Effects Of Two Kinds Of Biochars On Red Soil Aggregate Stability

Due to the disadvantage characteristic of red soil in heavyclay soil,low organic matter content and poor structure.The objective of this paper was to study the influences of biochar derived from tobacco stems and mulberry branches on red soil aggregate stability,organic carbon fractions,microbial community structure abundance,and the relationship between them was analysised seriously.The availability and appropriate appilication rates of biochar was definited.This paper provided the scientific evidence for the comprehensive utilization and application ratio of biochar in red soil quality improveing.Soil samples were incubated for four months by adding four different rates(1%,2%,4%and 6%)of tobacco stems biochar(Y1,Y2,Y4,and Y6)and mulberry branches biochar(S1,S2,S4,and S6),and non-biochar control(CK).Repeated three times for each treatment.Soil samples were collected for 4 months under constant temperature of 25 degrees.Then,sieving methods were used to detect the distribution of aggregates(>2,1?2,0.5?1,0.25?0.5,<0.25 mm)and stability(estimated by the mean weight diameter:MWD,>0.25 mm soil aggregates:R0.25 and percentage of aggregate disruption:PAD).Measured soil organic carbon(TOC)and organic carbon fractions(easily oxidized organic carbon(ROC),dissolved organic carbon(DOC),water soluble organic carbon(WOC)).The numbers of soil fungi,bacteria and actinomycetes were measured by microbial dilution plate counting cultivation method.Analysised the response of the three to biochar of derived from tobacco stems and mulberry branches and the relationship between the latter two and aggregate structure.The main results are as follows:(1)Water-stable aggregates were changed significantly after biochar additions.Compared with CK,Y4 and S4 treatments significantly increased the 0.5?1 mm fractions by 61.0%and 43.6%;Y1 and S2 treatments significantly increased the 0.25-0.5 mm fractions by 40.8%and 27.1%,while the<0.25 mm aggregates reduced by 9.2%and 8.4%.Compared to CK,both Y2 and S2 enhanced the values of MWD more than 10%and Y1 and S2 treatments increased R0.25 by 31.4%and 28.7%,respectively.Accordingly,the PDA in the Y6 and S6 treatments were decreased by 22.0%and 18.2%?(2)Compared with CK,the organic carbon of the 0.25?1 mm particle size aggregates was the most significant.compared with the control,under Y1 and S1 treatment,the organic carbon of0.25?0.5 mm aggregates increased by 37.3%and 31.6%,and under Y2 and S2treatment,the 0.5?1 mm aggregates increased by 26.5%and 23.2%,respectively.Under Y4 and S4 treatment,ROC/TOC were significantly decreased by 34.8%and 24.9%.Under S1 and S2 treatment,DOC/TOC were significantly decreased by 20.6%and 23.5%.Under Y1 and S1 treatment,WOC/TOC was significantly reduced by 61.7%and 43.3%.Under the same condition,the biochar derived from tobacco stems was more significant to reduce the relative proportion of soil active organic carbon than the biochar derived from mulberry branches.after the two biochar additions,soil total organic carbon and its components were significantly correlated with R0.25(P<0.05),and extremely significant correlated with PAD(P<0,01).(3)biochar additions significantly increased the soil fungi,actinomycetes and bacteria community.The Y4 and S4 treatments resulted in a richest amount of microbial community.In the tobacco stems treatments,a significant correlation existed between the aggregate stability index(MWD,R0.25)with the fungi(r=0.89,P=0.030;r=0.86,P=0.039)and actinomycetes(r=0.87,P=0.035;r=0.90,P=0.021).Moreover,PAD significantly reduced with the increased fungi(P<0.01),actinomycetes and bacteria(P<0.05).The biochar derived from tobacco stems and mulberry branches enhanced the formation of macro-aggregate(0.25?1 mm),soil aggregates stability,Significantly reduce PAD,Significantly increased total organic carbon content of soil,reduce the proportion of active organic carbon to total organic carbon,enhanced the abundance of soil microbial communities.The effect of tobacco stems biochar was better than that of mulberry branches,and the appropriate application is 2%?4%.