Legumes included in corn-based crop rotation systems provide a variety of benefits to the subsequent crops and potentially to the environment. This review aims to synthesize available data from the literature on legume N credits and the effects of crop rotations on water quality, as well as to analyze the cost benefits associated with different legume-corn rotation systems. We found that there was much variation in reported values for legume N credits to subsequent corn crops, from both empirical results and recommendations made by U.S. land grant universities. But despite inherent complexity, accounting for this contribution is critical when estimating optimal N fertilizer application rates as part of nutrient management. Results from research on the influence of crop rotations on water quality show that including legumes in corn-based rotation systems generally decreases nitrate-N concentrations in subsurface drainage discharge. Our cost analysis showed that incorporating legumes in cropping systems reduced N fertilizer and pesticide costs compared to conventional cropping systems, i.e., continuous corn and corn-soybean rotations, but extended rotations, such as corn-soybean-alfalfa-alfalfa-alfalfa, are not as profitable as conventional systems in the U.S. Midwest. In comparing continuous corn and corn-soybean rotations, although their impacts on water quality are not significantly different when using overall means from the literature data, corn-soybean rotations are more profitable than continuous corn. When using data from papers that directly compared the two, we found that switching from continuous corn to corn-soybean can provide a benefit of $5 per kg N loss reduction. The cost analysis methods used could be tailored to any location or management scenario with appropriate inputs and serve as a useful tool for assessing cost benefits for other agricultural conservation practices. Legume-corn crop rotations have the potential to be an effective conservation practice with the ultimate goal of improving water quality, and, with further research, these rotations could be made even more effective by integrating them into a multi-practice system.
Worldwide, the use of uncrewed aerial vehicles (UAVs) for pesticide application has grown tremendously in the past decade. Their adoption has been slower for Midwestern row crops. This study compared droplet size, coverage, and drift potential of sprays from UAV application methods to those from ground (implement) sprayer methods on corn in the Midwest. Droplet sizes measured during UAV spray trials [geometric mean diameters of 179 and 112 μm for UAV (boom) and UAV (no boom), respectively] were substantially smaller than those deposited during implement spray trials [mean diameters of 303 and 423 μm for implement (regular) and implement (pulse)]. Droplet coverage was high and localized in the middle swath of the field for the UAV with boom (10 to 30 droplets cm-2) and with no boom (60 droplets cm-2). Droplet coverage was broader, covering the entire field width for the implement methods (10 to 40 droplets cm-2). Vertical coverage of droplets was more uniform for UAV methods than implement methods. Although the UAVs produced smaller droplets than the implement methods, we still observed greater potential for downwind pesticide drift during the implement spray trials. Because localized application may be beneficial for pest control and drift reduction, the findings indicate a strong potential for "spot" or "band" spray coverage using UAV methods. This is likely due to the smaller size, reduced spray volumes, and increased agility of UAVs as compared to more conventional methods.
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