Effects of polymer coated urea and sulfur fertilization on yield, nitrogen use efficiency and leaf senescence of cotton

Nitrogen (N) and sulfur (S) fertilization play important roles for improving cotton yield, but no studies have been implemented to explain their interaction on yield, nitrogen use efficiency and physiological characteristics of cotton. In order to investigate the interaction effects of polymer coated urea (PCU) and S fertilization on the contents of inorganic N and available S, enzymes activities of leaves and yield of cotton, the field experiment with different types of N fertilizers and S rates was carried out in 2014 and 2015. The experiment consisted of two N fertilizer types including PCU and common urea fertilizer (Urea) in combination with three S rates (0, 60 and 120kgha−1) in the split-plot design, where the types of N fertilizer were the main plot and S rates were the subplots. The results indicated that the N release characteristic of PCU in field condition was closely matched to the N requirements of cotton, the contents of soil nitrate nitrogen (NO3−-N) and ammonium nitrogen (NH4+-N) were significantly increased from the first bloom stage to the initial boll-opening stage by using PCU compared with urea. And the content of available S was significantly increased in full boll setting stage. Meanwhile, the number of bolls and lint yields of PCU were 7.03–8.91% and 5.54–11.17% higher than urea treatments. Lint yields were also increased 3.77–9.26% by S fertilization, evidencing a clear interaction between N and S, but no significant difference was observed between S60 and S120 treatments. In addition, the N apparent recovery use efficiency (RUE) and agronomic use efficiency (AUE) were increased, fiber length and strength were improved, the nitrate reductase and peroxidase activities and photosynthetic rates (Pn) were enhanced by PCU and S fertilization. However, the lint percentage, micronaire and fiber elongation were neither affected by the type of N fertilizers and S rates, nor by their interaction. Consequently, the application of PCU combined with 60kgha−1 sulfur fertilizer on cotton could not only increase the yield and nitrogen use efficiency but also improve the fiber quality and physiological properties of leaves.