Study On The Influencing Factors Of Se In Seleniferous Paddy Soil And Its Response To Straw And Straw Biochar Retuning

Selenium(Se)is the micronutrient that are not only necessary for human being but also beneficial for plant growth.Rational utilization of Se-rich soil,which is abundant in China,is of great significance for safeguarding the health of our citizens.Rice is the staple food worldwide,and it is ideal to increase the intake of Se through increasing its’ concentration in rice.However,the concentration of Se in rice could not meet the standard even if grown on the Se-rich paddy soil.Hence,it is important to explore the dominant factors that increase the availability of Se in rice and further regulate its’ bioavailability through reasonable agronomic practices for the development of Se-rich agriculture and the sustainable utilization of Se resources in soil.Therefore,this study analyzed the characteristics and influencing factors of Se rich in the paddy soil through a combination of filed investigation and pot experiments,and explored the effects of straw and straw biochar returning on the transformation of soil Se forms and the adsorption and transportation of Se in rice.The main progresses of this study are as follow:(1)The content of Se in Se-rich paddy soil is jointly affected by soil chemical properties and parent material types in subtropical hilly areas.The contents of Se in different parent material types ranges from high to low are followed as carbonate regolith> peat rock regolith>lake and river sediments> quaternary red clay> acidic crystalline rock regolith,with an average content of 0.54 mg/kg,0.52 mg/kg,0.43 mg/kg,0.37 mg/kg,0.30 mg/kg.The results of multiple logistic regression model analysis showed that the main factor affecting the degree of Se enriched in this area was soil p H,soil organic matter,and Total K.(2)Straw and biochar returning affected the transformation of soil Se forms in Se-rich paddy soil.Straw and biochar returning increased the contents and distribution ratio of watersoluble Se(SOL-Se)in soil,but decreased the contents and distribution ratio of iron manganese oxide bound Se and organic bound Se.The contents of exchangeable,carbonate bound,and residual Se in soil varies slightly.The increased contents of available Se in soil mainly originated from the activation of iron manganese oxide bound Se and organic bound Se.(3)The increase of available Se in soil after straw and biochar returning to the field is regulated by soil chemical properties.There was a significant or extremely significant positive correlation between the concentrations of SOL-Se and soil p H,organic matter,total nitrogen,available phosphorus,and available potassium(p<0.05),with correlation coefficients of 0.85,0.86,0.68,0.82 and 0.91,respectively.The results of redundancy analysis(RDA)represented that the content of soil available Se was regulated by soil p H and available potassium,and the distribution plot explained 10.8% and 66.4% of the variations in soil available Se.(4)Straw and biochar returning to the field affected the absorption and accumulation of Se in rice in Se-rich paddy soil.Compared with the application of inorganic fertilizers,the contents of Se in stems and panicles of rice were increased by 43.75%,69.22%,37.27%and 38.09%,respectively under straw and biochar returning.However,the contents of Se in leaves decreased.There was no significant difference in the accumulation of soil Se between the application of straw and biochar returning,but both were significantly higher that those of inorganic fertilization.(5)Straw and its’ biochar returning altered the transformation of Se in soil-rice system.Applications of straw and biochar returning significantly increased the transport coefficients of root/soil and plant/leaf,but deceased the coefficients of leaf/stem and stem/root.Variance partitioning analysis(VPA)represented that the migration of Se in different parts of rice plant and the interaction between nutrients affected the transformation of Se in different parts of rice.The partial least squares path model(PLS-PM)was used to analyze the effects of soil-rice system on the enrichment of Se.And the results suggested that the interaction between soil chemical properties and nutrient in rice root was the prominent factors that influencing its transformation,while the adsorption of Se in roots and the transport of Se from leaves to panicles were the critical processes that contributed to Se enriched in rice.In summary,the main factor affecting the degree of Se enrichment in subtropical Serich paddy soil is soil p H.And the application of straw and its biochar returning to the fields mainly improves the availability of Se in Se-rich soil and promotes the enrichment of Se in rice grains by regulating changes in soil chemical properties.So,we recommended that the applications of straw and its biochar returning are the feasible agricultural practices for enhancing the bioavailability of Se in agricultural products which grow in Se-rich paddy soil.