Incorporating cover crops in the corn-soybean rotation is one way to improve soil quality over time and reduce nitrogen and erosion losses. In the Upper Midwest, however, cover crops can be difficult to establish after harvest of the main crop due to the short growing season. Overseeding prior to harvest may allow more time for growth. Three experiments were conducted to determine what factors are most likely to affect successful establishment of overseeded winter rye into standing corn and soybeans. The first experiment field tested aerial seeding at multiple locations in southeastern Minnesota to characterize the physical and chemical properties that affect fall biomass production. Precipitation within a week of seeding was found to be the most important factor in establishing a successful cover crop. The second experiment further elaborated on this by testing soil water potential and temperature on germination of rye seeds under laboratory conditions. Total germination was significantly decreased by decreasing water potential in the sandy loam, but not the clay or silt loam, suggesting that moisture content may be more important than water potential at the soil surface. Increasing temperature decreased total germination, most likely due to the increased incidence of mold at higher temperatures. The third experiment evaluated three overseeding techniques for standing soybeans: aerial seeding (AS), tractor-mounted air-flow spreader (TAF), and tractor-mounted fertilizer broadcast spreader (TBS). The AS treatment resulted in the lowest seeding density overall while the TBS treatment resulted in the highest density and was the most variable across plots. The differences in seeding density led to significant above-ground rye biomass differences in fall, although by spring, biomass was not different across seeding treatments. Soybean yields were not different across seeding techniques, suggesting that any of these practices are viable for on-farm use. Finally, the potential for overseeding cover crops, aerial seeding in particular, as a practice in the Upper Midwest was evaluated. Some of the current limitations include unpredictable weather, lack of aerial applicators, inconsistent stands due to pilot error and seed predation, and high costs.
University of Minnesota Ph.D. dissertation. July 2012. Major: Soil science. Advisors: Dr. John M. Baker and Dr. Deborah L. Allan. 1 computer file (PDF); vi, 103 pages.
Wilson, Melissa Loraine.
Factors affecting the successful establishment of an overseeded winter rye cover crop in northern climates.
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