Effects Of Mixed Returning Of Rape Straw And Milk Vetch On Phosphorus Components And Availability In Paddy Soil

Rape straw is a type of straw with high carbon to nitrogen ratio,while milk vetch is a typical green manure with high nitrogen content.The mixture of them can regulate the soil C/N ratio,affect the abundance and diversity of soil microorganisms,promote the decomposition and release of nutrients in rape straw,thus improve soil fertility.In order to better understand the impact of the combination of rape straw and milk vetch on soil phosphorus,achieve reasonable utilization of straw resources,and provide a basis for scientific management of phosphorus nutrients in farmland,this study conducted indoor soil culture experiments.This study conducted an indoor soil culture experiment by mixing rapeseed straw with purple vetch in a ratio of 1:0（R）,2:1（R2V1）,1:2（R1V2）,and 0:1（V）for returning to the paddy soil.By measuring the soil physical and chemical properties,different forms and activties inorganic phosphorus content,total organic phosphorus,as well as different activties organic phosphorus content and phosphatase activity,and changes in soil microbial community after the return of rape straw and milk vetch to the paddy soil.Exploring the effect of different proportions of rape Straw and milk vetch on soil phosphorus composition and availability when Returned to the paddy soil.The main conclusions are as follows:（1）The combined application of rape straw and milk vetch significantly increased the content of soil organic carbon,total nitrogen,and available phosphorus.After 110 days of cultivation,the content of soil organic carbon of R,R2V1,R1V2,and V treatments increased by 8.88-20.74%,total nitrogen content increased by2.80-7.49%,and available phosphorus content increased by 12.3-18.1%.The content of soil organic carbon,total nitrogen,and total phosphorus showed a rapid increase in the early stage,and gradually stabilized in the later stage.On the 20th day of cultivation,compared with the V treatment,the release rate of organic carbon from the straw treated with R1V2 increased by 18%,indicating that compared to single application of mlik vetch or rape straw,the combination of rape straw and milk vetch1:2 application accelerated the decomposition rate of straw.（2）The combined application of rape straw and milk vetch significantly changed the form and availability of inorganic phosphorus in the paddy soil.The results of inorganic phosphorus form grading showed that the combination of rape straw and milk vetch mainly increased the content of Fe-P and Al-P in the paddy soil and decreased the content of Ca-P.Compared with R treatment,the content of Al-P in R2V1 and R1V2 treatments increased by 4.16 mg·kg^-1and 3.75 mg·kg^-1,respectively.Compared with V treatment,the content of Al-P in R2V1 and R1V2 treatments increased by 2.72 mg·kg^-1and 2.31 mg·kg^-1,respectively.At the same time,R1V2treatment increased the proportion of Fe-P and Al-P in inorganic phosphorus,decreased the proportion of Ca-P,and promoted the conversion of Ca-P to Fe-P and Al-P.Correlation analysis shows that there is a significant positive correlation between Fe-P,Al-P and available phosphorus in the tested soil.The Hedley phosphorus grading results showed that compared to R treatment,R1V2 treatment significantly increased the content of Na HCO₃-P,indicating that compared to single application of rape straw,the combination of rape straw and milk vetch in a ratio of1:2 could increase the effectiveness of soil inorganic phosphorus.（3）The return of rape straw and milk vetch to the paddy soil enhanced the mineralization of soil organic phosphorus.Compared with R treatment,the accumulated mineralization of soil organic phosphorus in R1V2 and V treatments increased by 1.12 mg·kg^-1and 2.57 mg·kg^-1,respectively.R2V1 and R1V2treatments increased the mineralization rate and phosphatase activity of organic phosphorus.The mineralization rate of organic phosphorus in R2V1 and R1V2treatments reached the maximum value of 0.73 mg·kg^-1·d^-1on the 10th day of cultivation,and was significantly higher than that in R and V treatments.The results of organic phosphorus classification showed that the mineralization of organic phosphorus was mainly mediated by moderately active organic phosphorus.Compared with V treatment,R2V1 and R1V2 treatments significantly reduced the content of moderately active organic phosphorus.Compared with R treatment,the activity of acid phosphate monoesterase increased by 0.060 mg·g^-1·h^-1and 0.111mg·g^-1·h^-1in R2V1 and R1V2 treatments,respectively.Compared to V treatment.The correlation analysis results showed a significant positive correlation between the activity of acidic phosphate monoesterase and moderately active organic phosphorus.（4）The combined application of rape straw and milk vetch significantly changed the composition and diversity of microbial communities in paddy soil.The dominant flora of each treatment were Proteobacteria,Chloroflexi,Acidobacteria,Actinobacteria,Gemmatimonadetes and Firmicutes.Among them,Proteobacteria,Firmicutes,Actinobacteria,and Gemmatimonadetes have phosphorus solubilization effects.Compared with the blank treatment,the relative abundance of Proteobacteria increased by 18.0%and 13.6%in R2V1 and R1V2 treatments,respectively,promoting the dissolution of phosphorus and increasing the availability of soil phosphorus.The results of this study indicated that,compared with single application of returning to the paddy soil,the combination of rape straw and mlik vetch at a ratio of1:2 created a suitable nutrients and environmental conditions for soil microorganisms by regulating the carbon to nitrogen ratio of organic matter to 35,accelerated the decomposition rate of rape straw,improved the effectiveness of soil inorganic phosphorus,increased the net mineralization amount and rate of soil organic phosphorus,and also changed the abundance of dominant microbial communities in soil,enhancing phosphorus solubilization.More conducive to improving soil phosphorus availability.