Changes Of Soil P Fractionation Under The Regime Of Phosphorous Reduction In A Rice-wheat Rotation Plant Area In The Taihu Lake Region

Phosphorus?P?is an essential component of life,and adequate supply of P is necessary for maintaining crop yields.Chemical phosphate fertilizer has gradually replaced the organic fertilizer?human and animal manure,straw,etc.?and been applied to farmland largely.Due to the low utilization efficiency of phosphate by crop,most of P fertilizer can not be used effectively in soil,resulting in excessive accumulation of soil P.Meanwhile,it has heavy burden to water environment.In this paper,we selected the typical rice-wheat rotation farmland in Changshu National Agro-Ecosystem Observation and Research Station?CS1,31°32'N 120°41'E?and Changshu Institute of Agricultural Sciences?CS2,31°41'N 120°40'E?to study the feasibility of the regime of reduceing phosphorus fertilization for rice season.The experiment was conducted under four phosphorus treatments and set three parallel with each treatment:P fertilization for both rice and wheat?PR+W?as traditional fertilization,P fertilization only for rice?PR?,P fertilization only for wheat?PW?,and no P fertilization during either season?Pzero?as control.The effects of different P treatments on the changes of soil P fractions and soil microbial community composition were analyzed by using P fractionation method and phospholipid fatty acids?PLFAs?map method respectively.The main results of this study were as follows:1.The response of agronomic index to the regime of reducing phosphorus fertilization for rice season was analyzed by crop yield,phosphate utilization efficiency and soil available phosphorus concentrations changes.The results showed that there was no significant difference between PW treatment and PR+W treatment?p<0.05?,and the utilization efficiency of phosphate fertilizer increased slightly?CS-1:4.9%;CS-2:6.1%?.Compared to PR+W treatment,the available phosphorus concentration in PW treatment decreased by 34.7%⁶9.9%?CS-1?and 29.8%³6.6%?CS-2?,respectively.2.The soil P fractionation and microbial community were analyzed by the method of Tiessen and Moir and PLFAs map method respectively.The results showed that the main forms of P in CS-1 and CS-2 soils were stable P?CS-1:84.6⁸6.8%;CS-2:65.9⁷0.1%?,labile P?CS-1:4.96⁸.03%:CS-2:16.4²2.3%?and moderately labile P?CS-1:5.77¹0.4%;CS-2:10.6¹6.6%?.Phosphorus can not only increase the soil labile P component content,but also improve the soil microbial biomass.Compared with PR+W treatment,there was no significant difference in soil P fractionation and soil microbial community composition?p>0.05?.The results of two-way ANOVA showed that soil types had significant effects on soil phosphorus forms and soil microbial community composition?Bacteria,G^-bacteria,AMF?,but different phosphate treatments did not have significant effect on them?p<0.05?.The correlation between soil microbial community composition and different extracted P fractions in CS-1 and CS-2 was analyzed by Pearson test,but no significant correlation was found between them?p>0.05?.The results of PCA showed that 84.5%of the first two principal components?PC1 and PC2?were analyzed by different P fertilizer treatments.Cluster analysis of PC1 and PC2 components showed that strong covariance exsited in CS-1 and CS-2field experiment.The results of typical correspondence analysis?CCA?showed that CS-1 soil microbial community was mainly related to crop yield?straw/grain yield?and soil Olsen-P concentration,while in CS-2,soil microbial community composition was related to soil pH,TC?total carbon?,TN?total nitrogen?,TK?total potassium?,crop total P,labile P,moderately labile P,acid phosphatase activity and alkaline phosphatase activity.3.The field experiment in Changshu Institute of Agricultural Sciences?CS2?was selected to analyze the changes of soil P fractions by sequencial-extreated P fraction?focusing on labile P and moderately labile P?.The results showed that phosphorus fertilizer application did increase the soil P concentration,mainly increased soil inorganic P concentration,however,had little effect on soil organic P.Compared with the rice season?2015R?,the Olsen-P concentration in wheat season?2015/2016W?was higher.Compared to PR+W treatment,there is no significant difference in both Olsen-P and part of sequencial-extrated P fractions?except for NaHCO₃-Pi and NaOH-Pi?.There is also no significant difference in Resin-P,NaHCO₃-Pi and NaOH-Pi.Meanwhile,compared with the rice season in 2013,the content of labile P was increased and the moderately labile P was decreased in 2015 rice season,whereas the labile Pi and moderately labile Pi increased but labile Po and moderately labile Po decreased.