Development Of A New Type Of Biochar-based Slow-release Fertilizer And Their Slow And Controlled Release Mechanism Research

The amount of fertilizer application is increasing year by year in the world,but the problems of soil compaction,soil degradation and micro-ecological destruction caused by improper fertilization are becoming more and more serious.A large number of studies have confirmed that the main reason for the low fertilizer utilization is that the dissolution rate of commonly applied fertilizer is too fast,and the nutrient release rate of commonly used fertilizers is usually dismatched with the absorption rate of plants.In addition,long-term single partial fertilizer application,humus cannot be timely supplement,resulting in the decline of soil organic matter,soil hardening and cracking.Therefore,relying on the advantages of abundant and cheap biomass resources in Xinjiang and using local materials,various biochar based slow-release fertilizers were developed,which can improve soil quality and simultaneously adapt to the law of plant nutrient absorption.The sustained-release characteristics,water retention performance,plant growth promotion and soil improvement performance of slow-release fertilizers were studied.In addition,the release model and actual slow-release experiment were used to optimize the fertilizer release law,maximize the fertilizer utilization.Moreover,the interaction mechanism between slow-release fertilizer and plants was also revealed.1)Excessive phosphorus discharge leads to eutrophication and deterioration of water.Even if phosphorus concentration is low,it can accelerate the eutrophication process of water body.Herein,to meet the requirements of wastewater discharge,sustained release phosphorus resources are in short supply,we developed bentonite modified biochars derived from the co-pyrolysis of biomass and bentonite,which exhibited much higher phosphate adsorption capacities and superior P-slow release kinetics compared to that of the biochar without the modification of bentonite.The mechanistic study revealed that the improved adsorption and release performance of the as-prepared biochars originates from the presence of Ca and Mg in bentonite which leads to the formation of desirable porous structure,the reduced negative charge on the surface of the derived biochars,and the formation of Ca and Mg related precipitations.Moreover,we demonstrated that the P-release kinetics of the as-prepared biochars can be precisely tuned by controlling the amount of bentonite,and a modified Fick model was developed to establish a quantitative relationship between biochars with different formulations and their P-release kinetics.2)A new strategy for the synthesis of improved BSRFs by co-pyrolysis of biomass（cotton straw）,nutrients（K₃PO₄）,and bentonite under microwave irradiation was developed.The results show that the presence of bentonite during the co-pyrolysis process is beneficial for improving the slow-release performance of BSRFs.The mechanistic study based on SEM,TEM,XRD,and XPS characterizations integrated with the release kinetics reveal that the presence of bentonite in the pyrolytic process facilitates the formation of a desirable structure within BSRFs to improve the slow-release performance,and the formation of P-related chemical bonds during the bentonite participated pyrolysis process also contributes to the improved slow-release performance for P.Moreover,the slow-release performance of BSRFs agrees very well with their positive effects on the growth of pepper seedlings in pot experiments.The economic assessment suggests that the as-synthesized BSRFs should have the advantage of low production costs.3)Although biochar-based fertilizers prepared by the co-pyrolysis of biomass and other nutrients containing feedstocks have been extensively demonstrated to be promising slow-release fertilizers,a further improvement of their slow-release performance is still highly required.The slow-release law is more consistent with the growth cycle of plants and reduces the frequency of fertilizer application.Here,new coated biochar-based slow-release fertilizers（CSRFs）by the integrated co-pyrolysis and coating technology were developed.The results indicate that the application of coating to the surface of biochar-based slow-release fertilizers（BSRFs）derived from the co-pyrolysis of cotton straw,Mg₃（PO₄）₂and bentonite can significantly improve the slow-release performance.The cumulative release concentration of P is found to be 1.98 g/L from BSRFs within 30 days,while the maximum cumulative release concentration of P from CSRFs is only 0.82 g/L.The P-release rate constants of CSRFs are only about half of those of BSRFs.In addition,the as-prepared CSRFs exhibit superior degradability compared to BSRFs,and 35.21%of CSRFs is degraded within 60 days,which is much higher than that of BSRFs.Finally,pot experiments reveal that pepper seedlings fertilized by CSRFs grow much better than those fertilized by BSRFs.4)Modern agriculture is strongly calling for the development of environment-friendly slow-release fertilizers with high water retention.A new biochar embedded-Semi-IPN based SRF is developed by the incorporation of biochar into semi-interpenetrating polymer networks（Semi-IPN）via grafted co-polymerization,which holds great potential to combine the advantages of biochar and Semi-IPN when they are used in SRFs.The results show that the as-prepared biochar embedded-Semi-IPN based SRF（Bi Be-SRF）exhibits a high water-retention capacity with the value of 73.50%after 25 days,which far outstrips that of Semi-IPN based SRF without the incorporation of biochar.Bi Be-SRF also has a better slow-release performance of nutrients than the Semi-IPN based SRF.The release ratios of N,P and K from Semi-IPN based SRF within 30 days reach in the range of 95.5%e100.0%,but they are less than 80.0%for Bi Be-SRF.The degradation ratio for Bi Be-SRF is 62.63%after 90 days’degradation experiment which is higher than Semi-IPN based SRF,suggesting that the presence of biochar significantly improves the degradability of Bi Be-SRF.Pot experiments reveal that pepper seedlings fertilized by Bi Be-SRF grow better than those fertilized by Semi-IPN based SRFs,which further highlights its great potentials for the practical application.5)In order to develop biochar-based SRFs with good water retention,slow release,biodegradable properties.a new class of biochar-based SRFs are developed by an integrated co-pyrolysis and co-polymerization process（PSRFs）.The water-retention performance and P slow-release behavior of PSRFs are evaluated,which are compared with other types of biochar-based SRFs derived from biochar-based phosphorus adsorption（BSRFs）,co-pyrolysis of biomass-bentonite-nutrients（BSRFs）,and the application of coating on BSRFs（CSRFs）.The results show that the obtained PSRFs exhibits high water retention with the maximum swelling capacity of 94.2 g/g,far outstripping other tested SRFs.The water-retention performance of PSRFs is found to be positively correlated with their crosslinking agent contents.In addition,PSRFs has excellent P slowrelease performance which is comparable with CSRFs（～51.5%of P release after 30 days）,but much better than MSRFs and BSRFs with a complete P release after 30 days.Furthermore,pot experiments reveal that PSRFs has the highest P utilization efficiency（75.83%after 60days）,which can promote the growth of pepper seedlings better than other SRFs.Moreover,the soil burial tests indicate that PSRFs has a good biodegradability with the degradation ratio of 33.46%in 75 days.Finally,biological abundance analysis further reveals that Actinobacteria in soil is mainly responsible for the metabolism of starch and sodium alginate in PSRFs.A series of biochar-based slow-release fertilizers were developed,and their release kinetics was deeply analyzed.The responses of biochar-based sustained release fertilizers to plant growth promotion were revealed,and the soil microbial diversity of pepper rhizosphere was analyzed.Overall,this study may provide theoretical guidance and practical application cases for more rational application of biochar-based slow-release fertilizers.