Abstract
Grain crop rotations are common in temperate semiarid regions, but the effect of long-term tillage and fertilizer-nitrogen (N) rate interaction on sorghum (Sorghum bicolor L. Moench ssp. Bicolor) grain yield in a winter wheat (Triticum aestivum L.)-sorghum-fallow rotation is not well understood. This study was conducted from 2015 to 2020 using long-term plots established in 1965. Experimental design was randomized complete block with split-plot arrangement of treatments. Main plots were conventional tillage (CT), reduced tillage (RT), and no-tillage (NT), and subplots treatments were 0, 45, 90, and 135 kg N ha-1. Tillage x N rate and year x tillage x N rate interactions had no effect on grain yield, but yield was greatest with NT in 2016 and unaffected by tillage in other years. The year x N rate had significant effect on grain yield because of no response to N fertilizer in 2015 and greater responses from 2018 to 2020. Across years and tillage treatments, mean grain yield increased quadratically by 52%, 70%, and 83% as N rate increased from 0 to 45, 90, and 135 kg ha-1, respectively. On average, grain yield, N agronomic efficiency (NAE), and grain N recovery efficiency (GNRE) were 6%, 20%, and 15% greater, respectively, under NT compared with CT and RT. Quadratic models explained yield response to N rate and growing season pre-cipitation for each tillage practice. Grain yield increases per growing season precipitation were 22.9, 14.9, and 11.9 kg ha-1 mm-1 with NT, CT, and RT, respectively. Fertilizer-N application increased sorghum grain yield and protein concentration, but NAE and GNRE decreased beyond 45 kg ha-1 N. In conclusion, NT is the best management practice to increase grain sorghum yield, NAE, and NRE in nonirrigated winter wheat-sorghum-fallow rotations.