Soil Quality Improvement with Cover Crop Mixtures

Final Report for LNC98-140

Project Type: Research and Education
Funds awarded in 1998: $93,256.00
Projected End Date: 12/31/2001
Matching Non-Federal Funds: $30,045.00
Region: North Central
State: Indiana
Project Coordinator:
Kladivko Eileen
Purdue University
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Project Information

Summary:

The goal of this research was to use cover crop mixtures to improve soil quality and diversify the corn-soybean cropping system in the eastern Corn Belt. Specific objectives were to evaluate the effect of cover crops on soil aggregation, water infiltration, and microbial community structure. Soil aggregation and water infiltration were increased by the growth of the cereal (wheat or rye) cover crops in the mixtures. The effect of one season of cover crop growth on microbial communities was small but observable. On many soils, several years of cover crops may be needed before soil quality is improved.

Introduction:

Many farmers have a great interest in improving soil quality within their fields, but they often don’t know practical ways to improve their particular soils within their overall farming system. Some farms may be able to reintroduce hay crops and animals into a longer rotation, but other strategies are needed for many farms in the eastern Corn Belt. Winter cover crops are one such tool available to improve soil structure, biological diversity, and overall quality. A mixture of morphologically diverse cover crops may be able to mimic the beneficial effects of longer (3-4 yr) rotations within a shorter time period. For example, some of the benefits of longer, sod-based rotations include breakup of pest cycles, different rooting patterns proliferating in different depths of soil, greater soil biological diversity due to differences in plant root and residue substrates, and greater protection of the soil surface by crops that grow earlier in spring and later in the fall. By using a mixture of two cover crops each winter in a 2-yr corn-soybean rotation, many of these same benefits may be achieved.

For cash-grain farmers, the use of cover crops can be a way to diversify the landscape and increase the resilience of the cropping system to temporary weather stresses. In addition to the benefits discussed above, improved soil quality can result in improved water infiltration and water-holding capacity, better root growth and aeration, and greater resistance to soil erosion. Cover crops also contribute to weed suppression and may result in less residual herbicide use.

Although generally it is known that winter cover crops can improve soil structure, the particular cover crops to choose for a given soil type, climate, crop sequence, and degree of soil improvement desired is generally not known. Cover crop performance has been unpredictable in much of central and northern Indiana, and many farmers are reluctant to try cover crops because of their sometimes negative impact on yield of the cash crop. Studies are needed on a variety of soils to determine their effect on soil structure, biological diversity, nutrient cycling, and crop performance. Few studies have considered combinations of cover crops with different root system morphologies for their potential synergistic effects on soil quality.

Crop rotation, the practice of growing a sequence of crops on the same land, has been a valuable tool for farmers almost since farming began. Rotations traditionally have been important in maintaining soil productivity through management of fertility or crop insect, disease, or weed pests. During the 1950s and early 1960s the availability of synthetic fertilizers and chemical pesticides led some to think that rotation could be eliminated without loss of yield (Bullock, 1992). That line of reasoning proved to be false and the current consensus is that crop rotation allows for sustained production and improved yield (Mitchell et al., 1991). However, modern rotations have become more short-term and usually are only 2 or 3 years in a cycle. The inclusion of long-term meadow or forage crops has nearly disappeared as a normal production rotation. With economic pressures pushing producers to move away from long-term rotations, the ability to use winter cover crops in short rotations to keep some of the advantages of long rotations could be a valuable tool to crop producers.

Cover crops may be defined as crops that are grown specifically to cover the ground with living or dead mulch that will help to improve soil structure, soil fertility, and nutrient and pest management. There are many different niches or purposes that cover crops may fill in a particular field. When selecting appropriate cover crops, a producer must identify the primary goals or niches for the cover crop as well as some secondary goals, and then try to match the plants with the goals. The primary goal for our work is to improve soil structure, nutrient conservation and availability, and microbial diversity.

Bullock (1992) concluded that the shift from extended rotations to short rotations has resulted in the degradation of soil structure as measured by soil aggregate stability, bulk density, water infiltration rates and soil erosion. Classic review articles by Allison (1968) and Harris et al. (1966) explained that rotations involving sod, pasture and hay improve soil aggregate stability better than short rotations because they contain varied species with different growth habits and morphology, and there are generally longer periods without tillage. In general, as soil aggregation improves soil structure and tilth also improve (Allison, 1968).

Cover crops have been shown to improve water-stable aggregation and increase water infiltration rates compared to soil without cover crops (McVay et al., 1989). The beneficial effects of plants on soil aggregate formation come from several factors including: protection of the soil surface from raindrop impact; the formation of extensive root systems that help to break the soil apart and open it to aeration and water infiltration; the addition of organic matter through the death and decay of root and stem tissues; the supplying of a food source for soil microbial populations that in turn may directly or indirectly play a role in soil aggregate formation. These effects are generally accepted to be present in long-term rotation systems. The introduction of winter cover crop mixtures that mimic the various root system morphologies of the species found in traditional long-term crop rotations may be one strategy to improve soil structure while meeting the economic demands for short rotations.

The issue of species selection is another significant unknown in the use of cover crops for on-site nutrient retention and enhanced nutrient-use efficiency of the cash crops in a cropping system. In the eastern Corn Belt, the majority of research has focused on the grasses including winter wheat (Triticum aestivum L.) and cereal rye (Secale cereale L.), species that are relatively closely related to corn. Research in plant ecology has shown that increased diversity results in an increase in system productivity and stability (Tillman et al., 1996). The principle appears to apply to agro-ecosystems as both corn and soybean monocultures have reduced yields when compared to yields achieved in an annual corn-soybean rotation. Diversifying a rotation by including a winter cover crop may confer additional productivity benefits, but research has shown that not all alternative species confer the same benefits on system productivity. For corn, closely related grass species have been found to be relatively ineffective rotation crops (Porter et al., 1997) and cover crops (Raimbault et al., 1990), highlighting the need to move beyond current standard cereal cover crop species and evaluate novel, non-leguminous dicots for their efficacy as cover crops in corn based cropping systems.

The detrimental effects of deleterious soil microorganisms are well known but little has been documented regarding the beneficial members of the community (Nehl et al. 1996). Some bacteria have been shown to enhance plant growth. For example, when Bacillus polymyxa is co-inoculated with Rhizobium etli, it modifies the host plant growth (including increased lateral root formation and number of nodules) when compared to single inoculation with R. etli alone (Petersen et al., 1996). Some microorganisms act as antagonists toward others; for example, arbuscular mycorrhiza associates within plants and can aid in controlling infection by soil pathogens (Azcon-Aguilar and Barea, 1996). Changes in nutrient status resulting from different crop management practices can cause shifts in the microbial community. One illustration is that in reduced tillage cropping systems with plant litter localized near the soil surface, fungi have been found to dominate the microbial community (Newman, 1985). In ecosystems where litter is incorporated into the soil, the bacteria have a competitive advantage over fungi and dominate the community. Most studies have been conducted at a rudimentary level or by tracking specific species, but evidence is mounting that the soil microbial community as a whole is highly linked to agronomic practices and to crop performance.

To improve or design new cropping systems that will sustain the soil resource base while maintaining crop productivity, we must gain a better understanding of rhizosphere microbial community composition and function. Until recently, the methodology available only permitted us to indirectly examine the general ecology of these microorganisms at a very rudimentary level. Now, with the advent of molecular genetics methods, a number of tools are available to begin unraveling the complex ecology of microorganisms in the rhizosphere. Recently researchers have used profiles of differences in DNA fingerprints generated by PCR (polymerase chain reaction) to study microbial communities (Ferris et al., 1996; Muyzer et al., 1993). This method is now being used in a study by two of the team members (Nakatsu and Brouder) to determine the relationship of the rhizosphere microbial community and crop development under different agronomic treatments. Distinct and reproducible “fingerprint” patterns were generated from DNA extracted from the rhizosphere of growing corn and soybean plants in soils that had been either plowed or in no-till. Specifically, our results show that distinct and different populations of bacteria dominate the rhizospheres of corn and soybean when these crops are grown in rotation with each other (Wells et al., 1997). The dominant plant-specific populations also appear to change with different stages of development of their higher plant host, as well as with tillage system.

Ultimately, this research and its approach have the potential to revolutionize the way we select crop species for a rotation. “Fingerprinting” for beneficial and undesirable profiles in the rhizosphere may permit rapid screening for viable new or alternative crops to diversify current agro-ecosystems. Increasing the options for crop selection in rotational systems not only offers the inherent environmental quality benefits of increased biodiversity but it will improve the economic viability of farmers by allowing them to increase their commodity base and enter alternative and specialty markets.

Project Objectives:

1) Evaluate the potential for cover crop mixtures to improve soil structure, microbial biomass and diversity, and nutrient conservation and availability on four Indiana soils under no-till and conventional tillage systems and a corn/soybean rotation.
2) Determine the impact of cover crop mixtures on corn and soybean yields and weed suppression, on four Indiana soils under no-till and conventional tillage systems.
3) Evaluate and demonstrate cover crop mixtures and the resulting soil quality changes, on three producers’ fields in Indiana.

Cooperators

Click linked name(s) to expand
  • Sylvie Brouder
  • Darrell Brown
  • Dan DeSutter
  • Mark Evans
  • John Graveel
  • Michael Hickman
  • Cindy Nakatsu
  • David Swaim
  • C.K. Wilkins
  • Ward Wilkins
  • Jim Wilkinson

Research

Materials and methods:

The overall goal of this research was to improve soil quality and diversify the corn-soybean cropping system of the eastern Corn Belt by incorporating the use of cover crop mixtures. The first two objectives were performed on replicated research plots on four Purdue University research farms spanning a range of soil types and latitudes within Indiana. Soils included a Pinhook loam (Mollic Ochraqualf) at the Pinney Purdue research farm in northwestern Indiana, a Drummer silty clay loam prairie soil (Typic Endoaquoll) at the Agronomy Research Center and a rolling light-colored Miami silt loam (Typic Hapludalf) at Purdue Throckmorton research farm in west-central Indiana, and a flat, light colored Clermont silt loam (Typic Ochraqualf) at the South East Purdue Agricultural Center (SEPAC) in southeastern Indiana.

The cover crops were selected from a suite of cover crops representing different root system morphologies. For a given location, project team members consulted with research farm superintendents to identify the species most suited to the region/soil type. The seven cover crops we considered were forage turnips (Brassica rapa L.), winter canola (Brassica campestris L.), buckwheat (Fagopyrum esculentum Moench), cereal rye (Secale cereale L.), annual ryegrass (Lolium multiflorum Lamarck), winter wheat (Triticum aestivum L.), and winter barley (Hordeum vulgare L.). Our philosophy was to select plants with different root system morphologies in order to obtain the combined benefits of shallow or fibrous rooting on soil structure near the surface, and deep rooting on soil structure deeper in the profile. The specific cover crops chosen were different for northern and southern Indiana based on crop adaptability to both the climate and the soils. Combinations chosen were canola and rye for the Pinney Research Center, and turnips and wheat for the Throckmorton and SEPAC Research Centers. At the Agronomy Research Center, the experiment consisted of 9 different combinations of cover crops, as an initial screening of the potential suitability of a wide range of covers. Table 1 summarizes the main treatments at each site.

At Pinney, Throckmorton, and SEPAC, plots were established under no-till and conventional tillage for both corn and soybeans. Cover crop mixtures included 5 different ratios of the two covers(100:0, 75:25, 50:50, 25:75, 0:100% of full seeding rate of rye:canola or wheat:turnip) as well as a control. This results in 96 plots per location (2 tillages x 2 crops x 6 covers x 4 reps). Cover crops were seeded soon after harvest of the corn and beans each fall.

Measurements on these three sites included a suite of soil quality and plant growth data. The above-ground biomass production of the cover crop was measured in the spring before killing the cover crop. Samples were collected from two 1m2 frames per plot, cut at ground level, dried and weighed. Aggregate stability, a primary means for assessing soil structure, was measured once per year at Pinney and twice per year at SEPAC and Throckmorton. The first sampling was taken right before the cover crops were killed (late April or early May), while the second set was taken in June, to represent a stage of usually higher aggregation due to some microbial decomposition of the cover crop. Water infiltration was measured on a subset of plots from SEPAC and Throckmorton, using ponded infiltration techniques. Corn and soybean yields were determined at harvest each fall.

The Agronomy Research Center site had 9 combinations of cover crops plus a no cover crop control in a replicated trial in summer/fall 1998, followed by corn in 1999. The ten treatments were control, oats (Avena sativa L.), yellow sweetclover (Melilotus officinalis L.), dwarf rape (Brassica napus L.), forage turnip, buckwheat, wheat plus rape, oat plus rape, oat plus turnip, oat plus yellow clover. In spring/summer 1999, intensive sampling for microbial diversity and root/shoot growth was done on these plots. Whole plant samples were taken at V1, V2, V3, and V6 growth stages as well as right before harvest. Leaf surface area was measured to assess shoot development. Roots were scanned to compare root development and morphology. Rhizosphere and bulk soils were analyzed for microbial diversity using DNA fingerprinting techniques.

Demonstration plots were established on three cooperating farms in west-central Indiana, the Wilkins’ Farm, the Wilkinson Farm, and the DeSutter Farm (Table 1). The Wilkins’ site had the best success during the first year, in part due to the early seeding possible following wheat. They drilled covers in July 1998 following harvest of wheat and baling of the straw. They tilled the covers in late fall, and corn was planted in spring 1999. Corn yields from the different cover strips were measured that fall at harvest. At the Wilkinson site in 1998, the farmer broadcast-seeded oats, oilseed radish, and a mixture of the two crops into standing soybeans in late August. The resulting growth was not sufficient to warrant any further measurements from that site that year. At the DeSutter farm, covers were drilled after corn harvest in late October, 1998. Treatments were buckwheat and a ryegrass/oilseed radish combination. Establishment in the fall was poor, but some ryegrass did grow the following spring.

Demonstration plots in 1999-2000 were established on the Wilkins’ farm and the DeSutter farm (Table 1), while the Wilkinson farm decided not to participate in the project those years. In fall 1999 and again in 2000, the demonstration plots were established in collaboration with the Oregon Ryegrass Growers’ Seed Commission. The Commission provided annual ryegrass seed to the farmers and paid for aerial seeding of about 15 acres on each farm, in exchange for the farmers’ observations and efforts to develop a viable management system for the cover crop. The aerial seeding was done in September into standing corn and soybeans, which should reduce the constraint of poor cover establishment due to the typical late seeding after harvest of the cash crop. Aerial seeding involves less cost per acre than drill-planting after harvest, and makes cover crops more attractive to producers who already are too busy through October and November.

Research results and discussion:

The two-year SARE-funded grant began in fall, 1998, but experiments were begun at two research farms in fall 1997 with funds from Purdue Agricultural Research Programs. This report discusses findings from fall 1997 through fall 2000, which includes observations of three cycles of cover crop growth.

SEPAC, Throckmorton, and Pinney sites:

Three of the Purdue research farms had the different ratios of wheat/turnip or rye/canola in the no-till and conventional corn and beans. At SEPAC and Throckmorton, the turnip and wheat cover crops established well in the long, mild fall weather of both 1998 and 1999. Although the turnip establishment was good, plants were small by the time winter weather began. We anticipated that our October planting dates would not be early enough for the turnips to fully develop, however we tested whether the establishment of many small plants in the fall was sufficient to enhance aggregation in the spring. No surface residue from turnip plants was present in the following spring. As with the turnip, the canola at the Pinney location was unable to produce a harvestable crop. Some canola plants were present in the 100% and 75% canola treatments in each spring, but the stand was light and highly variable. Based on these results, any further work at these sites will use broadcast seeding into standing corn or soybeans in early September, to provide more time for establishment and growth of the covers.

Spring growth of the wheat and rye was good at all three sites, providing excellent surface cover as well as root growth to aid in aggregation of the soil. In general the 100% and 75% cereal treatments produced the most biomass and the 25% cereal treatment produced the least biomass, but the mass was not directly proportional to the seeding density, since plants grew larger where there were fewer of them.

Soil structure was assessed by measuring wet aggregate stability at all three sites and infiltration rates at two sites. Aggregation was improved by the growth of any amount of the cereal crops compared to the control and the 0% cereal/100% turnip or canola treatments at both SEPAC and Pinney. As discussed above, the canola treatments did not establish well, and so they had minimal effect on aggregation. Although the turnips had good cover in the fall, they were apparently still too small to have any measurable impact on soil aggregation the following spring/summer. Trends were the same in both the May and July sampling dates. On the low organic matter, poorly structured Clermont soil at SEPAC, the cover crop tended to have a greater impact on the soil following soybeans as compared to corn, likely due to the lesser residue remaining after soybeans and its faster degradation. The cover crop also established better after soybeans than after corn, due to the lesser cover, and therefore more cover growth could have contributed to greater aggregation. On the poorly structured Clermont soil, the cover crop tended to have a greater impact on aggregation in conventional tillage than in no-till, because of the relatively bare soil surface in conventional tillage. The cover crop treatments had a smaller effect on aggregation at the Throckmorton site than at the other two sites. This site had only had two seasons of cover crop growth by summer 2000 whereas SEPAC and Pinney had already had three seasons of cover crops, which probably explains part of the difference in results. It is likely to take more than one or two winters of cover crop growth before measurable impacts on soil structure will occur on many soils. Improvement of soil structure and quality is a long-term proposition, especially when trying to improve soil quality within the constraints of producing a cash crop each year.

Water infiltration rates at SEPAC and Throckmorton tended to be higher in the wheat cover crop treatments compared to the controls, but there were few statistically significant differences due to large variability. The larger differences occurred at SEPAC on the more poorly-structured soil, as expected. Both the growth of a cover crop and the use of no-till rather than conventional tillage tended to increase infiltration at that site. At Throckmorton the cover crop appeared to have a small effect, but more years of cover crops are likely needed to see any significant improvement.

There were few significant differences in corn or soybean yields under any of the treatments in this study. In the cases where trends or significant differences occurred, they were inconsistent from one year to another or between corn and beans. At Pinney, the highest yields in beans tended to be for the plots with either 100% rye or no rye (control), suggesting that the cover crop had no consistent effect on yield. In two of three years at SEPAC, there seemed to be an effect of the 100% turnip treatment on bean yields, even though the good stand in the fall did not carry over to the spring and the turnip plots looked like the “control” treatments. In those years the 100% turnip treatment had the highest or second highest yield while the true control was lowest or second lowest, with the remaining cover crop treatments (different wheat stands) intermediate. These observations need much more detailed study to determine whether there is some subtle effect on the soil microbial community which may affect crop growth, similar to the work on the corn rhizosphere microbial community discussed later.

Weed control was adequate at all sites, and there were no large differences in weed pressures as a result of the cover crop treatments. Cover crops had been killed each spring with glyphosate ((N-(phosphonomethyl)-glycine), and subsequent weed control followed the farm superintendents’ usual practices.

Agronomy Research Center:

The fourth Purdue research farm had a different experimental design, and it was the focus of the detailed work on soil microbial community structure and nutrient availability. During July 1998, a total of 9 different combinations of cover crops (plus a control) were planted after wheat harvest on a field at the Agronomy Research Center. These treatments were sampled for soil aggregate stability during the late summer/fall of 1998. In part due to the dry conditions at that time, there was little difference in aggregation among the different treatments. These plots were planted to corn in spring 1999, and soil samples were taken at several times during the growing season for microbial community structure, root growth, and nutrient availability.

After the one season of cover crop growth only small differences were observed in rhizosphere microbial community structure and development of the subsequently planted corn crop. Some differences were observed among treatments in a number of plant development, nutrient, and rhizosphere community parameters. Among the treatments, the most commonly observed significant differences occurred between the no cover crop control and the combination of oat plus dwarf rape. There were also other subtle, but not statistically significant, differences found between all the cover crops and the no cover controls. There were no differences in corn grain yield at the end of the growing season. An important point to note is that there was no measurement made of the plant, nutrient or microbial community that consistently showed a negative impact of one season of cover crops on the subsequent cash crop, corn.

Differences in early corn development response among treatments were small and generally not statistically significant. After some cover crop treatments the corn at some growth stages showed greater leaf surface area, root surface area, or shoot dry weight compared to the no cover crop control. When corn growth responses were present, there was also usually a difference in microbial community structure between the control and the cover crop treatment. Based on our present results the different soil microbial populations selected under these conditions in the rhizosphere are not necessarily either “beneficial” or “harmful,” but they do indicate that cover crops have the potential to affect their selection. Of the cover crops tested, treatment mixtures that included oats as one of the cover crops tended to have more impact than the others, with the oat plus dwarf rape treatment being the combination with the greatest effect. An important limitation of these findings is that the cover crops were planted in July after wheat harvest, and thus had a longer growth period than would be possible when seeding covers after corn or soybean harvest. On the other hand, these results reflect only one season of cover crop growth, and it can be hypothesized that several seasons of cover crop growth would induce larger differences in the soil microbial community. Longer-term studies should be conducted to evaluate changes after 3 to 5 years of cover crop growth (see section on “Areas needing additional study”).

Farmer demonstration sites:

The demonstration plots established on three cooperating farms had mixed results during the first year of the project. The Wilkins’ site had the best success during this first year, in part due to the early seeding date that is possible when following wheat. Timely rains shortly after seeding in July 1998 contributed to excellent establishment and growth. Above-ground biomass production was measured in late September and was 1.7, 1.6, 1.0, 0.5, and 0.25 tons per acre for the oats, oats/buckwheat, oats/forage turnip, a fast-growing, non-winter-hardy alfalfa, and the control strip, respectively. The Wilkins’ tilled the covers in late fall, and corn was planted in spring 1999. Corn yields from the different cover strips were measured that fall and were not significantly affected by cover crop treatment. The Wilkins brothers took video footage of cover crop growth in early fall 1998, which may be useful for educational programs. We (two farmers and two Purdue scientists) were also interviewed on local TV for a short news story about sustainable agriculture and cover crops. The Wilkins brothers are excited about the possibilities of some additional cover crops that they might be able to incorporate into their system. In addition to corn-soybean rotation fields, they grow some alfalfa and thus have some land in a corn-soybean-wheat-alfalfa rotation.

At the DeSutter farm in 1998, covers were drilled after corn harvest in late October. Treatments were buckwheat and a ryegrass/oilseed radish combination. Establishment in the fall was poor, but some ryegrass did grow the following spring. At the Wilkinson site, a late-August (1998) broadcast seeding into standing soybeans gave spotty results. He seeded oats, oilseed radish, and a mixture of the two crops, but then there was almost no rain for the following 6 weeks. Immediately after soybean harvest there was little growth, but by late fall there was some growth and establishment of both crops. The limited growth in only a few spots in the field was not sufficient to warrant any further measurements from that site that year. Mr. Wilkinson decided not to participate in the project the following year.

In 1999 at the Wilkins and DeSutter farms, the focus shifted to annual ryegrass seeded aerially into the standing crop in September or drilled after harvest in October. The September aerial seeding of annual ryegrass into standing corn and soybeans gave excellent results in fall 1999 and fall 2000 at both farms. The ryegrass established well and provided good coverage of the field in both fall and spring. The aerial seeding produced more uniform coverage of the soil than did the drilling of the cover crop after harvest of corn or beans in fall 1999. Both the Wilkins’ brothers and the DeSutter’s decided that the aerial seeding performed better and fit their work schedules better than drilling, and thus both farms used only aerial seeding in fall 2000. The DeSutter’s also planted some buckwheat as a cash crop after they harvested a wheat crop in July, in part due to our discussions about various crop alternatives.

Literature Cited:

Allison, F.E. 1968. Soil aggregation-some facts and fallacies as seen by a microbiologist. Soil Sci. 106:136-140.

Azcon-Aguilar, C, and J. M. Barea. 1996. Arbuscular mycorrhizas and biological control of soil-borne plant pathogens-an overview of the mechanisms involved. Mycorrhiza 6: 457-464.

Bullock, D.G. 1992. Crop Rotation. Critical Reviews in Plant Sciences 11:309-326.

Ferris, M. J., G. Muyzer, and D. M. Ward. 1996. Denaturing gradient gel electrophoresis profiles of 16S rRNA-defined populations inhabiting a hot spring microbial mat community. Appl. Environ. Microbiol. 62: 340-346.

Harris, R.F., G. Chesters and O.N. Allen. 1966. Dynamics of soil aggregation. Adv. Agron. 18:107-160.

McVay, K.A., D.E. Radcliff, and W.L. Hargrove. 1989. Winter legume effects on soil properties and nitrogen fertilizer requirements. Soil Sci. 53:1856-1862.

Mitchell, C.C., R.L. Westerman, J.R. Brown, and T.R. Perk. 1991. Overview of long-term agronomic research. Agron. J. 83:24-28.

Muyzer, G., E. C. De Waal, and A. G. Utterlinden. 1993. Profiling of complex microbial populations by denaturing gradient gel electrophoresis analysis of polymerase chain reaction-amplified genes coding for 16S rRNA. Appl. Environ. Microbiol. 59: 695-700.

Nehl, D. B., S. J. Allen and J. F. Brown. 1996. Deleterious rhizosphere bacteria: An integrating perspective. Appl. Soil Ecol. 5:1-20.

Newman, E. I. 1985. The rhizosphere-C sources and microbial populations. In A. H. Fitter (ed.). Ecological Interactions in Soil. Blackwell Sci. pp. 107-121.

Petersen, D. J., M. Srinivasan, C.P. Chanway. 1996. Bacillus polymyxa stimulates increased Rhizobium etli populations and nodulation when co-resident in the rhizosphere of Phaseolus vulgaris. FEMS Microbiology Letters. 142: 271-276.

Porter, P.M., R.K. Crookston, J.H. Ford, D.R. Huggins, and W.E. Lueschen. 1997. Interrupting yield depression in monoculture corn: Comparative effectiveness of grasses and dicots. Agron. J. 89: 247-250.

Raimbault, B.A., T.J. Vyn, and M. Tollenaar. 1990. Corn response to rye cover crop management and spring tillage systems. Agron. J. 82:1088-1093.

Tilman, D. D. Wedin and J. Knops. 1996. Productivity and sustainability influenced by biodiversity in grassland ecosystems. Nature (London) 22: 718-720.

Wells, J.E., S.M. Brouder, and C.H. Nakatsu. 1997. Soil microbial community analysis using denaturing gradient gel electrophoresis. Agronomy Abstracts, p. 213.

Research conclusions:

The short-term (2-year) funding cycle of the SARE program is too short to show significant impacts from the type of research project conducted here. The SARE program should consider ways to facilitate adequate longer-term funding and research if it hopes to encourage long-term, sustainable improvements in soil quality and crop production. Nevertheless, the results of this current project will potentially contribute to an improved environment in the eastern Corn Belt. Soil structure and water infiltration were increased by cover crop growth in the corn-soybean systems. These improvements in soil quality may also lead to improved crop growth and yield as well as reductions in soil erosion. For cash-grain farmers, the use of such cover crops may be a way to diversify the landscape and increase the resilience of the cropping system to temporary weather stresses.

The study has provided new information about the effects of cover crops on soil microbial communities. This is an area that is poorly understood but that has great potential to improve plant production and health. The underlying hypothesis is that the cover crops will change the dominant microbial populations in the soil, which will in turn improve nutrient availability and overall crop health. Increased crop growth due to the presence of particular populations can result from 1) microbial production of growth stimulating chemicals, 2) competition with plant pathogens, or 3) production of chemical compounds that aid in soil aggregation. Results showed some subtle changes in the microbial community of the corn rhizosphere after one season of cover crop growth. This project has therefore provided preliminary data to justify further research work in this area.

Economic Analysis

The use of cover crops in this research project did not result in a consistent effect on cash crop yield. Although cover crops improved soil structure and water infiltration, it is always difficult to show economic benefit of these improved soil physical conditions over the short-term. Over a longer timeframe economic benefits may accrue, if crops are more resilient to stresses as discussed in the Impacts section. The changes in soil microbial communities might result in economic impacts on crop growth, but much more research is needed to understand the potential contributions in this area. There were some additional risks incurred by the farmers, as discussed in the Farmer Adoption section, which also affects the willingness of other farmers to try cover crops.

Farmer Adoption

Because this has been a short-term research project, no meaningful assessment of farmer adoption is possible yet. The farmers we are working with are still excited about the project and the possibilities of using more cover crops in their operations. The DeSutter’s also tried raising buckwheat as a cash crop in 1999, in part due to our discussions of buckwheat and other crops as either covers or alternative cash crops. They expanded their buckwheat acreage in 2000 because their initial experiences showed some potential. So an unexpected benefit of the cover crop project has been to add another potential crop to the rotation used on their farm. Due to poor wheat prices as well as disease pressure, many Indiana farmers do not think they can afford to grow wheat, and thus they often are locked into a corn-bean rotation. By adding buckwheat as a potential cash crop after wheat, Mr. DeSutter thinks he may be able to afford putting wheat back in the rotation.

The Wilkins brothers are excited about the possibilities of some additional cover crops that they might be able to incorporate into their system. In addition to corn-soybean rotation fields, they grow some alfalfa and thus have some land in a corn-soybean-wheat-alfalfa rotation.
Other farmers have expressed interest in knowing more about the cover crop results and the farmers’ thoughts about practicality as the project progresses. We are not in a position yet to make specific recommendations about what a farmer should do or stop doing as a result of our study. As discussed in the Results section, the improvement of soil quality is not a short-term proposition, and it is not realistic to think that farmers will adopt new practices based on two years of this cover crop project.

The new collaboration that began with the Oregon Ryegrass Growers’ Seed Commission about halfway through the project period, helped the project continue to evolve with the farmer interests. The farmers have been especially interested in the aerial seeding of cover crops into standing corn and beans, and the Oregon growers who visited our sites have become a good resource for further ideas and assistance with managing cover crops. Although both the Wilkins and DeSutter farm families were pleased with the establishment and growth of the annual ryegrass cover crop, there were some practical challenges that remain a concern for these farmers and for others who might consider using cover crops. The ryegrass must be completely killed in spring or it will compete with the corn or bean crop. One of the farmer cooperators had some difficulty in getting the ryegrass completely killed, due to experimenting with reduced herbicide rates one year. The next year he planted corn early before spraying the ryegrass, and then an unusual combination of weather factors caused the corn to emerge so quickly that he was not then able to use the prescribed burndown herbicide. His conclusion after these two successive experiences is that the cover crop must be killed with full prescribed herbicide rates and definitely sprayed before planting the cash crop. The other farmer observed that the cover crop dried the soil a little too much in a year with a dry spring, causing some reduced soybean stands that year. This occurrence is another example of the unpredictability of response to cover crops in the eastern Corn Belt, because weather variations are so large from year to year. Weather in the fall also greatly affects the establishment and growth of the cover crop. The success of the ryegrass in this study is due in part to prolonged moderate conditions in each fall during the study. And although the seeding occurred in early- to mid- September, one year the seed did not germinate and establish until mid-October due to lack of rain. The variability of soil moisture conditions and overall weather in fall will therefore have a large effect on the success of a cover crop system. Producers would need to consider the potential benefits of cover crops over a longer time period than one year, realizing that in some years the cover crop may not establish well enough to have any impact.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Two M.S. students did their thesis research work on this project, and their theses titles are listed below. In addition to the conference proceedings and the meeting abstracts listed below, we plan to publish two scientific journal articles on their work.

Outreach activities related to this project have taken a variety of forms. A major outreach effort was organized by the Project Coordinator for the Farm Progress Show held near Purdue University in September 2001. With partial funding from the Kellogg Foundation and Purdue, a large exhibit tent featured displays on “Sustaining Family Farms and Rural Communities.” The exhibit tent included information on specialty crops, value-added enterprises, new technologies, and many other ideas to stimulate new thinking. The use of cover crops was one of many practices highlighted in the displays about natural resource conservation. The farmers cooperating in our cover crop project were present as resource people for discussion about cover crops, conservation tillage, and custom hay and lumber operations. Although the SARE project results played only a small direct role in the exhibit tent, the networking from the SARE project (farmers, NRCS, crop consultant, Purdue staff) greatly facilitated the work and organization of this major event.

The current collaboration with the Oregon Ryegrass Growers’ Seed Commission is also extending project results to larger areas and audiences. Several Oregon growers have visited Indiana and Illinois several times, met the cooperators, toured the sites, and considered ways to increase interest and willingness to try cover crops among farmers. Project team members and the research farm superintendents have informally discussed the project with farmers at various extension meetings, and the farmer cooperators have talked with other farmers and neighbors about the project. The video footage taken in 1998 by the Wilkins’ brothers may be able to be used as part of an educational packet about cover crops. Several team members include our results in their extension presentations on cover crops or soil quality improvement, including NRCS personnel (Brown) and Purdue extension staff (Evans, Brouder, Swaim).

Ackerman, C.E. 2001. The effects of various cover crop treatments on the rhizosphere bacterial community and development of the subsequent corn crop. M.S. Thesis. Dept. Agronomy, Purdue Univ., West Lafayette, IN. 179 pp.

Ackerman, C.E., C.H. Nakatsu, J.A. Kerstiens, S.M. Brouder, and M.V. Hickman. 2000. Corn rhizosphere bacterial community structure and plant development after various cover crop treatments. Agron. Abs. p. 258.

Ryan, K.E. 2000. Soil physical property improvements with cover crop mixtures. M.S. Thesis. Dept. Agronomy, Purdue Univ., West Lafayette, IN. 169 pp.

Ryan, K.E., E.J. Kladivko, M. Hickman, S. Brouder, C. Nakatsu, and J. Graveel. 1999. Soil quality improvement with cover crop mixtures. p. 92 in Abstracts of 10th International Soil Conservation Organization Conference, held May 23-27, 1999 in West Lafayette, IN.

Ryan, K.E., E.J. Kladivko, M. Hickman, S. Brouder, C. Nakatsu, and J. Graveel. 1999. Soil quality improvement with cover crop mixtures. Agron. Abs. p.280.

Ryan, K.E., E.J. Kladivko, M.V. Hickman, S.M. Brouder, C. Nakatsu, J.G. Graveel, and J. Santini. 2000. Soil quality improvement with cover crop mixtures. Proc. 15th Int’l. Soil Tillage Research Organization (ISTRO) Conf., July 2-7, 2000, Ft. Worth, Texas. (published on CD)

Project Outcomes

Recommendations:

Areas needing additional study

Much more study is needed on the effects of cover crops on soil microbial communities. Some specific questions include: 1) whether oats in combination with other plant species can produce similar results to the oat combinations in the current study, 2) whether the treatment effects observed are driven by specific groups of indigenous rhizosphere bacteria, and 3) whether these specific bacterial groups can be manipulated to enhance agronomic systems. Studies should be conducted for 5 years or longer, to observe treatment effects as they develop with time.

Further development of practices to establish cover crops earlier in the fall are needed. Although the cereal cover crops established sufficiently well when seeded after corn and bean harvest, the other crops tried (turnips, canola) did not achieve sufficient fall growth to have a measurable impact on soils. Aerial seeding of annual ryegrass into standing corn and soybeans is an alternative we are now evaluating, but the addition of a second cover crop has not been attempted. Additional research needs include a) screening a wide variety of possible cover crops for their ability to establish rapidly in a corn or soybean canopy in early fall and for desirable root morphological properties, b) developing perennial cover crop systems, that could be induced into dormancy in spring at the time of cash crop planting but would revive in the early fall when the cash crop is mature, c) quantification of cover crop impacts on the nutrient cycle/balance of agroecosystems (do cover crops minimize the off-site movement of N?). Another practical question of the producers is whether an earlier kill date of the cover crops in spring would still provide sufficient root growth for improved aggregation compared to letting the cover crops become too big and therefore hard to manage before corn or bean planting.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.