| China is a large agricultural country with more people and less land.The land that could be used for cultivated land accounts for about 10%of China’s area.The application of chemical fertilizer in agricultural production have improved the problem of food shortage in China.Chemical fertilizer played a key role in the development of agriculture in China.With the increase of the use of common fertilizer,the yield per unit area of grain is decreasing.The reason is that the utilization rate of common fertilizer is low and the nutrient waste is serious.Nitrogen fertilizer could provide nitrogen nutrition for crops in the process of growth,increase crop yield and improve the nutritional value of agricultural products.Data showed that the utilization rate of nitrogen fertilizer in foreign countries was more than 50%,but as a large agricultural country,China have a huge demand for nitrogen fertilizer,but the utilization rate is only35%-50%.The low utilization rate of nitrogen fertilizer directly caused the rapid deterioration of soil environment in recent years,accompanied by the serious waste of resources.Compared with other nitrogen fertilizers,urea has obvious advantages,such as high concentration of available nutrients,affordable price and no effect on soil.Therefore,the preparation of low-cost slow/controlled release coated urea can effectively improve the utilization rate of nitrogen fertilizer,save resources and reduce environmental pollution.In this study,two degradable macromolecule materials,polyvinyl acetate（CX）and isocyanate（KX）,were used as film-forming materials,and were formulated with emulsifiers,plasticizers,and pigments and other additives to prepare a composite urea coating agent.Through single factor experiments and orthogonal experiment to determine the best conditions for preparation.The controlled-release properties of KSFCK-3 were investigated by measuring the initial release rate,differential release rate,cumulative release rate and nutrient release period of coated common urea,and compared with sulfur coated urea and uncoated urea;The p H,viscosity,film-forming property,film-forming time,water solubility of coating film and coating time of KSFCK-3 were investigated;The physical and chemical properties of urea coating agent were studied by measuring the uniformity of the coating and the rate of falling off of the coating;The effects of temperature,p H,fertilizer water ratio and other environmental factors on nutrient release of coated urea were investigated.The purpose was to provide scientific basis for the development,performance evaluation and application of coated urea.The main conclusions were as follows:（1）The results of single factor experiment and orthogonal experiment showed that the optimal preparation conditions of composite urea coating agent KSFCK-3 were:the composite ratio of film-forming materials（CX:KX）was 2:1,and the total amount of film-forming materials was 13%,the amount of emulsifier OP was 0.9%,the amount of plasticizer tributyl phosphate was 1.8%,the amount of pigment basic fuchsin was0.12%,and the amount of solvent ethyl acetate was 84.18%,reapectively.（2）The research results of the controlled release performance of the compound urea coating agent showed that the initial release rate of KSFCK-3 coated urea was6.87%,which was in line with the slow/controlled release fertilizer industry standard established by the European Standards Committee and the Chinese slowed release fertilizer standard（GBT23348-2009）,which stipulated that the initial dissolution rate was less than or equal to 15%,while the initial release rate of sulfur-coated urea was43.22%,which did not meet the requirements;the differential release rate of KSFCK-3 coated urea was 2.85%,which was 3.03 times as much as that of sulfur-coated urea.KSFCK-3 coated urea could continue to provide nutrients for crops in the late stage of fertilization,while the differential release rate of sulfur coated urea was much lower than that of KSFCK-3 coated urea,which was insufficient for continuous feeding;The cumulative release rate of KSFCK-3 coated urea for 28 days reached 72.9%,which was in line with the requirement that the 28d cumulative release rate≤80%in the national standard of（GBT23348-2009）slow-release fertilizers.The cumulative release curve was gentler than that of sulfur-coated urea,which could continuously provide nutrients to crops.Sulfur-coated urea releases most of the nutrients within 1-7 days,resulting in the loss of nutrients that could not be absorbed by the early crops and insufficient nutrient supply in the later crops;the nutrient release period of KSFCK-3 coated urea was much longer than that of sulfur-coated urea.The controlled release performance of urea was better than that of sulfur-coated urea,which was 3.9 times that of sulfur-coated urea,indicating that it could provide nutrients to crops for a long time.Therefore,compared with sulfur-coated urea,KSFCK-3 coated urea could realize the gradual release of nutrients,effectively avoided resource waste and environmental pollution caused by repeated fertilization and low utilization rate.（3）The physical and chemical properties of the compound urea coating agent KSFCK-3 were studied.The results showed that the p H of the compound urea coating agent KSFCK-3 was 5.85,which was weakly acidic and would not affect the normal growth of crops.The viscosity of KSFCK-3 was 9.50 m Pa·s-1,which was low and suitable for coating,and the coating effect was good.The film-forming property was moderate and uniform.The film-forming time was 7.1 min,which could reduce production time,save production cost and facilitate large-scale production;The results showed that the coated urea was completely insoluble in water and had good slow/controlled release performance;the uniformity of the coated urea was 82.5%,and the falling off rate of the coated urea was 6.88%.The coated urea had good uniformity,and the coated urea was firm and easy to transport and store;the moisture resistance of the coated urea was far better than that of the uncoated urea,which indicated that the coated urea could be placed in humid environment for a longer time and was not easy to absorb moisture and pulverize.Therefore,the physical and chemical properties of KSFCK-3were good.（4）The effect of environmental factors on nutrient release of coated urea was studied.The results showed that temperature,p H and ratio of fertilizer to water had certain effects on nutrient release of coated urea.The nutrient release rate increased with the increase of the ratio of fertilizer to water,increased with the increase of temperature,and decreased first and then increased with the increase of p H.the effect of temperature on the nutrient release rate of coated urea was the most significant.Compared with sulfur coated urea,the nutrient release rate of KSFCK-3 coated urea was less affected by temperature,p H and the ratio of fertilizer to water,indicated that the slow/controlled release effect of KSFCK-3 coated urea was better than sulfur coated urea under the effect of environmental factors. |
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