”(40 M « 6'

 

ABSTRACT
ARTHROPODS ASSOCIATED WITH BREAKDOWN
OF CORN (ZEA MAYS) RESIDUES
IN THE FIELD
BY

Rosa Somera Quiachon

A preliminary field survey was made of animal
populations associated with decomposing surface litter
from a previous corn crop (Egg gays). Three collections
from each of 12 sampling sites were made at 2-month inter-
vals from May to September. No crop or growing vegetation
was present at the sites sampled. Two types of litter had
been deposited at each site and were sampled separately:
1) corn cobs and 2) corn stalks and leaves. The soil
(0-5 cm) under each litter type was also sampled. Animals
were extracted with heat (Berlese extraction). Dry matter
changes in litter and changes in carbon and nitrogen in
litter and soil were followed. Changes in mineral nutri-
ents were followed in soil. Air, litter, and soil temper-
atures and soil moisture were recorded at the time of sam-
pling and related to area weather records.

1

Rosa Somera Quiachon

Animal populations encountered were similar to
those reported for grasslands and for mull-type forest
litter associations. Acarina and Collembola together
comprised 90 to 97 percent of total arthropod numbers.
The biomass represented by these two mesofaunal groups,
however, would have been very much less than that of the
dominant macroarthropods: Diptera, Coleoptera, Chilopoda
and Araneida. Other arthropods present in substantial
numbers only in certain samples included Psoc0ptera (May
and July), Hemiptera (September), Hymenoptera (sporadic).
A very few diplopods were found in May, mainly in cob
litter. ISOpods, present in both litters in May, were
found only in soil under stalks in July and September.

A few earthworms (Annelida) were found in litter
in May but not again until September when a few were re—
covered from soil.

All major meso- and macro-arthropod groups were
already well established in both litter and soil in May.
A much smaller proportion of the total Acarina popula-
tions was found in the soil at this time than in the
case of Cole0ptera, Diptera and Collembola. Acarina
may have been deterred from moving into the soil by

2

Rosa Somera Quiachon

high moisture (in excess of field capacity) or by low
temperature (lo—12°C).

In later samplings, there was a marked shift in
numbers of all major groups from litter to soil. The
shift was greater at stalk sites than at cob sites.
Several factors appeared to have influenced the observed
patterns of increased residence in soil: 1) litter-soil
temperature gradients, 2) differences in physical prop-
erties of the litter such that stalks and leaves lost
moisture more rapidly after wetting than the cobs, and
3) differences in available energy content of organic
materials translocated from litter into soil.

With regard to the last factor, dry matter in the
litter layer disappeared more rapidly from cobs than from
stalks and leaves (60% X§° 35% loss during the study
period).

Due to the more rapid substrate utilization, it
appeared that less available energy remained residually
in September at cob sites than at stalk sites. Total site
numbers (litter plus soil) were higher at cob sites in May
but substantially lower than at stalk sites in September.

A higher C/N ratio in the stalk litter was consistent

Rosa Somera Quiachon

with the view that it was at a less advanced stage of de—
composition, hence higher in residual energy content than
the cobs.

Evidence that qualitative and quantitative changes
occurred in available substrates and/or food chain struc-
tures during the study period was provided by a near linear
replacement over time of Collembola by Acarina in the meso-
faunal component of arthropod pOpulations in both litters
and in the soils underneath. This change was accompanied
by release of basic cations and increasing pH.

The implications of these observations for critical
research in relation to minimum tillage or no-till manage-
ment systems are discussed. In the absence of tillage,
animal activities may control the distribution of recycled
nutrients and profoundly influence the rooting behavior

and nutritional requirements of crOps.

ARTHROPODS ASSOCIATED WITH BREAKDOWN
OF CORN (ZEA MAYS) RESIDUES

IN THE FIELD

BY

Rosa Somera Quiachon

A DISSERTATION
Submitted to
Michigan State University

in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of CrOps and Soil Sciences

1973

TO MYP

ACKNOWLEDGEMENTS

The author wishes to place on record an expression
of appreciation of the help and kind treatment she received
from the faculty and staff of the Department of Soils.

She wishes first to make a special mention of the
profound debt of gratitude to her major professor, Dr. A“ R.
Wolcott. She wishes to thank him in a very special manner
not only for having undertaken the responsibility of plan-
ning the author's course work and the unlimited help, un-
ending encouragement and utmost consideration he showed
her during the preparation and submission of the thesis,
but also for the extraordinarily kind concern he showed
for the author's personal welfare.

Her most sincere thanks and deepest gratitude to
Dr. R. J. Snider for his unselfish help and assistance
during this study.

A special note of thanks to Dr. J. W. Butcher and
Dr. P. E. Rieke for their valuable help and kind concern

and for serving on her guidance committee.

iii

Thanks is also extended to Dr. J. M. Tiedje and
Dr. M. J. Zabik for serving on her guidance committee.

Special thanks to Dr. Ernie for his utmost patience
and understanding during the preparation and submission of
the manuscript.

Use of the Michigan State University computing
facilities was made through support, in part, from the

National Science Foundation.

iv

TABLE OF CONTENTS

LIST OF TABLES. . . . . . . . . .

LIST OF FIGURES . . . . . . . . .

INTRODUCTION. . . . . . . . . . .

REVIEW OF LITERATURE. . . . . . .

Role of Soil Arthropods in Decomposition

of Litter . . . . . . . . .

Changes in the Chemical Composition of the
Litter Due to Animal Activities . . . . .

Action of Invertebrates on the Physical
Properties of Soil and on Soil Formation.

Action of Invertebrates on the Chemical
Properties of the Soil and Mineral Cycling.

Distribution of Arthropods. .
MATERIALS AND METHODS . . . . . .
Experimental Area . . . . . .
Sampling. . . . . . . . . . .
ExtraCtion and Identification

Soil Analyses . . . . . . . .

of ArthrOpods

Total Nitrogen of Soils and Litter. . . . .

Page
vii

viii

14

18
20
23
23
26
28
.33

34

TABLE OF CONTENTS (Cont'd.)
Page
Total Carbon of Soils and Litter. . . . . . . . . 35
Air and Soil Temperature. . . . . . . . . . . . . 36
RESULTS . . . . . . . . . . . . . . . . . . . . . . . 37
Major Animal Groups . . . . . . . . . . . . . . . 37
Collembola-Acarina Populations. . . . . . . . . . 42
Collembola Species. . . . . . . . . . . . . . . . 45

Vertical Distribution of Animal Groups and
Collembola Species. . . . . . . . . . . . . . . 49

Environmental Parameters in Relation to

P0pulation Distribution . . . . . . . . . . . . 49
1. MOisture. I O O O O O O O O O O O O O O O 52

2. Temperature . . . . . . . . . . . . . . . 58

3. Nature of Substrates. . . . . . . . . . . 61
Changes in Soil Nutrient Status . . . . . . . . . 65

DISCUSSION. 0 O O O O O O O O O O O O O O O O 0 O O O 68

CONCLUS IONS O O O O O O O O O O O O O I I O I O O O O 8 2

LITEMTURE CITED 0 O O O O O O O O O O O O O O O O O O 87

vi

Table

LIST OF TABLES

Numbers of principal animal groups in litter
and soil by sampling dates. . . . . . . . . .

Numbers of adults and juveniles, and juvenile/
adult ratios for the three principal species
of Collembola . . . . . . . . . . . . . . . .

Ratios of numbers in soil to numbers in litter
for principal animal groups . . . . . . . . .

Ratios of numbers in soil to numbers in litter
for Collembola species. . . . . . . . . . . .

Numbers of Collembola, Acarina and other
arthropods in soil under litter in relation
to soil carbon, Kjeldahl nitrogen, moisture
and temperature . . . . . . . . . . . . . . .

Total site numbers (litter plus soil) of
Collembola, Acarina and other arthrOpOds in
relation to dry matter, carbon and nitrogen
retained in surface litter. . . . . . . . . .

Probabilities (P) for significance of F
associated with replications, dates, and

litter site, for data in tables 5 and 6 . . .

Soil and air temperature (°C) at and near
(1 km) study area . . . . . . . . . . . . . .

Soil nutrients and acidity under cobs and
stalks in relation to sampling date . . . . .

vii

Page

38

47

50

51

54

56

57

59

66

LIST OF FIGURES

Figure Page

1. General view of the experimental area,
looking west toward Baker Woodlot.
May 11' 1969. O O O O O O O O O O O O O 0 0 O 24

2. Condition of corn trash at representative
sample site. July 22, 1969. Note soil
thermometer, right'foreground . . . . . . . . 24

3. Diagram showing the 12 sampling areas which
were treated as replicates when no signifi-
cant effects of distance from woodlot could
be shown. Corn rows ran east and west.
Sampling areas varied from 8 to 10 rows
(8.5 to 10.6 m, south to north) . . . . . . . 25

4. Collection frame (12" X 12") used in obtaining
cob samples (top) and stalk samples (bottom). 27

5. Collecting undisturbed soil core after removal
of litter sample. Top: 4 X 4 X 2-1/2 in.
core frame inserted to 2-in. depth within
area delineated by litter-sampling frame.
Bottom: Excised soil core being transferred
to waxed carton for transport to laboratory . .29

6. Collection tools and samples of litter and
soil (top) and ice-cooled styrofoam chest
(bottom) used to transport samples to the
laboratory. . . . . . . . . . . . . . . . . . 30

7. Extraction apparatus: Tullgren-Berlese funnels
(against rear wall), used for extraction of
soil animals from larger litter samples;
standard Berlese funnels (on rack foreground),
used for extraction of undisturbed soil cores
and smaller litter samples. . . . . . . . . . 31

viii

LIST OF FIGURES (cont'd.)
Page

8. Distribution of Collembola, Acarina and other
arthropods as percent of total arthropod
numbers . . . . . . . . . . . . . . . . . . . 43

9. U. S. Weather Bureau records (M.S.U. South Farm
Station). Upper figure: monthly rainfall
and average cardinal air temperatures. Lower
figure: Daily rainfall, maximum and minimum
air temperatures, and soil temperatures
(7 A.M. and 10 A.M.) at 5 cm under grass
sward . . . . . . . . . . . . . . . . . . . . 53

10. Numbers of Collembola and Acarina in litter and
soil under litter (above) in relation to
litter and soil parameters at sites asso-
ciated with corn cobs (left) and corn stalks
(right) . . . . . . . . . . . . . . . . . . . 75

ix

INTRODUCTION

The soil in its natural state is not only a complex
mixture of mineral matter and decaying organic substances,
but is also the home of myriads of living moeities of var-
ious sizes and forms. Plant residue reaching the soil under
natural field conditions undergoes decomposition involving
many complex processes. During the decay process the litter
loses weight, energy and minerals primarily through activi-
ties of the litter-soil biota.

Much research has been directed toward assessing
the relative importance of soil fauna vs. the microflora in
residue decay. It is becoming increasingly evident that
soil animals play numerous important roles in the degrada-
tion of plant litter. Their contributions in specific situ-
ations may be of paramount importance.

Fragmentation of plant tissues by soil animals in-
creases the surface exposed to leaching and to colonization
by microflora. Physical changes associated with ingestion

and defecation expose cellular contents and structure to

attack by microbial populations in the gut and in the ex-
ternal environment.

Enzymatic alteration of certain substrates and the
mixing of diverse substrates and nutrients during gut pas—
sage favors microbial utilization. These effects and the
moisture retentiveness of feces favors their colonization
by the soil microflora.

Soil animals also effect alterations in soil physi-
cal properties. Their burrows contribute to pore volume
and to continuity of pore systems for gas exchange and
water movement. Their traffic between litter and soil
leads to translocation of litter fragments and fecal pel-
lets into the mineral matrix where further decomposition
and humification produces structure-stabilizing deposits of
organic matter (humus). Soil animals are therefore active
agents in the formation and the stabilization of friable
soil structure.

Much of the data bearing on microflora—fauna inter-
actions has come from non-agricultural habitats and micro-
cosm experiments.r Conventional tillagedestroys the strati—
fication characteristic of natural litter-soil asSociations

and disrupts living spaces and traffic channels in the

mineral matrix. Excessive mechanical tillage leads to pro-
gressive deterioration of soil structure. Where residues of
the previous crOp are left on the surface of the soil, there
is an approach to natural litter systems in which the role
of soil animals in development and stabilization of favor-
able soil structure may be an important factor in crop per-
formance. There is current rapid trend toward "no till"
management practices in many areas of the country. In many
situations, success of these practices requires control of
insect pests with chemicals. Since beneficial animals may
also be reduced in numbers, it becomes important to identify
them and evaluate their beneficial roles.

The objective of the present study was to effect a
preliminary gross characterization of animal populations
and seasonal successions associated with surface litter
from corn (Ega'mays).. Two different types of litter were
considered (corn cobs,and corn stalks and leaves), since
these present a different array of substrates and physiCal
prOperties which might influence their selection and colon-
ization by different animals. Changes in C/N ratio of
litter and soil and in available nutrients in Soil were
followed. Relationships to seasonal Changes in temperature

and moisture were observed.

REVIEW OF LITERATURE

Early in the development of biology as a science,
the heterotrophic microflora were recognized as principal
agents in the chemical breakdown of organic matter. More
recent studies of the fauna in soils and litter has not
changed this basic cOnCept. However, these studies have
revealed important, frequently essential, direct and indi-
rect effects of the fauna on the rate of breakdown, the
nature and distribution of products, and on the environment
in which these changes occur.

Chemical and physical effects of the larger inverteé
brates were reCOgnized early and have been studied exten-
'sively. At the other end of the scale, the protozoa and
their activities as secondary consumers have been subjects
for investigation since the early days of microbiology. It
is only within comparatively recent times that critical
studies have been directed to soil and litter animals of
intermediate size: the mesofauna.

It has long been recognized, in general terms, that
soil and litter animals are integral links in the overall

4

cycling of energy and nutrients, that important activities
include comminution of litter and translocation of organic
and mineral materials, and that synergistic interactions
occur between fauna and flora in decomposer food chains.
Recently, functional studies have been initiated to
quantify the ecological impact of soil invertebrates living
in the organic horizons at or near the soil surface. The
invertebrates that have been studied most frequently in
this context include acarine mites, collembola, nematodes,
annelid and enchytraeid worms, millepedes, centipedes and

insects, mainly dipterous flies, beetles, and their larvae.

Role of Soil Arthropods in
Decomposition of Litter

 

 

The fertility of soils beneath the fresh litter de-
pends on the rate and nature of the decomposition of plant
residue. Studies of the primary decomposition of fresh
plant litter in the field offer evidence of the importance
of animal activity in this process.

Kurcheva (1962) used naphthalene to prevent the

participation of invertebrates in the decomposition

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processes in an oak forest litter. Naphthalene drives away
animals but does not inhibit bacterial and fungal activity.
Under these conditions oak litter lost only 9% of its orig-
inal weight in 140 days whereas untreated litter lost 55%
in the same time. Crossley and Witkamp (1964) found that
55% by weight of oak leaf litter was retained after 1 year
in plots treated with naphthalene, whereas untreated con-
trol plots retained only 40%.

Edwards and Heath (1963) exposed litter contained
in nylon bags of different mesh sizes to various sections
of the fauna and to microorganisms alone. Litter disappeared
three times faster from bags to which earthworms had access
than from bags from which they were excluded. When animals
were completely excluded for nine months, no visual break-
down occurred.

Headu §£_213 (1966) found that allowing earthworms
to feed on them considerably accelerated rates of disappear-
ance of "tough" leaves such as beech and oak, whereas animal
activity did not affect the rate of disappearance of "soft"
leaves such as kale, beet and lettuce. Curry (1969b) made a
study of the role of soil animals in the decay and the dis-

appearance of grassland herbage confined in nylon bags of

different mesh sizes in the soil and on the soil surface.
The size of the animals admitted was controlled by mesh
size. Animal activity contributed little to the rate of
decay and disappearance of grassland herbage on the soil
surface and did not accelerate decay of herbage in the soil.

The rate at which soil arthropods consume litter
depends on many factors. It is believed that the suitabil-
ity of litter for saprophages depends on the chemical com-
position (nitrogen content, C:N ratio, Ca content, presence
of flavored and tannic substances), mechanical properties
and moisture content of the litter (Dunger, 1958). Wall-
work (1958) noticed that factors affecting food preferences
are particle size, stage in chemical decay of food, and
moisture content.

Handley (1961) suggested that phenolic compounds
precipitate protein complexes, rendering the residual leaf
proteins resistant to decomposition and forming a protec-
tive layer on the cellulose of the cell walls. Heath and
Arnold (1966) suggested also that the food preferences of

soil fauna probably depend on the palatability of leaf ma-

terial rather than its digestability. The unpalatability

Of leaf material rich in polyphenols may be because of its

astringence. On the other hand, sugars or readily hydro-
lyzed carbohydrates likely enhance palatability. Edwards
and Heath (1963) and Satchell and Lowe (1969) suggest that
fresh leaf litter remains unpalatable to soil fauna until
{polyphenols become leached out. King and Heath (1967)
sshowed that the amount of polyphenol found was inversely
IDrOportional to the rate at which leaves disappeared, and
tzhat "hard" leaves had more polyphenolic substances than
"soft" ones.

The rate at which soil invertebrates consume litter
<iepends also on the temperature and the amount of moisture
in the litter (van der Drift, 1951; Gere, 1956). Seasonal
‘variations are observed in the activity of soil arthropods.
Crossley and Hoglund (1962) found a good correlation be-

tween the number of microarthropods in litter bags and the
rate of litter disappearance. They also found that the num-'
ber of arthropods depended on the moisture content of the
litter. Edwards and Heath (1963) observed that, after
heavy rain, leaf discs disappeared more rapidly than in dry
periods. Van der Drift (1962) suggested that moisture was

more important than temperature in litter decay.

Changes in the Chemical Composition
of the Litter Due to
Animal Activities

 

 

In evaluating the role of soil invertebrates in the
decomposition of litter, important factors include, not
only the amount of litter eaten by the animals, but also
the qualitative changes in the chemical composition of the
litter due to their activities. Two general mechanisms
must be distinguished in assessing the effects of soil
arthropods on chemical properties of plant litter. First
is change directly dependent on the animals' metabolism and
second is indirect participation of invertebrates through
their action on microflora, where the role of the animal is
more like the action of a catalyzer (MacFadyen, 1961).

According to recent data, direct participation by
invertebrates in the decomposition of plant litter is on a
very small scale. From approximate estimates of MacFadyen
(1961), of the total calories contained in dead plant re-
mains entering the soil in a temperate zone pasture, 85
percent was freed by microbial activities and only 15 per-
cent by the activities of soil animals. Feeding experi-

ments with larvae on forest oak litter showed that 93 percent

10

of the consumed food was defecated and only 7 percent was
assimilated (van der Drift, 1970).

The change in chemical composition of litter that
passes through the alimentary canal of animals has been in-
vestigated. Several workers have found that feces immedi-
ately after excretion differ little in chemical composition
from the litter eaten (Dunger, 1963; Bocock, 1963). On the
other hand, van der Drift (1970) reported that the non-
cellulosic decomposable carbohydrate content of oak litter
was reduced significantly in the excrement.

While comminution and incorporation of organic
matter into the mineral soil is an important contribution
of the soil mesofauna, this is perhaps secondary to their
effect on the decomposer microflora. McBrayer and Reichle
(1971) showed that approximately 60 percent of the total
biomass of the soil fauna was contained in the fungivore
trophic level. At an average feeding rate of 7.1 percent
dry wt day-1, this trophic level would remove by grazing
nearly 24 mg fungus m-2 day-l.l Additional quantities of
microflora would be ingested by surface-feeding saprophages.

Burges (1967) reported that maximal faunal activity occurred

immediately following fungal blooms in litter. Engelmann

11

(1961) suggested that grazing by Oribatei stimulated the
microfloral population as a whole and thus promoted decom-
position.

The indirect action of soil dwelling animals on the
process of decomposition is well illustrated by data of
Anstett (1951). He found that, when worms were removed
after having been in the test boxes for a long time, the
rate of decomposition of grape vines was still much higher
than in the control boxes where the worms had never been.
Microbial analysis showed that the population density of
'microflora in the test boxes was five times as high as in
the controls. Obviously, eartthrm activities had greatly
increased the availability of energy and otherwise altered
the nutritional environment in ways which stimulated activ-
ities of the microflora. Reyes and Tiedje (1973) found a
more rapid and extensive mineralization of l4C-labeled
yeast by an animal-miCrobial system than when either was
acting independently.

Investigations by several authors have shown that
the number of microorganisms is much higher in animal excre-
ment than in the soil (van der Drift g£_gl., 1960; Ghilarov,

1963). It is not clear where the increase in reproduction

12

of the microorganisms takes place, whether in the alimentary
canal of the animals or in their excrement, which does
afford a favorable environment for the development of micro-
flora (Day, 1950).

Atlavinyte (1971) suggested that arrival of fecal
material from both arthropods and earthworms in the more
favorable moisture conditions in deeper strata, the opening
of cell contents, and a usual rise of litter pH during gut
passage induce rapid microbial growth, particularly by bac-
teria. Van der Drift (1970) found the pH changed from 4.3
in oak leaves to 6.7 in the fecal pellets of larva.

Stebaev (1968) suggested that feces could be enriched with
vitamins promoting the growth of other organisms. Rangaswar-
mi (1966) reported that proteins in the form of enzymes
associated with the excrements provide favorable nutrients
to enhance microbial growth. When feeding on forest litter
and other plant litter, invertebrates break it up finely and
mix it with soil, and so create conditions for more inten-
sive microbial activity. The action of microarthropods is
particularly effective in that respect. Adcording to sev-
eral estimates (Sukachev and Dylis, 1964), oribatids, when

feeding on pine needles, increased the surface area of the

13

ingested material to approximately 10,000 times the original
figure.

The soil is inhabited by a multitude of animals that
feed on microorganisms, but they are also capable of bene-
ficial action on the activity of microflora. When inverte-
brates are introduced into a soil culture, widespread senile
deterioration'of fungi and bacteria (due, it is believed, to
the presence of antibiotics in the soil) is arrested (Wit-
kamp, 1960). It is proposed that animals that eat microbes
are able to intensify the activity of microflOra, i.e. to
accelerate energy transfer by breaking up the compactness
of colonies of bacteria and fungi (MacFadyen, 1961);

In addition, soil animals aid in the distribution
of microorganisms. Experiments with four species of fungi
have shown (Hutchinson and Kamel, 1956) that the rate of
dispersal of microorganisms in sterile soil was substan-
tially higher when earthworms were introduced. Similar re-
sults were obtained in experiments with Oribatidae, which
inoculate the soil with microorganisms, carrying them on
the body surface and in the alimentary canal. It has been
shown that fungus spores remain viable after passing through

the intestinal tracts of Collembola (Poole, 1959).

14

Action of Invertebrates on the
Physical Properties of Soil
and on Soil Formation

 

 

 

By moving about in search of food or in migrations
due to unfavorable climatic conditions, animals open up
systems of burrows and passageways which increase the total
porosity of the soil matrix and the continuity of pore
systems for rapid exchange of gases and movement of water.
These physical rearrangements in mineral matrix geometry
create conditions favorable for plant root function and for
aerobic microbial processes and rapid decomposition of or-
ganic matter and release of mineral nutrients.

A structural effect of even greater significance in
some situations derives from the fact that all soil-dwelling
invertebrate saprophages, while feeding on plant litter, in-
gest at the same time a certain proportion of soil mineral
particles. These mineral particles, mixed in the animals'v
alimentary canal with finely divided and partially digested
plant matter, are excreted in the form of small crumbs that
constitute durable structural aggregates (Sukachev and Dylis,
1964).

The amount of excrement discharged by black mille-

pedes during a single season, in the forest belts planted

15

in the north of the steppe zone, may be as much as 686 kg/ha
(Sokolov, 1957). This author also estimates that earthworms
on soddy, medium-podzolized soil in Moscow Province are able
to work over the entire mass of soil in the 0-20 cm layers
in the course of Six years. The part of their excrement
discharged as casts on the surface alone amounts to 16 tons
ha-l yr“1 (Ponomareva, 1950).

The contribution to water infiltration capabilities
of this surface deposition of stable aggregates and of traf-
fic channels Opening at the surface of the soil would be
difficult to assess, but would be of the greatest signifi-
cance.

Soil animal activity also is important in the down-
ward transportation of litter fragments and fecal pellets
into the mineral matrix, where further microbial decomposi-
tion produces structure-stabilizing deposits of residual
organic matter (humus) that is relatively resistant to fur-
ther decomposition (van der Drift, 1970). Thus, soil ani-
mals not only create structural arrangements (pore systems)
essential for aeration, permeability to water andrmoisture

retention, but they contribute to the stabilization of

these structures as well.

16

Vertical redistributions of organic materials and
minerals by soil animals are important soil forming pro-
cesses. Variations in faunal composition can lead to unique
variations in horizon development (Ghilarov, 1971; van Rhee,
1969). Large invertebrates (earthworms, large insect larvae,
diplopods, etc.) can influence the development of pedological
features directly and to great depth (Sukachev and Dylis,
1964). In the absence of these larger animals, direct
effects of the meso- and micro-fauna (springtails, mites,
nematodes, etc.) extend to, at most, a few centimeters below
the litter-soil interface.

A number of important forest soil types are differ-
entiated on the basis of the extent to which animals influ-
ence the fate of surface litter: its accumulation, commi-
nution and incorporation with mineral soil (Wood, 1962).

In the absence of comminution, litter accumulates
as raw humus, or mor (the L layer in gleyed, podzolic
earths). Accumulation and comminution, without incorpora-
tion leads to the formation of moder (F and H layers in
gleyed, podzolic brown earths). Comminution and mechanical
incorporation with mineral soil at the surface produces

mull-like moder fabrics (mull-like rendzinas and the A

l7

horizon of brown earths). Where the litter is comminuted
and mixed with mineral soil, and conditions are favorable
for further rapid decomposition by the microflora, chemical
incorporation of residual humified matter with soil minerals
leads to the formation of mu11..

Mull formation is associated with plant species and
with soil and environmental conditions where litter fall is
quickly and completely decomposed year by year. There is a
high annual flux of nutrients, and vegetative production is
characteristically high. Large invertebrates and their mix?
ing function appear to be key factors in the rapid turnover
of nutrients, as well as in the organic enrichment of min-
eral horizons to greater depth in these situations.

Ghilarov (1968) has proposed that the productivity
of many forest.ecosystems can be increased.bw'management
directéd toward increasing populations of beneficial inver-
tebrates. For this purpose, there are experimental data in
support of such practices as mulching, liming and drainage.
Once limiting environmental factors have been identified
and corrected, it would be feasible to introduce beneficial

animals where they are absent.

18

Action of Invertebrates on the
Chemical Properties of the
Soil and Mineral Cycling

 

 

 

Soil dwelling invertebrates not only break down
plant litter and mix it with the mineral part of the soil
but also, change its chemical composition. Their excre-
ment, as experiments with earthworms have demonstrated,
cOntains a greater total amount of organic matter, of par-
tially converted humates, of available forms of N, and of
mineral nutrients required by plants, than does the soil,
and it also contains higher total of assimilated (immobil-
ized) elements (Sukachev and Dylis, 1964).

Where invertebrates are represented mostly by small
forms (Acarina, Collembola and other microfauna) which live
mainly in litter and the surface layer of humus, their role
in transporting organic and mineral matter is negligible and
is limited to a depth of a few centimeters in the topmost
soil layers.‘ Larger animals may go down to the subsoil,
later bringing to the surface mineral particles containing
elements of value for plant nutrition. Where carbonates
lie not far from the surface earthworms bring them to the
topmost layers (Sokolov, 1956).. In addition, they enrich

the soil with secretions from their oeSOphageal (lime)

19

gland (Ponomareva, 1950) which helps to neutralize acid
soils.

The ability to change soil reaction is observed
also in ants. Ants tend to neutralize soil reaction by
their excretiOns which are highly buffered at a slightly
alkaline pH (SukaChev and Dylis, 1964).

In ecosystems in which litter constitutes an impor-
tant storage reservoir for minerals, the activities of
microflora and fauna in soils may control the rate of min-
eral cycling. Natural reforestation and natural succes-
'sions of vegetation usually depend upon the activity of
soil animals which are an obligatory link in mineral turn-
over (Ghilarov, 1968).

The two main mechanisms in mineral turnover are
mineral transfer via litter consumers and mineral release
by microbial decomposers. Witkamp and Frank (1970) used
a series of microcosm experiments to study mineral transfer
relative to system structure and environment. In general,
temperature appeared as the most influential environmental
variable in forest-floor processes where moisture is not
limiting for long periods of time. The major factor in

mineral transfer appeared to be the physico-chemical and

20

biological prOperties of minerals. Leachable and normally
plentiful K was leached out, 137CS with a strong affinity
for sand remained in the soil, biologically essential Mg
apparently was immobilized in the humus, whereas most of
the organic carbon lost from the leaves eventually ended

up as CO released to the atmosphere.

2

Distribution of Arthropods

Usher (1969) observed three types of distribution
of arthropods within a block of samples: 1) uniform, 2)
random, and 3) aggregated. Using a coordinate technique
for specifying locations, numbers and distance between
aggregations, he concluded that aggregation resulted from
some field attribute of the species such as size of the egg
cluster, or availability of a food niche.

It is generally known that the horizontal patterns
of animal populations are not random, but are aggregated or
clumped (MacFadyen, 1952; Haarlov, 1960; Poole, 1961; I
Block, 1966; and Gerard, 1966). Klopfer (1969) has sug-
gested that heterogeneity of the environment has resulted

in reduced interaction between species, consequently

21

permitting more species to coexist. If the environment was
uniform, interspecific competition would be intensified re-
sulting in a reduced number of different species. Other
factors, biotic and abiotic that may affeCt, in different
degrees, the distribution and abundance of soil animals are
[(1) competition for food, (2) reproduction behavior, (3)
mutual attraction for other individuals of the same species,
(4) response to daily and seasonal weather changes, and (5)
increased survival of the species through clumping. Indi-
viduals in groups often experience a lower mortality rate
during periods of stress (such as attacks of other organ-
isms) than do isolated individuals, because the surface
area exposed to the environment is less in proportion to
the mass and because the group may be able to favorably
modify the microclimate or microhabitat (Allee, 1931;
1959).

Seasonal abundance of soil organisms has been corre-
lated by numerous authors with such parameters as moisture
and temperature (MacFadyen, 1952; Block, 1966). Madge
(l965a,b) showed that tropical leaf litter disappeared most
rapidly during the wet season due mainly to activity of
mites and collembola. The effects of cultivation, mOis-

ture temperature and many other factors have been reviewed.

22

thoroughly by Christiansen (1964) and Burges and Raw
(1967).

According to Ghilarov (1965), composting during
autumn encourages invertebrate develOpment during the
winter. Also, composting of urban wastes is promising.
Various organic wastes with the addition of soil and sew-
age sludge have almost the same life forms as can be ob-

served in leaf composts.

MATERIALS AND METHODS

Experimental Area

 

In the spring of 1969, 12 plots were laid out just
to the east of the Baker Woodlot on the University Farm
(Fig. l). The area had been planted to experimental corn
breeding materials the year before. The corn had been
planted in blocks of 25~foot (7.6 m) rows and harvested
with a l-row picker-sheller.' The corn cobs had been dumped
in a pile at the end of each row.

The area was not plowed in 1969 so that arthropod
populations could be studied in surface litter and the soil
underneath. The 12 plots for the study were selected to
contain 6 uniform rows of stalks and their associated corn
cobs (Fig. 2). The plots were arranged to provide sampling
sites at 4 incremental distances from the edge of the wood-
lot, with 3 replications at each distance (Fig. 3). This
was done in consideration of the possibility that the wood-

lot might serve as a source of colonizing species or that a

23

24

 

Fig. 1. General view of the experimental area, looking
west toward Baker Woodlot. May 11, 1969.

 

Fig. 2. Condition of corn trash at representative
sample site. July 22, 1969. Note soil thermometer,
right foreground.

NOMINAL DISTANCE FROM WOODS (m)

S+N

25

BAKER WOODLOT

 

 

I9.0-+—

26.6 AI-

34u2'+-

 

 

 

 

 

 

 

 

 

___ ____________ 'K'
ROADWAY 7.6m

[_

r BUFFER STRIP I
(Com residues from I968) 7.6
(Unplowed) l ‘*

*-

R.D| R20. R30. i;
RIDZ R202 R302 7;
RID3 R203 R303 i;

‘ RID4 R294 R304 1.:

J

*R=replicotion D=distonce

FIG. 3. DIAGRAM SHOWING THE 12 SAMPLING AREAS WHICH

WERE TREATED As REPLICATES WHEN N0 SIGNIFICANT
EFFECTS OF DISTANCE FROM WOODL T COULD BE SHOWN.
ORN ROWS RAN EASI AND WEIA' AMPbING AREAS
VARIED F 0M 8 T0 0 ROWS .5 TO 1 .6 M. SOUTH
To NORTH .

26

micro-climate gradient might be associated with proximity
to the woodlot.
The soil is classified as: Berrien fine sandy loam

(Aquic Udipsament, sandy, mixed Mesic).

Sampling

ArthrOpod populations in litter and in soil to a 2-
in depth under the litter were estimated three times during
the season (May 22-24, July 15—17, September 14-16). On
each colleCtion date, one of the six corn rows on each plot
was selected at random for sampling.

Corn cobs were sampled separately from the portions
of corn stalks and leaves which had been beaten to the
ground by the action of the picker-sheller and of snow and
rain (Fig. 2). These two types of litter are distinguished'
hereafter as "cobs" and "stalks."

Litter over a square foot of ground surface was col-
lected, using a 12 x 12-inch steel frame.(930 cm2) and a
knife to trim away litter outside the sample area (Fig. 4).

An undisturbed soil core, 16 in2 (103 cm2) to a depth of 2

 

Fig. 4. Collection frame (12" x 12") used in
obtaining cob samples (top) and stalk samples
(bottom).

28

in. (5.08 cm) was taken immediately under the litter sample
at each site (Fig. 5).

Litter samples were placed in plastic bags, soil
samples were placed in wax-coated cake boxes and sealed.
Samples were placed immediately in a styrofoam chest con-
taining ice to keep them cool until they could be trans-

ported to the laboratory for extraction (Fig. 6).

Extraction and Identification
of Arthropods

 

 

Extraction was initiated on the day of collection.
Each litter sample was emptied on the screen in the wide
portion of a Tullgren-Berlese funnel (Fig. 7). The soil
cores were transferred to standard Berlese funnels, with
care to avoid damaging their structural integrity. A
marked vial containing 95% ethanol was placed beneath each
funnel exit to collect the arthropods falling from the
sample. A light bulb (25 watt) fixed at the tOp of the
funnel provided a source of heat. The drying and heating
effects of the light bulb forces the soil animals to seek

more moderate temperature and humidity regimes toward the

Fig.

29

 

5. Collecting undisturbed soil core after removal
of litter sample. Top: 4 x 4 x 2 1/2 in core frame
inserted to 2-in depth within area delineated by
litter-sampling frame. Bottom: Excised soil core
being transferred to waxed carton for transport to
laboratory.

30

 

Fig. 6. Collection tools and samples of litter and
soil (top) and ice—cooled styrofoam chest (bottom)
used to transport samples to the laboratory.

31

 

Fig.

7. Extraction apparatus: Tullgren—Berlese funnels
(against rear wall), used for extraction Of soil
animals from larger litter samples; standard Berlese
funnels (on rack in foreground), used for extraction of
undisturbed soil cores and smaller litter samples.

32

narrow mouth of the funnel where they eventually fall into
the collecting vials. Extraction of the arthropods was
allowed to proceed for 4 days for the litter samples and

5 days for the soil samples.

The vials containing the arthropods were cleared of
debris and mineral matter that fell through the screen by
employing a modified flotation method. Ethanol in the col-
lection vial was replaced with water. Magnesium sulfate
was added to separate the organic from the mineral material.
The buoyant organic materials were decanted and treated with
xylene to separate the arthropods from the other organic
debris. The arthrOpod cuticle is wetted by xylene and they
accumulate in the xylene-layer which settles out on the
water surface. The xylene-water interface was scanned
under a low power stereoscope and the arthrOpods were
picked out. They were then brought back in 95% ethanol.

The above procedure posed the risk of losing some
of the smallest arthropods but extra care was exercised to
minimize such loSS. Considering the preliminary nature of
the study, no attempt was made to recover very small arthro-

pods that may have been lost by entanglement in debris.

33

The arthropods were sorted, counted, and recorded
to the smallest readily recognizable group: to order or
family for the insects, to species for springtails, and to

class or morphological group for the other arthropods.

Soil Analyses

 

After extraction of arthropods, the 4 soil samples
from each replication were composited, passed through a 2-mm
sieve and sub-sampled. Soil pH, K, Ca, Mg, and P were de-
termined according to routine methods of the Soil Testing
Laboratory, Michigan State University.

Soil pH was determined in a 1:1 water suspension,
using a Beckman Zeromatic glass electrode pH meter. Phos—
phorus was extracted with Bray P-l reagent using a 1:8 soil
to solution ratio; available K, Ca, and Mg with 1.0 N NH4OAc
(pH 7.0) using a 1:8 soil to solution ratio.

The determination of exchangeable NHZ-N and NOS-N
was done by semi-micro distillation according to Bremner
(1965), using Devarda's alloy to reduce No; to NHZ. (It was
assumed that rapid drying in the Berlese extractors would

have minimized microbial transformation of mineral and or-

ganic N.)

34

Moisture content determination was accomplished by
measurement of loss of weight of a field-moist sub-sample
after oven drying for 48 hours at 110°C. Water capacity
at 1/3 atm tension was determined using the method described

by Klute (1965).

Total Nitrogen of Soils and Litter

 

The semi-micro Kjeldahl method of Bremner (1965) was
used to determine total N in soils and litter except that in
the KZSO4-catalyst mixture, HgO was used as catalyst instead
of CuSO4. This necessitates the addition of NAZSZOB to the
alkali solution used in the distillation step.

One-half gram of finely ground soil (BO-mesh) or
50 mg of litter (dried at 65°C and ground to pass a 40-mesh
sieve) was wrapped in a cigarette paper and added as a
package into a 100-ml Kjeldahl flask. After adding 2 m1
of distilled water the flask was allowed to stand for 30
minutes. Then 1.1 gm of K SO -catalyst mixture and concen-

2 4

trated H SO

2 4 (3 ml for soil and 2 ml for litter) were added.

The mixture was digested until clear (2-1/2 hrs. for soil'
and 1 hr for litter). The digested mixture was made alka-

line with 40% NaOH-Na28203 solution and distilled for 5

35

minutes into 2% boric-acid-methyl purple indicator solution.

The NH liberated was estimated by titration with 0.01 N

3
HCl and is reported as total N.

Total Carbon of Soils and Litter

Total carbon in soils and litter was determined
with a Leco carbon analyzer (Model 70). Sub-samples for
analysis were ground to pass an 80-mesh screen. One-
hundred mg of soil (10 mg of litter) was weighed into a
icombustion crucible. Approximately 1 gm each of iron chips
and tin catalyst were added. Combustion in the induction

furnace occurred in a stream of 02 at 1670 °C. Combustion

products in the 0 carrier stream was passed through a pur-

2

ification train to remove particulate matter, water and $02

I

and to convert CO to C02. Purified 02 + CO2 was collected

terminally in the analyzer cylinder at 45 °C where CO2 was
estimated from the change in thermal conductivity relative
to pure 02. The thermistor signal on this instrument is

read out digitally as % carbon in a 1-gm sample and must

be converted to actual size of the combusted sample.

36

Air and Soil Temperature

 

Air temperatures at the experimental area were
observed during each sampling period. Soil temperatures
at the surface and at a 2-inch depth under both cobs and

stalks were likewise measured and recorded.

RESULTS

ngor Animal Grogps

 

A preliminary analysis of variance showed no sig-
nificant effects of proximity to Baker Woodlot or varia-
tion in numbers of any animal group. Examination of the
grid distribution of the numerically dominant groups (Acar-
ina, and Collembola) showed non-uniform distributions at
each sampling, but centers of concentration were distrib-
uted in a random fashion.

Analysis of aggregation or migration phenomena was
not among the objectives of this study. Therefore the 4
distances from the woodlot were combined with the 3 field
replications (Fig. l) to give 12 replications for factorial
comparison of animal numbers in relation to litter sites
(cobs Xfi' stalks), strata (litter l§° soil), and sampling
date (Table l).

The probabilities in Table l-C show significant
main effects of both sampling date and stratum for all

groups except those present in low or transient numbers.

37

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40

Only in the case of Diptera did the main effect associated
with litter site approach significance at P (05).

Nevertheless, seasonal and vertical distributions
were different at cob sites than at stalk sites, giving
rise to significant first order interactions for several
groups and second order interactions for two (Hymenoptera,
Psocoptera). Seasonal changes in numbers were usually
parallel in litter and soil. However, except for the May
sampling, numbers of most groups were greater in soil,
and seasonal variation in soil was also greater. As a
result, means for the soil tratum were more often statis-
tically different than were means for the litter popula-
tions.

Even where statistical significance was not
attained, the relationship of specific groups to litter
site and/or stratum varied uniquely through the season,
and these differences will be pointed out.

Acarina, Araneida and Hemiptera increased in num-
bers as the season progressed, reaching maxima in Septem-
ber. This maximum for Acarina was five-fold greater in

soil under corn stalks than under cobs.

41

Chilopoda in the litter layer decreased sharply
in the second sampling but increased in the soil. There
weregsignificant first order interactions of stratum with
site and date: centipedes in the litter layer were more
numerous at cob sites than stalk sites, but soil popula-
tions were greater under stalks, significantly so in
September.

~Population patterns for Coleoptera and Diptera
were similar to those for Chilopoda, except that much
larger numbers were encountered in both soils and litter
in May. Fewer numbers of Diptera remained in the litter
after May, but all three groups were recovered in much
greater numbers from soil than from litter in July and
September.

HymenOptera were found mainly in soil and in spor-
adic seasonal numbers under both litter types.

Diplopods were found only in May but more fre-
quently at cob sites. ISOpOdS were found in both litter
types in May but appear to have moved later into soil only
under corn stalks. The data for these two groups may have

behavioral significance, but the plot layout and statistical

42

design were inappropriate for a critical evaluation of
these sparse and irregularly distributed groups.

Psocoptera showed a marked preference for corn
stalks early in the season, although they appeared in the
soil stratum earlier and in higher numbers under cobs.
None at all were encountered in September.

Annelids were recovered from both litter types and
from soil at cob sites in May but seem to have moved later
into lower (unsampled) soil strata in July. They appeared
in the upper 0-5 cm soil stratum at both sites in Septem-
ber.

Collembola were the most numerous group in the
May sampling--both in litter and in soil. In litter, their
numbers decreased in each successive sampling. The soil

population, however, reached a peak in July.

Collembola--Acarina Populations

The dominant animal groups encountered, numeric-
ally, were Acarina and Collembola. There was an inverse
seasonal distribution in their numbers (Fig. 8), but these

two groups together comprised 90 to 99 percent of the

% OF TOTAL ARTHROPODS

 

 

 

 

 

 

 

 

 

'00"? LITTER I’ LITTER
O O
BOT A counmou —I. A
-~‘\“-<f:“ “:::;>-..__.A\
counlaou
60«- A\ __
40+ ._
‘cgm/o AcM/m
200 o n u;———/
0mm; A o\mms
o P ‘P D ,
'°°‘ SOIL T SOIL
A
80~- mun/sou “ COLLEAIBOLA
60" _.
40" “4’9”“ ‘- ACAR/IM
20“ __
arr/ms D \omms
o l 9
0_L “V2?- 24 JULY I5 -I7 SEPT l4- l6 uszz- 24 JULYIS- -I7 5ng .4- ,5
DATE

CORN COBS SITE

 

CORN STALKS SITE

FIG. 8. DISTRIBUTION OF COLLEMBOLA, ACARINA AND OTHER ARTHROPODS
AS PERCENT OF TOTAL ARTHROPOD NUMBERS.

44

total arthropod numbers in each sampling. The biomass
represented by other arthrOpod groups would have been
relatively of greater magnitude (Edwards, gp_gl., 1970).
Nevertheless, since respiration rates per unit mass are
inversely related to body size, Acarina and Collembola
must contribute significantly to the faunal component

of energy turnover. They certainly play unique roles

in reworking of feces from other animals, disintegration
of litter, redistribution of organic matter and interac-
tion with the microflora (Jongerius, 1963; Ghilarov,
1968; Atlavinyte, 1971).

The data in Table 1 indicate that Collembola were
prepared to move from the litter into the soil underneath
much earlier in the season than Acarina. It is signifi-
cant that Chilopoda, Coleoptera and Diptera were already
present in the soil in large numbers in May. These larger
animals would have opened up passageways and deposited
substrates to support downward migration of the mesofauna.

Many species of mites are phoretic or pass through
inactive hyp0pial stages attached to larger animals, not-
ably Cole0ptera and Diptera (Wallwork, 1970; Kevan, 1962).

Physical transport on larger animals may have been an

45

additional factor in the very large increases in numbers
of Acarina in the soil which occurred between.the May and
July samplings. These increases coincided with disappear-
ance from the litter of several groups of larger animals
in substantial numbers: Chilopoda, Coleoptera, Diptera,
IsopOda (Table l-A). At the same time there were substan-
tial increases in the soil populations of larger animals.
Araneida, Chilopoda, ISOpoda (Table l-B).

The very dramatic September increase in Acarina in
soil under corn stalks was also accompanied by increased
soil numbers of Chilopoda and Coleoptera. Fairly large
numbers of Hymenoptera were also recovered, where none had

been found in July.

Collembola Species

 

Separation of Acarina to lower taxa proved imprac-
tical. It is possible that increased numbers in succes-
sive Samplings reflect increases in species diversity as
well as numbers of individuals.

In the case of Collembola, however, three species

comprised 78 to 98 percent of the populations in litter

46

and in soils: Isotoma eunotabilis (Folsom), Isotoma viri-

 

gig (Bourlet) and Entomobry§_griseoolivata (Packard).
Juvenile-to-adult ratios in Table 2 indicate that a single
generative population was involved in each case.

Reproduction and recruitment appear to have taken
place primarily in the litter early in the season. In the
May samples, juveniles represented half or more of the
litter population but were relatively much less numerous
in the soil.

At the time of maximum numbers in July, juveniles
were diStributed in a rather uniform prOportion (.4 to .6)
to adults in both litter and soils, except for I. eunota-
pilig. This species appears to have developed somewhat
more slowly than the other two: the litter population re-
tained a larger proportion of juveniles and was associated
with a larger soil population.

The large decrease in numbers of all three species
in September was accompanied by a marked decrease in aver-
age age of the population (juvenile/adult ratios of .2 or

smaller).

47

 

 

 

 

 

 

 

 

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mm. NMA nmm ®0m mm. ppm nAm men Am. mom vvm mAm nAImA Add
mA.A mom can mmo mm.A mmAA mmm oNAN mm.A AmmN NASA meme vNINN xmz woos Chou
Amcmoe quQINAV uwuuMA :A .4
N E mAmsnA>Hch m E mAmsmH>Apcm E mAmspA>AUCH
I | N'
.p<\.>5w mmAAcm>sn muA3C< Hooch .p4\.>3n mDAAco>3o mqupd AmUOH .c¢\.>5n mOAAco>3h muAspd AODOB
mufim
Toma
nausea
Apznxommv mum>AAcomemm mMpnOEOucm AquuDomv mflpwuw> mEouomH AEOmAOmv mAAHQmuccso mEOuOmH
.OAOQEOAAOQ u moflooam AmaAocAna omncu 0CD DOM mcenmn DASUO\DAAco>sn Esp LmoAAco>sn can muAscm mo mumflEDZII.N mqmdh

'

48

Eopoouw mo mowumwp nouuwxEocomuw Ho mowumop >uoooDuO n mp

 

m
uchAwAcmAmIcoc n ma
A
nvm. mmm. mmm. AAw. va. vow. omm. wNm. vmo. 00A. who. AAm. mm\N Q x m x m
bOM. 5mm. 5N0. nmA. nob. omo. hmA. vmm. omm. 0AA. VNN. MVA. QM\A m x m
mooo.v mooo.V Aoo. mooo.v mooo.v mooo.v voo. Aoo. mooo.v mooo.v Aoo. mooo.v mm\N Q x m
mooo.v mooo.v mooo.v mooo.v mooo.v ohm. mooo.v nAo. mooo.v 0mm. mooo.v Aho. mm\A AmC oumuum
oNN. ovo. 0A0. ham. Awm. Nob. hmv. wvm. mNm. mvo. mmA. one. AA\N D x m
ovA. Ohm. voo. va. omo. Nev. ohm. Mvm. vow. moo. mwm. mvm. AA\A «my mmuAm
mooo.v mooo.V Noo. Aoo. mooo.v mooo.v moo. Aoo. mooo.v 0A0. 0N0. vAo. mm\N «QC mound
mmv. ohm. mmm. mom. owe. Nub. mvv. mmm. va. mmh. who. mmn. NN\AA «KC mmmm
MI .Nuomwumu
N
wumuum pcm .mqum .mwump .mcoAumoAAaon EDA: pouonommm m mo wocmOAMAcmAm AOL Adv mwAuAAAanOna .U
mmump CA£DA3
m: m: oov m: we m: m: m: me m: m: m:
mmu Am. Ame» de.
mmoAm canoes
NN. oAm mmv Nmn Am. hvm mob moAA mc mmoA NCAA moAN .
mmump Amoc QmA
NA. MAA @AOA mNAA 0A. Am Amm NAm mA. MAA Nmm mooA bAIvA mom
Av. Amm mAmA ovom Av. Hob wmbA vaN ov. Nva anN mmov hAImA Ann
mxAmDm
mm. mmm mmm OmNA mm. mAv ONm mMMA NN. mom MAAA mOmA «NINN >mx Hops: AAOW

49

Vertical Distribution of Animal
Groups and Collembola Species

The numbers of most animal groups in soil relative
to their numbers in litter increased sharply between May
and July (Table 3). The soil/litter ratios in July for
a number of groups at cob sites were similar to those at
stalk sites. In the September sampling, however, vertical
distributions were very different. A substantially larger
proportion of the animals associated with corn stalks were
recovered from soil than at cob sites.

Changes in vertiCal distribution of the Collembolan
species (Table 4) tended to parallel each other and the

changes for major arthropod groups.

Environmental Parameters in Relation
to Population Distribution
The vertical distribution of litter—soil popula-
tions is frequently associated with temperature and/or

moisture gradients (Kevan, 1962; Wallwork, 1970).

50

O o
.A my AAOm Eouw no A Av nauuAA Beum pmuoroowu mAmEAcm Oz

 

 

 

A
o o o
A.AA A m A 0.0 o.MA A.m o.m A.AA o.m v.AA oAIvA mom
0 o o o
N.m m A o.m m A w.m A.N m.mA m.v M.m nAImA Ann
0 o
o.A m m 0.0A m. A.A m.A A.N o.v A. vNINN xmz mxAMum cuoo
o o o
e.A A A m A H.A m.v m.m ~.v A.m m.A v.A oAIvA new
0 o
m.v m A A.oA o.mo h.AA m.M 0.N m.m A.v m.o hAlmA ASH
O
m. o.A ~.m m e. o. o.A v. v.m A. vawm sex mnou cuoo
m u u OOAAUGC< CNOUQOUOmm muoumocuaxm muvuon onnEUAAOU muuumOvou upomoAAnu mpawcmut chumu<
pose as a memo OuAm Amused
Anuoe

umsouu AmEAct

 

 

.mmaoum AmEAcm AOQAUGAAQ Mew uwuuAA GA mumnfis: Ou AAOm CA

muonsnc mo moADmmII.m mamas

51

TABLE 4.--Ratios of numbers in soil to numbers in litter for
Collembola species.

 

 

 

 

 

Litter Date Isotoma Isotoma Entomobrya Other
Site eunotabilis viridis griseoolivata species
Corn cobs May 22-24 .4 .6 1.7 .6
Jul 15-17 4.1 3.1 5.3 3.8
Sep 14-16 2.8 1.9 5.0 9.4
Corn stalks May 22-24 .9 .9 - '2.0 1.4

Jul 15-17 4.4 3.1 5.5 1.8

Sep 14-16 6.8 ' 6.7 11.6 5.5

 

52

Seasonal changes in composition, size and distribution of
populations are further influenced by the changing nature

of available substrates as decomposition proceeds.

1. Moisture

Rainfall from March through the July 15-17 sampling
totaled 36 cm (Fig. 9). This is normal for this 4-1/2
month period. The September sampling came near the end of
a long drought period which included most of August. I

Soil moisture in the May sampling was much higher
than moisture capacity at 1/3 atmosphere tension (Table 5)..
This was due to the imperfeCt drainage at this site and
the fact that free water was still present in the subsoil
at a relatively shallow depth. By the time of the July
sampling, drainage had lowered this free water surface and
moisture content in the soil at 0 to 5 cm approximated that
. at 1/3 atmosphere tension. In spite of the long drought
period which preceded the September sampling, the soil
under litter at that time was Still perceptibly moist,
well above the wilting point for plants.

.Moisture in the litter itself was not determined.

The stalks and leaves are less dense tissues than corn

cobs and they were more loosely distributed in the litter

TEMPERATURE °C

53

 

 

 

 

 

 

 

 

 

 

 

 

 

FIS

PIC)

 

 

30! I‘ ~—-MAx.
20-
MEAN
IO‘
NHL
0‘ I},
-‘O-
I A II
0 A

3C)?

MAX.

.2.»
l:!

 

 

 

 

 

 

 

_5. e flflf n

 

 

 

 

 

I'I May 2'3 4 July I'6 5 Sept. (5

FIG. 3. U. 6. WEATHER BUREAU RECORDS (M. S. U. SOUTH FARM
TATION . PPER FIGURE: MONTHLY RAINFALL AND AVERAGE

CARDINAL AIR TEMPERATURES. LOWER FIGURE: DAILY RAINFALL,
MAXIMUM AND MINIMUM AIR TEMPERATURES. AND SOIL TEMPERATURES

(7 A.M. AND 10 A.M.) AT 5 CM UNDER GRASS SWARD.

PRECIPITATION (cm)

554

.conuwu AAOm ou COAumAuH :A nouuAA Hops: AAom :A

.ousuouomEUu can ousumAOE .cwmouuAc AAMUAUAM

mvomounuuo Honuo can .mcwumod .OAOAEDAAOU mo mumnESZII.m NAm4E

acmOAuAcoANIco: I n:

 

 

 

 

M
ucwuuom M.NA n coAmcuu Sun m\A an advance unsunAOSN
M BO 80 MM.A u unon3 oEsAo> mcwaanmdA
I I II II 2 a2. . 8 II a: n: 3. me I mouse 55 A:
nouAm .moo oma
th.v voa.m m. a: u: no. nouAm :Anqu
M mount Ame. omA
an. m.v v.Ao Amm vmo.M Nom.mv m.mA m.oA M.AA woo. wA.A m.ho wAIcA mow
om. A.MA M.NA vcv Moh.m oMN.o o.MN A.MA m.AA Mao. AA.A m.ho MAIMA Asa
ow. m.h wA. @Av MMN.m MAA m.NA m.hA o.NA mmo. vo.A m.ho VNINN >mz axAsua choc
mm. m.N o.AA omv whA.N MhM.m o.mA m.oA 0.AA omo. MA.A m.ho oAIVA mum
ms. h.AA A.AA 0mm AMm.m MBA.m o.NN m.MA h.AA Moo. mo.A m.ho FAIMA Ann
no. N.o MN. va amm.v omA o.Nh A.MA N.AA omo. mo.A m.ho «mINN um: onou :uou
Uo a o v NIE x ox
30353.2 838.52
a o o as Moo 0 o o acausu
uocuo Aona AA 0 A 4 nonuo Aona AA U . < unvos
z\u z u A
AAom
on :A U a ham ov>uouno ousuwuoosoa ousunAo! mama ouaa uouuaA
AA AAom AAom . .

 

.50 nlov AAOI EA Nll aAuavA>Aflcu

ABU mlov AAOm

 

 

can conuno Auuou ou :oAunAou GA HmuuAA

Hons: AAom :A mpomounuuo uonuo can

.AAom we» cA cmuouuAc AnuuAuAs
.MGAHmum .nAonEoAAOU no mHonESZII.m NAmda

55

layer. Consequently, they lost moisture more rapidly after
wetting. The generally more moist condition of the cobs
observed in the field is reflected in the slight but con-
sistently higher moisture content of the soil under the
corn'cobs.

The generally more moist conditions in the corn
cobs may have contributed to the larger numbers of most
arthropods encountered in litter at cob sites than at
stalk sites in all samplings (Table l) and the much smal-
ler proportion in soil at cob sites in the September samp-
ling (Table 3). I I

The litter structure at cob sites would have in-
cluded extensive interconnected spaces between the corn
cobs, facilitating movement within the litter layer. This
and the more equable moisture regime in cob litter would
have encouraged mobile animals to spend more time in the
litter. Longer residence times for larger animals would
favor increased numbers of less mobile pOpulations depend-
ent upon them for substrates (excreta, comminuted litter
fragments).

Acarina numbers in soil (Table 5) and their total

site numbers (Table 6) were inversely related to seasonal

56

 

 

 

 

II II II II II II II n.m co. mv.~ ~.Ae~ mmumu gasses
mOOAm Amos oma
II II II II II II II M.v no. a: M.oMm HODAm nAnDA:
moump .moo omA
m.A v.m m.vAA coo «mo.v mmm.ov m.m~ m.~v am. m.em AvAA DAIwA mom
o.A o.m~ m.aA Amm nv~.~A men.oA o.m~ e.ev Nm. m.mn mVMA hAImA Ase
v.A m.vA M.A ova mmm.m omm o.AA o.~m we. m.on moeA v~I- so: mxAmum :uoo
o.A v.m w.o~ vow Amm.~ mA~.vA o.~m m.n~ mo.A v.0n mneA oAIvA mum
n. o.AA A.oA mmo Amm.oA mvv.m 0.0” m.Am vo.A m.~M AvMN FAImA Ana
0. e.m n.A oma em~.~A Aew.A m.oA m.mm no. e.~m mAmv «NINN an: unou :uoo
Uo 0 0 “'5 N U
mvomounuut noomounuu< shuns nevus:
A aAonauAAoO naAumu‘ umnuo «AoasuAAoo anAumua quaaua 2\O z D Aug
__o mama muAm
N0
uouuaA :« u a non vo>uuwno uudA
MouuAA cucuusm

AAom «9AA MQUUAA :A

N

In «AnnuA>AucH

 

.umuuAA Odouusn :A pocAnuou somOHuA: was conudu .uwuuma hut ou soAusAmu

EA «monounuum Rocuo new chumu< .mAOAEuAAOU no AAAOD nsAQ HUuUAAA nuvnEss Dawn AmuOHII.m mAm<H

57

TABLE 7.--Probabilities (P) for significance of F associated with
replications, dates and litter site, for data in
Tables 5 and 6.

 

 

 

- l __

Category df1 Kjeldahl N Total C C/N Dry Matter
A. Litter materials

ReplicatiOns 11/22 .032 . .943 .465 .083

Dates (D) 2/22 <.0005 .418 '<.0005 .<.0005

Materials (M) 1/33 <.0005 . <.0005 .<.0005 .<.0005

D x M 2/33 <.0005 . .114 .002 '<.0005
B. Soil samples

Replications 11/22 .596 .661 .379

Dates (D) 2/22 .182 .030 .647

Site (8) 1/33 .088 .442 .178

D X S 2/33 .029 ‘ .671 .113

 

l .
df a category degrees of freedom/error degrees of freedom

58

changes in moistUre status as reflected in soil moisture
content (Table 5). However, there was no consistent rela-
tionship to seasonal changes in moisture status with num-
bers of Collembola or other arthropods. The data in Fig.8
suggest that Acarina simply increased to fill a trophic
niche made vacant as numbers of Collembola declined in re-

lation to the total animal pOpulation.t

2. Temperature

Litter and soil temperatures were recorded at the
‘experimental site only at the time of sampling. Samples
were taken routinely between 7:00 A.M. and 10:00 A.M.
One replication (Fig. 3) was sampled each day, 3 days be-
ing required for complete sampling Of the study area.

Soil temperatures encountered at 5 cm under the
litter (Table 8) were very similar to those recorded dur-
ing the same morning period at 5 cm under grass sward at
the M.S.U. South Farm Weather Station (cf. lower half of
Fig. 9). The 7:00 A.M. reading frequently coincides with
the daily minimum soil temperature at this depth.

The May sampling had been preceded by 6 to 8 weeks
of mean air temperatures above freezing. Soil tempera-

tures during the previous 2 weeks would have averaged

59

 

 

 

 

TABLE 8.--Soil and air temperature (°F) at.and near (1 km) study area.
Sampling Periods
T i m e May July Sept.
22 23 24 15 16 17 14 15 16
DC —
U.S. Weather Bureau Records
Air Temp 7 AM 4.5 6.1 8.1 17.2 26.6 23.8 15.0 17.2 17.8
8 AM 5.0 9.0 10.5 21.1 22.8 24.7 16.6 17.8 17.8
9 AM 5.6 10.6 13.6 23.3 24.4 26.0 19.4 21.1 17.8
10 AM 6.1 11.7 15.5 25.0 26.1 27.2 22.2 21.6 17.8
1
Soil Temp 7 AM 10.6 9.2 10.7 22.2 22.4 25.0 17.2 18.9 18.9
8 AM 10.6 9.2 11.7 21.9 22.7 25.0 16.6 19.2 19.2
9 AM 10.6 10.6 12.8 22.2 23.3 24.7 18.3 18.9 19.2
10 AM 10.7 10.6 13.9 23.0 23.3 24.7 18.3 20.0 19.2
Experimental Area
Air Temp 7-10 6.1 12.2 14.4 23.3 25.0 26.1 21.1 20.5 17.8
(mean)
Soil Temp2 7-10 10.6 10.6 13.3 22.2 23.0 24.7 18.3 18.6 18.6

(mean)

 

1
Soil temperature at S cm depth under grass sod.

2Soil temperature at 5 cm depth under litter (means
sampled each day).

for all sites

60

about 12 to 15°C (allowing for afternoon peaks higher than
recorded at 10:00 A.M.).

The July samples were taken during the period of
seasonally maximum temperatures. Soil temperatures during
the preceding 2 weeks would have averaged well above 20°C.

The September 14 to 16 sampling was made during a
period when soil temperatures were rising rapidly from a
local minimum of about 12°C on September 10.

Litter temperatures (litter-soil interface) re-
corded at the time of sampling (Table 6) were consistently
about 2°C lower at cob sites than at stalk sites. This
reflects the higher moisture content and higher heat capa-
city due to the water in the cobs.

Soil temperatures at 5 cm (Table 5) were l'to 2
degrees lower under cobs in the May and September samplings
but slightly higher than under stalks in July. Although
these differences are small, they do relate to preceding
temperature sequences (Fig. 9) and illustrate the role of
moisture content and heat capacity of water in litter ma-
terials in moderating temperature regimes in the litter
itself and in underlying soil.

The only consistent relationship to animal numbers

is the consistently lower temperature (Table 8) and higher

61

numbers of most groups in cob litter 35. corn stalks (Table
l). The overriding influence on numbers was probably the
higher moisture content of the cobs. However, extremes of
high temperature may well have occurred in stalk litter,
resulting in greater movement of animals into the soil
stratum. Maximum numbers of Collembola in soil coincided

with seasonally high air and litter temperatures in July.

3. Nature of Substrates

Before the May sampling, litter materials had been
subject to biological decomposition, physical weathering
and leaching through the fall, winter and spring. At the
time of the May sampling, the corn cobs were 2 to 3-fold
higher in N than reported values (Morrison, 1959). They
were also higher in N and had a narrower C/N ratio than the
stalks and leaves (Table 6). This would indicate that, in
May, the cobs had already undergone more extensive decompo-
sition (dissipation of carbon) than the stalks and leaves.

Conditions were more favorable for rapid decompo-
sition of the cob litter. Because of their greater den-
sity and the more compact arrangement in small piles, the

cobs were more retentive (If moisture and made more

62

intimate contact with underlying soil than the bulkier
stalks and leaves. The effect of these differences in
physical structure of the two litter types can be judged
from differences in the rate of disappearance of dry
matter during the study period (Table 6). Thus 60 percent
of the dry matter present in corn cobs in May had dis-
appeared by September, as compared with 35 percent for
stalks and leaves.

The net effect of more rapid decomposition of the
cob litter was that readily available energy materials
were dissipated more quickly. This is reflected in the
narrower C/N ratios for cobs X§° stalks (Table 6). It
was also reflected in the seasonal changes in total site
number of arthropods. Thus, the totals for litter plus
soil of most major groups was greater at cob sites in May,
whereas in September the totals for stalks sites were
greater.

When total site numbers are calculated per gram
of carbon in the litter, it would appear that the residual
availability of energy substrates for animal populations
was greater in stalks and leaves than in corn cobs at

each sampling date (Table 6).

63

A similar calculation relating animal numbers in
soil to carbon in soil indicates no difference in availa-
bility of energy to soil populations in May or July (Table
5). In September, however, it would appear that more energy
was available to soil animals under stalks than under cobs.

The indicated differential in energy substrates in
soil in September was not reflected in the analyses for soil
C, since differences in soil C under the two litters were
not significant. There is evidence that organic materials
were translocated from both litter materials into the under-
lying soil during the season, increases in soil C after May
being significant under stalks.

The average increase in soil C for the two materials,
from May to September, was .05 percent. This is equivalent
to 34 g C or 58 g humified organic matter per m2 to a depth
of 5 cm. If allowance is made for respiratory loss, actual
transport into the 0-5 cm soil stratum could have been 2 or
3-fold greater. Thus, the increases in soil carbon lead-
readily to the estimate that as much as a ton of organic
matter per hectare (litter fragments, excreta, etc.) were
translocated from litter into the 9-5 cm soil layer during

the 5 months of the study.

64

The higher carbon content in May under cobs than
stalks indicates that substantially larger translocations
had occurred prior to the study period, as might be ex-
pected due to the greater numbers of larger animals,
notably Diptera (Table 1).

It is probable that soil populations are dependent
upon surface litter for a continuing supply of energy sub-
strates and that mobile larger animals play an important
role in this transfer of energy from litter into the soil.
In this connection, it may be noted that Chilopoda and
Coleoptera increased in September to much larger numbers
in soil under stalks than under cobs (Table l). Diptera
and Hymenoptera were also present and would have contrib-
uted to downward transport of substrates.

A unique feature of arthropod populations in Sep-
tember was the very large number of Acarina encountered
in soil under corn stalks. It is likely that these were
supported by substrates translocated from the litter by
the increased numbers of larger animals with which they

were associated.

65

Changes in Soil Nutrient Status

 

Soil tests for pH and extractable nutrients are

and NO , significant to

given in Table 9. Except for NH4 3

highly significant main effects and interactions were ex-
pressed.

Ammonium concentrations of 30 to 40 ppm were main-
tained through the season in soil under both litters. In
adjoining experimental areas, concentrations in excess of

10 ppm NH - N are rarely encountered in cultivated soil

4

after May due to rapid conversion to NO Here, in soil

3.
under litter and in the absence of growing vegetation to
remove it, nitrate nonetheless did not accumulate and re--
mained at low levels throughout the study periOd.
Exchangeable cations appeared in increasing con—
centrations in soil under litter as the season progressed
(Table 9). Calcium and magnesium accounted for most of
the increase during the study period. Since potassium in
plant materials is readily leached, its major movement
from the litter would have occurred during the winter and
spring before the first sampling. I

Exchangeable potassium was significantly higher

under cobs than under stalks. This relates to the fact

66

TABLE 9.--Soi1 nutrients and acidity under corn cobs and stalks in rela-
tion to sampling date.

 

 

 

 

Exchangeable .
. . Available
Litter Site Date p P“
NH -N NO -N K Ca M
4 3 g
----------------- ppm----—------------------—---
A. Soil Analyses (lZ-plot means)
Soil under May 22-24 39.93 1.34 105 347 69 7.3 5.90
b
0° 5 Jul 15-17 34.24 1.39 121 410 77 7.3 5.96
Sep 14-16 38.32 1.39 119 621 104 8.3 6.23
Soil under May 22-24 32.03 1.39 87 410 72 5.6 6.03
st 1ks
‘3 Jul 15-17 34.24 1.39 87 440 80 7.0 6.00
Sep 14-16 30.42 1.39 89 694 128 8.0 6.23
LSD (05) dates ns1 ns 8 72 6 .6 .06
within sites
LSD (05) sites ns ns 5 22 5 .3 .05
within dates
B. Probabilities (P) for significance of F
associated with replication, dates, sites and strata
Category df2
3
Replication 11/22 NS NS <.0005 1.000 <.0005 .022 <.0005
Dates (D) 2/22 NS NS .065 <.0005 <.0005 <.0005 <.0005
Sites (S) 1/33 .050 NS <.0005 <.0005 <.0005 <.0005 .001
SXD 2/33 NS NS < . 0005 . 009 < . 0005 . 002 . 031
1 . . .
ns = non-significant P (0.05)
2

df - category degrees of freedom/error degrees of freedom

NS = non-significant at P (0.10)

67

that the initial weight of litter at cob sites was 3-fold
or more greater than at stalk sites (Table 6).

Soil pH increased between the July and September
samplings (Table 9). This was due to a large net release
of calcium and magnesium. The accelerated release, at this
time, of basic cations suggests that marked qualitative
changes were taking place in the nature of organic mater-_
ials being translocated from the litter, as well as in the
residual humified materials appearing in soil through con-
tinued degradation of previously translocated materials.
It is to be expected that changes in concentration of
mineral species and in soil pH at local sites of animal '
and microfloral activity would have been much greater

than detected by gross soil analyses.

DISCUSSION

The animal populations which were observed here at
2-month intervals from May to September were similar in
many ways to populations which have been described in grass-
land, agricultural and forest soils. The numerically domin-
ant groups were Acarina and Collembola, present in numbers
well within the range reported by others (Curry, 1969a;
Davis, 1963; Dhillon and Gibson, 1962; Salt gE_31., 1948;
Wood, 1967a). The dominant Collembola species encountered

in this study, Isotoma eunotabilis, I. viridis and Entomo-

 

brya griseoolivata, are commonly found in Michigan in leaf

 

litter, grass sweepings and field soils (Snider, 1967).
Large arthropods were present in substantial num-

bers in all samplings. Many of these animals or their

progenitors would have made their initial invasion into

litter the previous fall. Although present in lower num-

bers than the mesofauna, the biomass of Diptera, Coleop-

I tera, and ChilOpoda would have been much greater (Edwards,

et al., 1970). Their activities in macerating litter,

68

69

translocating litter fragments and feces, and in develop-
ing subterranean passageways and living spaces would have
been an important factor determining the distribution of
the Collembola and Acarina (Wallwork, 1970).

The greatest numbers of Collembola were observed
in the litter in May, but in the soil not until July.
Many workers have reported seasonal maxima for Collembola
between late autumn and early Spring, declining to mini-
mal numbers in the summer months (Davis, 1963; Haarlov,
1960). The apparently later decline in Collembola popu-
lations in the present study may have been due to the un-
usually large quantities of litter present on the sampling
sites (Table 6). Dry matter present in the piles of cobs
in May was equivalent to 43 metric tons per hectare (19
tons English per acre). Stalks and leaves had not been
chopped or spread, and dry matter on the sites sampled
was equivalent to 17 tons per hectare (8 tons/acre).

The Collembola and'Acarina together comprised a
rather constant proportion of the total arthrOpod popula-
tion (90-97%). Within their combined total, however, the
proportion of Collembola declined (Fig. 8). It is tempt:
ing to infer that this reflects an antagonistic relation-

ship, Acarina preying on Collembola. However, since

70

predatory species are present in both groups, predation
preSsure could work to reduce numbers in either group
(MacFadyen, 1952; Sheals, 1956; Poole, 1959; Sharma and
Kevan, 1963a). Also, both groups have predators among
the Chilopods, Araneida and Coleoptera (Kevan, 1962;
Kfihnelt, 1961; Wallwork, 1970). Reproductive behavior,
life cycles and ecological successions must be considered,
as well as effects of changing temperature, moisture and
substrate availability (McMillan, 1969; Dhillon and Gib-
son, 1962; Weis-Fogh, 1948).

No simple explanation for the behavior of Collem-
bola and Acarina appears when their numbers are compared
with moisture and temperature in litter and soils (Fig.10).

It would appear that Collembola in the May sampling
were more tolerant of cool temperatures and high moisture
than the Acarina. In particular, Acarina appeared reluc-
tant to move into very moist soil at 12 to 13°C (cf.

Table 3).

Both groups had moved extensively into the soil
in July. The moisture content of the soil was now down
to field capacity (1/3 at m tension), and would probably

have been favorable for most animals considered in this

71

study. The negative temperature gradient from air to
litter to soil during this period of high summer temper-
atures was probably responsible for the marked shift from
litter to soil observed for most major groups in Tables 1
and 3 (Murphy, 1953; Bellinger, 1954; Poole, 1961; Dhil-
lOn and Gibson, 1962; Wallwork, 1970). The diurnal traf-
fic of larger animals between soil and litter would have
served to maintain a substrate supply for the smaller
forms in the soil (Cloudsley—Thompson, 1964).

Temperatures were somewhat cooler in September,
but the air-litter-soil gradient was such that a larger
proportion of animals were still found in the soil than
in the litter (Table 3). The temperatures were not low
enOugh to have interfered with growth or reproduction in
Collembola (Hale, 1965a, b; Sharma and'Kevan, 1963 a, b).
Collembola do have high moisture requirements (Mayer,
-1957; Christiansen, 1964), however larger numbers of Col-
lembola were found in the slightly drier soil under corn
stalks (Table 5).

Thus it would appear that factors other than
IMDisture and temperature were involved in this late sea-

son decline in Collembola. The low juvenile/adult ratios

72

suggest that reproductive activity was low and that Collem-
bola poPulations were declining in vigor, perhaps due to
exhaustion of apprOpriate substrates.

It has been pointed out by McMillan (1969) that
effects of temperature and soil moisture on Acarina num-
bers frequently cancel one another out because the two are
usually highly and negatively correlated. Both Acarina
and Collembola species appear to have similar requirements
for high moisture (humidity) but Acarina may prefer some-
what higher temperatures. This difference in temperature
response would explain the behavior of the two groups in
May but not in September.

There was a marked increase in exchangeable bases,
accompanied by a small but highly significant increase in
soil pH in September (Table 9). These gross changes likely
reflect much more drastic microenvironmental changes, per-
llaps directly beneficial to Acarina, but also indicative of
Czhanges in the nature of organic materials being decomposed
.Ln.the litter or in the soil. In other words, degradation
tuna proceeded to a point where net mineralization of min-
erals could proceed. Readjustments in microfloral popula-

tions might be expected at this time.

73

For example, fungi normally initiate decomposition
of plant materials and are later superceded by bacteria and
streptomycetes. Increasing pH would favor this succession.
Many species of Collembola are grazers on fungi, whereas
Acarina are incompatible with large fungal populations
(Kevan, 1962; Wallwork, 1970). It has been noted by Curry
(1969c) that Acarina appear in large numbers during later
stages in decomposition of grass herbage.

Changes in C/N ratio during decomposition of plant
materials provide a gross index of the degree of decomposi-
tion and of energy balance in relation to net immobilization
or net mineralization of mineral nutrients, notably N.

Net immobilization of N occurs during early stages
of decomposition of plant residues containing less than
1.2% N and frequently with residues containing up to 1.8% N
(Bartholomew, 1965; Harmsen and Kolenbrander, 1965).

Critical C/N ratios for different plant materials
\rary with the energy availability of carbonaceous constit-
Iaents. Net immobilization will be associated with nar-
rower C/N in materials containing a large proportion of
' carbohydrates (cellulose, hemicellulose) than in materials

5J1 which a substantial proportion of the carbon is present

74

as lignin. The physical properties and chemical nature of
lignin make it relatively much less accessible for enzymatic
degradation and lead to a much lower yield of energy to the
microflora. The dilution of available energy associated
with increasing lignin content reduces the size of the mi-
crobial population which can develop and its requirements
for N and other nutrients.

Because of these variations in the availability of
energy due to varying lignin content, critical C/N ratios
for net immobilization 25. net release of mineral N vary
over a range of about 25 to l to 35 to l.

The nature of organic components in the two litter
materials was not examined. Such determinations will be
necessary in more critical studies. The differences in C/N
ratios of the two litters during the study period (Table 6,
Fig. 10) were probably influenced both by differences in
‘their initial composition and by the probability that the
(corn cobs had lost more dry matter, hence more carbon, dur-
ing the fall, winter and spring prior to the May sampling.
TPhe low N content and wide C/N ratio of both litter mater-
.Lals (Table 6) would have led to extensive immobilization

0f both NH and NO

4 3, at least in May, if they had

75

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

aoeraoo LITTER .. LITTER
30 -* 60 "
O
.4
20 + 40 connect T coutuaou
— W
. O
‘I' 5 I0 -- 20 ° 0 \
2 ,J‘ ACAg/NA A MAR/Iva A
O ‘ A //\
o X
x < «IL | b
( 350 00 SOIL I SOIL
E a
55 In 40» so 4+
0 :’I
< o
0 30.. 50 .I couuaou
COLLEUBOLA o
O
20 .. 40 «-
[CIR/NA
'0 " 2° ACAR/fll "
0 A/ l 4 A/ 1 L
55 IF 25 LITTER «~ . A\LITTER
rupsmrm N A
A 6:” O 9
45 «F 20 -»
A o
0 CW \0
0 25 -I- l0 T
9 g L l l 1 l l
t- a A
< ~2
a: < __ o
I3.04~300 SOIL» » SOIL Is.
2 {5 3; ”0’3"”?! l o 30/2 Ala/s run: m
.. a.
o film-25 _ .. °Y ~I6 g
7 UP RAN/RE
’- E\ E can/7 ,A ('7,
l2.0 - t .. °\A - l4 5
\A 2
\o
' I.5'I _ J» /” L\: . '2
A .J
II.0- ° I -~ - I08
MAY 22-24 JULY I5-I7 SEPT. l4-l6 MAY 22-24 JULY I5- I? SEPT I4-I6
DATE
CORN COBS SITE CORN STALKS SITE
FIG. 10. NUMBERS 0F COLLEMBOLA AND ACARINA IN LITTER AND SOIL UNDER LITTER (ABOVE) IN RELATION To

LITTER AND SOIL PARAMETERS AT SITES ASSOCIATED WITH CORN COBS (LEFT) AND CORN STALKS (RIGHT).

76

been plowed down or otherwise incorporated into the soil.
Increasing N contents and decreasing C/N ratios (Table 6)
indicate that energy balances within the litter layer
were, in fact, favorable for net immobilization of N in
both litter materials.

In the soil under both litters, however, NH4
accumulated and was maintained at unusually high levels
through the 5-month period of the study (Table 9). This
indicates that the organic materials actually being
translocated into the soil were different than the bulk
of the materials in the litter. [Their energy content had
been reduced to the point where further decomposition
could proceed without net immobilization of N. It appears
reasonable to infer that much of the translocated organic
matter was delivered in the soil as feces and that its
average energy content had been substantially reduced by
Iearlier decomposition in the litter layer and during pas-
ssage through the digestive systems of transporting animals.

The temporary isolation of surplus energy in sur-
face litter serves to minimize direct competition between

decay populations and the roots of plants. Animals in

Emach syStems play a number of roles. Among these would

77

appear to be the translocation into the soil of organic
materials substantially reduced in energy and/or enriched
in minerals, so that further decomposition is accompanied
by net release of minerals in the root zone.

Animals themselves contribute to the diSsipation
of energy from translocated organic materials. However,
microbial decay populations acting directly on the litter,
and gut microflora must be credited with the major release
(Edwards, gt_al., 1970). There is also the probability
that animals may feed selectively on certain components
of the litter, or that they may draw upon both litter and
soil, to balance their requirements for minerals and
energy.

In situations where macrofauna are present, it is
likely that the mesofauna play somewhat different roles
than when larger animals are absent or present in small
.numbers. In the present study, the total of Acarina plus
Collembola tended to vary with, and as a fairly constant
;pr0portion of, the total arthropod population. This sug-
Igests that the two groups occupied similar niches in re-
ilation to the total pOpulation. One important role would

11a as secondary decomposers, feeding on feces distributed

78

through the litter and in the soil by more mobile larger
animals.

In relation to immobilization-mineralization
balance, coprophagous species would be important in re-
ducing energy/mineral ratios.

Although an energy balance favoring net release
of NH4 was maintained in the soil, nitrate did not accum-
ulate (Table 9). In many forest soils, nitrate does not
appear because nitrifying bacteria are inhibited by cer-
tain water-soluble compounds (polyphenols in particular)
which enter the soil from the canopy or from decomposing
surface litter (Messenger et_al., 1972). However, the
fact that ammonium did not increase from one sampling to .
the next and that nitrate was present in detectable quane
tities suggests that an active nitrifying populationpwas
present. It then becomes necessary to postulate that ni-
trate and/or nitrite were removed as rapidly as formed,
by re-assimilation or by chemical and/or biological de-
nitrification (Broadbent and Stevenson, 1966; Frederick
and Brdadbent, 1966).

Soil organisms do not assimilate nitrate readily

if ammonium is also present, since ammonium is preferred

79

by most microflora. Thus, denitrification appears the
most likely explanation for failure of nitrate to accum-
ulate. One implication of this conclusion is that sub-
stantial quantities of nitrogen carried over in litter
from the previous crop was recycled back into the atmos-
phere. Another implication is that a crop growing in the
presence of surface litter may be maintained on ammonium
rather than nitrate nutrition for substantial portions of
its growth period, and this may influence its requirements'
for other nutrients (Thompson, 1966).
Another factor which may influence crOp perform-
ance under no—till or trash mulch management derives from
the fact that surface mulches decompose much less rapidly
than the same materials incorporated into the soil.
Slowér decomposition delays the release of mineral nu- '
trients carried over in residues from the previous crop,
even when energy balances favor net mineralization.

In the present study, rapid release of Ca and Mg
did not occur until September (Table 9). Phosphorus re-
leased by this time would have been of no consequence to

a growing crop. Such effects on the seasonal pattern of

:release of recycling nutrients can influence materially

80

the fertilizer requirements of a crop, as well as appro-
priate placement and time of application.

Decomposition of litter and release of nutrients
take place rapidly in mull litters which supply energy
materials and nutrients favorable for development of large
macrofaunal pOpulations. Organic materials are translo-
cated in larger quantities and to greater depths in min-
eral strata under mull than in mor situations where animal
populations are principally Acarina and other meso- or
microfauna. Large animal activities are reflected by much
more friable, well-aggregated structure in the upper min—
eral horizons of mull soils (Wood, 1967b; van der Drift,
1970).

By analogy, under conditions of no-till or trash
mulch management, it can be expected that the rapid re-
lease of carryover nutrients and beneficial effects on
soil structure will depend on activities of larger animals
(earthworms, macro~arthropods). Mesofauna and microfauna,
and their interactions with the microflora cannot be ig-
nored, however, since these are responsible for actually
dissipating much of the energy carbon. Dissipation of

carbon is the essential process whereby mineral nutrients

81

tied up in organic residues are concentrated to the point
where net release of the nutrients in forms available to
the succeeding crop can occur.

Minimum tillage concepts, including non—tillage,
are being adopted rapidly by U.S. farmers in many areas..
It becomes important to examine the roles of soil animals
in such systems and to assess the effects of management
practices such as chemical pest control on important ani-
mal groups. An attempt was made here to identify impor-
tant groups and to point out probable functional relation-

ships for future investigation.

CONCLUSIONS

An important factor in successful application of
no-till management concepts has been the development of
chemical methods for control of weeds and of disease and
insect pests. The use of chemicals to control insect
pests can result also in the elimination of beneficial
soil animals. Therefore, it becomes important to iden-
tify beneficial animals and evaluate their roles so that
rational judgments can be made regarding probable benefits
and hazards from pest control practices.

The preliminary nature of the present study does
not support any generalized conclusions. The data do
draw attention to several aspects of animal activity and
fauna-microflora interaction which warrant critical in-
vestigation.

1. Relation of Macroarthropods
to Soil Structure
The role of earthworms in generating soil struc-

tures favorable for development and function of plant

82

83

roots in agricultural soils has been and continues to be
studied intensively. Earthworms were not numerous in the
study area, and this is frequently the case in cultivated
soils.

Fairly large numbers of Chilopods and larvae of
Coleoptera and Diptera were encountered. These animals
include active burrowers. The nature of macroarthrOpod
effects on soil structure under litter from agricultural
crops and the extent to which these effects influence
root distributions need to be examined and evaluated.

2. Material Transport
by Macroarthropods

Increases in soil carbon over the 5-month period
of this study indicate that as much as a ton per hectare
of organic material was translocated into the top 5 cm of
mineral soil. Under trash mulch systems of management,
soil-litter animals are the principal agents for incorpor-
ation of crOp trash into the mineral soil. The rate of
translocation and the depth of incorporation will deter-
mine, very largely, the distribution of recycled mineral
nutrients in the root zone and the seasonal pattern of

their release.

84

CrOps characteristically develop shallower root
systems under surface trash than in plowed soil. Altered
moisture and temperature relationships are involved. How-
ever, the distribution of recycled nutrients and the na-
ture and stability of favorable soil structures are prob-
ably overriding factors determining root distribution.

It appears important to assess the material
transport capabilities of important macroarthrOpods and
to evaluate management practices which may influence this
activity.

3. Population Structure and
Dynamics in Relation to
Dissipation of Carbon and
Cycling of Mineral Nutrients

Together, Acarina and Collembola comprised 90 to
97% of the animals counted in this study. Changes in num-
bers and vertical distribution of this mesofaunal compon-
ent paralleled changes in dominant groups in the macro-
fauna. It was inferred that the distribution of Acarina
and Collembola was determined mainly by the distribution
of substrates deposited as feces and litter fragments by

mobile larger animals. In particular, large soil popula-

tions of Collembola and Acarina were probably maintained

85

on substrates transported by the diurnal traffic of
larger animals between litter and soil.

Thus, the mesofauna would have entered into the
decomposition process as secondary decomposers. The res-
piratory capacity of these small animals, per unit bio-
mass, is much greater than that of larger animals. Their
activities represent an important stage in the dissipation
of carbon and enrichment of residues with N and other min-

erals which must precede net release of mineral nutrients

 

El!
(
I

available to plants. Coprophagy would be among the impor-
tant mechanisms for stepwise dissipation of surplus energy.
Experimental designs and modeling concepts for
studying population structure and dynamics in relation to
cycling of energy and nutrients are being developed, but
mainly in relation to non-agricultural litter associa-
tions. Similar studies are needed in relation to agri-

cultural crOps and management practices.

4. Fauna-microflora Interactions

A striking feature of the mesofaunal population
in the present study was the apparent progressive re-
placement of Collembola by Acarina as decomposition

proceeded. The appearance of Acarina in increased

86

numbers at advanced stages of decomposition has been re—
ported by others.

An important interaction with the microflora may
be involved. Thus, Collembola are known to graze on
fungi, whereas Acarina are adversely affected by large
fungal populations. Fungi normally initiate the decompo-
sition process and are later superceded by bacteria and
streptomycetes.

Studies of the parallel changes in fauna and
flora associated with varying stages of decomposition
have not been reported and were not attempted here.

They should prove informative. In such studies, changes
in minerals and pH should be considered. In the Septem-
ber sampling of this study, large decreases in Collembola
and increases in Acarina were associated with a large re-
lease of basic cations and an increase in pH. Increasing
pH, magnified in microhabitats, would favor a microfloral

succession from fungi to bacteria and streptomycetes.

 

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