Effects Of Biochar On Stability Of Red Soil Aggregates And Release Of Colloidal Phosphorus

Red soil is critical to food production in south China.It is important to protect and improve the quality of the red soil to ensure food security in China.Recently,the productivity of red soil has been severely limited by the problems of mechanization tillage,high fertilizer input,soil acidification and nutrient loss.In this study,the effects of biochar on aggretates stability,phosphorus adsorption characteristics,and colloidal phosphorus releasing potential of red soil were studied in the laboratory.Three soils(S1,S2,S3)with different phosphorus contents were studied.After addition of woody biochar(WBC),chicken manure biochar(MBC),and rape straw biochar(SBC),the responses of three soil aggregate composition and stability,phosphorus adsorption,soil colloidal phosphorus(P_coll)releasing potential to biochar amendments were investigated.In addition,the effects of soil aggregates stability and phosphorus adsorption properties on colloidal phosphorus release were comprehensively evaluated.The main research results were followed:1?All the three biochars promoted the dispersion of the soil dry-sieve macroaggregates,which resulted in macroaggregates transformed to microaggregates and thus reduced the stability of the dry-sieve aggregates.However,the effects of biochars on soil water stable aggregates were different.Addition of WBC could promote the transfer of three soil microaggregates to macroaggregates and enhance the water stability of soil aggregates.The effect of MBC and SBC was similar:the addition of these two biochars had no significant effect of the composition and water stability of S1 soil aggregates,reduced the content of S2 soil aggregates and reduced the water stability of aggregates.It promotes the transfer of S3 soil microaggregates to macroaggregates and increases their aggregate stability.2?Among the three soils,S2 had the strongest phosphorus adsorption capacity(S_max=702 mg/kg),followed by S1(S_max=320 mg/kg)and S3(S_max=355 mg/kg).Soil amorphous iron(Fe_OX³⁺)content contributed mostly to the differences in soil phosphorus adsorption capacities.Fe³⁺_OXcontent of S2(8.4 g/kg)was higher than S1(4.9 g/kg)and S3(3.2 g/kg).Phosphorus adsorption capacity of the three biochars was mainly determined by the calcium and magnesium minerals content in biochar(the order of phosphorus adsorption capacity was SBC>MBC>WBC).Only the addition of SBC with stronger phosphorus adsorption could increase phosphorus adsorption of S2,which had high phosphorus adsorption capacity.On the contrary,the addition of biochar with relatively weak phosphorus adsorption ability can enhance phosphorus adsorption in soil with weak phosphorus adsorption ability.3?Biochar could promote the release of soil colloid,but the release of soil water dispersible colloidal phosphorus was not only determined by the amount of soil colloids release.In the three soils,S1 with the highest phosphorus content had the highest P_colland soluble phosphorus content,whereas that of S2 and S3 was less than 1 mg/kg.The SBC with strong phosphorus adsorption ability can reduce the P_colland soluble phosphorus content of S1,but the MBC with high phosphorus content can significantly increase the P_colland soluble phosphorus content of three soils.4?Correlation analysis showed that the stability of soil aggregates was negatively correlated with the release of colloidal phosphorus(The correlation coefficients between P_colland PAD_0.25,GMD,MWD were 0.323,-0.281,-0.295,respectively;significance:p<0.01).Therefore,the increases of the stability of soil aggregates was beneficial to inhibit the release of colloidal phosphorus,thus reducing phosphorus loss and environmental risk.There was a very significant positive correlation between the release of colloidal phosphorus and the K,a constant related to the bonding strength(r=-0.594,p<0.01),which indicated that the adsorption performance of soil phosphorus was also a factor affecting the release of colloidal phosphorus.