Development Of Organic And Inorganic Coated Slowed-release Fertilizers And Study On Their Mechanism Of Improving Soil Fertility

With the increasing population of the world,the demand for food is also increasing year by year.In order to meet the global demand for food,large amounts of chemical fertilizers have been applied in many areas to increase grain yield per unit area.Although it can improve crop yield,the loss of excess nutrients can easily lead to environmental pollution.So how to improve the nutrient utilization rate of fertilizer becomes the key to solve the problem.In recent years,coated slowed-release fertilizers have been widely studied and applied in crop production,and have also obtained good feedback benefits.However,many coated fertilizers contain toxic,harmful and non-degradable components,which pose potential threats to soil,water and atmospheric environment.Thus,the focus of this study is to develop an environmentally friendly fertilizer product,which can not only improve the nutrient utilization rate of fertilizer,but also avoid secondary pollution to the environment.Therefore,two environmentally friendly coated slowed-release fertilizers are studied in this paper.The effects of different parameters on the slowed-release performance of coated fertilizers are investigated by studying the specific surface area,pore structure,membrane structure image and types of functional groups of coated fertilizers.It is also applied in pot experiment to explore the feedback effect of coated fertilizer products on soil fertility and crop growth.Two main conclusions of this study are as follows:（1）Bio-oil coated carbon-based slowed-release fertilizer:Biochar and bio-oil are produced by pyrolysis of wheat straw.The pyrolysis mode and atmosphere have an impact on the physical and chemical properties of biochar and bio-oil.Compared with one-step pyrolysis,the biochar of two-step pyrolysis has better performance in nutrient retention.The retention rate of N,P and K increases by 6.47%,10.95%and 8.58%,respectively.At the same time,the specific surface area and pore volume are also improved.CO₂is a more suitable atmosphere for the preparation of high adsorption biochar materials than N₂.The bio-oil from two-step pyrolysis to 800℃contains a large number of hydroxyl functional groups,which plays a promoting role in improving the coating properties of bio-oil.The biochar prepared by pyrolysis is evenly mixed with nutrient powder in proportion,and the composition of nutrient are divided into（NH₄）₃PO₄and KCl.Using clay as a binder,the disk granulation mechanism is used to make granular fertilizer.In the water chestnut coating machine,the bio-oil is sprayed onto the fertilizer surface and is carried out at 80℃and 40r/min by mixing heat curing reaction.After drying,bio-oil coated carbon-based slowed-release fertilizer is obtained.In terms of nutrient leaching rate in aqueous solution,carbon-based slowed-release fertilizers can improve the slow-release performance of fertilizers.Compared with traditional fertilizer,nutrient release rates decrease by 7.0%-18.9%.The slowed-release ability of bio-oil coated fertilizers continue to improve,and the nutrient release rates decrease by 14.6%-28.1%.In terms of soil nutrient leaching rate,compared with traditional fertilizers,the nutrient leaching rate of carbon-based slowed-release fertilizers decrease by 37.6%-47.7%.The fertilizer coated with bio-oil is even more effective in reducing leaching loss,by 45.2%to53.9%.The coated slowed-release fertilizers with two-step pyrolysis in CO₂atmosphere show the best slow-release ability in both aqueous solution and soil environment.In terms of soil fertility and wheat growth,the dry matter accumulation of plants added with bio-oil coating fertilizer increase.Compared with blank control group and traditional fertilizer group,the contents of N,P and K in plants are significantly increase.Among them,the two-step pyrolysis of bio-oil coated carbon-based slowed-release fertilizer in CO₂atmosphere is the best technology for the preparation of bio-oil coated carbon-based slowed-release fertilizer,which meets the needs of plant growth.（2）Ethyl cellulose coated chicken manure slowed-release fertilizer:The chicken manure and clay are added into the disk granulator in a ratio of 1:1,and the speed is set at20r/min to prepare the chicken manure granular fertilizer.Put an appropriate amount of ethyl cellulose into a beaker and stir the beaker in a magnetic stirrer at 45℃for 20min to obtain the coating solution of ethyl cellulose.The chicken manure granular fertilizer is placed in a water chestnut coating machine,and ethyl cellulose is sprayed onto surface of fertilizer.The mixing heat curing reaction is carried out at 80℃and 40r/min.The ethyl cellulose coated chicken manure slowed-release fertilizer is obtained.The concentration of ethyl cellulose have affected the slow-release performance of coated chicken manure fertilizer.Compared with uncoated chicken manure granular fertilizer,the coating with ethyl cellulose is able to improve the slowed-release performance of fertilizer.The water solubility of nutrients at 56 days decrease by 6.78%to 19.90%.The release lives of N,P and K are 56d,70d and 28d,respectively.The coated fertilizer with 0.10g/ml ethyl cellulose has the best slow-release ability.Through the analysis of pore structure,scanning electron microscope and surface functional groups of coated fertilizers,it is found that the increase of film thickness,the decrease of average pore size and the increase of hydrophobic groups in the coated materials are the reasons for the improvement of nutrient release by coated fertilizers.Meanwhile,the difference of ethyl cellulose concentration can affect of soil fertility and crop growth.The N content of wheat plant in 0.05g/ml,0.10g/ml and 0.15g/ml of ethyl cellulose fertilizer increases by 2.89%,3.85%and 2.04%,respectively,compared with that in pure dry chicken manure group.The leaching rate of cumulative N content in the three groups decrease 29.24%,33.62%and 28.64%.P and K nutrients also have corresponding effects.The P content of wheat plants increases by 1.49%,2.33%and 1.13%compared with the pure dry chicken manure group,respectively.The leaching rate of cumulative P content decreases by 31.18%,39.88%and 46.51%,respectively.The K content of wheat plant increases by 1.43%,3.26%and 2.42%,respectively,and the leaching rate of cumulative K content decreases by 13.23%,15.89%and 13.51%,respectively,compared with the pure dry chicken manure group.Ethyl cellulose coated chicken manure fertilizer shows better performance in improving nutrient utilization rate and reducing nutrient leaching loss,which can not only improve soil fertility,but also further promote the growth of crops.The above two methods of preparing novel coated slowed-release fertilizers have opened new ideas for the selection of coated materials for slowed-release fertilizers.At the same time,it also provides a theoretical guidance for the resource utilization of agricultural wastes such as straw and livestock manure.