. The primary cementing agents which
hold aggregates together are microbial gums (Foth, 1978). These are
produced by microbes feeding on the organic carbon. Periodic plowing
of no-tillage could lead to improved soil structure by distributing the
carbon throughout the plow layer.

The effect of tillage on soil pH determined on samples obtained on
4/10/87 is illustrated by data given in Table 6. In the surface 5 cm,
NT was found to have the lowest pH. This difference was significant at
the five percent level. This agrees with the reports of Shear and
Moschler (1969), Blevins et al.(1977), and Dick (1983), who reported
that no-till soils had lower pH values at the surface than
conventionally tilled soils. This process is attributed to the
broadcast application of acidifying nitrogen fertilizer on the surface
. of no-tilled,soils (Blevins, et al., 1977; and Letaw, et al., 1984)
These acidic conditions can be harmful to crop growth. Low pH
conditions can cause aluminum toxicity (Tisdale and Nelson, 1985), poor
weed control by deactivating herbicides, and inhibiting nitrification
(Tisdale and Nelson, 1985). No significant differences occurred

between treatments at the lower three depth increments.

63

Table 6. Soil pH, phosphorus content, and potassium content

from 4/10/87.

 

 

Tillage Depth (cm)
0-5 5-10 10-15 15-20
Soil pH
CT 6.2 a 6.2 a 6.1 a 6.2 a
NTP6 6.1 a 5.8 a 5.8 a 6.1 a
NTP5 6.0 a 6.2 a 6.2 a 6.1 a
NT 5.5 b 6.0 a 6.4 a 6.4 a
LSD (.05) .5 .5 .5 .6
Phosphorus
------------------ mg kg'1 ------------------
CT 113 a 112 a 117 a 107 a
NTP6 103 a 134 a 120 a 115 a
NTP5 91 a 116 a 109 a 131 a
NT 118 a 103 a 88 a 89 a
LSD (.05) 54 54 32 35
Potassium
------------------- mg kg"1 -----------------
CT 101 c 110 b 135 ab 135 a
NTP6 124 bc 159 a 164 a 158 a
NTP5 131 b 110 b 122 b 135 a
NT 177 a 133 ab 112 b 92 b
LSD (.05) 26 27 33 29

 

Means in each column which are
not significantly different at
Duncan's Multiple Range Test.

followed by the same letter are
the indicated alpha level by

64
Plowing buried and mixed the acidic surface layer of the NT treatment,
thus eliminating any potential adverse plant responses.

The exchangeable potassium (K) contents of the four tillage
treatments are presented in Table 6. In the surface 5 cm, NT contained
significantly greater exchangeable K concentrations than the other
three tillage treatments. In the 5 to 10 cm depth, the NTP6 treatment
contained significantly more exchangeable K than either the NTP5
treatment or the CT treatment. At the 10 to 15 cm depth, the NTP6
treatment contained more K than the other treatments. The differences
between the NTP6 and the NT and NTP5 treatments were significant at the
five percent probability level. At the 15 to 20 cm depth, the
exchangeable K contents for the CT, NTP6, and NTP5 treatments were
similar and significantly higher than the NT treatment.

Potassium has been shown to accumulate at the surface of no-till
soils (Shear and Moschler, 1969; Triplett and Van Doren, 1969; Fink and
Wesley, 1974; Juo and Lal, 1979; and Hargrove, 1985). This
accumulation is attributed to the fact that K is a relatively immobile
nutrient and remains at the soil surface when K fertilizers are
broadcast applied to no-till soils. The NT treatment had the greatest
amount of exchangeable K at the surface and the least amount at the 15
to 20 cm depth. Plowing tended to decrease the K content of the
surface and distribute it throughout the plow layer. Research has
shown that in terms of plant uptake, the nutrient layering which occurs
when K fertilizer is broadcast on no-till fields does not present a
problem where soil test levels are adequate. This was because plant

roots tended to proliferate in the nutrient-rich surface layer.

65

The phosphorus (P) concentration of the four tillage treatments
presented in Table 6 are all at high soil test levels. No significant
differences were found between the four tillage treatments. This could
be attributed to the fact that P fertilizer was banded near the row and
the sampling was performed between the rows in the NT plots.

Plant Response and Yields

Corn seedling emergence data are given in Table 7. Tillage did not
significantly affect the emergence of corn seedlings in 1986. However,
seedling emergence was significantly affected by tillage in 1987 (Table
8). At 15 days after planting, the NT treatment had less than half the
number of seedlings as either the CT treatment or the NTP6 treatment.
At 22 days after planting, the NT treatment had approximatly 15,000
fewer plants than either CT or NTP6. The NTP5 treatment had
significantly fewer seedlings at 15 days after planting than both CT
and NTP6. By 19 days after planting, the plant population of the NTP5
treatment was similar to that of the CT and NTP6 treatments.

Soils under no-tillage management have been shown to warm up slower
in the spring than conventional tillage (Kladivko, et al., 1986). This
is caused by the surface crop residues intercepting radient energy and
providing thermal insulation. Reduced soil temperatures can cause a
delay in seedling emergence in no-till. Periodic plowing buries the
residues which leads to increased soil temperatures favoring
germination and seedling growth.

The 1986 plant tissue nitrogen concentrations are presented in Table
9. Tillage did not significantly affect the tissue nitrogen
concentrations of the ear leaf, stover, or grain. This indicates that

the nitrogen fertilizer application of 181 kg ha'1 was sufficient.

66

Table 7. Emergence data from 1986.

 

Tillage Days after planting
12 14 17 26

 

-------------- plants ha’1 ---------------

CT 49,674 a 52,722 a 53,619 a 53,619
NTP6 46,984 a 56,619 a 54,516 a 54,695
NTP5 49,315 a 50,212 a 51,109 a 51,109

NT 45,908 a 50,212 a 51,288 a 51,647

0’03””

LSD (.05) 6,758 5,895 5,453 5,595

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

Table 8. Emergence data from 1987.

 

Tillage Days after planting

 

15 17 19 22
-------------- plants ha'1 ---------------
CT 54,604 a 56,486 a 56,755 a 56,755 a

NTP6 57,831 a 58,907 a 58,907 a 58,907 a
NTP5 36,313 b 46,265 b 50,031 a 51,914 a
NT 24,477 c 36,313 b 40,078 b 41,692 b

LSD (.05) 11,315 10,109 9,453 8,387

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

67

Table 9. Total nitrogen contents in ear leaf, stover, and
grain from 1986.

 

 

Tillage Plant material
Ear leaf Stover Grain
.................. 8 kg-1 -----------------
CT 26.55 a 7.35 a 13.10 a
NTP6 27.63 a 7.00 a 12.58 a
NTP5 24.68 a 7.60 a 13.28 a
NT 24.70 a 7.20 a 12.33 a
LSD (.05) 3.31 .99 1.06

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
duncan's Multiple Range Test.

68

No-till has been shown to have increased immobilization and
denitrification rates and decreased rates of N mineralization when
compared to conventional tillage. These processes can be important
factors in determining N availability especially at low application
rates. Since we applied a surplus of fertilizer N, the effects of
these factors on N uptake were minimized.

Yield data for the 1986 and 1987 field seasons are presented in Table
10. The moisture content of the grain, plant populations, grain yield,
and stover yield were measured and compared over tillage treatments.

In 1986, tillage did not significantly affect grain moisture, plant
population, or stover yield. However, grain yield was significantly
different between tillage treatments. The highest yield (8.31 Mg ha'l)
and the lowest yield (7.46 Mg ha'l) occurred in treatments NTP6 and NT
respectively. Both of these treatments were in their sixth year of
continuous no-till. There are no apparent explanations for this
observation.

In 1987, grain moisture was significantly affected by tillage. The
NTP5 and NT moisture contents were 15.8 percent and 15.6 percent
respectively. These were significantly higher than either of the
plowed treatments, indicating delayed maturity. This probably resulted
from the reduced early growth of the seedlings in the these treatments.

The NT treatment had approximately 10,000 fewer plants ha'1 than the
other treatments at harvest. This affected the grain yield with NT
having approximately 1 Mg ha'1 less grain than all other treatments.
The NTP5 treatment produced the highest grain and stover yields, 7.37
and 4.34 Mg ha"1 respectively despite having approximately 2,000 fewer

plants ha'l than CT or NTP6.

69

Table 10. Yield data from 1986 and 1987.

 

Tillage Grain Plant Grain Stover
moisture population yield yield
(Z) (plants ha'l) (Mg ha'l) (Mg ha'l)

 

------------------------ 1986 -----------------------
CT 36.6 a 51,109 a 8.07 a 4.89 a
NTP6 37.5 a 54,875 a 8.31 a 4.95 a
NTP5 37.5 a 54,337 a 7.83 ab 5.37 a
NT 37.8 a 51,288 a 7.46 b 4.91 a
LSD (.05) 1.1 3,312 .47 1.13
------------------------ 1987 ------------------------
CT 14.9 b 55,233 a 6.57 ab 3.04 b
NTP6 15.0 b 56,309 a 6.75 a 3.45 b
NTP5 15.8 a 52,543 a 7.37 a 4.34 a
NT 15.6 a 43,756 b 5.74 b 3.22 b
LSD (.05) .5 4,559 .93 .75

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

70
CONCLUSIONS

When a no-tilled Conover loam soil was plowed, the soil's physical
properties became similar to those of a continuously plowed soil. The
bulk density was significantly decreased and the pore size distribution
of the soil was altered by plowing. The volume of soil occupied by
pores with radii greater than 24 um was increased, while the pore
volume with radii less than 24 um was decreased after plowing. The
total porosity of the soil was increased significantly by plowing. The
change in total porosity and pore size distribution improved the soil's
ability to conduct water when saturated.

Nitrogen mineralization was increased throughout the plow layer by
plowing. This was probably brought about by increasing soil-residue
interaction, increasing nitrifier populations, increasing soil
temperature, and increasing the air-filled volume of the soil. Plowing
redistributed P and K stratification throughout the plow layer. The
acidic surface layer found in the NT plots was buried and mixed
throughout the plow layer.

Plowing distributed the high organic matter surface layer found in NT
throughout the plow layer. This material is converted to microbial
gums which cement aggregates together (Foth, 1978). Thus, plowing this
high carbon layer down and returning to no-tillage for five or more
years could eventually lead to improved soil structure.

Wheel traffic compaction significantly affected the plowed soil, but
not the NT soil. Soil bulk density was increased by wheel traffic.
Pore size distribution was significantly affected. There was a
decrease in the volume of pores greater than 24 um and an increase in

the volume of pores with radii less than 24 um. Total porosity was

71
also significantly reduced in the wheel track. These reductions in
total porosity and the volume of large pores could potentially cause
aeration problems. The saturated hydraulic conductivity of the wheel
track was significantly reduced, thus possibly causing a reduction in
infiltration and an increase in surface runoff and soil erosion.

The 1986 emergence data showed no significant differences to exist
between tillage treatments. However in 1987, the emergence of the two
no-till treatments was delayed by as much as a week. This was probably
due to lower soil temperatures.

Total nitrogen uptake was not significantly affected by tillage.
This was probably due to the high application rates of nitrogen
fertilizer.

Grain yields were the highest and the lowest in the NT treatments in
1986. In 1987, the plant populations were approximately 10,000 plants
per hectare less than the other treatments. This resulted in a yield
decrease for the NT treatment. Grain moisture was significantly higher
in the two no-tillage treatments. This is probably due to the delayed
emergence experienced by the plants in these treatments.

For whatever reason no-till fields are plowed, periodic plowing
mixes soil nutrients, improves soil physical properties, and increases

nitrogen mineralization throughout the plow layer.

LIST OF REFERENCES

Bauder, J.W., G.W. Randall, and J.B. Swan. 1981. Continuous
tillage what it does to the soil. Crop and Soils Magazine.

Blake, G.R. 1965. Bulk density. p. 374-390. In Black C.A.
(ed.) Methods of soil analysis part 1. Am. Soc Agron.,
Madison, WI.

Blevins, R.L., Doyle Cook, S.H. Phillips. 1971. Influence of
no-tillage on soil moisture. Agron. J. 63:593-596.

Blevins, R.L., G.W. Thomas, P.L. Cornelius. 1977. Influence of
no-tillage and nitrogen fertilizer on certain soil
properties after five years of continuous corn. Agron. J.

69:383-386.

Bremner, J.M. and 0.8. Mulvaney. Nitrogen--total. p. 595-624. In
Page, A.L. (ed.) Methods of soil analysis part 2. Am. Soc.
Agron., Madison, WI.

Cannell, R.Q., and M.B. Jackson. 1981. Alleviating Aeration
Stresses. p. 141-192. In G.F. Arkin and H.M. Taylor (ed.).
Modifying the root environment to reduce crop stress. Am.
Soc. Agric. Eng., St. Joseph, MI.

Cohron, G.T. 1971. Forces causing compaction. p. 107-121. In
K.K. Barnes et al. Compaction of agricultural soils. Am.
Soc. Agric. Eng., St. Joseph, MI.

Dick, W.A. 1983. Organic carbon, nitrogen, and phosphorus
concentrations and pH in soil profiles as affected by
tillage intensity. Soil Sci. Soc. Am. J. 47:102-107.

Doran, J.W.* 1980.‘ Soil microbial and biochemical changes
.associated_with'reduced tillage. ASoil Sci. Soc. Am. J.
44:765-771.‘ ’ '

Eckert, D.J. and J.W. Johnson. 1985. Phosphorus fertilization
' in no-tillage corn production. Agron. J. 77:789-792.

Fink, R.J. and D. Wesley. 1974. Corn yield as affected by
fertilization and tillage system. Agron. J. 66:70,71.

Foth, H.D. 1978. Fundamentals of soil science. John Wiley and Sons,
New York, NY.

72

73

Gantzer, C.J. and G.R. Blake. 1978. Physical characteristics of
a Le Sueur clay loam soil following no-till and conventional
tillage. Agron. J. 70:853-857.

Hargrove, W.L. 1985. Influence of tillage on nutrient uptake
and yield of corn. Agron. J. 77:763-768.

Hill, R.L., and R.M. Cruze. 1985a. Tillage effects on bulk
density and soil strength of two Mollisols. Soil Sci. Soc.
Am. J. 49:1270-1273.

Hill, R.L., R. Horton, and R.M. Cruze. 1985b. Tillage effects on
soil water retention and pore size distribution of two
mollisols. Soil Sci. Soc. Am. J. 49:1264-1269.

Juo, A.S.R., and R. Lal. 1979. Nutrient profile in a tropical
alfisol under conventional and no-till systems. Soil Sci.
127:168-173.

Keeney, D.R., and D.W. Nelson. 1982. Nitrogen--inorganic forms. p.
643-693. In Page, A.L. (ed.) Methods of soil analysis part 2.
Am. Soc. Agron., Madison, WI.

Kladivko, R.J., D.R. Griffith, and J.V. Manering. 1986.
Conservation tillage effects on soil properties and yield of

corn and soya beans in Indiana. Soil & Tillage Research
8:277-287.

Klute, A. 1965. Laboratory measurement of hydraulic
conductivity of saturated soil. p. 210-221. In Black C.A.
(ed.) Methods of soil analysis part 1. Am. Soc. Agron.,
Madison, WI.

Leamer, R.W., and B. Shaw. 1941. A simple apparatus for measuring
non-capillary porosity on an extensive scale. J. Am. Soc. Agron.
33:1003-1008.

Letey, J., L.H. Stolzy, and G.B. Blank. 1962. Effect of
duration and timing of low oxygen content on shoot and root
growth. Agron. J. 54:34-37.

Letaw, M.J., V.A. Bandel, and M.S. McIntosh. 1984. Influence of
sample depth on soil test results in continuous no-till fields.
Commun. In Soil Sci. Plant Anal. 15:1-14.

Linn, D.M., and J.W. Doran. 1984. Aerobic and anaerobic
microbial populations in no-till and plowed soils. Soil
Sci. Soc. Am. J. 48:794-799.

Phillips, R.E., and S.H. Phillips. 1984. No-tillage agriculture,
principles and practices. p. 201-203. Van Nostrand Reinhold
Company Inc. New York, NY.

74

Rice, C.W., and M.S. Smith. 1982. Denitrification in no-till
and plowed soils. Soil Sci. Soc. Am. J. 46:1168-1173.

Rice, C.W., and M.S. Smith. 1983. Nitrification of fertilizer
and mineralized ammonium in no-till and plowed soil. Soil
Sci. Soc. Am. J. 47:1125-1129.

Rice, C.W., and M.S. Smith. 1984. Short-term immobilization of
fertilizer nitrogen at the surface of no-till and plowed
soils. Soil Soc. Am. J. 48:295-297.

Rice, C.W., and M.S. Smith, and R.L. Blevins. 1986. Soil
nitrogen availability after long-term continuous no-tillage

and conventional tillage corn production. Soil Sci. Soc Am.
J. 50:1206-1210.

Russell, R.S. and M.J. Goss. 1974. Physical aspects of soil
fertility--the response of roots to mechanical impedance. Neth.
J. Agric. Sci. 22:305-318.

Shear, G.M., and W.W. Moschler. 1969. Continuous corn by the
no-tillage and conventional tillage methods: a six year
comparison. Agron. J. 61:524-526.

Snyder, J.D., and J.A. Trofmow. 1984. A rapid accurate wet
oxidation diffusion procedure for determining organic and
inorganic carbon in plant and soil samples. Commun. in Soil
Sci. Plant Anal. 15:587-597.

Tisdale, S.L., W.L. Nelson, and J.D. Beaton. 1985. Soil
fertility and fertilizers. Macmillan Publishing Co., New
York, NY.

Triplett, G.B.Jr., and D.M. Van Doren Jr. 1969. Nitrogen,
phosphorus, and potassium fertilization of non-tilled maize.
Agron. J. 61:637-639.

Van Ouwerkerk, C., and F.R. Boone. 1970. Soil physical aspects
of zero-tillage experiments. Neth. J. Agric. Sci. 18:247-
261. .

Vomocil, J.A., and W.J. Flocker. 1961. Effect of soil
compaction on storage and movement of soil air and water.
Trans. ASAE. 4:242-246.

Vomocil, J.A. 1965. Porosity. p. 299-314. In Black C.A. (ed.)
Methods of soil analysis part 1. Am. Soc. Agron., Madison, WI.

Chapter 3

Immediate and Residual Effects of Zone Tillage
on Soil Physical Properties and Corn Yields

INTRODUCTION

Subsoiling is a practice used to improve soil physical conditions
below the normal depth of plowing with the purpose of increasing
yields. Busscher et al. (1986) found that soil strength was
significantly reduced immediately following subsoiling, but after one
year no residual effects were observed. Chaudhary et al. (1985) showed
that subsoiling increased rooting depth and rooting density in coarse
textured soils in India. Mukhtar et al. (1985) reported that
subsoiling increased infiltration rates when compared to conventional
tillage and no-tillage. Trouse (1983) found that subsoiling increased
the availability of water to plants by two mechanisms: deeper root
growth and increased soil water recharge. Grain yields have been
increased by subsoiling in areas where root restricting layers exist
and rainfall is limiting (Trouse, 1983; and Box et al., 1984).

Zone tillage refers to a tillage system where the rigid tines of the
subsoiling tool are set at the same spacing as the crop rows. This
‘allows the crop row to be planted directly above the loosened zone.
This practice has been widely used on the coastal plain soils of the
southeastern United States. These soils have a dense A2 horizon which
restricts root growth and water movement (Campbell, 1974). These

properties cause yields to be reduced when rainfall is limited.

75

76

Normally, to achieve maximum.shattering, subsoiling should be
performed when the soil is dry (Spoor and Godwin, 1978). This
condition rarely occurs in the spring in Michigan.

The objectives of this research were to: 1) determine if satisfactory
soil loosening can be achieved by spring subsoiling operations; 2)
determine if the loosened zone created by subsoiling will persist for
one or two years after the initial tillage operation was performed; and
3) determine the effects of zone tillage on corn production and yield.

MATERIALS AND METHODS

The experiment was conducted from 1985 to 1988 on the research plots
of Michigan State University. The soil at the experimental site was a
Riddles (Fine-Loamy, Mixed, Mesic, Typic Hapludalf) and is naturally
well drained. The experiment covered four adjacent ranges: A-3, A-4,
B-3, and B-4.

Zone tillage (subsoiling in the row) was evaluated against chisel
plowing (CP) and no-tillage (NT) in each of three years. Zone tillage
was accomplished with a Bushhog Ro-Till and a Howard Paraplow in 1985
and 1986. The Ro-Till (RT) and Paraplow (PP) are rigid tined
subsoilers which operated at depths of 30 to 45 cm. In 1987, the
Paraplow was replaced with the Tye Paratill which had the same tine
design as the Paraplow. The Ro-Till was set at the 76 cm tine spacing
for all years of the experiment.

In the spring of 1985, the four treatments implemented in range A-4
were CP, NT, RT, and the Paraplow at the 51 cm tine spacing (PP51).

In the spring of 1986, five tillage treatments were implemented in
ranges A-3 and B-3: CP, NT, RT, the Paraplow at the 51 cm tine spacing

(PP51), and the Paraplow at the 76 cm tine spacing (PP76).

77
In 1986, only the CP treatment from range A-4 was tilled. The two
subsoiled treatments were planted as no-tillage. Wheel traffic was
controlled in all plots so that the vehicle tires remained in the
previous year's tracks.

Four tillage treatments were implemented on range B-4 in the spring
of 1987. These were: CP, NT, RT, and PT76 (the Paratill at the 76 cm
tine spacing). In 1987, both the subsoiling treatments from 1985 and
1986 were planted as no-tillage. Vehicle traffic was restricted to the
previous years' tire tracks.

Corn was planted on range A-4 for all three years of the experiment.
Ranges A-3 and B-3 were planted to corn in the 1986 and 1987 field
seasons. Corn was planted on range B-4 only in 1987. A Buffalo no-
till planter set to deliver 65,000 seeds ha'1 was used in all three
years of the experiment. The row spacing was 76 cm and every effort
was made to plant the row directly over the loosened zone in all
subsoiled treatments having 76 cm tine spacings. Pioneer 3744 seed
corn was planted in 1986 on May 12. In 1987, Pioneer 3737 was planted
on April 28.

Chemical weed control was employed in all years and involved the
following herbicides and application rates: 5.8 liter alachlor ha’l,
2.3 liter atrazine ha'l, and 3.5 liter cyanazine ha’l. Paraquat was
applied at 2.3 liter ha”1 to the no-till plots. These chemicals and
rates were applied in all years of the experiment. The same
fertilizers and application rates were applied to all the plots.
During planting, 13 kg N ha'1 and 19 kg P ha"1 as ammonium
polyphosphate were banded near the row. Ammonium nitrate was surface

broadcast at the rate of 168 kg N ha'1 prior to seedling emergence.

78

The number of plants emerged in two 20-foot rows were recorded in
1986 for ranges A-3 and B-3, and in 1987 for range B-4. In 1986,
emergence counts were made 16, 18, and 21 days after planting. In
1987, seedling emergence was monitored 15, 17, 19, and 21 days after
planting. In 1986, corn earleaf samples were taken when 50 percent of
the plants were silking. Fifteen leaves, sampled opposite and below
the ear, comprised a composite sample from each plot. Grain and stover
were hand-harvested from two 30-foot rows in the center of each plot.
In 1986, the earleaf, grain, and stover from the 1985 and 1986 tillage
plots were analyzed for total nitrogen.

In May and June of 1987, intact soil cores were sampled from all
ranges. The sampling depths were 0 to 7.5 cm, 7.5 to 15 cm, and 22.5
to 30 cm. Thirteen cores were sampled from each plot: six cores from
the surface, four cores at the 7.5 to 15 cm depth, and three cores at
the 22.5 to 30 cm depth. In the subsoiled treatments, care was taken
to ensure that the cores were sampled from the loosened zones. In the
CP and NT treatments, the cores were sampled from the non-wheel-tracked
areas of the plots. Initially, only the NT and CP treatments from the
1987 tillage treatments were sampled. However, in December of 1987,
the NT and CP treatments from the 1985 and 1986 tillage plots were
sampled. Only the 7.5 to 15 cm and 22.5 to 30 cm depths were sampled
due to a 5 cm deep layer of frozen soil.

The cores were saturated from the bottom for 48 hours before the
saturated hydraulic conductivities were determined by the constant head
method (Klute, 1965). The cores were resaturated and weighed.

Moisture retention was determined at matric potentials of -1, -2, -4,

-6, and -33.3 kPa for the cores sampled from the 1985 and 1986 tillage

79
plots. The cores from the 1987 plots were subjected to matric
potentials of -l, -2, -3, -4, -6, -10, -33.3, and -100 kPa. Moisture
retentions for the cores sampled in December were determined only at
the -1 and -6 kPa matric potentials. Matric potentials from -1 to -6
kPa were applied using the blotter paper method (Leamer and Shaw,
1941). Moisture retention at matric potentials from -10 to -100 kPa
were determined using pressure plates (Richards, 1965). The pore size
distribution of the soil was determined by applying the capillary rise
equation to the moisture retention curve (Vomocil, 1965). Bulk density
was determined on a dry mass per volume basis.

A recording cone penetrometer was used to measure mechanical
resistance (cone index). In the subsoiled treatments, the penetrometer
readings were taken in the loosened zone. Moisture samples were taken
at depths of 0 to 10 cm, 10 to 20 cm, and 20 to 30 cm from each plot
(see Appendix Table 2). These samples were oven dried at 105 degrees
centigrade for 48 hours and gravimetric moisture contents were
determined. These values were converted to volumetric water contents
by multiplying by the soil bulk density.

The experimental design was a randomized complete block in all years
and the treatments were replicated four times. Analysis of variance
was used to detect significant differences between tillage treatments.
Duncan's Multiple Range Test was employed to separate and rank the
treatment means. A split plot design was used to compare the effects
of time on the physical properties of the zone tillage treatments.
Time made up the main plots and tillage made up the subplots. There
was no interaction between time and tillage, so the reported means in

this section were averaged across replication and tillage.

80
RESULTS AND DISCUSSION

The immediate effects of zone tillage on soil bulk density are
presented in Figure 20. At the 0 to 7.5 cm depth, the NT treatment had
the highest bulk density. This was at least .12 g cm"3 higher than the
other treatments. At the 7.5 to 15 cm depth, the soil bulk densities
of the CP and NT treatments were similar. However, the bulk density of
the NT treatment was significantly higher than the two zone tillage
treatments. At the 22.5 to 30 cm depth, the soil bulk densities of the
CP and the NT treatments were 1.56 g cm73. This was .2 g cm"3 higher
than the bulk densities of the zone tillage treatments. The bulk
densities of the RT and the PT76 treatments were not significantly
different at all depths. Zone tillage significantly reduced the bulk
density of the soil to a depth of 30 cm.

Zone tillage significantly affected the soil's pore size distribution
(Figure 21). At the 0 to 7.5 cm depth, the CP, RT, and PT76 treatments
significantly increased the volume of soil occupied by pores with radii
greater than 146 um.over that of the NT treatment. The volume of soil
occupied by pores with radii between 146 and 24 um was significantly
increased by the CP, RT, and PT76 treatments. However, the CP, RT, and
PT76 significantly reduced the volume of soil occupied by pores whose
radii were less than 24 um.

At the 7.5 to 15 cm depth, the volume of pores with radii greater
than 146 um was increased by a factor of 1.6 by zone tillage. The zone
tillage treatments increased the volume of pores with radii between 146
and 24 um by a factor of 1.5 over that of the NT treatment. The RT
treatment reduced the volume of pores with radii less than 24 um by a

factor of 1.5 compared to the NT treatment.

81

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0.50
, m CHISEL PLOW a
:21 NT .
040* - RO-TILL
- IZZZI PARATILL =
0.301
I
0.20-
I LSD (.05) I
0.10-I ,
0.00 \§ '/
i?" 0.50
E 1 m CHISEL PLOW b
o o 40 I: NT
0 ° " - RO-TILL
g - IZZZI PARATILL I
v 0.30- ,
“S - N
. I \
3 020 \
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0.10- ' \
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. m CHISEL PLow c
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0.30-
0.20-
0.10_ LSD (.05)_I ” p' I‘
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PORE RADIUS INTERVALS (pm)
Figure 21. Immediate effects of tillage on pore size distribution at

0 to 7.5 cm (a), 7.5 to 15 cm (b), and 22.5 to 30 cm (c).

83

Zone tillage significantly affected the soil's pore size distribution
at the 22.5 to 30 cm depth. The volume of pores with radii greater
than 146 um for the PP76 treatment was double that of the NT treatment.
Both the RT and the PP76 treatments increased the volume of pores with
radii between 146 and 24 um over that of the NT treatment. The volume
of pores with radii less than 24 um was not significantly different
between the treatments.

Zone tillage increased the volume of pores greater than 24 um at all
depths. These are the pores which will drain at the soil's field
capacity (Cannel and Jackson, 1981). This property, in turn, affects
the volume of soil which will be filled with air at field capacity.

Water retention data for the 0 to 7.5 cm depth are presented in
Figure 22. The volumetric water contents at the 0 to 7.5 cm depth were
lower for the CP, RT, and PT76 treatments than the NT treatment at
matric potentials less than -6 kPa. At 7.5 to 15 cm (Figure 23), the
RT and the PT76 treatments tended to have higher volumetric water
contents at high matric potentials and lower volumetric water contents
at low matric potentials than the CP and NT treatments. At the 22.5 to
30 cm depth (Figure 24), these same trends were exhibited.

The importance of these properties is two-fold: the water holding
capacity of the soil is reduced and the air-filled volume of the soil
was increased by zone tillage.

Tillage significantly affected the air-filled porosity of the soil.
Air-filled porosity data for the 0 to 7.5 cm, 7.5 to 15 cm, and 22.5 to
30 cm depths are presented in Figures 22, 23, and 24 respectively.

Foth (1978) stated that the field capacity of medium to coarse textured

soils occurs at a matric potential of -6 kPa. Therefore, particular

0 (cm3 cm")

I. (cm’ cm")

84

 

 

    

 

 

 

 

 

 

 

0.50

..V» a
0.45-
0.40-1
035- LSD (.05) I \3\;

I \i .

D.30~ I \g = :

H PARA‘I'ILL I \‘k .
0.25- H RO-TILL I I

' a—m NT I

0 20 o—o CHISEL PLOW I
O T I I I I I I II I I r I I I I I r I I I TI fir
0.30

e—o CHISEL PLOW b

_ e—e NT I

0'25 o—o RO-TILL I I

H PARATILL I , '
0.20-I I I -//
0.15- I 2 I
0.10-
0.05-
0000 I I I I I I I I TIT! I I I TI II
-0.1 -1.0 -10.0 -100.0

‘Irm (kPa)

Figure 22. Immediate tillage effects on moisture retention (a) and

air-filled porosity (b) at the 0 to 7.5 cm depth.

6 (cm’ cm“)

f. (cm’ cm“)

85

 

0.50

0.30-

0.25-

 

I LSD (.05)

XIII

   
 

PARATILL
RO-TILL
NT

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0.20

I ITIIrT I I I—rIIIrI I I

I rrIfi

 

0.30

0.25-

0.20-

0.15-

0.10-

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CHISEL PLOW

:2-.. I I I I

PARATILL

LSD (.05) I

 

 

1

I r I IIIIIr I I I rr1ri r r

—I.o -15.D
.‘Irm (kPa)

Figure 23. Immediate tillage effects on soil moisture

retention (a) and air-filled porosity (b) at
7.5 to 15 cm depth.

IITIIII

- 100.0

the

6 (cm3 cm")

f. (cm3 cm")

. 0.25.4 H RO-TILL

86

 

0.50

I LSD (.05)

0.45-
0.40-
0.35—

0.3CWT
H PARATILL

a—aNT

  
   

 

 

 

o—o CHISEL PLOW

0020 f I— T l' fl I I I I ffil’ I

0.30

 

G—o CHISEL PLOW

o—o RO—TILL

H PARATILL
0.2od I I I

0.15-
LSD (.05) I

0.10- ..2/

0.05q /

 

0.25_ a—a NT I

 

 

0000 I r r rIIIIl f I ITIITIr r

—0.1 -1.0 —‘|0.0

Figure 24. Immediate tillage effects on soil moisture

retention (a) and air-filled porosity (b) at the

22.5 to 30 cm depth.

87
attention will be given to the air-filled porosity which occurred at
this matric potential. At the 0 to 7.5 cm depth, the CP, RT, and PT76
treatments contained significantly higher air-filled porosities than
the NT treatment at all matric potentials. The air-filled porosity at
the -6 kPa matric potential was 1.5 times higher for the CP, RT, and
PT76 treatments than for the NT treatment. At the 7.5 to 15 cm depth,
the volume of air-filled pores was significantly higher for the RT and
the PT76 treatments when compared to the NT treatment at all matric
potentials. The volume of air-filled pores in the CP treatment was
intermediate between those of the zone tillage and NT treatments. The
volumes of air-filled pores at a matric potential of -6 kPa for the RT
and PT76 treatments were increased by a factor of 1.5 over the NT
treatment. At the 22.5 to 30 cm depth, zone tillage significantly
increased the volume of air-filled pores over both the NT and the CP
treatments at matric potentials from -2 to -100 kPa. The volume of
air-filled pores at a metric potential of -6 kPa was below 10 percent
for the CP and NT treatments. These values were increased by a factor
of 1.7 in the RT and PT76 treatments. The volume of air-filled pores
in the PT76 and RT treatments were never significantly different. Zone
tillage significantly increased the volume of air-filled pores at -6
kPa over that of the NT treatment to a depth of 30 cm. The volume of
air-filled pores fell below 10 percent in the NT and CP treatments at
the 22.5 to 30 cm depth. Vomocil and Flocker (1961) stated that no gas
exchange occurs between the atmosphere and the soil when the volume of
air-filled pores was around 10 percent. The lack of gaseous exchange
can cause aeration stress to occur in plants when precipitation is

significant.

88

Total porosity was significantly affected by tillage (Table 11).
Total porosity was higher in the CP and PT76 treatments than in the NT
treatment at the 0 to 7.5 cm depth. The total porosities ranged from
.47 to .43 cm3 cm'3 for the PT76 and NT treatments respectively. At
the 7.5 to 15 cm depth, the RT and PT76 treatments had significantly
higher total pore volume than the NT treatment. The total porosity of
the CP treatment was intermediate between the zone tillage and the NT
treatments. Total porosity was significantly higher for the RT and
PT76 treatments than for the CP and NT treatments at the 22.5 to 30 cm
depth.

The saturated hydraulic conductivity (Ksat) was significantly
affected by tillage (Table 11). At the 0 to 7.5 cm depth, the CP, RT,
and PT76 treatments significantly increased the Ksat values over that
of the NT treatment. The Ksat values ranged from 28.2 cm hr"1 to 7.0
cm hr'1 for the CP and NT treatments respectively. At the 7.5 to 15 cm
depth, the RT and the PT treatments significantly increased the Ksat
over that of the NT treatment. The CP treatment's Ksat was
intermediate between the zone tillage and NT treatments. At the 22.5
to 30 cm depth, no significant differences occurred between the tillage
treatments. The soils in the zone tillage treatments were very loose
when intact cores were sampled. Some disturbance may have occurred
when these treatments were sampled affecting Ksat by altering pore
continuity and tortuosity.

Zone tillage significantly increased the Ksat of the soil to a depth
of 15 cm. The CP treatment significantly increased Ksat values to a
depth of 7.5 cm. The CP treatment also demonstrated a trend to

increase Ksat to a depth of 15 cm. However, Ksat at this depth for the

89

Table 11. Immediate effects of tillage on total porosity and
saturated hydraulic conductivity (Ksat) from 1987.

 

Tillage Depth Total porosity Ksat

 

 

 

(cm) (cm3 ...-3) (cm H)
0-7.5
Chisel Plow .47 a 28.2 a
NT .43 b 7.0 b
Ro-Till .46 ab 25.7 a
Paratill .47 a 23.6 a
LSD (.05) .04 12.2
7.5-15
Chisel Plow .44 ab 15.8 ab
NT .40 b 6.9 b
Ro-Till .46 a 24.2 a
Paratill .45 a 19.8 a
LSD (.05) .04 11.1
22.5-30
Chisel Plow .39 b 6.3 a
NT .38 b 5.3 a
Ro-Till ' .44 a 6.1 a
Paratill .43 a 4.6 a
LSD (.05) .04 5.1

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

90

CP treatment was not significantly different from the NT treatment at
the five percent probability level.

The strength of the soil was significantly reduced by tillage (Figure
25). The soil moisture contents at the time of sampling are shown in
Appendix Table 2. The CP, RT, and PT76 treatments significantly
reduced the cone index to a depth of 10 cm. From 10 to 30 cm, the cone
index values of the RT and the PT76 treatments were significantly lower
than those of the CP and the NT treatments. The cone index values at
30 cm ranged from 28.6 kPa to 2.6 kPa for the NT and PT76 treatments
respectively. No significant differences were found between the cone
index values of the RT and the PT76 treatments.

When the cone index of the soil is high enough, root growth can be
mechanically impeded (Taylor and Burnett 1964). Russell and Goss
(1974) found that barley root elongation was reduced by 50 percent at
pressures of 20 kPa. The cone index values at the 30 cm depth were
28.6 kPa, 3.2 kPa, and 2.6 kPa for the NT, RT and PT76 treatments
respectively. Reduced root elongation could occur in the NT treatment.
Residual Effects of Zone Tillage

After one year, the bulk density of the RT treatment at the 7.5 to 15
cm depth was significantly lower than the NT treatment (Table 12). The
bulk density values ranged from 1.41 g cm'3 to 1.53 g cm'3 for the RT
and NT treatments respectively. The bulk density of the PP treatment
was intermediate between the RT and the NT treatments. At the 22.5 to
30 cm depth, no significant differences occurred between the tillage
treatments. However, there was a trend for the zone tillage treatments

to have slightly lower bulk densities than the NT treatment.

DEPTH (cm)

20~

 

 

91
CONE INDEX (We)

20 30

l l

CHISEL P LOW
NT

RO-Tl LL
PARATI LL

IIEI-

l——-i

F—l LSD (.05)

 

4O

 

 

2.5-l
30j|
35
Figure 25. Immediate tillage effects on cone index.

92

Table 12. Residual effects of zone tillage on bulk density
after one year.

 

Tillage Depth (cm)
7.5-15 22.5-30

 

Bulk density

.......... 8 cm‘3 ----------

NT 1.53 a 1.54 a

Ro-Till 1.41 b 1.52 a

Paraplow 1.47 ab 1.49 a
LSD (.05) .08 .06

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

93

After two years, the soil bulk density values were not significantly
different between the tillage treatments at the 7.5 to 15 cm depth
(Table 13). However, there was a trend for the zone tillage treatments
to have lower bulk densities than the NT treatment. At the 22.5 to 30
cm depth, the bulk density values for the RT and PP treatments were
significantly lower than the NT treatment after two years. The bulk
density values ranged from 1.38 g cm”3 for the RT treatment to 1.57 g
cm'3 for the NT treatment.

At the 7.5 to 15 cm depth, the soil bulk density in the RT treatment
was significantly lower than that of the NT treatment after one year,
but after two years it was not. At the 22.5 to 30 cm depth, the soil
bulk density of the tillage treatments were not significantly different
after one year, however after two years the zone tillage treatments
were significantly lower than the NT treatment. There are no apparent
explanations for these observations.

The soil's pore size distribution after one year (Figure 26) was
significantly affected by tillage. At the 7.5 to 15 cm depth, no
significant differences occurred between the tillage treatments for
pores whose radii were greater than 24 um. However, the pore volume
with radii less than 24 um was significantly increased in the zone
tillage treatments. This would indicate that soil aggregates were
fractured by zone tillage which led to a reduction in aggregate size,
creating a reduction in pore size. At the 22.5 to 30 cm depth after
one year, no significant differences occurred between tillage
treatments for pore volumes with radii greater than 146 um. The pore
volume with radii from 146 to 24 um was the highest for the NT

treatment and lowest for the RT treatment. The PP treatment was

94

Table 13. Residual effects of zone tillage.on bulk density
after two years.

 

Tillage Depth (cm)
7.5-15 22.5-30

 

Bulk density

......... 8 cm'3 -----_----

NT 1.57 a 1.57 a

Ro-Till 1.51 a 1.38 b

Paraplow 1 51 a 1.40 b
LSD (.05) .10 .10

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

PORE VOLUME (cm’ cm")

PORE VOLUME (cm’ cm")

,OASC)

95

 

0.44)-

0.3CL-

0.2CL-

0.1()~

 

SEED NT 0

‘ c: RO-TILL

IIII PARIFWIDN

LSD (.05) I I§::l

 

 

 

 

 

 

0.0C)

0u5C)

>146 146-24
PORE RADIUS INTERVALS (:m)

 

0.4T}-

0.3CL-

0.2CL-

0.1Cf-

 

(JJDO

‘ :3 RD-nLL

IIII PARIFHIMN

LSD (.DS) I

Nil

 

“4%

 

 

 

 

 

 

 

 

>146 , 146- 24 '

PDRE RADIUS INTERVALS (:m)

Figure 26. Residual effects of zone tillage after one year on

soil pore size distribution at the 7.5 to 15 cm (a)
and 22.5 to 30 cm (b) depths.

96
intermediate between the RT and the NT treatments. All the treatments
were significantly different from each other at the five percent
probability level. This would indicate that the PP treatment was less
destructive to the soils structural units than the RT treatment. The
pore volume with radii less than 24 um was significantly increased in
the zone tillage treatments.

Pore size distributions after two years are shown in Figure 27. No
significant differences occurred between tillage treatments in the
volume of pores with radii greater than 24 um. This was true at both
depths. At the 7.5 to 15 cm depth, pore volumes with radii less than
24 um were significantly higher in the zone tillage treatments. At the
22.5 to 30 cm depth, the pore volume with radii less than 24 um was the
highest in the RT treatment and the lowest in the NT treatment. These
two treatments were significantly different at the five percent
probability level. The reduction in pore size in the zone tillage
treatments indicates increased consolidation with time due to fracture
of soil aggregates.

The water retention data for one year after subsoiling are presented
in Figures 28 and 29. At the 7.5 to 15 cm depth, the RT had
significantly higher volumetric water contents than the NT treatment at
matric potentials from -.11 to -6 kPa. The PP treatment had
significantly higher volumetric water contents than the NT treatment at
matric potentials from -1 to -6 kPa. At 22.5 to 30 cm, the volumetric
water content of the zone tillage treatments were significantly higher
than the NT treatment at a matric potential of -6 kPa.

The water retention data for two years after subsoiling are presented

in Figures 30 and 31. At the 7.5 to 15 cm depth, the RT and the PP

PORE VOLUME (cm’ cm")

PORE VOLUME (cm’ cm")

97

 

0.5C)

0.4CL-

(1304

OJZCLq

(L10-

 

(L00

5313 NT

‘ r::1 RO-TILL

IIII FTTUUDLOMI

LSD (.05) I

 

 

(150

>146

§1

 

I

 

 

 

W]

 

 

146-24
PORE RADIUS INTERVALS (pm)

 

 

<324

 

j

0u40-‘

0430-

OJZCL-

0.1CL-

 

5329 h”'

[:3 RO-TILL
IIII FVGUMaLOMV

LSD (.05) I

W

 

 

 

(3130

>146

 

 

 

146-24
PORE RADIUS INTERVALS (pm)

 

 

Figure 27. Residual effects of zone tillage after two years on
soil pore size distribution at the 7.5 to 15 cm (a)

and 22.5 to 30 cm (b) depths.

 

 

 

 

 

0.50
I LSD (.05) a
0.454
3" I
'E 0.40-1
o
.. 0.351 I
E
0
V 0.30~
0:
0.25.1 H PARAPLOW
H RO-TILL
0.20 ”NT. 4 ...-..r . ..ee...
0.25
e—o NT 6
o—o RO-TILL
0.20- H PARAPLOW
1‘ I
g 0.154
n
E
0
V
“-0

 

 

 

 

Figure 28. Residual effects of zone tillage after one year on
soil moisture retention (a) and air-filled porosity
(b) at the 7.5 to 15 cm depth.

0 (cm3 cm")

f. (cm3 cm”)

 

99

 

 

 

 

 

 

 

 

0.50
a
0'45“ I LSD (.05)
0.40~ I
0.35-J I
0.30-
0257 H PARAPLOW
H RO-TILL J
0.20 “NT. .-.”-.. . ......L
0.25
e—o NT
H RO-TILL b
0.204 H PARAPLOW I
3:100

‘Irm (kPa)

Figure 29. Residual effects of zone tillage after one year on
soil moisture retention (a) and air-filled porosity
(b) at the 22.5 to 30 cm depth.

100

 

 

 

 

 

0.50
a
0°45‘ I LSD (.05)
G“
'E 0.40- I
L)
0555-4
"E I
(J
V 0.30%
C3
025... H PARAPLOW
o—o RO-TILL
0.20 H "T. .r , W
0.25
- o—o NT b
o—o RO-TILL
0.20“ H PARAPLOW
? I
E
L)
n .
E
o
v
M”I!
' '-'1'0.0

 

 

 

 

Figure 30. Residual effects of zone tillage after two years on

soil moisture retention (a) and air-filled porosity
(b) at the 7.5 to 15 cm depth.

6 (cm’ cm")

f. (cm’ cm")

101

 

0.50

I LSD (.05)

0.45-

0.40-

0.35-

0.30-

H PARAPLOW
o—o RO-TILL
o—o NT

0.25-

 

 

 

0.20 r r r

r T V U I

 

 

0.25

o—o NT
H RO-TILL

0.2m PARAPLOW

 

 

 

 

—10.0

Figure 31. Residual effects of zone tillage after two years on
soil moisture retention (3) and air-filled porosity

(b) at the 22.5 to 30 cm depth.

102
treatments had significantly higher volumetric water contents than the
NT treatment at a matric potential of -6 kPa. At the 22.5 to 30 cm
depth, the RT treatment had significantly higher volumetric water
contents than the NT treatment at matric potentials from -.11 to -6
kPa. The PP treatment had higher volumetric water contents than the NT
treatment at matric potentials from -.11 to -1 kPa.

The air-filled porosity data are presented in Figures 28, 29, 30, and
31. At a matric potential of -6 kPa, the only significant differences
in the volume of air-filled pores occurred at the 22.5 to 30 cm depth
one year after subsoiling. The NT treatment had the largest volume of
air-filled pores at this depth. The volume of air-filled pores was
below 10 percent one year after subsoiling for the RT treatment at the
22.5 to 30 cm depth. Air-filled porosity was around 10 percent for
both zone tillage treatments at the 7.5 to 15 cm depth after two years.
Air-filled porosity is a function of the total porosity and the pore
size distribution of the soil.

The zone tillage treatments tended to have a larger volume of small
pores which retain water at field capacity. This property caused the
zone tillage treatments to have a smaller volume of air-filled pores at
field capacity than the NT treatment.

Total porosity after one year (Table 14) was significantly affected
by tillage. At the 7.5 to 15 cm depth, the RT treatment had the
largest total porosity and the NT had the lowest total porosity: .43
and .38 cm3 cm"3 respectively. At the 22.5 and 30 cm depth, no
significant differences in total porosity were found between the

tillage treatments.

103

Table 14. Residual effects of zone tillage on total porosity
and saturated hydraulic conductivity (Ksat) after one

 

 

year.
Tillage Depth (cm)
7.5-15 22.5-30
Total porosity
........ cm3 cm'3 --------
NT .38 b .38 a
Ro-Till .A3 a .39 a
Paraplow .41 ab .40 a
LSD (.05) .04 .04
Ksat
........ cm h'l ------_-
NT 8.63 a 7.70 a
Ro-Till 19.31 a 5.18 a
Paraplow 16.27 a 10.98 a
LSD (.05) 16.84 6.13

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

104

Two years after subsoiling, the total porosity of the soil was
significantly affected by tillage (Table 15). At the 7.5 to 15 cm
depth, no significant differences were found. However, there was a
trend for the zone tillage treatments to have larger total porosities
than the NT treatment. At the 22.5 to 30 cm depth, the zone tillage
treatments had significantly larger total pore volumes than the NT
treatment. The total porosities at the 22.5 to 30 cm depth were .44
cm3 cm’3, .43 cm3 cm'3, and .37 cm3 cm'3 for the RT, PP, and NT
treatments respectively.

Saturated hydraulic conductivity was not significantly affected by
tillage after one year (Table 14). However, at the 7.5 to 15 cm depth,
the Ksat values for the zone tillage treatments were double that of the
NT treatment. The saturated hydraulic conductivity was not
significantly affected by tillage after two years (Table 15). Although
at both depths, the Ksat values of the zone tillage treatments were
double that of the NT treatment.

Zone Tillage Effects on Soil Properties Compared over Time

There was no interaction between time and tillage. Therefore, in all
of the following results, the means were averaged across replication
and tillage.

The soil bulk densities of the zone tillage treatments were
significantly affected by time (Table 16). At the 0 to 7.5 cm depth,
the bulk density of the first year treatment was .11 g cm'3 lower than
the bulk densities after one and two years. At the 7.5 to 15 cm depth,
soil bulk density during the first year was .10 g cm'3 and .17 g cm-3
lower than the bulk densities after one and two years respectively.

However, at the 22.5 to 30 cm depth, the bulk densities in the first

105

Table 15. Residual effects of zone tillage on total porosity
and saturated hydraulic conductivity (Ksat) after two

 

 

years.
Tillage Depth (cm)
7.5-15 22.5-30
Total porosity
......... cm3 cm'3 ---------
NT 38 a .37 b
Ro-Till 40 a .44 a
Paraplow 40 a .43 a
LSD (.05) 04 .03
Ksat
.......... cm h'l ---------_
NT 5.49 a 7.97 a
Ro-Till 11.73 a 20.19 a
Paraplow 11.65 a 28.39 a
LSD (.05) 11.82 23.23

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

106

Table 16. Residual effects of zone tillage on bulk density
compared over time.

 

Time Depth (cm)
0-7.5 7.5-15 22.5-30

 

Bulk density

-------------- g cm‘3 ------------n-
First year 1.31 b 1.34 b 1 36 b
Second Year 1.42 a 1.44 a 1 50 a
Third year 1 42 a 1.51 a 1 39 b
LSD (.05) .05 .08 .06

 

The means are averaged across replication and tillage. Means in
each column which are followed by the same letter are not
significantly different at the indicated alpha level by Duncan's
Multiple Range Test.

107
year and the third year were not significantly different. The bulk
density one year after subsoiling was significantly higher than the
first year or the third year.

Water retention for the zone tillage treatments compared over time
are presented in Figures 32, 33, and 34 for the 0 to 7.5 cm, 7.5 to 15
cm, and 22.5 to 30 cm depths respectively. Time did not significantly
affect the volumetric water contents of the soil at matric potentials
from -1 to -33.3 kPa. This was true at all sampling depths.

The volume of air-filled pores in the zone tillage treatments was
significantly affected by time. At the 0 to 7.5 cm depth (Figure 32),
the volume of air-filled pores was significantly higher in the first
year than in the second or third year at a matric potential of -6 kPa.
The volume of air-filled pores was 1.6 times higher in the first year
than for the second or third year. At the 7.5 to 15 cm depth (Figure
33), the volume of air-filled pores at -6 kPa was significantly higher
for the first year than for the third year. The air-filled porosities
at -6 kPa were .17 cm3 cm'3 and .10 cm3 cm'3 for the first and third
years respectively. The volume of air-filled pores at the 22.5 to 30
cm depth (Figure 34) was similar for the first year and the third year
at -6 kPa. The volume of air-filled pores in the second year was
significantly lower than the first and third years. The air-filled
porosity of the second year at -6 kPa was reduced by a factor of 1.4 in
comparison with the other two years.

The total porosity of the soil was significantly affected by time
(Table 17). At the first two sampling depths, the total pore volume of
the first year was significantly higher than that of the third year.

At the 7.5 to 15 cm depth, the total pore volume of the second year was

0 (cm3 cm")

f. (cm3 cm")

108

 

 

 
 

    

 

 

 

 

 

   
 

 

 

0.55
0

0.50-1 LSD (.05)
0.45-
0.40-
0.35-
0.30-
0 25_ H THIRD YEAR
- a—a SECOND YEAR
0.20 H .“RgtYWm, . . . Wm, . , e. ...
0.30

o—o FIRST YEAR b

H SECOND YEAR
0'25 H THIRD YEAR 1 I
0.20- I
0.15-

LSD (.05) 1
0.104
0.05-
0.00 , , .7. r ....,
- 0.1 -10 —10.0 —100.0

’Figure 32. Zone tillage effects on soil moisture retention (a)

and air-filled porosity (b) compared over time at
the 0 to 7.5 cm depth.

0 (cm3 cm")

f. (cm’ cm")

109

 

     

 

 

 

 

 

 

 

0.55
O
0.50-
I LSD (.05)
0.45-
0.40-
0.35-
0.30-
0 25_ H THIRD YEAR
° a—e SECOND YEAR
o—o FIRST YEAR
0020 r t fif U 00"] t r I I D—TTrl V U I ' trU‘IT
0.30
H FIRST YEAR b
O 25_ a—a SECOND YEAR
' H THIRD YEAR 1
0.20-I I I .
0.15- I . '
LSD (.05) 1
0.10-
0.05- "
0.00 U I 17' I'l" ' I fifrr‘r'l I I I Ur'fll
- 0.1 - 1.0 -10.0 — 100.0

\Irm (kPa)

Figure 33. Zone tillage effects on soil moisture retention (a)

and air-filled porosity (b) compared over time at
the 7.5 to 15 cm depth.

6 (cm3 cm")

f. (cm‘s cm“)

110

 

 

      

 

 

 

 

   
  

 

 

 

0.55
0
0.50-
0.45} LSD (.05)
0.40-
0.35-
0.30-
0 25_ H THIRD YEAR
° a—a SECOND YEAR
0.20 H.F'R§TTE.A'3..., . ......r . ....n,
0.30
o—o FIRSTYEAR b
H SECOND YEAR
0'25 H THIRD YEAR 1
0.204 I
0,15-1 I
LSD .05
0.10- ( ) I
0.05-
0.00 ... ... .....-
--0.1 -1.0 -10.0 —100.0

Figure 34. Zone tillage effects on soil moisture retention (a)

and air-filled porosity (b) compared over time at
the 22.5 to 30 cm depth.

111

Table 17. Residual effects of zone tillage on total porosity
and saturated hydraulic conductivity compared over

 

 

time.
Time Depth (cm)
0-7.5 7.5-15 22.5-30
Total porosity
.............. cm3 cm'3 --------------
First Year .47 a .45 a .43 a
Second Year .43 b .42 ab .40 b
Third Year .43 b .40 b .44 a
LSD (.05) .03 .04 .02
33.8.11.
................ cm h'l ---------------
First Year 24.54 a 21.99 a 5.34 b
Second Year 12.90 b 17.79 a 8.29 b
Third Year 12.13 b 11.69 a 24.29 a
LSD (.05) 8.69 10.62 9.08

 

The means are averaged across replication and tillage. Means in
each column which are followed by the same letter are not

significantly different at the indicated alpha level by Duncan's
Multiple Range Test.

112
not significantly different than the first or the third year. The
total porosity at the 22.5 to 30 cm depth was not significantly
different between the first year and the third year. However, the
total porosity of the second year was .03 cm3 cm'3 lower than the first
year. This difference was significant at the five percent probability
level.

The saturated hydraulic conductivity at the 0 to 7.5 cm depth was
significantly affected by time (Table 17). The Ksat mean of the first
year was double that of the second or third year. The Ksat means at
the second depth were not significantly different. However, the first
year had the highest Ksat and the third year had the lowest Ksat. At
the 22.5 to 30 cm depth, the Ksat of the third year was about three
times higher than the first or second year. The low Ksat values of the
first year can probably be attributed to disturbance during sampling.
The soil was very loose and some rearrangement may have occurred which
affected the Ksat by altering pore continuity and tortuosity.

Soil strength, as indicated by cone index, increased with time
(Figure 35). The first year of subsoiling had significantly lower cone
index values than one and two years after subsoiling. However, the
cone index after one and two years was still less than 10 kPa. Soil
strengths in this range should not significantly inhibit root
elongation (Russell and Goss, 1984).

Plant Responses and Yields

Seedling emergence was not affected by tillage in 1986 (Table 18).
However, in 1987, tillage did significantly affect seedling emergence
(Table 19). At 15 days after planting, the NT treatment had at least

12,000 fewer emerged seedlings per hectare than the CP and the RT

DEPTH (cm)

 

 

113

CONE INDEX (kPo)
10 20
9—0 FIRST YEAR

B—E: SECOND YEAR

o—e THIRD YEAR

I—I LSD (.05)

30

 

 

Is- ...

- l-—I
20- ....
25- ~ ._.
30

Figure 35.

Residual tillage effects on cone index.

114

Table 18. Immediate tillage effects on seedling emergence from

 

 

1986.
Tillage Days after planting
16 18 21
Seedling emergence
----------- Plants ha'1 -----------
Chisel Plow 58,100 a 58,369 a 58,369 a
NT 59,983 a 60,790 a 60,790 a
ParaplowSl 58.907 a 59,445 a 59,445 a
Ro-Till 51,645 a 52,183 a 52,183 a
Paraplow76 55,948 a 56,217 a 56,217 a
LSD (.05) 5,986 5,839 5,839

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

Table 19. Immediate tillage effects on seedling emergence in
1987.

 

Tillage Days After Planting
15 17 19 21

 

Seedling emergence

-------------- Plants ha.1 -------------

Chisel Plow 44,113 a 53,797 a 55,410 a 56,755 a
NT 25,284 c 41,961 b 49,762 b 52,990 a
Ro-Till 37,927 ab 53,527 a 56,486 a 56,755 a
Paratill 28,512 bc 44,382 b 50,569 b 53,797 a

LSD (.05) 9,660 6,310 4,198 ' 3,872

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

115
treatments. Seedling emergence in the PT76 treatment was significantly
lower than the CP treatment. At 17 days after planting, the NT and
PT76 treatments had at least 9,000 fewer emerged plants per hectare
than the CP and RT treatments. Seedling emergence at 19 days after
planting continued to be significantly reduced in the NT and PT76
treatments. However, at 21 days after planting, no significant
differences occurred between tillage treatments.

The 1986 plant tissue nitrogen contents are presented in Table 20.
Tillage significantly affected the tissue nitrogen contents of the ear
leaf, stover, and grain. The NT treatment had the highest nitrogen
content in the ear leaf tissue and the PP76 treatment had the lowest
level. The nitrogen content of the grain was significantly higher in
the RT treatment than for the PP76 treatment. The nitrogen contents of
the grain were 11.2 g lcg'1 and 9.8 g lcg’1 for the RT and PP76
respectively. The NT and RT treatments had significantly higher stover
nitrogen contents than the PP76 treatment. The stover nitrogen
contents were 6.5 g kg'l, 6.9 g kg'l, and 5.3 g lcg'1 for the NT, RT,
and PP76 treatments respectively.

The 1986 yield data are shown in Table 21. Grain moisture, plant
populations, grain yield, and stover yield were not significantly
affected by tillage in 1986. This was true for plots that were
subsoiled in 1986 and those that were subsoiled in 1985.

The 1987 yield data are shown in Table 22. In the first year of
subsoiling, the PT76 treatment had a significantly lower plant
population than the NT and RT treatments. However, no significant
differences occurred between tillage treatments for grain moisture,

grain yield, and stover yield. One year after subsoiling, grain

116

Table 20.

Plant tissue nitrogen contents from 1986.

 

Tillage Earleaf Grain Stover
N content N content N content
(3 kg‘l) (g kg'l) (g kg‘l)

 

First year of subsoiling

Chisel Plow 25.1 ab 10.4 ab 6.4
NT 25.7 a 10.5 ab 6.5
ParaplowSl 24.6 ab 11.0 ab 6.1
Ro-Till 25.3 ab 11.2 a 6.9
Paraplow76 23.3 b 9.8 b 5.3
LSD (.05) 1.8 1.1 5.3

One year after subsoiling

Chisel Plow 24.4 a 11.5 a 7.0
NT 25.9 a 11.5 a 6.6
Ro-Till 25.4 a 11.3 a 7.1
Paraplow 25.5 a 11.4 a 7.0
LSD (.05) 2.6 7 9

0,0103
O‘ 0‘

0‘0,

“3030,03

 

Means in each column which are followed by the
not significantly different at the indicated
Duncan's Multiple Range Test.

same letter are
alpha level by

117

Table 21. Yield data from 1986.

 

Tillage Grain Plant Grain Stover
moisture population yield yield
(Z) (plants ha'l) (Mg ha'l) (Mg ha'l)

 

First year of subsoiling

Chisel Plow 25.9 a 56,847 a 9.0 a 4.5 a
NT 26.4 a 56,309 a 9.2 a 4.9 a
ParaplowSl 26.9 a 52.543 a 9.1 a 4.0 a
Ro-Till 26.6 a 56,847 a 9.0 a 4.5 a
Paraplow76 26.2 a 57,565 a 9.1 a 4.6 a
LSD (.05) 1.1 5,715 1.3 6
One year after subsoiling
Chisel Plow 27.7 a 53,799 a 9.1 a 3.7 a
NT 27.3 a 56,130 a 8.9 a 4.8 a
Ro-Till 28.0 a 53,619 a 9.0 a 4.8 a
Paraplow 28.1 a 55,950 a 9.3 a 4.3 a
LSD (.05) 1.4 5,202 8 1.3

 

Means in each column which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's Multiple Range Test.

118

Table 22. Yield data from 1987.

 

Tillage Grain Plant Grain Stover
moisture population yield yield
(Z) (plants ha'l) (Mg ha'l) (Mg ha‘l)

 

First year of subsoiling

 

Chisel Plow 17.0 a 55,413 ab 8.2 a 4.6 a
NT 17.7 a 58,999 a 9.1 a 4.5 a
Ro-Till 16.9 a 57,744 a 9.0 a 4.5 a
Paratill 17.3 a 50,929 b 8.4 a 4.8 a
LSD (.05) 1.1 5,001 1.2 1.0
One year after subsoiling
Chisel Plow 16.6 a 56,309 a 8.0 a 4.0 a
NT 16.5 a 55,592 a 8.1 a 4.5 a
ParaplowSl 16.9 a 52,723 a 8.5 a 4.4 a
Ro-Till 17.1 a 50,929 a 8.6 a 4.3 a
Paraplow76 17.3 a 50,929 a 7.2 a 4.3 a
LSD (.05) 1.2 5,785 1.5 .7

Two years after subsoiling

Chisel Plow 17.7 b 56,847 a 8.3 a 4.4 a
NT 19.3 a 54,876 a 8.5 a 4.4 a
Ro-Till 18.7 ab 54,516 a 7.9 a 4.1 a
Paraplow 19.1 ab 53,799 a 8.1 a 4.0 a
LSD (.05) 1.2 5,125 7 1.1

 

Means in each cOlumn which are followed by the same letter are
not significantly different at the indicated alpha level by
Duncan's MultipleaRange Test.

119
moisture, grain yield, plant population, and stover yield were not
significantly affected by tillage. Two years after subsoiling, grain
moisture was similar for the NT, RT and PT76 treatments. However, the
CP treatment had significantly lower grain moisture than the NT
treatment. Plant populations, grain yield, and stover yield were not
affected by tillage two years after subsoiling.
CONCLUSIONS

Zone tillage performed in the spring significantly improved the
physical condition of the Riddles sandy loam soil. The volume of pores
which were air-filled at the soil's field capacity was increased by
zone tillage. This could decrease the frequency and duration of
aeration stress under high precipitation. The saturated hydraulic
conductivities at the 0 to 7.5 cm depth were improved by zone tillage.
When the soil is saturated, infiltration rates are dependent on the
Ksat of the soil. Ksat was increased under the zone tillage
treatments, suggesting that infiltration would also be increased. The
soil strength, as indicated by cone index, for the NT treatment was at
a level where root growth has been shown to be impeded (Russell and
Goss, 1974). Zone tillage significantly reduced the soil strength.

Some residual effects of the zone tillage treatments persisted for
one or two years after the original subsoiling operations were
performed. The soil bulk density was decreased in the two zone tillage
treatments at the 22.5 to 30 cm depth. After one year, the total
porosity at the 7.5 to 15 cm depth for the RT treatment was still
significantly higher than the NT treatment. After two years, the total
porosities at the 22.5 to 30 cm depth for the zone tillage treatments

were higher than for the NT treatment. Cone index values increased

120
with time. However, the values after two years were below 10 kPa and
should not significantly impede root growth.

Tillage did not significantly affect seedling emergence in 1986.
However, in 1987, tillage did significantly affect seedling emergence.
In the NT and PT76 treatments, seedling emergence was significantly
delayed by as much as a week. 1986 plant tissue nitrogen contents in
the first year of subsoiling were the lowest for the PP76 treatment.
One year after subsoiling, there was no effect of tillage on the plant
tissue nitrogen contents. Grain and stover yields were not
significantly affected by tillage in 1986 or 1987.

Zone tillage performed in the spring improved the physical condition
of the Riddles soil. Some of the beneficial effects of zone tillage
persisted for two years. However, corn yields were not affected by

zone tillage.

LIST OF REFERENCES

Box, J.E. Jr., and G.W. Langdale. 1984. The effects of in-row
subsoil tillage and soil water on corn yields in the
southeastern coastal plain of the United States. Soil &
Tillage Research. 4:57-78.

Busscher, W.J., R.E. Sojka, and C.W. Doty. 1986. Residual
effects of tillage on coastal plain soil strength. Soil
Science. 141:144-149.

Campbell, R.B., D.C. Reicosky, and C.W. Doty. 1974. Physical
properties and tillage of paleudalts in the southeastern coastal
plains. J. of Soil and Water Conservation. 29:220-224.

Cannell, R.Q., and M.B. Jackson. 1981. Alleviating Aeration
Stresses. p. 141-192. In G.F. Arkin and H.M. Taylor (ed.)
Modifying the root environment to reduce crop stress. Am.
Soc. Agric. Eng., St. Joseph, MI.

Chaudhary, M.R., P.R. Gajri, S.S. Prihar, and Romesh Khera.
1985. Effect of deep tillage on soil physical properties
and maize yields on coarse textured soils. Soil & Tillage
Research. 6:31-44.

Cohron, G.T. 1971. Forces causing compaction. p. 107-121. In
K.K. Barnes et al. Compaction of agricultural soils. Am.
Soc. Agric. Eng., St. Joseph, MI.

Foth, H.D. 1978. Fundamentals of soil science. John Wiley and Sons,
New York, NY.

Klute, A. 1965. Laboratory measurement of hydraulic
conductivity of saturated soil. p. 210-221. In Black C.A.
(ed.) Methods of soil analysis part 1. Am. Soc. Agron.,

.Madison, WI. . .

Léamer, R.W., and 8. Shaw. 1941.- A simple apparatus for measuring
non-capillary porosity on an extensive scale. J. Am. Soc. Agron.
33:1003-1008.

Mukhtar, S., J.L. Baker, R. Horton, D.C. Erbach. 1985. Soil

water infiltration as affected by the use of the Paraplow.
Trans. ASAE 28:1811-1816.

121

122

Richards, L.A. 1965. Physical condition of water in soil. p. 128-
152. In Black C.A. (ed.) Methods of soil analysis part 1. Am.
Soc. Agron., Madison, WI.

Russell, R.S. and M.J. Goss. 1974. Physical aspects of soil
fertility--the response of roots to mechanical impedance. Neth.
J. Agric. Sci. 22:305-318.

Spoor, G., R.J. Godwin. 1978. An experimental investigation
into the deep loosening of soil by rigid tines. J. Agric.
Eng. Res. 23:243-258.

Taylor, H.M., and E. Burnett. 1964. Influence of soil strength
on the root-growth habits of plants. Soil Sci. 98:174-180.

Trouse, A.B.Jr. 1983. Observations on under-the-row subsoiling
after conventional tillage. Soil & Tillage Research. 3:67-
81.

Vomocil, J.A., and W.J. Flocker. 1961. Effect of soil
compaction storage and movement of soil air and water.
Trans. ASAE. 4:242-246.

Vomocil, J.A. 1965. Porosity. p. 299-314. In Black C.A. (ed.)
Methods of soil analysis part 1. Am. Soc. Agron., Madison, WI.

SUMMARY AND CONCLUSIONS

No-tillage cropping systems cause a unique soil environment to form.
Some of these altered soil properties create unfavorable conditions for
crop growth. Periodic plowing of the Conover loam soil improved these
soil physical and chemical conditions.

Plowing the no-tilled Conover loam soil created soil physical
properties similar to a continuously plowed soil. Plowing lowered soil
bulk density and altered the soil's pore size distribution. The volume
of soil occupied by large pores was increased and the volume of soil
occupied by small pores was decreased by plowing. Plowing also
increased the total porosity and the saturated hydraulic conductivity
of the no-till soil.

Soil chemical properties were improved by plowing. Nitrogen
mineralization was increased after plowing. No-till soil surface
layers, having low pH values and high organic carbon, P, and K contents
were mixed throughout the plow layer.

In 1987, seedling emergence was delayed by as much as a week in the
no-tillage treatments. This may have caused the higher grain moisture
contents of the no-tilled treatments at harvest.

Soil compaction occurring below the normal depth of plowing can be
alleviated by subsoiling. Subsoiling only under the crop row (zone
tillage) ensures that the crop roots will explore the loosened soil.

Zone tillage performed in the spring improved the physical condition

of the Riddles loam soil. Soil bulk density was decreased, total

123

124
porosity was increased, and saturated hydraulic conductivities were
increased by zone tillage. Zone tillage significantly lowered the
strength of the Riddles soil, alleviating mechanical impedance to root
growth. Water availability to plants could be increased by zone
tillage due to two mechanisms: the increased saturated hydraulic
conductivity would indicate that the soil water recharge could be
increased and the lowered soil strength would allow for increased root
growth.

Some residual effects of the zone tillage treatments persisted for
two years after the original subsoiling operations were performed. The
total porosity and soil bulk density effects of zone tillage were still
present after two years. Also, the soil strength remained at a level
where mechanical impedance to root growth would be minimal.

Zone tillage did not affect corn yields. This would indicate that
adequate moisture was available to the plants in all treatments. In
1987, corn seedling emergence was significantly delayed in the no-till
and the Paratill treatments.

Recommendations

If it is suspected that soil physical or chemical properties in no-
till are inhibiting crop growth, periodic plowing could be performed.
Periodic plowing alleviated soil physical and chemical limitations to
crop growth.

When soil compaction occurs below the normal depth of plowing, the
soil should be subsoiled. Soil physical properties were significantly
improved by subsoiling. Subsoiling in the row combined with controlled
traffic will increase the probability that the loosened zone will

persist for more than one growing season. The benefits of zone tillage

125
will most likely be realized during a dry year in soils that have an

impermeable layer.

APPENDIX FIGURES

INORGANIC N (pg 9“)

 

 

 

 

 

 

 

 

 

O rrUrIlT'IIrU—rUlflUIIUTrfiIUIrT

 

40

:55q H CT 15-30 cm
H NTP5

30- H NT

2.54

15- I LSD (.05) I

10-

5_.

O

 

 

4 16 “II/15' ' U26 Wifzsr TEL/30' E's); 7'75

SAMPLING DATE

Figure 1. Inorganic nitrogen contents at three depths as
affected by tillage from 1986.

 

APPENDIX TABLES

127

Table 1. Soil volumetric moisture contents at the time of

subsoiling from 1986 and 1987.

 

Year Depth (cm)

 

1986 .15 .18

1987 .17 .17

 

128

Table 2. Soil volumetric moisture contents at the time of
penetrometer sampling of tillage treatments
implemented in 1985, 1986, and 1987.

 

 

Tillage Depth (cm)
0-10 10-20 20-30
1985
............. cm3 cm'3 ----_---_--__
Ro-Till .20 .21 .19
Paraplow .19 .20 .19
1986
------------- m3 cm-3 -----—-------
Ro-Till .19 .19 .22
Paraplow .20 .20 .20
m1
............. cm3 cm‘3 ------------_
Chisel Plow .18 .20 .21
NT .22 .22 .23
Ro-Till .19 .20 .21

Paratill .19 .20 .20