Project type: Research and Education Grant
Project number: LS01-121
Project dates: 2001–2004
Project reports: https://projects.sare.org/sare_project/LS01-121/
At the outset of this project, over 11.6 million acres in the Southeast United States was devoted to cotton production annually, of which only 13 percent was grown using conservation tillage. Prior research had demonstrated the beneficial role conservation tillage can play in reducing farm costs, which were achieved by improving the soil’s productivity and capacity to store water. However, this research had a negligible impact on cotton producers’ decision making, largely due to their perception that there were significant hurdles to overcome when implementing conservation tillage systems, including the cost of establishing such systems. Despite the best efforts of governmental conservation programs and local grower groups to respond to these concerns, national goals for conservation tillage adoption were not being met.
Hoping to encourage further adoption of conservation tillage practices, a team of USDA scientists investigated the effects of different cover crops on cotton production in a conservation tillage system. Their aim was to determine best production practices and to contribute to cotton producers’ knowledge of sustainable agriculture methods.
Methods and Practices
The team began by using greenhouse experiments to identify cover crop mixes for cotton farming that would maximize biomass, increase biological diversity and minimize parasitic nematodes. On-farm studies were then held during the 2001 and 2002 growing seasons at farms near Louisville and Tifton, Ga. Scientists observed insect dynamics, soil microarthropods and plant parasitic nematodes under the different cover crop regimes.
The preliminary greenhouse experiments identified a legume blend of balansa clover, crimson clover and hairy vetch that best provided food for beneficial insects while increasing soil organic matter. The legume blend was one of the four cover crop treatments used in the on-farm study; other treatments were a legume blend plus rye, rye or crimson clover, and a no-cover-crop treatment. All four treatments were planted into mowed cotton stubble on 10-acre fields at each farm with a no-till grain drill. Weekly samples were collected for the cover crops and cotton in the spring and summer of each year. Insect population size and diversity were measured weekly, and microarthropods and nematodes were sampled at pre-plant, mid-season and after-harvest periods. This served as a measurement of biological diversity. Cotton biomass samples were collected from each of the four treatment fields periodically throughout the growing season. The effects of cover crops on soil carbon dynamics were found by measuring microbial biomass carbon and nitrogen, potential carbon and nitrogen mineralization, particulate organic carbon and nitrogen, and water-stable aggregates prior to cotton planting and after harvest.
The results of this study indicated that the legume blend plus rye cover crop improved soil biological diversity and microbial diversity, while not clearly improving cotton biomass or yield. For both farms, cover crop biomass was found to be nearly two times greater in the legume blend plus rye treatment than in the legume blend or crimson clover treatments. The legume blend plus rye treatment also supported a more diverse above- and below-ground insect population. However, the effects of the legume blend plus rye cover crop on cotton yield were similar to the traditional (crimson clover) cover crop at the Tifton farm, while on the Louisville farm, no differences in yield were found between any of the cover crops. Similarly, differences in cotton biomass were statistically insignificant. The researchers also found no clear connection between cover crop treatment and declines in nematode populations, suggesting that farmers may be better off rotating a non-host crop (e.g., peanuts) to help in nematode reduction.
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