Optimization Of Preparation Technology Of Coated Phosphate Fertilizer And Its Blengding Application Effect In Wheat-Maize Rotation System

There are many difficulties in the preparation of coated P fertilizer due to their irregular particles and the unsmooth surface.The preparation of qualified coated controlled-release P fertilizer and the development of associated application technology are important prerequisites to improve the utilization rate of P fertilizer,reduce production cost and increase crop yield.Based on diammonium phosphate（DAP）,this paper discusses the optimization of DAP particles,the development of DAP coatings and the expanding of DAP products.Firstly,in order to solve the problem of irregular particle cores of coated DAP,the effects of two modification methods on the angle of repose,specific surface area and surface smoothness of DAP particles were discussed by using polyolefin wax and water as the modification medium,which provided theoretical basis for the fine preparation of coated P fertilizer.Secondly,the coated P fertilizer prepared at the present stage does not have excellent controlled-release performance and cost performance.Different particles of film materials such as castor oil-based polyurethane,epoxy resin,liquefied wheat straw-based polyurethane and modified liquefied straw-based polyurethane were used for coating.The effects of different coating materials on the controlled-release characteristics and preparation cost of coated P fertilizer were studied to explore the applicability of different coating materials in the preparation of coated P fertilizer.Furthermore,in view of the lack of scientific application guidance of coated P fertilizer,the effects of coated DAP on wheat and maize yield and yield components,P use efficiency,soil nutrient status and economic benefits were studied by a biennial pot experiment and a 4-year field experiment of wheat and maize.The main results are as follows:（1）Before coating,polyolefin wax was blended with DAP particles to evenly cover the surface of DAP particles to fill the holes on the surface of particles.Castor oil-based polyurethane,epoxy resin,liquefied wheat straw-based polyurethane,modified liquefied straw-based polyurethane and other membrane materials were used for further coating.The experimental results showed that the wax-based modification can significantly reduce the angle of repose and specific surface area of DAP particles,with a decrease of 18.45%¹9.47%and10.47%¹7.11%respectively.In addition,the hardness of the modified particles and the coated particles were significantly increased by 34.62%and 13.61%respectively.On the other hand,due to the lubrication of polyolefin wax,fertilizer particles can fully rotate in the drum during the coating process,making the coating of coating materials more uniform.In addition,coating polyolefin wax on the surface of DAP particles can improve the thermal insulation performance of particles and reduce energy loss,which can significantly reduce energy consumption and production cost in large-scale industrial production.The results also showed that the controlled-release performance of castor oil-based polyurethane coated DAP was improved significantly.Compared with the coated DAP prepared from traditional DAP particles,the initial release rate decreased from 3.63%to 0.22%and the release period extended from 60.41 days to 93.45 days at 4%coated amount.However,the other three membrane materials did not show good controlled-release performance.Adding water during the rotation of fertilizer particles can soften the particle surface and polish the edges and corners of the particle surface,making the shape of fertilizer particles more regular and the surface smoother.Compared with the wax-based modification,the cheaper and more easy-to-get water was used as the modified medium to further reduce the material cost.The test results showed that the angle of repose and specific surface area of polished particles decreased by 2.48%,39.78%,10.57%⁴8.76%,respectively,compared with the original particles.Particle roundness and hardness increased by 0.11%-1.53%and 10.66%¹2.09%,respectively.The release performance of castor oil-based polyurethane coated DAP prepared from polished particles improved significantly,compared with that prepared form the traditional particles.When 4%coating materials were used,the initial release rate decreased from 5.84%to 1.14%,and the release period extended from 60.40 to 108.53days.Similar to the results of wax-based modification,the controlled release properties of coated P fertilizer prepared by other three coating materials were poor.（2）The release characteristics of controlled-release doped P fertilizer can better match with the P absorption curve of wheat and maize.The results of pot experiment showed that compared with traditional P fertilizer,the yield of wheat and maize increased significantly by6.12%²9.47%and 5.11%²3.58%through applying a mixture of controlled-release P fertilizer and normal P fertilizer,and the soil available P content increased significantly by6.26%³5.41%and 19.44%²8.39%at the jointing stage and filling stage of wheat,and significantly increased by 45.95%⁵7.77%and 29.79%⁴9.64%at the jointing stage and big-bell stage,respectively.In addition,the leaf SPAD value,photosynthetic related enzyme activity,nitrogen and P metabolism related enzyme activity of maize plants were significantly increased,soil phosphatase activity was increased by 18.67%⁹0.54%,and plant root phosphatase activity was increased by 6.38%⁴9.64%.In field experiments,the number of ears of wheat and row number of maize increased significantly,and the yield of wheat and maize increased significantly by 7.49%¹4.52%and 5.95%¹9.69%,respectively.For 4 consecutive years,the application of controlled-release mixed P fertilizer can reduce the fixation of P in the soil,keeping the soil pH at a more stable level,and ensure the availability of P and other nutrients.（3）The results of three consecutive years of nitrogen and P application location experiment showed that,the best nitrogen application rate of wheat season was 134.41¹38.03kg?hm^-2,the best P application amount was 108.80¹12.34kg?hm^-2;the best nitrogen application amount of maize season was 172.42²09.25kg?hm^-2,the best P application amount was44.90⁵5.44kg?hm^-2,which were significantly lower than the local farmers’habitual fertilization rate,especially in the application of P fertilizer in maize season.In addition,the best application rate of nitrogen fertilizer increased year by year,while the best application amount of P fertilizer decreased...