The Release And Transport Of NP From Coated Fertilizers And The Law Of Absorption And Utilization By Crop In Soil

Encapsulating granular fertilizers with polymeric material is a new approach to improve nutrient uptake of crops and to reduce environment pollution by fertilization. In this research, polymer-coated urea and polymer-coated monoammonium phosphate developed by our own were employed and their membrane structures were studied. Meanwhile, simulation and pot culture experiments were conducted on crops fertilized by them and tests were carried out on the release and transport of nutrients in them and the nutrient uptake and utilization of crops by SEM (scan electron microscope), Conductometer and EUF (electron-ultrafiltration). The main results are as follows.The thickness and structure characteristic of the membranes of the coated fertilizers were obtained by SEM observation. The results showed the release rates of the coated fertilizers were controlled by the thickness of the membrane and the microporous route in it. The results provided theoretic basis for expounding the mechanism of nutrient release of polymer-coated fertilizer in the soil.The release kinetic characteristics of N in polymer-coated urea and polymer-coated monoammonium phosphate were observed by means of electroultrafil-tration. The curves of their kinetics were simulated by equation. The EUF coefficient described the release kinetics of N in coated fertilizers were proposed. This method has clear advantages over the traditional ones in speed and evaluating the characteristics of the nutrient controlled-release of coated fertilizer.The nutrient release rates of single granular coated urea and coated monoammonium phosphate were determined by using conductometer. This method had been verified with experiments and it was simple and applicable.The nutrient release rate of a coated fertilizer granule population was affected by the distribution field of release rates of all single granular.The nutrient release rate of the coated fertilizer was calculated by cumulative average of particles that each release nutrients at a different time. The basic law of nutrient release was simulated by equation y=x/(a+bx).The mechanism of nutrient release of polymer-coated fertilizer was deducedaccording to the membrane structure and simulated experiment of nutrient release of the coated fertilizer. The process of nutrient release can be described as follows: at first water or water vapor contact with opening additives in the coating; then the micro-passage in the membrane formed gradually, water infiltrated into coated fertilizer and dissolved solid fertilizer; finally, nutrient penetrated through the membrane and diffused because of nutrient concentration difference inside & outside the membrane, while water infiltrated into coated fertilizer under water potential gradient. Dissolved fertilizer, water and nutrient moved across membrane in circles.Laboratory soil incubation experiment was conducted to study the corelation between release rate of nutrient from coated urea in the soil and soil moisture, soil temperature and soil texture. When soil moisture was beyond 50% of the field capacity, soil temperature had a remarkable influence on the release rate of coated urea, while soil water and soil texture had not remarkable influence on it.The results from the pot culture experiment showed that the output of celery in two texture calcareous Chao soil applied with coated urea increased by 11.5%~15.2%, the quality of product was improved, the vitamin C content increased markedly, nitrate-nitrogen content decreased by 44.2%~58.9%; and residual effect-crop output of lettuce(Lactuca satival) increased by 14.4%~35.2% as compared with urea.In soil-crop system, the quantity of nutrient uptake in crop in two texture calcareous Chao soil applied with coated urea increased; the nitrogen loss reduced, ultilization rate of N element increased; the N uptake to celery increased by 2.4%~5.9% in sandy loam soil and 9.5%~11.0% in loamy sand soil, the N loss of ammonia volatilization reduced by 14.2%~14.9%, the N losses of leaching and denitrification reduced by 25.5...