Study On Preparation And Controlled-Release Properties Of Urea

Nitrogen as one of the most important nutrient elements, the nitrogen fertilizer made great contributions to grain production of our country. Urea is one of the widest scope of applications nitrogen fertilizer. But urea as an instant fertilizer, nutrients of ordinary urea were easy to be leached and volatilized. It was lead to low efficiency. Improve nitrogen utilization has become a key link of nitrogen management. Nutrient release rate of coated urea could be controlled, made them meet the requirement of crop growth in different stages. The slow nutrients release rate coudle reduce nitrogen volatilization and times of fertilization, increased the nitrogen utilization rate and saved the human resources. Coated urea became an important trend at present.The article used biodegradable organic high polymers as main film-forming materials, with emulsifier, plasticizer, pigment to prepare a coating agent. Explored optimum conditions of preparation, controlled-release properties, release mechanism and environment affection, and compared coated urea with sulfur coated urea. In order to get new coating agent had simple coating process, high performance and low price, and provide a scientific basis for performance evaluation and application. The main conclusions were as follows.The material filtration, single and orthogonal test showed that, the preparation optimum conditions of coating agent for controlled-release of urea were as follow:the amount of film-forming materials(AX) was 8.0%, emulsifier(T-80) was 1.5%, plasticizer(vegetable oil) was 2.0%, pigment(disperse brilliant red E-RLN) was 0.16%, solvent(ethyl acetate) was 88.34%, baking time was 25 min.The physico-chemical properties of coating agent for controlled-release of urea results showed that, the pH was 5.9, slightly acidic, conducived to the crop growth and had no impact on soil acidity and alkalinity; viscosity was 0.77 mpa·s-1, low viscosity was suitable for coating, coated urea did not adhesion; film-forming was moderate film was uniform; film-forming time was 8min, short time in favour of coating; coating film was water-insoluble, indicated that coated urea still had high controlled-release properties; the high coating uniformity could up to 85%;the coating-off rate was 7.23%, it indicated that the film could be firmLy attached to the urea surface, in favour of transportation and storage; the moisture resistant of coated urea were better than ordinary urea, it indicated that coating agent had moistureproof effect. In conclusion, coating agent for controlled-urea had good physico-chemical properties.The controlled-release properties of coating agent for controlled-release of urea results should that, coating agent KSFA-2 could reduce preliminary solubility rate of coated urea. The initial release rate of coated urea were 1.63%, less than 15%, that conformed to the industry standards of slow/controlled-release fertilizer specified in country and CEN, reducing the loss of nitrogen and environmental pollution. Compared with ordinary urea and SCU, coated urea the initial release rate reduction 92.59% and 72.26%. The differential release rate were 2.79, eleven times of SCU, it indicated that, coated urea could continue to supply nutrition, the release trend were more steady, fatty effect long. The cumulative release rate of 28 days were 77.03%, less than 80%, that conformed to the standards of slow/controlled-release fertilizer specified in country. The stated release time was 29.07 d, the controlled-release properties of coated urea were better than SCU. In the isothermal condition, the dynamics of coated urea KSFA-2 nitrogen release rate could be quantitatively described by Richards equation, the curves were "S" pattern, the supply nitrogen were consistent with the demand for nitrogen during the crop growth, suited for short growing period filed crops. The cumulate release curves were "L" pattern, it could be described by Gompertz equation, were not consistent with the demand for nitrogen during the crop growth. In conclusion, the coating agent for controlled-release of urea could slow nitrogen release rate effectively, preventing the loss of nitrogen and environmental pollution caused by overfertilization. Compared with SCU, the controlled-release properties more better and more suited to demand for nitrogen of the crop.The result of environment effected on controlled-release of coated urea KSFA-2 showed that, temperature, pH and water volume affected the nitrogen release rate of coated urea KSFA-2, The temperature and water volume were positively correlated with nitrogen release rate, that increased with temperature and water colume rise. Temperature was more significant. The effection curve of pH was parabola. Along with the enhancing of the acidity and the alkalinity the release rate of coated urea KSFA-2 increased.