Synchronized relationships between nitrogen release of controlled release nitrogen fertilizers and nitrogen requirements of cotton

Controlled release nitrogen fertilizer (CRNF) has been shown to increase yield of crops and improve the nitrogen (N) use efficiency of fertilizer in a number of production systems. However, the synchronized relationships between N release of CRNF and N requirements of cotton were rarely studied. In the present study, the effects of two CRNF including polymer coated urea (PCU) and polymer coating of sulfur-coated urea (PSCU) on yield and nutrients uptake of cotton were investigated under field conditions in 2012 and 2013. The results indicated that the successive release rate of N from CRNF corresponded well to the N requirements of cotton plants. In addition, significant linear correlations between N release rate of CRNF and N requirements of cotton were observed during the whole growth periods of cotton. Moreover, the release rate showed significantly positive correlations with cotton yield, soil inorganic N content, N use efficiency, total N uptake and biomass of aboveground. The seed cotton yields in treatments which applied PCU and PSCU once were increased by 14.81-18.15% compared with U1 (urea applied as basal fertilizer). However, there was no significant difference between CRNF and U2 (twice-split applications of urea fertilizer). Although the numbers of bolls and lint percentage were not significantly enhanced by using CRNF, the boll weight was 3.63-11.51% higher than that in urea treatments. In addition, the N uptake and N use efficiency of cotton plant were improved by CRNF compared to the urea treatments. The inorganic N content supplied by soil was also enhanced by using CRNF, especially from full bloom stage to initial boll-opening stage. The results suggest that the release rate curves of CRNF were ideal patterns which could synchronize N release with N requirements pattern of cotton. In addition, it could be economical and eco-friendly and widely used for cotton production.