Precision Manure Management Across Management Zones in the Western Great Plains of the USA.

In the western Great Plains of the USA, animal agriculture is an important contributor to agricultural economy. Most livestock farms are close to water bodies and pose a high risk in contaminating the environment. Precision manure management is a relatively a new concept that converges the best manure management practices along with precision agricultural techniques, such as management zones (MZs) for crop production. The objectives of the study were (i) to compare N mineralization rates of variable manure applications within and across management zones in a controlled environment, and (ii) to evaluate variable rate application of manure in improving topsoil quality and enhancing grain yield of low producing MZ. The study was conducted in north-eastern Colorado, under continuous corn (Zea Mays L.) fields under rainfed and irrigated conditions. For objective 1, a 120 day incubation study was conducted under laboratory conditions. For objective 2, experimental strips of 4.5 m wide and 540 m long spanned across all MZs with treatments nested within MZ in the field. Variable rate treatment for the study ranged from 0 to 134 Mg ha^-1 of animal manure, and farmers’ recommended N fertilizer rate for grain yield comparisons. Our results indicate that application of variable rates of manure mineralize differently (P≤0.05) within MZs. Grain yield was significantly different across MZ with low MZ showing a significant increase in grain yield than synthetic N fertilizer treatment in the second year of study. The enhanced grain yield in low MZ can be attributed to improved bulk density, supplementary organic matter and mineralized N from applied manure in the second year of on-going study. The study suggests that variable rate application of manure has a potential to improve soil quality and can be used as an alternative to or in conjunction with synthetic N fertilizer for improving or maintaining grain yield. The key is to find a balance between agronomically and environmentally sound manure application rates across spatially variable soils.