Preparation And Properties Of Coated Biochar-based Fertilizer

Biochar-based fertilizer actually is a kind of granular fertilizer with sustained-release property by mixing biochar and ordinary fertilizer in certain proportion with specific methods.Compared with ordinary fertilizers,biochar-based fertilizer has the advantages of improving soil environment and improving nutrient utilization,but the traditional biocharbased fertilizer has a serious loss due to its insufficient strength during transportation,and it still has the problem of nutrient release too fast for the fertilizer demand of crop growth cycle.Therefore,the coating can be considered to enhance the particle strength and improve the nutrient utilization.Based on this,this paper has screened out a new type of coating material on the basis of previous scholars' research,obtained the best ratio of membrane material composition and the optimum film forming process,and tested the nutrient permeability of the coating material.Then the coating process of biochar-based fertilizer was studied,and the optimum parameters of coating process were obtained.Finally,the comparison test of the nutrient release characteristics and the hygroscopic characteristics of the biochar-based fertilizer and the coated biochar-based fertilizer.The main work and conclusions are as follows:(1)Research on the ratio of coating materials of the biochar-based fertilizer.The coating material,crosslinking agent,plasticizer and emulsifier were selected as ethyl cellulose,glutaraldehyde,diethyl phthalate,tween 80.Taking the content of coating material,crosslinking agent,plasticizer and emulsifier as the test factors,the single factor test and orthogonal test were carried out with the tensile strength,breaking elongation,water absorption rate and loss rate as the evaluation index.The optimum formula was as follows: the coated materials with excellent comprehensive mechanophysical properties was obtained with 5%(mass percentage)of ethyl cellulose,1.2% glutaraldehyde,0.6% diethyl phthalate,0.4% twain 80.And its tensile strength was 16.72 MPa,the elongation at break was 3.35%,the water absorption was 8.96%,the loss ratio was 6.35%.(2)Research on the film forming process of coating materials of the biochar-based fertilizer.The effects of the time of cross-linking,the temperature of cross-linking,pH,drying time,drying temperature and drying quantity on mechanophysical properties of membrane materials were studied by single factor and orthogonal experiments.The orthogonal test results show that the optimal film forming process was as follows: The the time of cross-linking was 3 hours,the temperature of cross-linking was 50?,the pH was 5,the drying time was 8h,the drying temperature was 50?,the drying quantity was 25 g.The tensile strength of the film was 13.81 MPa,the elongation at break was 2.26%,the water absorption rate was 6.91% and the loss rate was 4.67% with 3 verification tests under the experimental conditions.The test results of nutrient permeability of coating materials show that: The cumulative nutrient permeation rate of the biochar-based fertilizer was 60.27% at twenty-eighth days,and the time required for the cumulative nutrient release rate of the biochar-based fertilizer reached 80% was 88 days.(3)Research on the coating process of biochar-based fertilizer.Based on the experimental results of the ratio of coating materials and the film forming process,the experiment of coating process of biochar-based fertilizer was explored from single factor and orthogonal test respectively.The results of orthogonal test show that the optimal process scheme of coating process of biochar-based fertilizer is as follows: The spray speed was 0.5ml/min,the coating temperature was 65?,the drying temperature was 65? and the spray times was 3.The results of orthogonal test variance analysis show that: the factors of the spray times had a very significant effect on the preliminary solubility rate and the particle strength(p<0.01),and the factors of the spray speed had a significant effect on the particle strength(p<0.05),and the interaction of spray speed and drying temperature had a significantly effect on the preliminary solubility rate(p<0.05).The variance analysis was the same as that of intuitionistic analysis,which ensured the accuracy of the process scheme.(4)Research on the basal characteristics of coated biochar-based fertilizer.In order to further research the different characteristics between the coated and uncoated biochar-based fertilizer,the nutrient leaching test and hygroscopicity test were designed and carried out.The experiment of nutrient leaching showed that the nutrient release rate of the coated biochar-based fertilizer decreased by 9.62% and the cumulative nutrient release rate was decreased by 20.84% in 30 days compared with that of the uncoated biochar-based fertilizer.The cumulative nutrient release rate of the coated biochar-based fertilizer was 70.46% in 60 days,but the cumulative nutrient release rate of the uncoated biochar-based fertilizer had reached 89.17% in 30 days.T-test results showed that the cumulative nutrient release rate of coated biochar-based fertilizer in the nutrient release duration was significantly lower than that of the uncoated biochar-based fertilizer,and the coated biochar-based fertilizer had better controlled-release effect.The test results of the hygroscopicity test showed that the hygroscopic rate of the coated biochar-based fertilizer was slower than that of the uncoated biochar-based fertilizer.The fastest hygroscopic rate of the coated biocharbased fertilizer was 3 days less than that of the uncoated biochar-based fertilizer,and the maximum difference in hygroscopic rate reached 7.59% on the 21 st day.The coating materials can effectively block the water vapor in the air into the biochar-based fertilizer,reduce the loss of fertilizer value,prolong its shelf life.