Manurial effect of several controlled-release N fertilizers (CRNFs) on forage maize and its physiological effects

The physiologic effects of crop, such as the change of photosynthesis rate and chlorophyll content, on CRNFs is a hot topic but remaining some unclearness. The effects of several CRNF on the number of tiller, chlorophyll content and photosynthetic rates of leaves of forage maize and N use efficiency were studied through a field experiment. The relation between these physiological indices and forage maize biomass was discussed in this paper as well. The results showed that the tiller number of maize treated with CRNFs was slightly lower than that of urea treatments in prophase, however, in the anaphase, tiller number of CRNFs treatment was much higher than that of urea treatment. Both the chlorophyll content and photosynthetic rates of leaves of CRNF treatments increased markedly comparing with N urea treatment with same dosage. The biomass showed a significant correlation with the tiller number in anaphase(r=0.9677), the chlorophyll content (r=0.8967) and the photosynthetic rates (r=0.8979). CRNF could reduce the nitrate content in maize notably. Comparing with the urea treatment with same nutrients, the application of CRNF could (reduce) nitrate by 73.77 mg/kg to 709.41 (mg/kg), while comparing with the urea treatment with same dosage, the application of CRNF could reduce nitrate by 469.26(mg/kg) to 1150.00(mg/kg). CRNF could increase N use efficiency and maintain soil fertility. We could concluded that: (1) The physiological indices, such as chlorophyll content and photosynthetic rates, are not only correlated to the nutrient quantity and variety, but also influenced obviously by nutrient released-rate. (2) Not only the regulation of nitrogen application rate, but also the regulation of releasing rate could decrease nitrate notably. This provided a new way of regulating dynamic balance for the purpose of nitrate minimization. (3) N use efficiency of CRNF was obviously higher than that of urea, however, residual mineral N content in soil wasn't reduced, even increased slightly, showing a better effect on soil fertility maintenance. (4) Suitable release-controlling complex materials are better than single release-controlling materials. Both of N use efficiency and biomass of the CRNF with complex material treatments increased obviously, showing an effect nothing less than that of plastic-coated urea.