Influence Of Poplar Biochar On Soil Physical And Chemical Properties And Nitrification

Purple soil is the soil formed after purple rock weathering.It has the characteristics of fast soil formation,slow development process,sufficient nutrients,and high fertility.It is widely distributed in southwestern China.However,due to the influence of climatic conditions and farming methods,the nutrients of purple soil are easy to lose.As a soil amendment,biochar can improve the physical and chemical properties of the soil,affect the transformation of nitrogen in the soil,and has the effect of retaining water and fertilizer.Poplar is one of the main tree species of artificial forests in China.In recent years,as the industrial consumption of poplar has increased,more and more poplar wastes are generated.It is urgently needed to explore the economically feasible resource utilization of poplar wastes.The use of poplar wood waste to prepare biochar is used to improve the purple soil,which can realize the recycling of poplar wood waste and improve the soil at the same time,and has great environmental significance and economic value.Nitrification occupies an important position in the process of soil nitrogen transformation,and is closely related to soil fertility and agricultural environmental pollution.Studies have shown that biochar has an impact on the nitrification process of soil,of which the main mechanisms include non-biological and biological mechanisms.However,there is currently no unified conclusion,and the relevant mechanism research is not thorough enough.In order to understand the potential of poplar biochar for improving purple soil and controlling nitrogen loss,the effect of poplar biochar on soil physical and chemical properties and nitrification was studied.In this study,poplar wood chips were used as raw materials to prepare poplar wood biochar at 400°C and 700°C,and were added to the soil at a ratio of 5%(w/w),which were recorded as BC400-5% and BC700-5% tests,respectively,the soil without biochar was used as a control(denoted as CK)to carry out a 6-week soil microcosmic culture experimentto study the effects of poplar biochar on soil p H,organic matter,cation exchange capacity(CEC),ammonia nitrogen,nitrate nitrogen and the influence of nitrification potential and soil mineralization,and then through the Person correlation analysis,to explore the correlation between soil p H,organic matter,CEC and soil nitrification.Ammonia nitrogen as a substrate of nitrification has a crucial effect on soil nitrification.Biochar can change the content and occurrence of ammonia nitrogen in the soil and then affect nitrification.In order to understand the occurrence of ammonia nitrogen in the biocharsoil system and its response to the addition of poplar biochar,the experiment of biochar on ammonia nitrogen volatilization and ammonia nitrogen adsorption in soil was carried out,mainly to explore the effects of poplar biochar on the soil ammonia volatilization rate,total ammonia volatilization,and the thermodynamics and kinetics of ammonia nitrogen adsorption.Finally,to explore the biological effects of biochar on soil nitrification,the paper taked soil samples from the first and sixth weeks of microcosmic culture as samples,using high-throughput sequencing to investigate the effects of biochar on the soil microbial community structure and nitrification function genes AOA-amo A and AOB-amo A gene abundance.Through the above research,the following conclusions have been obtained:(1)Compared with CK,BC400-5% and BC700-5% significantly increased soil p H,organic carbon content and soil CEC(p<0.05).BC400-5% and BC700-5% significantly reduced the content of ammonia nitrogen and nitrate nitrogen in the soil(p<0.05),and significantly inhibited soil nitrification potential and soil mineralization(p<0.05).(2)Compared with CK,BC400-5% and BC700-5% significantly reduced the total amount of ammonia volatilization in the soil(p<0.05),by about 23.78% and 8.53%respectively.BC400-5% significantly reduced the ammonia volatilization rate in the soil(p<0.05),while BC700-5% has no significant effect,which was related to the fact that BC400 contains more acidic oxygen-containing functional groups than BC700.The adsorption of ammonia nitrogen by CK,BC400-5%,and BC700-5% soil samples was mainly chemical adsorption,which followed the second-level kinetic model,and the adsorption process was complex,and internal diffusion was not the only factor that controls the rate.The adsorption process followed the Freundlich adsorption model,with the multi-layer heterogeneous adsorption as the mainstay.BC400-5% and BC700-5%were easier to adsorb ammonia nitrogen than CK.The addition of poplar biochar leaded to a decrease in the content of ammonia nitrogen distributed in the soil.(3)High-throughput sequencing found a total of 30 phyla,74 classes,163 orders,281 families,551 genera,and 602 species of bacteria in all soil samples,of which 10 dominant bacteria phyla were Proteobacteria,Firmicutes,Bacteroides,Acidobacteria,Actinobacteria,Chloroflexi,Gemmatimonadetes,Verrucomicrobia,Spirochaetes,Nitrospira,they accounted for 95.79%-97.84% of all sequences.BC400-5% significantly increased the diversity of soil bacterial community structure in the 6th week(p<0.05),BC700-5% significantly reduced the diversity of soil bacterial community structure in the first week(p<0.05).BC400-5% and BC700-5% could significantly change the relative abundance of most dominant bacteria phyla,and their effects on the dominant bacteria phyla were different.(4)According to the UPGMA cluster analysis,the species composition of BC400-5% was significantly different from that of BC700-5% and CK(p<0.05).The species composition of BC700-5% and CK was slightly different.At the level of species classification,BC400-5% had a significant impact on the relative abundance of the dominant species(p<0.05),while BC700-5% did not have a significant impact on the relative abundance of the dominant species.At the same time,compared with CK,BC400-5% and BC700-5% significantly reduced the gene abundance of soil AOA-amo A and AOB-amo A(p<0.05),inhibited soil nitrification,and the inhibitory effect of BC400-5% was more significant than BC700-5%(p<0.05).