Manure and Inorganic Nitrogen Affect Irrigated Corn Yields and Soil Properties

Manure can substitute for inorganic N fertilizers and can mitigate potential soil deterioration under irrigated corn ( Zea mays L.) silage production, but the impact on yields, soil C and N have not been thoroughly studied in the semiarid western United States. Five N source treatments (dairy manure [DM, 412 kg N ha −1 ], DM + AgrotainPlus [DM+AP], SuperU [SU, 179 kg N ha −1 ], urea [179 kg N ha −1 ], and control [no N applied]) were studied (3 yr) to determine effects on silage and grain yields, N uptake, and changes in soil properties (soil organic carbon [SOC], total soil nitrogen [TSN], nitrate‐nitrogen [NO 3 –N], and soil test phosphorus [STP]) in an irrigated, conventionally‐ tilled clay loam soil under continuous corn silage production. Silage, grain, and stover yields and N uptake were greater with N application than control, with no difference between DM, DM+AP, urea, and SU. Fall soil NO 3 –N was greater with N application than control (0–90‐cm depth), but lower with DM than for SU (0–180‐cm depth). Soil test P was seven times greater with DM than with inorganic P after 3 yr. The SOC and TSN were strongly related to root and DM inputs, increasing with DM application but decreasing or remaining constant for SU, urea, and control treatments. Dairy manure is a valuable source of C, N, and P for irrigated tilled corn silage production with minimal NO 3 –N leaching or excessive soil P after 3 yr and can ameliorate residue removal and tillage impacts.