Grain yield and greenhouse gas emissions from organic and conventional cropping systems on claypan soil landscapes
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] With increasing world populations, farmers must become more efficient at producing food, fiber and fuel while reducing negative environmental impacts. The first objective of this study was to determine the effects of tillage, cover crops, and compost rate on organic grain crop production, greenhouse gas (GHG) flux, and soil N content. Carbon dioxide (CO2) and nitrous oxide (N2O) of this organic management study were much lower than what others have reported, attributed to drought conditions and the use of compost. Across all crops, TNCC and TCC out-yielded NTCC, primarily due to increased germination in tilled systems and decreased weed pressure. The 1x and 1.5x compost treatments out-yielded the 0x and the 0.5x. The second objective of this study was to determine the GHG flux of fertilizer treatment within landscape positions of corn and switchgrass cropping systems. In 2014, switchgrass CO2 flux was approximately two times greater than corn. Corn N2O flux was almost 6 times greater than switchgrass. Synthetic fertilizer resulted in 2.5-8 times greater N2O flux than the other fertilizer treatments. The summit emitted at least 1.5 times greater GWP than the other landscape positions and synthetic fertilizer emitted about twice the GWP than other fertilizer treatments. In conjunction with this GHG research, an independent study was conducted to determine the effect of depth to claypan (DTC) on corn and switchgrass water use efficiency (WUE) and crop N recovery efficiency (REN). In dry years on depositional soils switchgrass had greater WUE and REN than corn. This research showed that in organic management systems, grain production generates low GHG emissions, NTCC yields less than tillage treatments, and at least 1x of compost is necessary to maintain yields. This research showed switchgrass to emit less N2O and be more efficient with water and N than corn. This could improve the productivity of marginal soils, such as found in Missouri, while providing a renewable fuel that emits less life-cycle GHG to meet the Renewable Fuel Standard (RFS).