Nitrogen fertilizer source, rate, placement, and application timing effect on sorghum (grain and forage) and corn grain yields

Abstract

Identifying the limiting nutrient, fertilizer source, rate, placement, additives, and timing of application are critical components of fertilizer management. The objective of this study was to quantify the impact of nitrogen (N) fertilizer source, rate, placement method, additives, application timing, and environment on yields of grain sorghum, forage sorghum [Sorghum bicolor (L.) Moench], and corn (for grain, Zea mays L.). Independent field experiments were conducted at 13 different environments in Kansas from 2008 through 2013 on grain sorghum, forage sorghum, and corn. Treatments were an incomplete factorial combination of four fertilizer placement methods, three fertilizer types, five fertilizer additives, three fertilizer application times, and six fertilizer rates that varied by location and across years. Results showed grain and forage sorghum yields responded to N fertilizer in environments that were not extremely dry (<136 mm) or wet (>651 mm). Corn responded to N fertilizer application only in high-precipitation environments. For grain sorghum, where rate × placement × source × additive interaction was significant, broadcast application of urea (source) at high rates (67–134 kg N ha⁻¹), with summer application timing, or with additive in winter (with environmentally smart nitrogen [ESN]) resulted in up to 43% greater yield compared with application of urea-ammonium nitrate (UAN; source) and surface band (placement) at 67 kg ha⁻¹ without additives. In the one site-year where forage sorghum responded to fertilizer application, forage yields with preplant application of UAN at 56–140 kg ha⁻¹ were 164% greater than the control. For corn, application of either urea or UAN fertilizer, UAN in coulter or surface band, with ESN blend, applied at planting, and at highest rates (160 kg ha⁻¹) resulted in best yields compared with the alternatives and 110% greater yield compared with the unfertilized control. We concluded that fertilizer rate is an important management component as it consistently affected yield regardless of crop considered. Fertilizer placement and timing have crop-specific importance as they were significant for only corn, but the main effect of additives (N stabilizers) was not significant for any of the crops. Environment and crop type influenced crop response to N fertilizer rate, timing, placement, and additives.