Effects Of Different Biochar Addition On Carbon And Nitrogen Nutrient Storage In Cow Manure Compost

Composting is currently the most widely used manure management method.Traditional composting leads to a large amount of carbon and nitrogen loss,which seriously affects the quality of compost.Biochar is a research hotspot in the field of composting additives in recent years with its functions of improving compost quality,reducing greenhouse gas emissions,and enhancing carbon and nitrogen retention effects.However,there are few reports on the effects of biochar preparation materials,preparation process and addition amount on carbon and nitrogen retention and microbial community in compost.Taking highland barley,broad beans and corn stalks,characteristic crops in Qinghai as biomass raw materials,this study conducts characterization analysis on biochar by elemental analysis and technical means such as SEM,EDS,BET,FTIR,etc,and systematically conducts a study on the effects of raw material composition,pyrolysis temperature,and pyrolysis time on the physicochemical properties,pore characteristics,and carbon components of biochar.Then,cow dung and highland barley straw were used as composting raw materials to explore the optimal preparation conditions of biochar for the retention of carbon and nitrogen nutrients in the process of cow dung composting,and to reveal the structure-activity mechanism of biochar.Then,the effects of different dosages of biochar on cow dung compost were studied,and the changes of physicochemical properties,pore structure and functional groups of biochar during the composting process,and the effect of biochar addition on the microbial community structure and composition of composting were studied.This paper aims to clarify the regulation mechanism of biochar on the carbon and nitrogen retention of cow manure compost,and provide theoretical and practical basis for the transformation of livestock and poultry manure into high value-added bio-organic fertilizer in Qinghai large-scale farms.（1）The biochar obtained from highland barley,broad bean and corn stalk under different preparation conditions were all alkaline,with large specific surface area and developed pore structure dominated by mesopores.The preparation temperature is the main factor affecting the physicochemical properties of biochar.With the increase of preparation temperature,the yield of biochar decreased,the ash content increased,and the degree of aromatization increased.After extraction with cold water,hot water or weak base,the solution obtained has reduced organic carbon content,increased content of stable carbon components,and enhanced biochar stability.（2）Adding biochar with different preparation conditions to cow dung compost can speed up the composting process,increase the compost temperature by 3.4℃on average,and allow it to enter the high-temperature period 3 days earlier.Compared with the CK group,the carbon loss in biochar addition group was reduced by 3.86%and nitrogen loss reduced by 10.44%on average;NH₄⁺-N content decreased by18.95%on average,NO₃^--N content increased by 36.41%,and soluble organic carbon decreased by 27.54%.Greenhouse gas emissions can be reduced by adding biochar.Compared with the control group,the emissions of CO₂,CH₄and N₂O were reduced by 14.81%～32.11%,36.59%～81.59%,14.89%～21.66%,respectively,and the global warming potential was reduced by 34.46%～75.00%compared with the CK group.Based on the comprehensive analysis of compost carbon and nitrogen retention effects and global warming potential,it concludes that the biochar prepared from highland barley straw,at a pyrolysis temperature of 500℃,and pyrolysis time of 2 h are the best biochar for compost carbon and nitrogen retention.（3）The addition of biochar of varying amounts to the cow dung compost can speed up the composting process,and generally enter the high-temperature period of compost 2 days earlier than that in the CK group.In the biochar addition group with different contents,the carbon loss was reduced by 10.78%,nitrogen loss was reduced by 8.19%on average,NH₄⁺-N content decreased by 50.15%on average,NO₃^--N content increased by 6.05%on average,and soluble organic carbon content decreased by 25.75%.Based on the comprehensive analysis of compost carbon and nitrogen retention effect,it concludes that when the addition amount of biochar prepared at the pyrolysis temperature of 500℃,and with the pyrolysis time of 2 h,is 10%,the effect of compost carbon and nitrogen retention is the best.（4）During the composting period,the p H value of highland barley biochar decreased continuously,the electrical conductivity first gradually increased during the composting period,reached the highest value in the high-temperature period,and then gradually decreased in the cooling period and the maturity period.The phenolic hydroxyl groups of acidic oxygen-containing functional groups increased during the compost maturity period,the specific surface area and pore volume gradually decreased during the composting process.The average pore size increased with the composting process.（5）Adding 10%highland barley biochar can promote compost maturity,increase the abundance of nitrobacteria inα-proteobacteria andδ-proteobacteria,and improve the nitrogen fixation effect of compost,inhibit the reproduction of anaerobic bacteria,reduce CH₄emissions,and enhance carbon retention effect,inhibit the reproduction of denitrifying bacteria and help to increase the nitrate nitrogen content of compost.Soluble organic carbon,p H,and temperature were positively correlated with the microbial communities in the CK and 10%NC groups,and electrical conductivity and humidity were negatively correlated with the microbial communities in the CK and10%NC groups,and the level of negative correlation between carbon retention rate and nitrogen retention rate was lower in the 10%NC group.In summary,the addition of biochar can enhance the carbon and nitrogen retention effect of cow dung compost,when the addition amount of biochar prepared from highland barley straw,at the pyrolysis temperature of 500℃,and with the pyrolysis time of 2 h,is 10%,the effect of compost carbon and nitrogen retention is the best.