effect of crop rotation and cropping intensity on …

The Pennsylvania State University

The Graduate School

College of Agricultural Sciences

EFFECT OF CROP ROTATION AND CROPPING INTENSITY ON

PHYSICAL INDICATORS OF SOIL QUALITY

A Thesis in

Soil Science

by

Wesley J. Neal

© 2009 Wesley J. Neal

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science

May 2009

ii

The thesis of Wesley J. Neal was reviewed and approved* by the following:

Sjoerd W. Duiker

Associate Professor of Soil Management and Applied Soil Physics

Thesis Advisor

Douglas B. Beegle

Professor of Agronomy

Daniel D. Fritton

Professor Emeritus of Soil Physics

Gregory W. Roth

Professor of Agronomy

David Sylvia

Professor of Soil Microbiology

Head of the Department of Crop and Soil Science

*Signatures are on file in the Graduate School.

iii

ABSTRACT

Soil quality is “the capacity of a soil to function, within ecosystem and land use

boundaries, to sustain biological productivity, maintain environmental quality and

promote plant and animal health.” The objective of this study was to evaluate the

effect of crop rotation and cropping intensity on several physical indicators of soil

quality. Physical soil quality factors measured were soil organic carbon content, bulk

density, aggregate stability, hydraulic conductivity, water retention, and soil

plasticity. The research trial was performed at the Penn State Southeast Research and

Extension Center in Landisville, Lancaster County, Pennsylvania (40° 2′ 23″ N,

76° 18′ 16″ W) from 2003 to 2007 on a well-drained Hagerstown silt loam (Fine,

mixed, semiactive, mesic Typic Hapludalfs). Crop rotations were corn monoculture

with winter fallow period, soybean/corn single crop rotation with winter fallow

period, corn double-cropped with rye, corn double-cropped with barley, soybean/corn

rotation double-cropped with rye, and alfalfa. All crops were harvested for silage

except soybeans. Effects of crop rotations and crop intensification on soil quality

were limited to the top 5 cm of the soil, with no significant effects in the 5-30 cm

depths. Corn monoculture resulted in low bulk density, high hydraulic conductivity,

and low aggregate stability. The soybean/corn single crop rotation led to higher bulk

density and lower hydraulic conductivity than corn monoculture, but similar

aggregate stability. Alfalfa resulted in higher aggregate stability than corn

monoculture, but had similar bulk density and lower hydraulic conductivity than corn

monoculture. Soil organic carbon content was not affected by rotation. Addition of

rye as a double-crop only improved aggregate stability when grown as a double-crop

with corn monoculture. Double-cropped barley did not result in any significant

improvement in measured parameters. The results of this study suggest limited

potential for soil quality improvements with cropping intensification and crop rotation

diversification when most above-ground biomass is harvested.

iv

TABLE OF CONTENTS

List of Tables………………………………………………………………………… v

Chapter 1. INTRODUCTION........………………………. ………………………..... 1

Soil Organic Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Bulk Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Aggregate Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Plasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Hydraulic Conductivity and Water Retention . . . . . . . . . . . . . . . . . . . . . . . . . 4

Use of Double Cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Chapter 2. MATERIALS AND METHODS. . .. . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 7

Field Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Sample Collection . . . . . . . . . . . . . . . . …………. . . . . . . . . . . . . . . . . . . . . .9

Laboratory Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Chapter 3. RESULTS AND DISCUSSION. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .13

Soil organic carbon .. . . . ……………….. .. .. ……………… .…………… 13

Bulk Density. . . . . . . . . . . ……………. .…………………………………. 16

Aggregate Stability…… ……………. . . . . . ……………………………… 19

Soil Plasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Hydraulic Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Water Retention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Chapter 4. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . 29

Appendix : Crop Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

v

LIST OF TABLES

Table 1. Crop rotation effect on soil organic carbon . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 2. Crop rotation effect on bulk density . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 16

Table 3. Crop rotation effect on aggregate stability . . . . . . . . . . . . . . . . . . . . . . . . .19

Table 4. Crop rotation effect on soil plasticity index, plastic limit, and liquid limit 22

Table 5. Crop rotation effect on hydraulic conductivity . . . . . . . . . . . . . . . . . . . . . . 23

Table 6. Crop rotation effect on pores of diameter 150 - 50 µ m and pores of

diameter 25 - 16.6 µ m. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Table A1. Corn management (population, tillage dates, planting dates, harvest dates,

fertilizer and pesticide timing and amount) . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table A2. Alfalfa management (population, tillage dates, planting dates, harvest

dates, fertilizer and pesticide timing and amount) . . . . . . . . . . . . . . . . . . . . . 39

Table A3. Soybean management (population, tillage dates, planting dates, harvest


Table A4. Barley management (population, tillage dates, planting dates, harvest


Table A5. Rye management (population, tillage dates, planting dates, harvest dates,

fertilizer and pesticide timing and amount) . . . . . . . . . . . . . . . . . . . . . . . . . . 42

1

Chapter I. INTRODUCTION

Doran and Parkin (1994) defined soil quality as “the capacity of a soil to

function, within ecosystem and land use boundaries, to sustain biological

productivity, maintain environmental quality and promote plant and animal health.”

Physical soil quality factors include soil organic carbon content, bulk density,

aggregate stability, hydraulic conductivity, water retention, and soil plasticity.

Soil Organic carbon

Soil organic carbon (SOC) content is affected by carbon inputs and losses.

Carbon inputs include compost, manure, and crop residues. Because crops return

varying amounts of crop residue, crop rotation is expected to influence organic

carbon content. Higher SOC content was observed after years of continuous corn

than in a corn-soybean rotation (Oelbermann et al., 2006; Hao et al., 2002). This can

be attributed to higher residue input from corn (Dolan et al., 2006) and faster break-

down of soybean residue (Jagadamma et al., 2007). In a study by Varvel (2006), on

the other hand, corn-soybean rotations had similar SOC content as continuous

soybeans, but winter cover crops in both rotations resulted in the highest SOC.

Kaspar et al. (2006), however, found that the main effects of cover crops on soil

quality were not significant. A rye cover crop after corn increased SOC relative to

the control in the soybean phase, but decreased soil carbon relative to the control in

the corn phase. Varying root systems can also affect organic carbon. Perennial crops

2

such as alfalfa and grasses have been reported to transfer more photosynthate to their

root system than annual corn (Zan et al., 2001). Increased soil organic carbon after

perennials compared with annuals is attributed to their higher root-to-shoot ratios,

die-down of part of the root system after cuttings (Su, 2007), and lack of disturbance

of the soil (Frank et al., 2006), indicating alfalfa has the potential to increase SOC

over corn monoculture due to root system effects. Jiang et al. (2006), however, found

a decrease in soil organic carbon in unfertilized alfalfa-grasslands on a short timescale

up to 19 years, at which point SOC increased.

Bulk density

Bulk density (the mass of the soil per unit volume) is an important measure of

soil quality as an indication of either porous or compacted soil. Bulk density

typically decreases with greater crop residue input due to its stimulation of biological

activity (Franzluebbers and Brock, 2007) and is inversely related to SOC content

(Naderman et al., 2004; Yang and Kay, 2001; Dolan et al., 2006). Continuous corn

tends to produce more residue than soybean/corn rotations and thus may result in

lower bulk density than soybean/corn rotations (Karlen et al., 1994). Double-crops

also have the potential to lower soil bulk density. Addition of a rye cover crop to a

no-till soybean/corn single crop rotation may result in lower bulk density as compared

to the corn/soybean single crop rotation (Villamil et al., 2006). Duiker and Curran

(2005) found that rye killed in late boot stage could reduce bulk density. Crop

rotations with alfalfa can have higher SOC content and lower bulk density as

3

compared to continuous corn and corn/soybean single crop rotations (Russell et al.,

2006; Su, 2007).

Aggregate stability

Aggregate stability refers to the ability of soil peds to resist disintegration

from raindrop impact and mechanical manipulation such as tillage (Jury and Horton,

2004). Organic matter has been observed to improve aggregate stability (Boix-Fayos

et al., 2001). Plant roots and hyphae are also known to stabilize aggregates (Tisdall

and Oades, 1982). Effects of crop rotation on aggregate stability will depend on the

ability of crop roots to penetrate and stabilize the soil and the amount of decaying

roots. High-residue crops as well as cover crops are expected to increase aggregate

stability (Villamil et al., 2006; Franzluebbers and Brock, 2007; Sousa Neto et al.,

2008). Aggregate stability is expected to be greater in alfalfa than continuous corn

while continuous corn is expected to result in greater aggregate stability than a

corn/soybean rotation since there is less residue following soybeans (Perfect et al.,

1990; Karlen et al., 1994).

Plasticity

Soil plasticity is an indicator of soil tilth and its sensitivity to compaction. The

plastic limit of a soil is that moisture content above which soil can just be molded into

different forms and shapes. At the liquid limit, soil particles begin to slide over one

4

another and the soil exhibits flow like a liquid. Soils with a high percentage of fine

particles (clay) exhibit considerable plasticity (Baver, 1930). Because soils with high

organic matter content can absorb larger amounts of water before reaching the plastic

limit, crop rotations are expected to impact plasticity indexes (Smith et al., 1985;

Zhang, 1994; Baver, 1930).

Hydraulic Conductivity and Water Retention

Hydraulic conductivity is influenced by pedogenic structure, parent material

composition and mineralogy, depth and degree of soil development, and hillslope

position (West et al., 2007). Hydraulic conductivity is greater in soils that are highly

porous, fractured or aggregated than in soils that are compacted; these conditions can

be affected by the type of decayed roots that have left channels in the soil (Hillel,

1971). Crop rotations and cover crops will affect hydraulic conductivity by

influencing pore space and soil structure. Soybeans tend to produce higher hydraulic

conductivity than corn due to rooting patterns, amount and quality of residue, and

stimulation of faunal activity (Blanco-Canqui et al., 2004; Villamil et al., 2006).

Alfalfa has the potential to create macropores after decomposition (Kavdir et al.,

2005).

Porosity also affects water retention. The largest pores will empty first

followed by smaller and smaller pores as more tension is applied (Scott, 2000). Soil

organic matter content was found to be directly proportional to macroporosity

(Silveira Neto et al., 2006). Porosity between corn monoculture and a soybean/corn

5

single crop rotation did not vary, but soybean/corn single crop rotations had higher

available water content than a corn monoculture treatment (Wahyuni, 1994). The use

of double-cropping can result in both more macropores and larger functional pores

(Carof et al., 2007; Villamil et al., 2006). Macropore presence can increase through

use of a corn/barley double-crop under no-till as compared to corn monoculture under

no-till (Carter et al., 2002).

Use of Double-Cropping

Double-cropping is the practice of growing two crops in sequence in the same

field in the same year. This practice may have important benefits. Greater

production per unit of area and time may result because of elimination of fallow

periods. The use of multiple crops may also provide opportunity to improve soil

quality over time. Rye is a crop that can be double-cropped in Pennsylvania after

corn silage or soybean harvest. It is the most cold-tolerant winter cereal available,

adept at growing quickly in the fall and tolerating winter conditions. Rye is also

capable of taking up unused soil nitrogen, preventing nitrogen loss to groundwater

(Sustainable Ag Network, 1998b; Brandi-Dohrn et al., 1997). Rye is also noted as an

excellent source of organic matter. It is capable of producing up to 10,000 lbs/acre

dry matter, while 3000 – 4000 lbs/acre is typical in the Northeast (Sustainable Ag

Network, 1998b; Gusta et al., 1997). Rye could therefore have a positive impact on

soil quality. An alternative to rye is barley. Barley is noted to be inexpensive and

easy to grow. Barley is not as winter hardy as rye but may provide a different option

6

as a forage crop (Sustainable Ag Network, 1998a).

The first objective of this study was to evaluate the effect of common forage

crop rotations on soil quality due to differences in crop properties and rotations. The

second objective was to evaluate the effect of cropping intensity through

implementation of a double-cropping system.

The first hypothesis was that the main crops would affect soil quality in the

order alfalfa>corn monoculture>corn/soybean single crop rotation. Second, double-

cropped small grains grown during the winter fallow period were expected to improve

soil quality through increased plant residue and increased root activity.

7

Chapter II. MATERIALS AND METHODS

Field Data

The research trial was performed at the Penn State Southeast Research and

Extension Center in Landisville, Lancaster County, Pennsylvania (40° 2′ 23″ N,

76° 18′ 16″ W) from 2003 to 2007. The average winter temperature (mid-December

to mid-March) is -0.5 o

C, whereas the average summer temperature (mid-June to mid-

September) is 22.2 oC. The average annual precipitation is 109 cm, of which 56%

falls from April to September (Custer, 1985). All crops were established using chisel

plowing and disking in the first year, but no other tillage was done after that. The

field was managed with chisel/disk tillage prior to this experiment and had received

manure in the past, but no manure was applied after the trial started. The plots were

located on a soil mapped as a well-drained Hagerstown silt loam (Fine, mixed,

semiactive, mesic Typic Hapludalf) with 0 – 3 % slope (Custer, 1985). In reality, the

soils exhibited more variability, with alluvial soils found at the toe-slope (bottom two

replications of the trial). However, the variability found was not expected to

dramatically affect the results of the trial. The crops grown included corn (Zea mays

L.), soybeans (Glycine max [L].Merr.), alfalfa (Medicago sativa L.), barley (Hordeum

vulagre L.) and rye (Secale cereale L.). Treatments were corn monoculture with a

winter fallow period, soybean/corn single crop rotation with a winter fallow period,

continuous alfalfa, corn with a winter rye double-crop, corn with a winter barley-

double crop, and a soybean/corn rotation with a winter rye double-crop.

The trial was laid out as a randomized complete block design with four

8

replications with each plot measuring 9 m long by 3 m wide. Blocks were

perpendicular to the slope. Crop planting and establishment dates were dependent on

harvest date of the preceding crop.

Crop management data is presented in tables A1-A5 in Appendix A. Corn,

rye, and barley were harvested for silage. Corn harvest height was approximately 15

cm above the soil surface. Alfalfa was harvested four times in 2003 and five times in

2004 and 2005. Soybeans were harvested for grain and post-harvest plant biomass

remained in the field. Corn was planted in 0.76 m rows, soybeans were planted in

0.38 m rows, and rye and barley were planted in 0.2 m rows.

Corn silage yields showed no difference between single and double-cropping

systems. Mean yields were 16.9, 18.3, and 15.2 Mg dry matter (DM) ha-1

in 2003,

2004, and 2005 respectively (Fouli, 2008). Soybean yields did not differ between

single and double-cropping systems in 2003 and 2005, with an average grain yield of

3.9 and 3.6 Mg ha-1

respectively. However, in 2004, double-cropped soybeans

yielded higher than single cropped soybeans, probably due to groundhog damage

early in the season (Fouli, 2008). Barley and rye silage yields were similar in 2004.

However, in 2005, rye planted after corn had higher yields than rye planted after

soybeans (Fouli, 2008). Barley after corn yields were not different from ryelage after

soybeans, but were lower than ryelage after corn (Fouli, 2008). The yields of 2006

were not recorded, although treatments were continued until soil samples were taken

for this study in spring of 2007.

9

Sample Collection

Soil samples were taken on 12 May 2007 and 3 June 2007. On the first

collection date, 5.4 cm diameter cores were taken with a hydraulically driven core

sampler and separated into 0-5 cm, 5-15 cm, and 15-30 cm depths. Cores were

removed from the sampler in one piece and then cut to their respective depths on site.

Three subsamples were taken in each plot (one sample approximately 1 m from each

end and a sample in the middle of the plot) between rows. This area was minimally

impacted by traffic from field operations. The samples were allowed to air dry before

any analysis began. The analysis conducted on these samples were bulk density,

aggregate stability, plastic and liquid limit, and organic carbon content.

On the second collection date, three 7.62 cm diameter x 7.62 cm deep cores

were collected in each plot by aluminum cores pounded into the ground with a hand-

held sampler; the sample locations were approximately 1 m from each edge of the

plot and one in the middle of the plot. The aluminum cores were driven into the

ground so that the top of the aluminum core was just below the soil surface. These

samples were refrigerated at 3.3 o

C for approximately one month before samples

were prepared as described below. When analytical tests were not being performed,

samples were returned to the refrigerator. To prepare the samples, the top of the

sample core was pushed downward so that the top of the soil core was flush with the

top of the metal ring and the remaining bottom soil was cut off with a knife.

Hydraulic conductivity tests and water retention analysis were performed on these

core samples.

10

Laboratory Analysis

Bulk density was measured with the core method (Blake and Hartge, 1986)

using the 5.4 cm diameter soil samples. Air dry samples were weighed, after which

moisture content was determined using a representative sample of approximately 10

grams dried in an oven at 105o C for 24 hours. The entire sample was then sieved

through a 2 mm sieve. Rock fragments greater than 2 mm were washed with water,

and all soil particles < 2 mm were removed from the fragments with sonic cell

dispersion. These rock fragment samples were then oven dried at 105 o

C for 24

hours, and weighed to correct the bulk density for rock fragment content. Bulk

density was calculated as (((Moist soil weight)*(1 – Moisture content)) – Rock

fragment mass)/(volume of soil – volume of rock fragments).

Aggregate stability was measured using the wet sieving method (Kemper and

Rosenau, 1986) using soil from the 5.4 cm samples that had been air-dried, ground,

and passed through a 2 mm sieve. This soil was sieved through a 1 mm sieve and the

soil and aggregates that did not pass through were collected. The 1-2 mm soil

fraction was then placed on a 0.25 mm sieve and placed in the dunking apparatus in

containers filled with distilled water. The samples were dunked in distilled water 30

times per minute for 3 minutes (2 cm amplitude). The soil that passed through the

sieve (called dunked soil) was dried for 24 hours at 105 oC and weighed. The soil left

on the sieve was dispersed with sonic cell disruption for 30 seconds. Soil that now

passed through the 0.25 mm sieve (called dispersed soil) was collected, dried at 105

oC and weighed. The percent stable aggregates was calculated as ((dispersed

11

soil)/(dunked soil + dispersed soil).

Hydraulic conductivity was assessed using the constant head method using the

7.62 cm diameter core samples (Klute and Dirksen, 1986). A second metal ring was

duct-taped to the top of the sampled core and then placed in the hydraulic

conductivity apparatus such that a 2.7 cm constant head of water was maintained

above the core. Percolating water was measured using a graduated cylinder every 15

minutes until it reached equilibrium. The saturated hydraulic conductivity (Ksat) was

calculated as Ksat=(Jw(b+L))/L) where Jw is volume flow through the sample, b is the

water head, and L is the length of the soil column.

Water retention was determined using the 7.62 cm diameter cores using

tension tables and pressure chambers. The tension tables measured water retention at

tensions of 10 cm, 30 cm, 60 cm, and 90 cm. The pressure chambers measured water

retention at 1/3 bar, 1 bar, and 15 bar pressures. Before placing the core samples on

the tension table, the cores were soaked in water for 24 hours and saturated weight

was recorded. Cores were allowed to reach equilibrium on the tension table at the

given tension and were then weighed. After weighing, samples were returned to the

tension table and the next tension was set.

Soil organic carbon samples were analyzed by dry combustion technique with

a Carlo-Erba © C-N Analyzer on soil samples taken from the 5.4 diameter samples

after being air-dried, ground, and passed through a 2 mm sieve (Nelson and Sommers,

1996). Samples used in combustion were approximately 40 µ g.

The plastic index was calculated using AASHTO procedure T-90 for the

plastic limit and procedure T-89 for the liquid limit. The plastic index was then

12

calculated by the following equation: PI = LL – PL.

Statistical analysis was performed using an analysis of variance test under the

general linear model (Minitab 15.1.3, 2008) by treatment, depth, and treatment x

depth interaction. Means were separated using the Tukey test at p < 0.05.

13

Chapter III. RESULTS AND DISCUSSION

Soil organic carbon

Soil organic carbon (SOC) concentrations did not differ between treatments at

any depth. However, SOC mass differed between treatments at the 0-5 cm depth,

although not at deeper depths (Table 1). The soybean-corn/rye double-crop rotation

and the corn/rye double-crop rotation had significantly higher organic carbon mass

than the corn/barley double-crop. The corn monoculture, the soybean-corn single

crop rotation and the alfalfa did not have different SOC mass from the other

treatments.

Table 1. Crop rotation effect on soil organic carbon content

Soil Organic

Carbon content

Crop rotation † 0-5 cm depth‡ 5-15 cm depth 15-30 cm depth

Mg Hectare-1

Mg Hectare-1

Mg Hectare-1

SB-R-CS 11.0 a 19.1 N/S 20.4 N/S

CS-R-CS 10.9 a 18.2 21.8

A 10.3 ab 18.4 22.2

CS 9.7 ab 19.1 20.4

SB-CS 9.6 ab 18.9 21.7

CS-BS-CS 8.6 b 18.2 20.4

p-value 0.033 0.647 0.739

† C = corn monoculture, SB-CS = soybean-corn single crop rotation,

A = alfalfa, SB-R-CS = soybean-corn/rye double-crop,

CS-BS-CS = corn/barley double-crop, CS-R-CS = corn/rye

double-crop

‡ Means followed by a similar letter are not significantly different at p<0.05

14

Oelbermann et al. (2006) and Hao et al. (2002) both reported higher SOC

after years of corn monoculture than in soybean-corn rotations, but this effect was not

seen here. The treatments may not have affected organic carbon mass because the

above-ground biomass of all crops except soybeans was harvested for silage.

Removal of above-ground biomass may result in nearly no change in SOC over many

seasons (Clapp et al., 2000). In a 13-yr corn monoculture treatment, SOC was only

maintained or increased when residue was returned (Wilhelm et al., 2004). Similarly,

Wilhelm et al. (2004) noted that relying only on no-tillage and un-harvestable plant

matter (roots, root exudates, and crowns) was insufficient to prevent carbon loss.

Wilhelm et al. (2004) also noted that the amount of residue required per year to

maintain SOC ranged from <1 Mg ha-1

yr in Montana to > 9 Mg ha-1

yr in Minnesota,

with studies indicating corn (stalks only) provides between 4.7 Mg ha-1

yr and 7.3 Mg

ha-1

yr (Larson et al., 1972; Allmaras et al., 2000). The small amount of plant matter

left behind after harvest in this study may not have been enough to maintain or

increase organic carbon content.

Multiple studies (Angers, 1992; Meyer-Aurich et al., 2006; Zhou et al., 2007)

report that continuous alfalfa results in higher carbon sequestration than continuous

corn, however in our trial alfalfa did not cause higher SOC mass than corn

monoculture or soybean/corn single crop rotation.

Varvel (2006) found that cover crops increased SOC content but that effect

was not seen here. Results were similar to Kaspar et al. (2006) in that the effects of

double-crops on SOC content were insignificant. The addition of rye to the soybean-

corn rotation resulted in higher SOC mass than corn monoculture at the p<0.1 level,

15

but not at the p<0.05 level. Villamil et al. (2006) found that adding a hairy vetch crop

at the end of a corn-rye-soybean-rye rotation would affect soil organic carbon, but

without the hairy vetch, there would not be enough nitrogen (even after soybean

harvest) in the soil to allow soil microbes to decompose rye and affect humified soil

organic matter. The authors concluded that rye was an excellent source of organic

matter, but without a good source of nitrogen, this organic matter would not be

converted into humified soil organic carbon. This factor, along with residue removal,

might explain why rye did not have an effect on soil organic carbon in the present

study.

The corn-barley double-crop rotation resulted in lower SOC mass than when

rye was used as a winter cover crop. The lack of effect of barley on SOC mass is

probably due to poor winter survival of barley compared with rye. Lower above-

ground biomass and, probably, below-ground root mass of barley compared with rye

may explain this different effect on SOC mass between the small grains. The lack of

effect of barley on SOC mass when double-cropped with corn may be due to delayed

planting of corn. The corn in both rye and barley double-crop rotations was planted

later than corn in the corn monoculture treatment. This may have resulted in a

smaller corn root system in double-crop corn compared to corn monoculture. The

vigorous rye crop that may have compensated for a smaller corn root system when

double-cropped in addition to the poor performance of barley may explain the

apparent detrimental effect of barley on SOC mass.

16

Bulk density

Bulk density was affected by treatment at the 0-5 cm depth (Table 2), but

differences were not observed at greater depths. The soybean-corn single crop

rotation had significantly higher bulk density than that resulting from the corn

monoculture, the corn/barley double-crop, and the corn/rye double-crop. The bulk

density in the soybean-corn/rye double-crop and alfalfa treatments did not have

significantly different bulk density from the other treatments.

Table 2. Crop rotation effect on bulk density

Bulk Density


g cm-3

g cm-3

g cm-3

SB-CS 1.24 a 1.35 N/S 1.40 N/S

A 1.22 ab 1.38 1.40

SB-R-CS 1.19 ab 1.38 1.40

CS 1.15 b 1.42

CS-BS-CS 1.12 b 1.33 1.42

CS-R-CS 1.12 b 1.33 1.40

p-value 0.001 0.455 0.941




double-crop


Bulk density tends to decrease with development of more porous structure,

which has been found to be correlated with organic matter content and decomposing

crop residue (Osuna-Ceja et al., 2006; Villamil et al., 2006). As reported by Karlen et

17

al. (1994) continuous corn resulted in lower bulk density than soybean/corn single

crop rotations which was attributed to the greater residue production of continuous

corn. However, in this trial all corn residue was removed in silage harvest. Russell et

al. (2006) and Su (2007) reported that alfalfa resulted in lower bulk density than corn

monoculture but there was no difference found in our trial. Jarecki et al. (2005)

found that bulk density did not differ between corn monoculture and an alfalfa

rotation (corn, corn, wheat-alfalfa, alfalfa) and attributed this to the lack of SOC

differences between the two treatments. Roseberg and McCoy (1992) did not find a

difference in bulk density between no-till corn and no-till alfalfa, similar to our study.

Because most crop residue was removed in silage harvest in this trial, root

systems would have been the major determinant of differences in bulk density.

Allmaras et al. (1975) found that soybean root length density (root length per volume

soil) was 50% to 80% of corn root length density in the Ap horizon. A larger root

length density could result in lower bulk density through larger pore creation upon

root decay. Alfalfa roots have a high turnover rate in the Ap horizon which was

found to be correlated to macroporosity (Rasse et al., 2000). In this study the effect of

the alfalfa root system on bulk density was no different from that in the corn or

corn/soybean rotations.

The double-cropped small grain crops did not significantly reduce soil bulk

density in this trial, although the corn-soybean rotation with double-cropped rye did

not have higher bulk density than corn monoculture (in contrast to the single cropped

corn-soybean rotation). Many studies cite increased organic matter input through

additional cover crops as a major reason for lower bulk density (Villamil et al., 2006;

18

Ram and Zwerman, 1960). It is possible that neither rye nor barley had an effect on

bulk density since both crops were harvested for silage. Crop residue returned from

the small grains to the soil was therefore limited to the stubble left after silage

harvest. Additionally, barley crop growth was poor, likely due to winter moisture or

temperature. Barley did not tolerate winter conditions as well as rye, especially in

2004 (Fouli, 2008). The limited duration of this trial may be another explanation of

the absence of double-crop effect on bulk density. The trial lasted five years, which

may not have been enough time for a difference to emerge. Finally, corn double-

cropped with small grains was established later than single-cropped corn (Table A1,

Appendix A). This may have resulted in a smaller corn root system than in the single

cropped systems. Although the double-cropped small grain added root biomass to the

soil, a smaller root system of the late-planted corn may have negated a significant

increase in root biomass in the double-cropped system compared to the single

cropped system. This may explain the negligible effect of the double-cropped small

grains on bulk density.

Our results were similar to those reported by Roseberg and McCoy (1992)

who did not find a difference in bulk density between no-till corn and no-till alfalfa.

The effects of a small grain crop on bulk density, however, differ from those reported

by Villamil et al. (2006) and Duiker and Curran (2005) who found that addition of a

rye or barley double-crop with residue return upon termination resulted in lower bulk

density than single crop treatments. Results seem to indicate that the return or

removal of residue may impact the effectiveness of the double-crop in regard to

improving soil quality.

19

Aggregate stability

Aggregate stability was affected by crop rotation at the 0-5 cm depth (Table

3), but not at greater depths. Alfalfa and corn/rye double-crop had the highest percent

stable aggregates. The corn monoculture, on the other hand, had the lowest percent

stable aggregates. Aggregate stability in the soybean-corn single crop rotation,

soybean-corn/rye double-crop and corn/barley double-crop did not vary from the

other treatments.

Table 3. Crop rotation effect on aggregate stability

Aggregate

Stability


% % %

A 67 a 66 N/S 59 N/S

CS-R-CS 66 a 67 57

SB-CS 64 ab 66 55

SB-R-CS 63 ab 62 51

CS-BS-CS 62 ab 66 49

CS 59 b 61 52

p-value 0.006 0.523 0.228




double-crop


Alfalfa resulted in higher aggregate stability than corn monoculture. Haynes

and Beare (1997) found that legume crops resulted in higher water stable aggregate

percentage than non-legume crops. The soil under legumes had proportionally higher

20

microbial biomass than non-legumes with similar root mass, had longer fungal

hyphae length, and also had higher viable bacterial numbers. Due to differences in

the amounts and types of organic compounds released by their roots, different plants

will have different rhizosphere populations. In legumes, organic matter from dying

roots and sloughed-off nodules has high nitrogen content which may result in high

microbial biomass (Haynes and Beare, 1997). The microbes in the rhizosphere

release polysaccharide and phenolic bonding agents that act as glue, which stimulate

soil aggregation (Haynes and Beare, 1997). Alfalfa is a legume crop, which may

explain the higher aggregate stability compared to continuous corn. The soybean/corn

single crop rotation may not have experienced the full effect of a legume crop on

aggregate stability because soybeans were rotated with corn.

Addition of a double-crop is generally expected to improve soil aggregation

due to an increase in residue return and increased root mass (McVay et al., 1989;

Villamil et al., 2006). In our trial, corn double-cropped with rye had higher aggregate

stability than corn monoculture, showing the positive effect of the winter crop on

aggregate stability. However, the winter crop did not affect aggregate stability in the

other rotations. In 2005, rye planted after corn had higher yields due to an earlier

planting date than rye after soybeans. Barley yields were lower than rye yields due to

its lower ability to accommodate winter conditions (Fouli, 2008). Lower above-

ground biomass yields probably reflect smaller root systems. Smaller root systems

would have less of an impact on aggregate stability and may also explain the lack of

effect of winter cover crops on aggregate stability in the corn-soybean/rye and

corn/barley double-crop rotations.

21

Soil plasticity

None of the plasticity measures were affected by treatments at any depth

(Table 4). The plastic limit, liquid limit, and plasticity index did not significantly

increase by depth between the 0 – 5 cm depth and the 5 – 15 cm depth, or the 5 – 15

cm depth and the 15 – 30 cm depth.

22

Table 4. Crop rotation effect on soil plasticity index, plastic limit, and liquid limit

Plasticity Index

Crop rotation † 0-5 cm depth 5-15 cm depth 15-30 cm depth

% % %

A 8.8 N/S 7.4 N/S 4.1 N/S

CS-R-CS 6.9 6.7 5.2

SB-R-CS 6.6 6.2 8.7

SB-CS 6.4 4.4 8.2

CS-BS-CS 6.2 7.1 8.8

CS 5.8 6.6 6.6

p-value 0.730 0.647 0.499

Crop rotation effect on plastic limit

Plastic Limit


% % %

A 24.6 N/S 24.0 N/S 25.7 N/S

CS-R-CS 27.2 25.8 25.5

SB-R-CS 26.5 26.1 22.0

SB-CS 26.3 24.6 23.7

CS-BS-CS 25.8 24.2 21.0

CS 26.9 25.8 24.0

p-value 0.539 0.095 0.084

Crop rotation effect on liquid limit

Liquid Limit


% % %

A 33.4 N/S 31.4 N/S 29.9 N/S

CS-R-CS 34.1 32.6 30.7

SB-R-CS 33.2 32.3 30.7

SB-CS 32.7 32.4 29.9

CS-BS-CS 32.0 31.4 29.8

CS 32.7 32.4 30.6

p-value 0.245 0.469 0.736




double-crop

23

Hydraulic conductivity

Corn monoculture, corn/rye double-crop, and corn/barley double-crop resulted

in the highest hydraulic conductivity (Table 5). None of these three treatments were

significantly different from each other. Alfalfa and the soybean-corn single crop

rotation had significantly lower hydraulic conductivity than corn monoculture. The

use of double-cropping did not affect hydraulic conductivity.

Table 5. Crop rotation effect on hydraulic conductivity

Crop rotation † Hydraulic conductivity‡x

ksat value (cm hr-1

)

CS 9.88 a

CS-BS-CS 6.09 ab

CS-R-CS 5.30 ab

A 5.17 b

SB-CS 4.58 b

SB-R-CS 4.10 b

p-value 0.006




double-crop

‡ Means followed by a similar letter are not significantly different at p<0.05 x Measured on surface 7.62 cm

Soybeans tend to produce higher hydraulic conductivity than corn due to

rooting patterns, amount and quality of residue, and stimulation of faunal activity

following legume crops (Blanco-Canqui et al., 2004; Villamil et al., 2006). Instead,

soybeans and alfalfa resulted in lower hydraulic conductivity than corn monoculture

in our study. Villamil et al. (2006) suggested that soybeans result in the highest

24

hydraulic conductivity values due to greater stimulation of faunal activity than corn,

but sampling after the corn phase of the soybean-corn rotation may have resulted in

lower hydraulic conductivity values compared to corn monoculture than if sampling

was done after the soybean phase.

Hydraulic conductivity is most likely influenced by macropore formation,

macropore presence in the soil, and bulk density (Blanco-Canqui et al., 2004). There

is evidence that microorganisms stimulated by legumes can clog pores or disrupt

continuous pores, which may explain the lower hydraulic conductivity under legumes

(Fahad et al., 1982; McCalla, 1951). Kavdir et al. (2005) reported that when alfalfa

was terminated in the early spring, hydraulic conductivity increased by July. Results

for alfalfa may have been different in the current trial if alfalfa had been terminated

and allowed to decompose somewhat before sampling since there is evidence that the

real benefits of alfalfa with regard to hydraulic conductivity occur upon

decomposition.

Double-cropping did not have an effect on hydraulic conductivity. The

addition of cover crops can result in larger functional pores due to root activity as

compared to treatments with no cover crops. However, this does not necessarily

result in a change in hydraulic conductivity values (Carof et al., 2007;Villamil et al.,

2006). Corn monoculture, corn/barley double-crop, and corn/rye double-crop

resulted in the highest hydraulic conductivity, but this seemed to be a function of the

primary crop (corn) because none of these three treatments were significantly

different from each other.

25

Water Retention

Water retention results were not significant at the p<0.05 level. Total porosity

did not differ between treatments. Water retention analysis indicated that the

corn/barley double-crop had a greater percentage of pores of size 150 µ m to 50µ m

than the alfalfa treatment at the p<0.10 significance level (Table 6). Alfalfa had a

greater percentage of pores of size 25µ m to16 µ m than corn monoculture at the

p<0.10 significance level (Table 6).

Table 6. Crop rotation effect on pores of diameter 150 - 50 µ m pores of diameter 25

- 16.6 µ m

Crop Rotation† Percent pores of diameter

150 - 50 µ m‡ x

Percent pores of diameter

25 - 16.6 µ m‡x

% %

CS-BS-CS 9.57 a‡ 4.49 ab

CS 8.52 ab 1.24 b

SB-R-CS 8.16 ab 3.66 ab

CS-R-CS 8.06 ab 3.99 ab

SB-CS 7.82 ab 4.82 ab

A 6.39 b 6.07 a

p-value 0.063 0.070


A = alfalfa SB-R-CS = soybean-corn/rye double-crop,


double-crop

‡ Means followed by a similar letter are not significantly different at p < 0.06 x Measured on surface 7.62 cm

26

CHAPTER IV: CONCLUSIONS

In this study, corn monoculture resulted in low bulk density, high hydraulic

conductivity, and low aggregate stability. The soybean/corn single crop rotation led

to higher bulk density and lower hydraulic conductivity than corn monoculture. The

soybean/corn single crop rotation had similar aggregate stability as the corn

monoculture. Alfalfa resulted in higher aggregate stability than corn monoculture, but

had similar bulk density and lower hydraulic conductivity than corn monoculture.

Double-cropped small grains had a small effect on soil quality in this study.

Addition of rye as a double-crop only improved aggregate stability when grown as a

double-crop with corn and had no measurable effect on other soil quality indicators.

Corn double-cropped with rye resulted in higher SOC mass than corn double-cropped

with barley; but neither double-cropped small grain differed from corn monoculture

with respect to SOC.

Some parameters, such as organic carbon concentration and plasticity were

unaffected by treatment. Removal of residue or limiting residue return can prevent

SOC accumulation (Mann et al., 2002). Removal of stover can increase soil

compaction, decrease plant available water, and decrease water retention (Blanco-

Canqui and Lal, 2007; Morachan et al., 1972). Organic matter is also instrumental in

the formation of soil aggregates which could affect the pore system (Baver, 1935).

Returning residue to the soil through production of corn grain instead of corn silage

might have affected more physical quality parameters especially since corn was used

in every rotation except continuous alfalfa.

27

Root systems may have played a larger role than residue on bulk density and

hydraulic conductivity since little residue was returned. The root system of corn may

have played a role in lowering bulk density and increasing hydraulic conductivity.

The soybean-corn treatment did not affect bulk density and hydraulic conductivity

like the corn monoculture treatment, probably reflecting a smaller root system in the

soybeans. In our study, alfalfa did not have a large positive effect on soil quality as

reported by others. Its beneficial effect was limited to high aggregate stability.

Residue removal could also explain why double-crops failed to produce

significant results. Previous authors reported that rye had an effect on soil quality

when used as a cover crop in which residue was returned to the soil (Beale et al.,

1954; Villamil et al., 2006). Barley has also been found to affect soil quality when

residue was retained (Franzluebbers and Brock, 2007; Malhi and Lemke, 2007). It is

possible that differences would have been more pronounced or significant if double

crop residue was killed and retained instead of harvested for silage.

Overall, soil physical quality did not vary much between the crop rotations in

this study. Effects of crop rotations and crop intensification were limited to the top 5

cm of the soil, with no significant effects in the 5-30 cm depths. Where significant

differences were observed, they were often small and inconsistent across several

properties. There is some evidence that rotations with legumes tend to have higher

bulk density and lower hydraulic conductivity than rotations with corn monoculture.

On the other hand, rotations with legumes tend to enhance aggregate stability.

Removal of most above ground biomass during harvest may explain the limited

extent to which crops could affect soil properties.

28

Double-cropped rotations did not result in improved soil quality except for the

corn/rye double-crop rotation. Corn double-cropped with rye resulted in higher

aggregate stability than single cropped corn. The benefits of double-crops on soil

quality are most likely due to residue than any other factor.

Barley as a winter cover crop had no effect or a negative effect on soil quality.

This may have been a result of poor winter survival of barley combined with later

planting dates for corn.

The study suggests that it is difficult to improve soil quality when most above

ground biomass is removed, even if no-tillage is used.

29

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38

Appendix: Crop Management

Table A1. Corn management (population, tillage dates, planting dates, harvest dates, fertilizer and pesticide timing and amount)

Corn 2003 2004 2005 2006

Tillage Chisel None None None

Variety DKC64-11

RR2/YGCB

DKC64-11

RR2/YGCB

DKC64-11

RR2/YGCB

DKC64-11

RR2/YGCB

Planting

date Single 6-Jun 2003 28-Apr 2004 20-Apr 2005 2-May 2006

Double-crop 6-Jun 2003 7-May 2004 9-May 2005 2-May 2006

Population

(Plants ha-1

)

69000 69000 69000 69000

Amm.

Nitrate at

planting

33% at 180 kg ha-1

33% at 180 kg ha-1

33% at 180 kg ha-1

33% at 180 kg ha-1

Herbicide 19-Jun 2003 22-Apr 2004 10-May 2005 ND

(glyphosate) 25-Jun 2005

Harvest

Single 26-Sep 2003 1-Sep 2004 29-Aug 2005 ND

Double-crop 29-Sep 2003 13-Sep 2004 7-Sep 2005 ND

ND = no data recorded

39

Table A2. Alfalfa management (population, tillage dates, planting dates, harvest dates, fertilizer and pesticide timing and amount)

Alfalfa 2003 2004 2005 2006


Variety WL357 HQ WL357 HQ WL357 HQ WL357 HQ

Seeding

Rate

(kg ha-1

)

20

20

20

Planting

Date

5-May 2003

Herbicide Raptor 19-Jun 2003

Insecticide Warrior 27-Jun 2003 21-Jun 2004 27-Jun 2005

Warrior 6-Aug 2003 26-Jul 2004 5-Aug 2005

Velpar 20-Mar 2004

Harvest 9-Jun 2004 9-Jun 2005 31-May 2006

25-Jul 2003 8-Jul 2004 13-Jul 2005

28-Aug 2003 6-Aug 2004 9-Aug 2005

20-Sep 2003 21-Sep 2004 8-Sep 2005

40

Table A3. Soybean management (population, tillage dates, planting dates, harvest dates, fertilizer and pesticide timing and amount)

Soybean 2003 2004 2005 2006


Variety Pioneer

93B68RR

Pioneer

93B68RR

Pioneer

93B68RR

ND

Planting

date

12-Jun 2003 30-May 2004 31-May 2005

Population plants ha-1

494,000 494,000 494,000

Herbicide Roundup 19-Jun 2003 22-Apr 2004 10-May 2005

25-Jun 2005

Harvest 13-Oct 2003 20-Oct 2004 20-Oct 2005

ND = No Data Recorded

41

Table A4. Barley management (population, tillage dates, planting dates, harvest dates, fertilizer and pesticide timing and amount)

Barley 2003 2004 2005 2006


Variety Pennco Pennco Barsoy Barsoy

Seeding

rate

108 kg ha-1

ND

Planting

date

3-Oct 2003 16-Sep 2004 14-Sep 2005

Amm.

Nitrate

top dress

Date

24-Mar 2004

22-Mar 2005

Rate 33 % at 45 Kg ha-1

ha-1 33% at 45 Kg ha-1

ha-1

ND = No Data Recorded

42

Table A5. Rye Management (population, tillage dates, planting dates, harvest dates, fertilizer and pesticide timing and amount)

Rye 2003 2004 2005 2006


Variety Not Stated Not Stated Not Stated Not Stated

Seeding

rate

125 kg ha-1

125 kg ha-1

125 kg ha-1

125 kg ha-1

Planting

Date

After corn 3-Oct 2003 16-Sep 2004 14-Sep 2005

After soybeans 21-Oct 2003 27-Oct 2004 27-Oct 2005

Amm.

Nitrate

top dress

Date

24-Mar 2004

22-Mar 2005

24-Mar 2006

Rate 33% at 45 kg ha-1

33% at 45 kg ha-1

33% at 45 kg ha-1

33% at 45 kg ha-1

Harvest 6-May 2004 9-May 2005 28-Apr 2006

effect of crop rotation and cropping intensity on …

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