Effect Of Long-term Application Of Different Organic Materials On Nitrogen And Phosphorus Forms And Microbial Characteristics In Purple Soil

Purple soil is characterized by low N,P,and organic C contents.The application of organic materials is an effective approach for improving crop productivity and soil quality.However,there are few studies on which organic material is more suitable for improving the fertility of purple soil,and the characteristics of N and P transformation in soil after long-term application of organic materials.Here,A 13-year field experiment(from 2007 to 2019)were conducted in Sichuan Province,China.Treatments included chemical fertilizer alone(NPK),NPK plus returned straw(NPKS),NPK plus pig manure(NPKM),NPK plus fungal residue(NPKF),and NPK plus green manure(Vicia villosa Rothvar.)(NPKG).Soil N and P forms,microbial biomass N and P,microbial communities,enzymatic activities and functional genes involved in N-,P-cycling were studied by acid hydrolysis of organic N method,sequential chemical extraction of P,employing microplate fluorometric protocol,phospholipid fatty acid,and Metagenomics technology.The main research results are as follows:(1)Changes of crop yields,nutrient uptake and soil nutrient to long-term application of organic materials in purple soil.Relative to NPK treatment,the application of four organic materials increased maize and wheat yields;fungal residue and pig manure treatments significantly increased maize yield 8.0%and 6.4%,and wheat yield 15.7%and 12.9%,respectively.Relative to NPK treatment,pig manure treatment significantly increased N and P uptake in wheat grain,fungal residue treatment significantly increased N and P uptake in wheat grain,N and K uptake in wheat stem and leaf,and P uptake in maize leaf and grain.Four organic materials had different effects on soil nutrients.Fungal residue treatment significantly increased soil organic C and available P contents,relative to NPK treatment,and the content of organic C increased from 6.95 g/kg to 9.12±1.06 g/kg,and the content of available P increased from6.87 mg/kg to 12.26±2.23 mg/kg.Relative to NPK treatment,fungal residue and green manure treatments significantly reduced soil p H,while straw and pig manure treatments showed no significant difference in soil p H.(2)Changes of N and P forms to long-term application of organic materials in purple soil.Relative to NPK treatment,the application of four organic materials increased soil total acid hydrolysable N content,amino acid N and amino sugar N to total N ratio,decreased the ratio of non-hydrolysable N to total nitrogen ratio.Applying organic materials increased the ratio of soil labile P and moderately labile P to total P,but decreased the ratio of non-labile P in soil,relative to NPK treatment.Thus,application of organic materials increased the availability of soil N and P.Fungal residue application was the best for improving the potential of N and P supply in purple soil.(3)Changes of soil microbial biomass and enzyme activities to long-term application of organic materials in purple soil.Relative to NPK treatment,the application of four organic materials increased the contents of microbial biomass C and N.Pig manure,fungal residue and green manure treatments increased the content of microbial biomass P.Relative to NPK treatment,the application of organic materials significantly increased L-leucine aminopeptidase and phosphatase activities while decreased peroxidase activity.Relative to NPK treatment,fungal residue treatment significantly increased the activities of soil C-cycling enzymes.Relative to NPK treatment,straw,pig manure and fungal residue treatments decreased phenol oxidase activity.The soil microbial biomass content and enzyme index in fungal residue treatment were the highest.(4)Changes of soil microbial community structure and functional genes involved in N-and P-cycling to long-term application of organic materials in purple soil.Relative to NPK treatment,the application of four organic materials increased soil total phospholipid fatty acid content by 18.3%-61.1%.Fungal residue and green manure treatments changed the microbial community structure,the relative abundance of G~+and the ratio of G~+/G~-were significantly increased,relative to NPK treatment.In addition,the relative abundance of functional genes in the process of nitrification,denitrification and dissimilatory nitrate reduction were significantly increased in organic materials treatments relative to NPK treatment,and were significantly positive correlation with soil organic carbon.The relative abundance of functional genes in the process of nitrification and denitrification were significantly negatively correlated with soil p H.The relative abundances of genes involved in P-starvation response regulation,P-uptake and transport system,and inorganic P-solubilization and organic P-mineralization were significantly increased in fungal residue and green manure treatments,and were also negatively correlated with soil p H.The relative abundances of genes involved in P-starvation response regulation,and P-uptake and transport system were significantly positive correlation with soil organic carbon.In conclusion,the application of organic materials improved crop yield,soil N and P availability,promoted the N and P cycle in purple soil,and soil p H and soil organic carbon played an important role in the regulation of soil N and P cycle.Combined application of fungal residue and chemical fertilizer was the ideal fertilization measures,which increased crop yield and nutrient uptake,promoted the transformation of N and P in purple soil,and improved the quality of purple soil.