Effects of Polymer‐Coated Urea Application Ratios and Dates on Wheat and Subsequent Double‐Crop Soybean

Abstract

Effective management of soil N fertilizer, including the use of enhanced efficiency N fertilizer sources and optimal dates of fertilizer application, may increase agronomic performance of double‐cropped winter wheat (Triticum aestivum L.) with soybean [Glycine max (L.) Merr.] under no‐till (NT) management. In a double‐cropping system, ratios and dates of application of polymer‐coated urea (PCU) may affect both wheat and subsequent soybean yields. The objectives of this research, conducted over three growing seasons (2008–2010) in northeastern Missouri, were to evaluate urea release over a range of PCU application dates, and to assess the effects of the fall to spring application dates of PCU and ratios of PCU with noncoated urea (NCU) compared with ammonium nitrate (AN) and NCU on wheat and double‐crop soybean yield. The experimental design was a factorial that included two N application rates (84 and 112 kg N ha−1), seven application dates (October–April), five N fertilizer source/ratios, and nontreated controls. Urea‐N release from PCU fertilizers applied on 15 October was <30% by 15 February in two of the three study years. Wheat yields were significantly (P ≤ 0.05) affected by the three‐way interactions of year × N source × N rate and year × N source × application date. In two of the three study years, yields were 450 to 500 kg ha−1 greater with an October application of 100% PCU compared to 100% NCU. Double‐crop soybean yields were not affected by preceding winter wheat N management.