Preparation Of Straw Biochar-based Biofertilizer And Its Synergistic Mechanism On Soil Fertility

The prominent contradiction between population growth and soil degradation makes new fertilizers urgent to be developed.In recent years,new fertilizers,including biochar and biofertilizer,have been successfully applied in modern agriculture.However,biochar has limit nutrient content and the application effect of biofertilizer is unstable.To improve soil nutrients and the stablility of the biofertilizer,biochar was selected as the inoculant carrier of biofertilizer considering its porous structure and large specific surface area in this study.Using straw biochar,different functional biofertilizer and N-P-K fertilizer as raw materials to prepare efficient and environmental friendly green biochar-based biofertilizer（BCMF）by optimizing preparation methods and process parameters and verified by pot experiments.The nutrient release pattern and synergistic mechanisms of soil fertility were also discussed.This study could provide technical support and theoretical guidance for sustainable agricultural development methods such as straw resource utilization and chemical fertilizer reduction.The main results were as follows:1.The straw biochar pyrolyzed at 450℃（BC450）possessed better pore structure,higher nutrient content,the highest nitrogen and potassium adsorption capacity（10.98mg/g,1.13 mg/g）and higher phosphorus adsorption capacity（0.90 mg/g）.Therefore,it was selected as the raw material to prepare biochar-based biofertilizer.Neutral and alkalescence environment could facilitate the adsorption capacity of N-P-K under which would be better to prepare BCMF.The nitrogen adsorption of straw biochar was mianly depended on electrostatic adsorption and hydrogen bonding of oxygen-containing functional groups,the phosphorus adsorption was relied on ligand exchange,whereas the potassium adsorption was mainly depended on physical adsorption and cation exchange.2.Determined by orthogonal experiment,it was showed that adsorption temperature of 35℃,p H of 7,rotating speed of 150 r/min and drying temperature of35℃were the optimum conditions for biochar to adsorb microbes.Under this condition,four types of BCMFs were prepared by mixing method（M）,adsorption method（A）,granulation method（G）and adsorption granulation method（AG）,respectively.Meanwhile,the physicochemical properties,effective bacteria number and slow-release effect of them were analyzed.The results indicated that adsorption by biochar facilitated to maintain the microbial activity.However,the granulation process reduced it.Adsorption and granulation could increase the content of total nitrogen and organic matter in BCMF and improve the slow-release performance.The nitrogen release experiment and model fitting results indicated that Elovich model was well simulated the nitrogen release process of BCMFs prepared by four methods.Diffusion and chemical processes were included in the nitrogen release process.Only BCMF-AG fitted Weber-Morris model,implying that the internal diffusion process could further improve its slow-release performance.The nutrient release period of BCMF-AG was50 days according to Elovich model.Column leaching experiment showed that BCMF had better slow-release effect than conventional fertilizer（CF）,especially in slowing the leaching of nitrogen and phosphorus.Since the BCMF-AG possessed higher nutrient content and better slow-release performance,it was suggested to be applied in pot experiments.3.With the premise of ensuring nutrients,increasing the addition amount of biochar in BCMF was helpful to play the advantages of biochar in water and fertilizer conservation and soil reclamation.Meanwhile,it could improve the photosynthesis level of plants and the structure of microbial community.Compared with conventional fertilizer,applying BCMF not only improved the soil available nutrients and soil quality,but also advanced the nutrient utilization rate,storage rate,and the relative bacteria abundance related to carbon and nitrogen metabolism in the soil.The results indicated that the 10%reduction of BCMF had no significant effect on the biomass of Brassica chinensis L.and the 20%reduction of BCMF had no significant effect on the photosynthesis of it.4.The synergistic mechanism of soil fertility by BCMF was discussed.RDA results indicated that CEC,NH₄⁺-N,NO₃^--N,BG,URE and Alk P were the main environmental factors affecting the microbial community structure,which could explain 94.8%of the difference in it.After applying BCMF,the content of above six soil environmental factors increased,especially for CEC and BG,which altered the microbial community structure and improved the soil fertility.FAPROTAX function prediction showed that the prepared BCMF had stronger functions in soil carbon and nitrogen cycling,nitrogen fixation and pathogenic microbes reduction.