Soil Quality Improvement with Cover Crop Mixtures

Soil Quality Improvement with Cover Crop Mixtures

Summary

The goal of this research is to use cover crop mixtures to improve soil quality and to diversify the corn-soybean cropping system in the eastern Corn Belt.

Specific objectives are to evaluate the effect of cover crop mixtures on:

1) Soil structure,
2) Microbial community structure,
3) Nutrient conservation and availability,
4) Corn and soybean yields, and
5) Weed suppression.

Experiments were conducted at Purdue University research farms that span a range of latitudes within Indiana and represent four soil types managed in no-till and conventional tillage systems. Three producers’ fields were used to demonstrate cover mixtures and resulting soil quality changes.

Cover crops were specifically chosen to represent different root system morphologies that could in turn impact different parts of the soil profile. For example, wheat has a shallow, fibrous rooting system whereas forage turnip develops a large tuber taproot. Two-way cover crop mixtures were chosen from different rooting types in order to minimize root competition between plants while maximizing their use of the soil profile. We hypothesize that cover crop mixtures will show more improvement in soil quality, as indicated by chemical, physical and biological measures, than will a single cover crop. This could then result in improved growth and yield of cash crops such as corn.

Different cover crop mixtures were planted at the various farm locations after cash crop harvest (July to Oct., 1998). The results showed that establishment and growth of the cover crops differed because of plant type, time of seeding and weather. In the fall after corn and soybean harvest, mixtures of wheat and forage turnips were seeded in southern and central Indiana and rye and canola in northern Indiana. The cereals (wheat and rye) grew well; however there was limited establishment and growth of turnips and canola. At one of the central Indiana research farms, 29 different cover crop mixtures were planted in July after wheat harvest. This earlier seeding time allowed most of the cover crops to become established despite the dry conditions of that year. In wetter years we would expect even more growth.

The same results were observed at the demonstration plots established on the three cooperating farmers’ fields. At one farm all cover crop treatments (oats, oats/buckwheat, oats/forage turnip, and a fast-growing, non-winter-hardy alfalfa) established well when seeded in July after wheat harvest. Above ground biomass in late September ranged from 0.5 to 1.7 tons per acre for the different treatments. At the other two farms, cover crop establishment was poor after fall seeding because of the dry weather and rapid onset of cold temperatures following the late seeding time. To overcome this problem, two of the farms used aerial seeding of cover crops (annual ryegrass) into established crop stands in 1999. The earlier seeding has resulted in much better cover crop establishment.

In fall 1999 after corn and soybean harvest on the research farms, mixtures of wheat and forage turnips were seeded in southern and central Indiana and rye and canola in northern Indiana. The cereals (wheat and rye) grew well, however there was limited establishment and growth of turnips and canola. These two years of results have led to seeding the cover crops earlier (September 2000, broadcast into standing corn and soybeans) and changing the second species in the 2-way mixtures (dwarf rape instead of canola or forage turnip). Demonstration plots on the producers’ fields in 1999 included a comparison of aerial seeding of annual ryegrass into standing corn and beans vs. drilling the ryegrass after harvest. The aerial seeding produced more uniform coverage of the soil and fit the producers’ work schedules better; thus aerial seeding was the only method used in fall 2000. The annual ryegrass shows promise for being a practical and manageable way to provide additional cover for the soil, but the potential benefits for soil quality have not yet been assessed on these demonstrations. At the research farms, plots with a cereal crop cover (wheat or rye) showed improved soil aggregation and increased water infiltration compared with the control plots. Neither the turnips nor canola provided enough growth to impact soil structure during the first two seasons. At one of the central Indiana research farms, 9 different cover crop mixtures were evaluated for their effect on microbial community structure and corn growth. Microbial genetic fingerprint patterns in the corn rhizosphere were complex, and there appear to be few discernible differences among the different cover crop treatments after one season of cover crop growth. Although there are few apparent differences after one year, microbial communities might be expected to develop and change over a several year period of a new cropping system.

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