Manure Biochar Influence Upon The Release Potential Of Soil Colloidal Phosphorus

Colloids widely exist in natural water environment with small molecules,large specific surface area and abundant organic functional groups.Therefore,they are easy to absorb some radioactive isotopes,trace elements and organic compounds on their surface.The migration of soil pollutants promoted by colloids has attracted wide attention.Phosphorus(P)can be combined with inorganic colloids such as iron-aluminium oxide or organic and inorganic mineral colloids to form colloidal P(TPcoll),which is an important source of the loss of P.Focusing on soil colloidal P,this study collected the paddy soils of different regions in southern China,and adopted 31P-NMR and X-ray absorption near-edge structure spectrum(XANES)to characterize the storage forms of legacy P and colloidal P at the molecular level in paddy soils.The mechanism of the basic physical and chemical properties of paddy soils affecting the release of colloidal P was explored,and the correlation between different forms of P and colloidal P was clarified,which provided a theoretical basis for the optimal management of P in farmland soil.At the same time,three kinds of manure biochar(pig biochar PM,sheep biochar SM,cow biochar CM)were applied to three different paddy soils through indoor simulation experiments.In this experiment,the effects of different kinds of manure biochar on the release of colloidal P in soil were studied,providing theoretical guidance for the application of manure biochars from the change of nutrient and the potential of colloidal P released from the soil.The research results were as follows:(1)The content of colloidal TP in paddy soils was greatly affected by pH and PAC.There was a strong negative correlation between pH and colloidal TP,while colloidal TP had a strong positive correlation with olsen-P and PAC(P<0.01).In addition,the release potential of colloidal TP in paddy soils can be predicted by two factors pH and PAC,the regression model was TPcoll= 94.454(±21.892)*PAC-4.097(±1.169)*pH + 31.603(±9.706)and the prediction accuracy of the regression model was 63.0%.(2)The content of colloidal TP in paddy soils was greatly affected by some metal elements in soil,which negatively correlated with divalent cation calcium and magnesium while positively correlated with aluminum respectively.Specifically,it had a positive correlation with aluminum phosphate and iron phosphate in inorganic phosphorus,and had a negative correlation with calcium dihydrogen phosphate and hydroxyapatite(P<0.05).(3)This study showed that the addition of different types of manure biochars would increase the pH,TC,TN,TP and olsen-P in paddy soils significantly.Among them,the effects of three biochars on TP and olsen-P were PM>CM>SM,while for TC,the effects were SM>CM>PM.(4)This experiment showed that the addition of PM promoted the release of TPcoll,MRPcoll and MUPcoll in three studied soils.The higher concentration of PM applied,the more release of TPcoll(1.31%-54.10%)and MRPcoll(0.52%-74.93%)was observed,while the promotion effect of the release of colloidal MUP was not observed.The addition of SM and CM significantly inhibited the release of TPcoll and MUPcoll.With the same concentration,the inhibitory effect of SM in all soils was greater than that of CM.During the 30 days of incubation,the release of TPcoll,MRPcoll and MUPcoll were substantially promoted or inhibited within one week,and reached equilibrium substantially after 15 days.(5)For SM and CM treatment,the release potential of TPcoll,MRPcoll and MUPcoll can be predicted by the amount of manure biochar,soil texture and olsen-P.The specific prediction model was TPcoll=-46.167(0.088)*SM + 0.078(0.002)*clay-0.006(0.005)*Olsen-P and TPcoll=-23.833(0.055)*CM + 0.096(0.005)*clay-0.007(0.000)*Olsen-P.However,the prediction of colloidal MUP in PM-treated soils was not related to the amount of manure biochar.