Long‐term in‐season grain sorghum and soybean response to tillage and nitrogen management

Abstract

AbstractInformation on tillage and N management is limited regarding in‐season N uptake by grain sorghum [Sorghum bicolor (L.) Moench] and growth of soybean [Glycine max (L.) Merr.] on claypan soils in the eastern Great Plains. The objective of this study was to determine the 20‐yr effects of tillage (conventional, reduced, and no‐till) and N fertilization (no‐N control; knifed anhydrous NH3; broadcast urea–ammonium nitrate solution, UAN; and broadcast dry urea) on grain sorghum N uptake and soybean biomass and their relationship to long‐term yields of those crops grown on a claypan soil. Nitrogen uptake at the boot stage during the first 10‐yr period was more than 20% greater with either conventional or reduced tillage compared with no‐till, and often greater with anhydrous NH3 and urea N sources than with UAN solution or the no‐N control. During the second 10‐yr period, N uptake was generally greater with conventional and reduced tillage than with no‐till at the 9‐leaf stage, but this response did not persist to the boot stage. Anhydrous NH3 often resulted in greater N uptake at both the 9‐leaf and boot stages compared with the other N sources. The relative yield increases with N uptake at the boot stage appeared due to increasing kernels head−1 but diminished as uptake exceeded 70−80 kg N ha−1. Although dry matter measured at the R2 growth stage of soybean rotationally grown in even‐numbered years was about 10% greater with tilled options than with no‐till, biomass was not related to yield increases.