Wheat and Grain Sorghum Yields as Influenced by Long-term Tillage and Nitrogen Fertilizer Application

Tillage, choice of crops in a rotation, and fertilizer management affect crop yields. Limited information exist on long-term interaction effects of tillage and nitrogen (N) fertilizer management on grain yield and precipitation use efficiency (PUE) in intensified cereal-based cropping systems. A study was initiated at the Kansas State University Agricultural Research Center-Hays in 1975 to investigate the effect of tillage intensity [conventional tillage (CT), reduced tillage (RT) and No-till (NT)] and N fertilizer rates (0, 22, 45 and 67 kg N ha-1) on wheat and grain sorghum yields. Grain yields and PUE for both wheat and grain sorghum were significantly (P< 0.0001) affected by year × N application rate × tillage interaction. Across all N rates and tillage practices, grain yields and PUE were greater in years of higher precipitation compared to years when precipitation amounts were below the long-term average. Wheat and sorghum yields for RT plots were equal or greater than CT in most years at each N rate. Grain yields and PUE in the NT plots were lower than CT and RT at lower N rates. However, at the highest N rate, grain yields were not different among the tillage systems. Regardless of tillage practice, grain yield increased with increasing N fertilizer application rate. Based on our findings, higher N application rates (> 67 kg N ha-1) may be required to maximize both wheat and grain sorghum yields with any of the tillage systems.