| Controlled-release fertilizer has been shown to increase the yield of crops and improve the fertilizer use efficiency in a number of production systems. However, the synchronized relationships between nutrient release of controlled-release fertilizer and nutrient requirements of cotton were rarely studied. The effects of two controlled-release nitrogen fertilizers(CRNF) which include polymer coating of sulfur-coated urea(PSCU) and polymer coated urea(PCU) on yield and nutrient uptake of cotton, during two cotton growing seasons(2012-2013) using the cotton cultivar ‘Guoxin 3’, in comparison with urea fertilizer were studied under field conditions in Dezhou. Beside, in order to investigate the interaction effects of PCU and sulfur(S) fertilization on the contents of inorganic N and available S, enzymes activities of leaves and yield of cotton, the field experiment about different types of N fertilizers and S rates was carried out in Hebei Province in 2014 and 2015; The experiment consisted of two N fertilizer types including PCU and common urea fertilizer in combination with three S rates(0, 60 and 120 kg hm-2) in the split-plot design was conducted, where the types of N fertilizer were the main plot and S rates were the subplots. Meanwhile, a potted experiment about the effects of controlled-release potassium fertilizer(CRK) on the yield and nutrient uptake was conducted. The release characteristics of controlled-release fertilizers in water and soil conditions were analyzed, the soil nutrient regime, nutrient uptake of cotton and physiological properties of cotton leaves were measured, to explore the synchronized relationships between nutrient release of controlled-release fertilizer and nutrient requirements of cotton.(1)The results indicated that CRNF significantly increased seed cotton yield by 6.10-9.78%, 14.81-18.15%, respectively, compared with the basal application of urea treatment and contrast treatment. It also increased boll weight significantly, but there were no significant effect on lint percentage. The nutrient release peak of PCU and PSCU were from peak bloom stage to full bolling stage and the first bloom stage to peak bloom stage, respectively, which were accord with the peak of cotton nutrient uptake stage(peak bloom stage to full bolling stage). Thus, 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 which R2 were 0.9712 and 0.8997, respectively, by PCU and PSCU, 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 CRNF increased cotton plant biomass accumulation by 2.90-6.14 %, significantly, compared with the basal application of urea treatment. The inorganic N content supplied by soil was also enhanced by using CRNF, especially from full bloom stage to the 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. Therefore, it could be economical and eco-friendly and widely used for cotton production.(2) The results of the split-plot design experiment revealed 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%, the nitrogen use efficiency was 27.80-34.21%, respectively, higher than urea treatments. Lint yields were also increased 5.08% by 60 kg hm-2 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 60 kg hm-2 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.(3)The potted experiment indicated that the contents of soil available K in CRK treatment were significantly higher at first bloom stage, full bloom stage, initial boll-opening stage and harvest stage than that in the basal application of potassium chloride(KCl) and potassium sulphate(KS) treatments. The lint yield of CRK treatment was 23.60% higher than KCl, 15.60% higher than KS, 16.00% higher than 40% basal and 60% top-dressing at the first bloom stage of potassium chloride(KClD), but was not significantly higher than that in 40% basal and 60% top-dressing at the first bloom stage of potassium sulphate treatment(KSD). The lint percentage of CRK was significantly higher than KCl, but not significant than other treatments in boll weight and lint percentage. The fiber length, fiber elongation and strength of CRK were significantly higher than KCl and KS, but the micronaire and fiber uniformity were not. The K use efficiency of CRK was increased by 41.90-50.90% than KCl, 27.30-29.90% than KS and even 21.10-25.20% than KClD. Thus, the releasing peak of K in controlled-release potassium fertilizer was 80-110 d, which was basically agreeable with the K uptake of cotton. CRK basal application increased the cotton yield, improved fiber quality and also enhanced K use efficiency, compared with common potassium fertilizer, no matter they are basal applied or basal plus top dressed. Therefore, potassium sulfate and potassium chloride could be replaced by controlled-release potassium chloride fertilizer in cotton production. |
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