Study On The Mechanism Of Biochar Regulating Soil Phosphorus Migration And Transformation To Improve Phosphorus Efficiency Of Maize

Phosphorus is a nutrient element that is indispensable for crop growth.However,the lack of available phosphorus in cultivated land and the lack of phosphate rock resources have substantially restricted agricultural production.In recent years,studies have shown that returning straw into biochar is an effective means to improve and fertilize the soil,which is highly effective at alleviating the contradiction between the supply and demand of phosphorus between soil and crops.This study is based on a five-year field experiment of biochar and studied the effects of different ways of returning straw to the field,including direct returning to the field and carbonization returning to the field,different rates of application of biochar returned to the field,and different methods of combining the application of biochar and fertilizer.The effects on the migration and transformation of soil phosphorus and the utilization of phosphorus by maize（Zea mays L.）were examined.The regulatory mechanism was analyzed from the aspects of soil physical and chemical properties,the migration and transformation of phosphorus fractions,phosphorus bioavailability,enzyme activity related to soil phosphorus cycling,and functional genes and microbial community characteristics to provide support for the research and application of biochar to improve soil fertility and efficiently utilize crop nutrients.The main contents and results of this research are as follows:1.The effects of maize straw and its biochar on the migration and transformation of phosphorus in the soil.Maize straw and its biochar significantly increased the content of total phosphorus（TP）in the topsoil,while the content of Olsen-P was significantly reduced.The application of maize straw and its biochar affected the organic and inorganic phosphorus fractions of the soil.In comparison,maize straw biochar had more effect on the soil inorganic phosphorus,while the maize straw had more effect on the soil organic phosphorus.Compared with the phosphorus fractions in the initial topsoil,treatment with biochar increased the fractions of soil inorganic phosphorus(octocalcium phosphate[Ca₈-P],hydroxyapatite[Ca₁₀-P],aluminum phosphate[Al-P]and iron phosphate[Fe-P])in 2017,while the treatment with maize straw increased the organic phosphorus fractions in the soil（moderately labile organic phosphorus[MLOP],moderately resistant organic phosphorus[MROP]and highly resistant organic phosphorus[HROP]）,but maize straw and its biochar significantly reduced the content of soil occluded phosphate（O-P）.The application of maize straw and its biochar improved the stability of soil aggregates,primarily by increasing the contents of macro-aggregates and micro-aggregates.Maize straw and its biochar also increased the accumulation of organic phosphorus and inorganic phosphorus in the small macro-aggregates and micro-aggregates in the soil.Maize straw and its biochar can all improve the ability of soil to adsorb phosphorus,and the soil with biochar adsorbed phosphorus more strongly.Maize straw and its biochar decreased the contents of total phosphorus（TP）,Fe-P,O-P and Ca₁₀-P in the subsoil,but the application of maize straw increased the contents of dicalcium phosphate（Ca₂-P）,Al-P,MROP and HROP in the subsoil.Therefore,maize straw biochar is a more effective measure to enhance the retention of soil phosphorus and reduce its risk of leaching.2.Effects of different biochar application rates on the migration and transformation of phosphorus in soil.The application of biochar reduced the contents of inorganic phosphorus（Ca₂-P,Ca₈-P,Al-P,Fe-P and O-P）in non-rhizosphere soil,but increased the contents of organic phosphorus（MLOP and HROP）in this type of soil.Biochar reduced the contents of Fe-P and MLOP in the rhizosphere soil.Compared with the initial topsoil,the contents of organic phosphorus fractions（MLOP,MROP and HROP）in different biochar treatments increased to varying degrees,while the contents of inorganic P fractions(Ca₈-P,Al-P,O-P and Ca₁₀-P)decreased.The application of biochar can improve the stability of soil aggregates,and small macro-aggregates contributed the most to the relative rate of different forms of phosphorus in the soil.The application of biochar can promote the distribution of forms of inorganic and organic phosphorus in soil aggregates,and the effect was more obvious when the rate of application of biochar application was 31.5 t ha^-1.In addition,the application of biochar can promote the ability of soil to adsorb phosphorus,and this effect increases with the increase in rate of application of biochar.However,the ability of soil to desorb phosphorus varied with different rates of biochar application,and the soil in which 31.5 t ha^-1 of biochar had been applied had the strongest ability to desorb phosphorus.The TP,Ca₂-P,Ca₈-P,Al-P,MLOP and MROP were primarily distributed in the topsoil.In addition,the application of biochar can increase the content of TP in the topsoil and reduce it in the subsoil.Therefore,it is readily apparent that biochar has a long-term effect on the migration and transformation of soil phosphorus,and the effect on different forms of phosphorus in soil was the most obvious after a one-off application of biochar at the rate of 31.5 t ha^-1for 5 years.3.Effects of biochar blended with fertilizer on soil phosphorus fractions,bioavailability,and phosphorus absorption and utilization of maizeBiochar increased the soil p H and electrical conductivity（EC）,as well as the contents of total carbon（TC）and TP.The contents of inorganic phosphorus(Ca₈-P,Al-P,Fe-P and Ca₁₀-P)and organic phosphorus（LOP,MLOP and HROP）all increased following the application of biochar.³¹P-NMR spectra showed that the contents of monoester and diester phosphate in the soil with biochar increased by 9.65-21.80%and71.70-98.57%,respectively.The contents of orthophosphate,monoester phosphate,and diester phosphate in the soil increased following the application of biochar.The application of biochar increased the contents of soil bioavailable phosphorus（Ca Cl₂-P,citrate-P,enzyme-P and HCl-P）.The highest contents of orthophosphate,monoester phosphate,diester phosphate and different bioavailable phosphorus forms were found in the treatments that combined the application of biochar and NPK fertilizer.Simultaneously,biochar can improve the yield of maize grain and the uptake and utilization of phosphorus.The application of biochar also increased the efficiency of utilizing phosphorus fertilizer（PUE）（12.4%-31.4%）and the agronomic efficiency of utilizing phosphorus fertilizer（AEP）（21.6%-51.2%）.Therefore,it is clear that biochar and phosphate fertilizer act synergistically.4.Effects of blended application of biochar and fertilizer on the activities of soil enzymes related to phosphorus cyclingBiochar had different effects on the activities of enzymes related to the phosphorus cycle in the maize rhizosphere and non-rhizosphere soil.The application of biochar to the maize rhizosphere soil increased the activities of phytase（V3,V6 and R3）,neutral phosphatase（V3,V6 and R3）and alkaline phosphatase（V6,R3 and R6）but decreased the activities of pyrophosphatase（V3,V6 and VT）and acid phosphatase（V3 and R3）.In maize non-rhizosphere soil,the application of biochar increased the activities of phytase and alkaline phosphatase but decreased the activities of pyrophosphatase,phosphodiesterase,and acid phosphatase at each stage of growth of maize.5.Effects of blended application of biochar and fertilizer on the abundance of functional genes and microorganisms related to phosphorus cycling in soilMetagenomics was utilized to analyze the effects of biochar combined with phosphate fertilizer on major functional genes and microorganisms related to phosphorus cycling in maize rhizosphere soil.In this study,we focused on 57 functional genes that are involved in the process of soil microbial phosphorus cycling.Among them,17 genes differed significantly,and these genes were primarily involved in the metabolism of phosphate.In particular,genes that play a role in the process of ester mineralization were identified.In the case of applying phosphorus fertilizer,the combined application of biochar had no significant effect on most of the functional genes related to phosphorus cycling in soil,and the abundance of some functional genes was even reduced.Simultaneously,the abundance of microorganisms that harbored these 17 genes that differed significantly between treatments was analyzed.The abundance of microorganisms at most phylum levels and the levels of dominant genera can be increased by applying nitrogen,phosphorus and potassium fertilizer without biochar.However,the abundance of microorganisms at most phylum and dominant genera levels could be reduced by applying biochar based on the application of nitrogen,phosphorus and potassium fertilizer.This could be owing to the fierce competition between the microorganisms that harbor these genes in the soil.This competition could have been exacerbated owing to the combined application of biochar and fertilizer,but further experiments are still needed to verify this hypothesis.