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Soil Compaction, Corn Yield Response, and Soil Nutrient Pool Dynamics within an Integrated Crop-Livestock System in Illinois

^a Dep. of Crop, Soil and Environmental Sciences, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
^b Dep. of Crop Sciences, Univ. of Illinois, Urbana, IL 61801

^* Corresponding author (bftracy{at}vt.edu).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Integrated crop–livestock systems directly link crop and livestock production together to generate positive economic and environmental outcomes. Some methods used in integrated systems, like winter grazing on cropland, could negatively affect soil properties and crop productivity. We compared soil compaction, corn (Zea mays L.) yield, and soil nutrient pools between an integrated crop–livestock system and continuous corn system to address this issue. The study was conducted near Pana, IL, between 2002 and 2006. Soil compaction was evaluated indirectly by measuring soil penetration resistance (PR) and surface CO₂ effluxes. Total soil C, N, and microbial biomass C, were measured from 2002 to 2005. Soil PR and CO₂ effluxes showed inconsistent trends related to soil compaction and cattle presence. Corn yield from 2004 to 2006 was higher (P = 0.01) in the integrated system (11.6 Mg ha^–1) compared with continuous corn (10.6 Mg ha^–1). Total soil C concentration increased significantly from 2002 to 2005 within components of the integrated system but remained unchanged in continuous corn. Microbial biomass C was also higher in the integrated system but only in 2005. The study determined that integration of crops with livestock had generally positive effects on crop yield and soil organic matter despite the potential for livestock to compact soil during winter grazing.

Abbreviations: CC, continuous corn • C-O-P, corn–oat–pasture • CSP, cool-season grass pasture • PR, penetration resistance • WSP, warm-season grass pasture

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
INTEGRATED CROP–LIVESTOCK systems involve linking crop and livestock production together to generate positive economic and environmental outcomes (Allen et al., 2007). The actual relationship between crops and livestock can vary in these systems. It may range from relatively intimate, within-farm integration of crops and livestock (e.g., grazing crop residues after grain harvest) to more indirect relationships (e.g., shared manure application among crop farms within a region). Most evidence suggests integrated crop–livestock systems are more environmentally protective, or restorative, than modern cropping systems that rely on monoculture and heavy external inputs of fertilizer and pesticide (Allen et al., 2005; Katsvairo et al., 2006; Sulc and Tracy 2007). Allen et al. (2005) found that an integrated cattle–cotton (Gossypium hirsutum L.) system with 54% of the land in permanent C4 grass pasture used 23% less irrigation water, 40% less fertilizer N, and fewer chemical inputs and was 90% more profitable than the cotton monoculture. In the northern U.S. Great Plains, diversifying cropping systems with forages was found to increase grain crop yields, reduce weed pressure, and improve soil quality (Entz et al., 2002). Integrated systems may also help reduce winter feed costs in temperate regions. Winter feed can often account for half of the annual production costs in a typical beef cow operation (Schoonmaker et al., 2003). Cost reductions are often achieved by grazing grain crop residues or cool-season annual crops after harvest to save on purchased hay or grain (Klopfenstein et al., 1987; Ward, 1978).

Some integrated systems involve grazing livestock on cropland. A concern is that livestock presence on cropland would negatively affect soil properties and subsequent crop productivity. This situation may occur when livestock trample on moist, non–sod-bearing cropland soils causing compaction and subsequent crop yield reductions though alteration of soil physical and biological properties (Krenzer et al., 1989; Mapfumo et al., 1999; Worrell et al., 1992). Soil compaction was one component addressed in an integrated crop–livestock system experiment that was initiated in 2002 at the University of Illinois, Dudley Smith Farm near Pana, IL. In this system, cash crops consisting of corn (Zea mays L.) and oat (Avena sativa L.) were grown in summer while cattle grazed adjacent perennial pastures (cool and warm-season grasses). When pastures became dormant in fall, cattle were moved to croplands where they spent late fall and winter grazing a mixture of cool-season annual cover crops and corn residues. In spring, cattle were returned to cool-season grass pastures. The objective of this study was to determine whether cattle presence on cropland would negatively affect soil quality parameters and subsequent crop yields.

To meet this objective, we compared soil compaction, soil nutrient pools, and corn yield between the integrated crop–livestock system and a continuous corn system between 2002 and 2006. Soil compaction from cattle trampling was evaluated indirectly by measuring soil penetration resistance (PR) and surface CO₂ effluxes. Soil PR is a measure of soil strength and can be used as an index of soil compaction (Clark et al., 2004; Unger and Kaspar, 1994). Surface CO₂ efflux is a measure of net CO₂ production of a soil that includes respiration of roots and mineralization of organic matter. Soil compaction from machine traffic or cattle trampling could reduce soil respiration by reducing pore space and limiting O₂ diffusion (Conlin and van den Driessche, 1996, 2000; Shestak and Busse, 2005; Torbert and Wood, 1992). Reduced soil respiration may indicate less microbial activity and anaerobic conditions, both of which could negatively affect crop yield. In this study, we used measurements of surface CO₂ efflux during the growing season as an integrative variable to determine potential persistence of soil compaction from winter grazing. We hypothesized that cattle trampling on cropland would increase soil compaction and reduce corn yield relative to corn that experienced no winter grazing.

We also measured several soil nutrient pools—total soil C, N, and microbial biomass C and used them as indicators of soil quality. Total C and N closely reflect quantity of soil organic matter and microbial biomass C is an active pool of organic matter whose size and activity strongly influences nutrient availability and plant productivity (Paul, 1984, Chapin et al., 2002). Microbial biomass C is frequently used as an indicator of soil quality since it tends to be more sensitive to management than total C (Brookes, 1995; Jordan et al., 1995). Because of the presence of cattle, perennial grasses, and cover crops in the integrated system, we hypothesized that soil organic matter and soil microbial biomass would be greater compared with continuous corn.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Site Description and Experimental Design
The study site is located on the Dudley Smith research farm near Pana, IL (39°23' N, 89°4' W). The farm had been in corn–soybean [Glycine max (L.) Merr.] rotation for at least 10 yr before it was converted for use in this experiment. In 2002 all 90 ha of the farm were converted to a replicated farming systems experiment that integrates cash grain crops with beef cattle produced on the same land unit. The area has mean annual temperature of 13.4°C and mean annual precipitation of 1001 mm. Weather data were taken from a nearby station (5 km) maintained by Illinois State Climatologist and Illinois State Water Survey. Soils at the Dudley Smith farm are of the Virden series. They consist of silty, clay loams classified as fine, smectitic, mesic Vertic Argiaquolls. Before start of the experiment, 84 soil samples were taken across the farm for baseline data. Soil pH averaged 6.3, while P and K averaged 32 mg kg^–1, and 152 mg kg^–1, respectively at a 0- to 15-cm profile depth. Before beginning the experiment, limestone, P, and K were applied to individual treatment plots within the farming system using recommendations based on soil test results.

The integrated farming system was replicated three times across the study site. Each farming system unit consisted of four treatments (Fig. 1 ) that included (i) corn–oat–pasture treatment (C-O-P) consisting of equal areas of corn and oats grown in summer and then used for winter grazing (19 ha), (ii) a continuous corn rotation (CC) that was managed exactly as corn in C-O-P plots except without winter grazing (2 ha), (iii) perennial cool-season grass pastures (CSP) (6 ha), and (iv) perennial warm-season grass pastures (WSP) (2 ha). The treatment plots differed in size because more land was needed to supply winter forage for cattle. Winter pasture cannot be grazed multiple times like summer perennial pasture in rotation and this necessitates using more land area. Details on grazing protocols are described below.

View larger version (7K): [in this window] [in a new window]   Figure 1. Schematic diagram of integrated farming system used in the experiment showing the four treatments. The farming system is replicated three times across the study site. C-O-P, corn–oats–pasture treatment; CSP, cool-season grass pasture; WSP, warm-season grass pasture; CC, continuous corn.

Production of corn and oat started in spring 2003 and continued through 2006. For both crops, conventional tillage was used for seedbed preparation that included chisel plowing and field cultivation in spring. In the C-O-P and CC treatments, a Roundup Ready corn hybrid was planted each year in mid-late April. Corn was planted to achieve a target population of 75,000 plants ha^–1 using 76-cm row spacing. Nitrogen was applied as urea both preplant and sidedress when corn was V6 stage. Nitrogen rates ranged between 150 and 190 kg N ha^–1. Corn was harvested in mid-late September. Oats planted for grain were sown in early April at a rate of 59 kg ha^–1 total weight with a 0.17-m row spacing. Oats were fertilized with urea at a rate of 60 kg N ha^–1 at planting. Corn and oats are rotated each year between adjacent fields (Fig. 1). Corn was treated with one application of glyphosate isopropylamine salt herbicide (1.12 kg a.i. ha^–1) in June to control weeds. Oats received no herbicide treatment. After oats were harvested in July, a cool-season annual mixture of oat, cereal rye (Secale cereale L.), and turnip (Brassica spp.) was sown into a clean, prepared seedbed with seeding rates at 70, 80, and 8 kg ha^–1, respectively.

Grazing Management
Grazing on the three replicate farming systems began in fall 2003 and continued through 2006. Cattle grazed cool-season pasture in spring, summer, and fall at a stocking rate of 2.5 cows ha^–1 (Fig. 1). In each replicate, cool-season pastures were divided into six equal-sized paddocks for rotational stocking. Warm-season grass pastures were divided into two paddocks and used to extend the rotation in midsummer. Paddock residency periods varied between 1 and 6 d during the growing season depending on forage availability. When perennial pastures become unproductive in late October, we moved cattle to croplands where they grazed cool-season annuals and corn residues (Fig. 1). Pregnant beef cows grazed each cropland area from November to March with calving occurring in February and March. Stocking rate was 1 cow ha^–1 on croplands. A strip grazing method was used on cropland by moving a single strand of portable electric fence 25 m approximately every 5 to 10 d depending on forage availability. Cattle had equal access to corn residues and cool-season annuals in each strip in addition to a stationary water source. Because cattle needed access to water during the strip grazing, we could not fence them from previously grazed strips in the field. Cattle were fed hay and grain as needed when forage became limiting on cropland pastures. Hay and grain were fed in dry lot areas separate from the treatment plots so they did not influence soil properties in sampling areas. Cattle were given ad libitum access to salt blocks throughout the year.

Crop and Soil Sampling
Due to logistical difficulties of sampling the large cropland plots (19 ha), we chose to confine sampling to smaller, semipermanent sampling areas that we felt were representative of each treatment. To do this, we located one 0.5-ha sampling area in each plot such that they would be grazed at the same time during the strip grazing progression. In this way, each sampling area across the three replications would be grazed at the same time. Because the strips were not back-fenced, cattle traveled through plots multiple times to get to a water source. Our placement of sampling areas maximized the likelihood of a similar cattle exposure to all plots throughout the winter. In the perennial pastures, we choose one random paddock in each replication for sampling and established a 0.5-ha sampling area in the center. Total soil C, N, and microbial biomass C were measured from soil samples collected in each fall from 2002 to 2005. Soil PR, surface CO₂ effluxes, and corn yield were measured in 2004 and 2005.

Soil PR was measured in late March 2004 and late April 2005 when soils were near or above field capacity. Twenty electronic penetrometer measurements (1-cm cone diameter, 2-cm cone length) were taken at a 90° angle to a depth of 46 cm. Measurements were recorded at 2.5 cm intervals and then averaged to obtain two values for 0- to 23-cm and 24- to 46-cm depth intervals. Because soil PR depends on soil moisture, we measured soil moisture gravimetrically from six locations in same depth increments. Soils were weighed wet then dried for 48 h at 50°C and weighed again. We suspected there might be differences between soil PR under grazed corn residues and cool-season annuals so we sampled both parts of the C-O-P treatments separately. Soil PR was measured in perennial pastures, but pastures were much drier than croplands in 2005. These differences made it difficult to make a meaningful comparison among the treatments in 2005 so data from perennial pastures will not be presented.

The yield component method was used to estimate corn grain yield in C-O-P and CC treatments (University of Illinois Extension, 2000). In each respective sampling plot, we selected 12 random areas to estimate corn yield. At each sampling point, the number of ears was counted within a 5.3-m length of row and kernel number estimated for three randomly selected ears. Those data were used to calculate grain yield. Sampling in 2004, 2005, and 2006 was done in mid to late August.

For soil variables, 18 soil cores (2.5-cm diameter) were taken from random locations within each 0.5-ha sampling area to a depth of 15 cm. Sampling was done in each October or early November after corn harvest. Subsamples were combined and dried for at least 48 h at 50°C. Roots >1-mm diameter were removed, and soil finely ground for analyses. Total C and N concentrations were analyzed using a CHN analyzer (ECS 4010, Costech Analytical Technologies Inc., Valencia, CA). The chloroform fumigation–incubation method was used for soil microbial C determination (Jenkinson and Powlson, 1976; Franzluebbers et al., 1996). For processing, 10 g of dry soil was placed in a 50-mL glass beaker. Soil moisture was brought up to 50% of soil water holding capacity. Samples then were pre-incubated in the dark for 5 d at 25°C in closed mason jars with a few milliliters of water to maintain humidity. After pre-incubation, samples were fumigated with chloroform for 24 h and then transferred to mason jars. Each jar contained a 20-mL scintillation vial containing 1-mL of 2 M NaOH to absorb the CO_2. Jars were incubated in the dark at 25°C for 10 d. After incubation NaOH was titrated with 1 M HCl, soil microbial biomass C was calculated using a k_C value of 0.41 for fumigated samples without subtracting an unfumigated control (Franzluebbers et al., 1999; Voroney and Paul, 1984).

Surface CO₂ effluxes were measured using a portable CO₂ infrared gas analyzer (LiCor 6400, LiCor Inc., Lincoln, NE) with a closed, static soil respiration chamber. Measurements were taken from three or four PVC collars (10-cm diameter x 7 cm) per plot that were inserted into soil to a depth of 2 cm. Surface CO₂ effluxes were measured twice each month from May to December in 2004 and May to October in 2005. Measurements were conducted between 0900 and 1500 h with exposure time for CO₂ efflux measurement averaging about 5 min per sampling point depending on soil conditions.

All variables were analyzed using analysis of variance (ANOVA) in the GLM procedure of SAS (SAS Institute, 2003). Farming system treatments included (i) C-O-P treatment, (ii) CC rotation, (iii) perennial cool-season grass pasture (CSP), and (iv) warm-season grass pasture (WSP). Subsamples for all variables were pooled within each treatment before analysis to give a sample size of n = 3. Treatment and year were used as independent variables and if significant treatment x year interactions were found (P < 0.10), years were analyzed separately. Corn grain yields were compared between continuous corn and cropland pasture (C-O-P). We did not have an ungrazed control for oat grain yield. Total C, N, microbial biomass C, and CO₂ effluxes were compared among the four main treatments, C-O-P, CC, CSP, and WSP. For these variables in the C-O-P treatment, data was pooled from corn residue and cool-season annual plots. Linear regression was used to determine relationships between total C, N pools, and time over the 4-yr study period. Carbon dioxide efflux data collected over each year were analyzed using a repeated measures ANOVA. Fisher's LSD test was used to evaluate treatment differences of significant main effects (P = 0.10).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Climatic Conditions
The majority of data in this study were collected between 2004 and 2005. In 2004, summer was cooler than long-term average data by about 2°C from June to August (Table 1 ). Temperature in 2005 was closer to the long-term average. Precipitation in 2004 was generally more variable than 2005 (Table 1). Annual precipitation in 2005 was 13% below the long-term (1950–2005) average (1016 mm). The precipitation in spring and early summer (March to June) in 2005 was drier, about 60% less than long-term average in this period. Because of precipitation and freeze-thaw events, soils were often wet when cattle were present on croplands during late fall and winter. Cattle trampling during these times caused severe soil disturbance.

Some studies suggest presence of cattle on cropland in winter can compact soils and reduce crop yield (Krenzer et al., 1989; Mullins and Burmester, 1997; Worrell et al., 1992). Our results suggest trampling and soil disturbance from cattle presence on cropland had no negative affect on subsequent corn grain yield and may have helped increase yield over CC plots. No year x treatment interactions were found and mean corn yield from 2004 to 2006 was significantly higher (P = 0.01) on C-O-P treatments (11.6 Mg ha^–1) compared with CC (10.6 Mg ha^–1). Differences between CC and C-O-P corn grain yield were greater in 2005 and 2006 compared with 2004 suggesting a potential rotational effect (Fig. 2 ). In a study from Iowa, Clark et al. (2004) showed that winter grazing on corn residues had a minimal effect on subsequent soybean yield. This was especially true if grazing was restricted to periods when soils were frozen or if soil was disked before soybean planting. In our study, grazing often occurred when soils were not frozen. We did, however, use conventional tillage before planting, and this may have alleviated some compaction. Moreover, we would probably expect to see greater yield effects related to compaction in a dry year when crops are under stress (Sidhu and Duiker, 2006; Unger and Kaspar, 1994). In this region, corn is especially sensitive to stress in July when pollination and grain fill occurs. Rainfall in 2004 and 2005 was above normal in July and near normal in 2006 so plants were not drought stressed during this critical period (Table 1). A review by Unger and Kaspar (1994) suggested that PR greater than 20 kg cm^–2 in a dry soil will severely restrict root growth. Our PR measurements approached this threshold in relatively wet soils (Table 2) so it is possible that PR measured in this study was sufficient to restrict root growth under prolonged dry conditions.

View larger version (13K): [in this window] [in a new window]   Figure 2. Estimated corn grain yield from 2004 to 2006 in continuous corn and cropland pasture (C-O-P) plots.

View larger version (13K): [in this window] [in a new window]   Figure 3. Trends in total soil C over the four year study period. C-O-P, corn–oats–pasture treatment; CSP, cool-season grass pasture; WSP, warm-season grass pasture; CC, continuous corn. LSD values are given for each year to compare treatments.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Our data indicated that cattle presence on cropland may have caused soil compaction in some years, but it had no negative effect on soil properties or corn grain yield. From a whole-farm perspective, we found significant increases in soil C pools within 5 yr of conversion from corn–soybean rotation. These results suggest a farming system integrating cattle with grain crops can build soil organic matter rapidly, and this should have many positive ramifications for system productivity overall. A critical component in this system appears to be integration of perennial pasture and annual cover crops within the system. Cover crop residues, fine root turnover, and manure inputs likely help boost soil organic matter levels and negate soil compaction that might result from cattle trampling on non–sod-bearing soils. Nevertheless, longer term evaluation of this integrated system will be required to make robust conclusions about its impact on soil quality and crop productivity. At this point though, our results suggest wintering cattle on crop residues and cropland pasture should help reduce winter feeding costs without negatively affecting crop productivity and soil quality.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
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Received for publication July 16, 2007.

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				B. F. Tracy and A. S. Davis Weed Biomass and Species Composition as Affected by an Integrated Crop-Livestock System Crop Sci., June 26, 2009; 49(4): 1523 - 1530. [Abstract] [Full Text] [PDF]

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