Sulfur Applications on No-till Cotton and Soil Sulfur Testing Method Comparison.

Field cotton trials were conducted on different soils across Tennessee with a total of 16 site-years during 2014-2016. Five sulfur (S) application rates of 0, 11, 22, 34, and 45 kg S ha^-1 were evaluated in a RCB design with four replicates. The fields had initial soil S fertility level ranging from very low to medium. The responses of leaf S concentration to S applications were often greater at early bloom than late bloom. Leaf S at early bloom responded significantly to S applications at 14 out of the 16 site-years. Lint yield responded significantly to S applications at seven site-years. Application of 11 kg S ha^-1 was adequate, and significantly increased yield by 7.6 to 25.1%. When data were combined across the seven site-years with significant yield responses, application of 11 kg S ha^-1 increased yield significantly by 10.4%, and 11 kg S ha^-1 was adequate for cotton to reach optimal yield. Averaged over all the 16 site-years, lint yield was significantly increased by 6.1% with application of 11 kg S ha^-1 relative to zero S. Fiber quality and soil residual S level after harvest rarely responded to S applications. When data were combined across the seven site-years with significant yield responses, there was a significant quadratic regression between yield and the total of ammonium acetate extracted soil S and S application rate. A highly significant and strong regression was observed between ammonium acetate extracted soil S and Mehlich 3 extracted soil S under a linear model when data were combined across all the site-years. This regression equation might be used to convert ammonium acetate extracted soil S to Mehlich 3 extracted soil S, and vice versa. In summary, more attention on S management is warranted for optimal cotton yield under Tennessee production environments.