In-Season Application of Nitrogen and Sulfur in Winter Wheat

Abstract

Decreased atmospheric S deposition in the past 20 yr has led to increased S fertilizer consumption in winter wheat (Triticum aestivum L.). Producers often apply S without any soil test information. Experiments were conducted at Lahoma, Lake Carl Blackwell, and Perkins, OK (2011–2013) to assess the effect of N and S applied preplant and foliar on grain yield and grain N for winter wheat. In 2011–2012, urea ammonium nitrate (UAN) was applied preplant at rates of 40 and 80 kg N ha-1 additionally; UAN and urea-triazone (NSURE) were foliar-applied at rates of 10 and 20 kg N ha-1. Sulfur was foliar-applied as gypsum (CaSO4×2H2O) at 6 kg S ha-1. In 2013, trials were altered to apply 40 kg N ha-1 as UAN preplant, and 20 kg N ha-1 foliar-applied. Gypsum rates were adjusted at 0, 3, and 6 kg S ha-1 preplant, and S (MAX-IN-S) at 3 and 6 kg S ha-1 was foliar-applied. Sulfur did not increase grain yield or grain N concentration at any site. The interaction between foliar S and N and preplant S and N was not significant. Sulfur fertilizer application is less likely to benefit this region unless low levels of soil test S are identified before planting. Use of recommended soiltesting guides are encouraged. Although S applications are encouraged commercially, no response was observed in these trials, and all were on sites where soil organic carbon was low (<8.5 g kg-1), where the possibility of seeing S deficiency was greater.