Grain sorghum productivity as affected by nitrogen rates and available soil water
Augustine K. Obour, Johnathon D. Holman, Yared Assefa
Abstract
Abstract Despite greater drought tolerance, soil water stress and low soil nitrogen (N) are major factors that affect sorghum ( Sorghum bicolor ) productivity and profitability in dryland environments. The main objective of this study was to determine the effects of available soil water at planting and N fertilizer on grain sorghum yield and net return. The study was conducted near Hays, KS, from Summer 1971 to Fall 2002. Treatments were four N rates (0, 22, 45 and 67 kg N ha −1 ) and depth of moist soil determined prior to sorghum planting each year. Results showed a −0.96, 14.4, 29.3, and 36.5 kg ha −1 yield change per kg N applied for very low yielding (yield < 1,269 kg ha −1 ), low yielding (1,269< yield <2,611), high yielding (2,611< yield <3,986), and very high yielding (yield > 3,986 kg ha −1 ) environments, respectively. Sorghum yield increased by rates of 9.6 and 20.4 kg ha −1 per mm increase in available soil water (ASW) at planting for 0 and 67 kg N ha −1 , respectively. A multilinear function showed that grain yield increased by 20 kg ha −1 for each kg N ha −1 applied, by 15 kg ha −1 for each mm increase in ASW, and by 0.67 kg ha −1 for each mm increase of in‐season precipitation (ISP). Net return was negative for all environments when depth of moist soil at planting was ≤76 cm. We concluded that ASW prior to planting is critical for sorghum production and can be used to adjust sorghum N fertilizer rates early in the season.