Date of Award
Master of Science
Plant and Soil Science
Agroecosystem sustainability as a framework for agriculture production systems requires attention to detail to multiple facets of the underlying production system. Production systems must achieve optimal cash crop yields while remaining profitable. Likewise, production practices must be tailored to reduce its environmental footprint. Identifying practices that encourage improved soil physical and chemical properties while maintaining yields have largely been challenging. Cover crops have been an integral part of the conversation regarding practices that can generally improve those properties of soil responsible for overall soil health. Use of winter cereal cover crops (WCCC’s) have shown promise as a tool for reducing soil and nutrient run-off, thereby reducing nitrogen (N) and phosphorus (P) nonpoint source pollution in the Upper Mississippi River Basin (UMRB). However, corn-cash crop yield penalties are often incurred following the use of WCCC’s such as winter cereal rye (Secale cereal) (WCR), as N is immobilized by cover crop residues in the decomposition processes. Additionally, traditional planting methods of cover crops have resulted in reductions of harvestable populations of corn and soybeans. These problems indicate a necessity for novel cover crop planting methods that reduce the consequential outcomes of implementing traditional cover crop practices. Using a method called “Skipping the corn row” (STCR), otherwise identified as “precision planted” cover crops, we aimed to reduce the cash crop yield-limiting interactions of cover crop residues within the cash crop row. We hypothesized that removing cover crop biomass from the subsequently planted cash crop row (chapter 1) could minimize N immobilization by residues, thereby increasing our subsequent yield potential and economic optimum return to N (EORN). In novel cover crop planting methods preceding soybeans (chapter 3), our hypothesis indicated that mixtures of WCR and crimson clover (Trifolium incarnatum) would impact biomass accumulation of weed communities, while novel measures that allowed for reduced seeding rates would permit competitive soybean yields while reducing input costs for cover crop seed. Chapter 2 focused on interseeding mixtures of WCR and crimson clover, where we hypothesized that residual rates would marginally impact percent cover of WCR and crimson clover mixtures. Our results indicated, in chapter one, that reducing seeding rate by using STCR planting method did indeed drive seed cost savings while improving yield and EORN in comparison to a traditionally planted cover crop. Our results in chapter 3 also indicated reduced seeding rates found in novel planting methods improved the on-farm economics of using cover crops while maintaining healthy soybean yields. Lower-than-average rainfall accumulations later in the growing season coupled with cover crop residues likely influenced soil moisture retention, benefiting the cash crop during the dry spell, helping maintain yields. Interseeding methods, as studied in chapter 2, did not show any significant impact on corn grain yield or yield components. Subsequently, half- and full-rate residual herbicides did not impact percent cover of cover crops. However, use of residual herbicides should be consistent with all herbicide labels and laws, and producers should use label-recommended amounts to maintain maximum efficacy of herbicides and to prevent resistant weed populations. Also, interseeded cover crops failed to successfully establish, resulting in minimal cover crop biomass in later sampling dates.
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