Effects Of Rice Straw Biochar On Nitrogen Balance And Nitrogen Cycle Functional Genes In Purple Soil

Purple soil is widely distributed in southern China.Influenced by local climatic conditions and farming methods,soil erosion is particularly prone to occur in purple soil covered areas.As a soil amendment,biochar is not only conducive to nutrient retention and nutrient utilization in farmland soil,but also can greatly enhance soil carbon pool and reduce greenhouse gas emissions such as N₂O.Studying the process of Nitrogen Transformation Driven by soil microorganisms and their functional genes can regulate soil nitrogen directionally,improve nitrogen use efficiency and reduce its negative effects.Using rice straw as raw material,biochar obtained by pyrolysis at 500,600 and700?was added to purple soil to explore the comprehensive effects of biochar on soil nitrogen fixation,plant nitrogen uptake and utilization,and soil nitrogen gas emissions.The variation of soil nitrogen cycle gene abundance caused by biochar addition was analyzed by DNA quantification and PCR detection.The conclusions are as follows:?1?As the final pyrolysis temperature rises from 500?to 700?,the yield and cation exchange capacity of biochar gradually decrease,the fixed carbon and ash content increase,and the pH value increases.The content of H,O and N in biochar decreases gradually,and the content of H/C and?O+N?/C also decreases.The aromaticity of biochar increases with the increase of pyrolysis temperature,and the hydrophilicity and polarity of biochar decreases.With the increase of pyrolysis temperature,the specific surface area of biochar increases,the pore size decreases gradually,the pore structure is developed and arranged closely,the stacking of lamellar structure is obvious,and the surface becomes more rough.?2?Compared with the control group,biochar increased soil NH₃ emissions by6.07%-14.32%.The stimulating effect of low temperature biochar on NH₃ emissions was more significant.Biochar can reduce the NO emission of soil by 7.96%-12.13%,and BC600 and BC700 have better emission reduction effect.The addition of biochar reduced the N₂O emissions by 12.49%-17.12%and increased the N₂ emissions by5.13%-10.55%compared with the non-addition of biochar.Among the soil gas emissions from different treatments,NH₃ was the highest in all treatments,followed by N₂O and N₂,and NO was the lowest.?3?Compared with CK group,BC500,BC600 and BC700 increased ryegrass plant growth by 9.72%,7.81%and 7.92%respectively,and the nitrogen content of plant was increased by 1.56%-3.69%.BC500 treatment showed better effects in promoting plant growth and nitrogen uptake and utilization.After the incubation,soil nitrogen residues in CK,BC500,BC600 and BC700 treatments were 76.29%,79.63%,80.60%and80.06%of the initial content,respectively.BC600 showed better effect in soil nitrogen fixation.?4?Compared with CK treatment,the biological nitrogen fixation of BC500,BC600and BC700 experimental groups increased by 43.20%,56.27%and 49.42%respectively.The priority order of nitrogen balance of three temperature biochars to purple soil system is BC600>BC500>BC700.?5?Compared with the control group,the addition of rice straw biochar increased the abundance of nifH,amoA,narG,nirK,norB and nosZ genes in purple soil,and decreased the copies of nxrA and nirS genes.Biochar promotes soil nitrogen fixation and ammonia oxidation,and inhibits soil nitrification,which is more conducive to the occurrence of denitrification by nitrifying bacteria and denitrifying bacteria.Among the three temperatures of biochar treatment,BC600 has the most obvious effect on enhancing soil nitrogen fixation,and BC500 is more conducive to reducing the emission of nitrogen-containing gases in denitrification process.