Release Characteristics And Fertilizer Efficiency Of Coated Controlled-release Urea For Rice

Polymer coated urea(PCU)and polymer-sulfur coated urea(PSCU)were used as materials to study the synergistic effect of coated urea nutrient release and nutrient uptake by rice.Meanwhile,the short-term effect and long-term fertilizer effect of coated urea were evaluated by field experiments and laboratory study.The main results were as follows:The results showed that the freeze-drying method kept highly consistent with the results of the chemical method.Under field condition,PCU can release 75%-80%of nitrogen throughout the rice growth period.In this study,it was found that the nutrient release rate of the bag containing 10.0 g PCU was higher than that of 3.0 g.The release rate of surface application of PCU was higher than that of deep application,however,it did not exceed 100%during the whole growth period.The nutrient release rate of PCU and days after transplanting rice was a quadratic curve.Field experiment showed that both coated urea could increase rice yield.The release pattern of PCU in field was the same as that obtained in laboratory,and the release of PSCU was much higher.Compared with common urea,the aboveground dry mass and nitrogen uptake of coated urea treatment significantly increased.Coated urea increased nitrogen use efficiencies,and PCU was better than PSCU.The average nitrogen recovery efficiency of PCU treatment was 50%,and that was only 17%for single application of common urea(Ui).Gradient experiment of coated urea for different genotype rice showed that the indica-japonica hybrid rice had more advantages than late japonica rice.The results showed that the nitrogen application rate for the best yield of the four cultivars was 225 kg ha-1.In this study,dry matter accumulation of Yongyou hybrid rice was significantly higher than that of late japonica rice.The recovery efficiency of N fertilizer in hybrid rice and late japonica rice was high.K deficiency and P deficiency affected the apparent N use efficiency of rice.Under the 300 kg N ha-1 application rate,the apparent P recovery efficiency of Yongyou 12 was 3.9%,while that of Yongyou 538 was 16.7% and 37.8%for the apparent utilization rate of K fertilizer.The results showed that soil NH4+-N of Ui and PSCU was significantly higher than that of the other treatments,and PCU treatment maintained at a low level.There was a certain fluctuation in the pH of the soil throughout the growth period,but the amplitude of the fluctuation was 0.4 units.PSCU did not significantly reduce soil pH.The results showed that soil available K was gradually decreased during the whole growth period,but the difference was not significant like soil organic matter and soil total nitrogen.It was found that long term application of coated urea did not lead to a significant decrease of soil pH,especially for deep soil layer.Reducing application of urea did not result in the decrease of soil nutrient,such as soil organic matter,ammonium nitrogen and nitrate nitrogen.Topsoil sulfate content of PSCU treatments was significantly higher than that of other treatments.The short-term mineralization experiment showed that soil N mineralization rate decreased with the increase of soil depth,but soil N mineralization rate was the same in the same soil layer from different treatments,and was not affected by the variety and application rate of fertilizer.Pot experiment in greenhouses showed that soil productivity was affected by fertilizers.In the absence of external fertilizers,soil from the blank areas could support more crop yield,whereas pots from coated urea treatments showed lower yield,but higher than those from common urea treatments.Compared with conventional cultivation treatments,the film mulching could maintain the soil pH,but decreased the soil organic matter,total N,available P and available K in the surface layer(0-10 cm).Different treatments affected the weed community structure during the winter season,however,Cardamine hirsuta,Mazus pumilus,and Alopecurus aequalis were the main species in winter.Multivariate statistical analysis showed that soil available K was the main factor affecting weed community structure.The effect of PCU on weed community structure was not significant.The highest amount of spring weed was in the plot without nitrogen fertilizer.In summary,single application of coated urea can be used as a simple fertilizer technology for single-season rice production in this region.single application of coated urea can increase dry matter accumulation and yield.No matter whether the rice production in the current season or the long-term application,coated urea would not have significant negative effects on soil nutrients.While the application of coated urea did not significantly reduce weed diversity in paddy field.The application rate of coated urea with 225 kg N ha-1 was recommended for different genotypical in this region.