The Research On Soil Apparent Phosphorus Balance And Availability Of Soil P In Different Cropping Systems

Phosphorus is one of the essential nutrients for crop growth,but due to its poor mobility in the soil,phosphorus is prone to adsorption and precipitation reactions,so its utilization rate is low in the agricultural system.In recent years,due to the massive application of chemical fertilizers and the low utilization rate of phosphate fertilizer in current season in China,a large amount of phosphorus has been fixed by the soil into invalid phosphorus,which increases the insoluble phosphorus content in the soil and the risk of soil phosphorus released to the water environment,resulting in agricultural non-point source pollution and eutrophication of water bodies.This study took three cropping systems which were rice-wheat?RW?,maize-wheat?MW?and rice-winter flooded fallow?RF?as the research object,and analysed the variation of soil Olsen-P,its relationship with the apparent P balance by using many years data of the long-term test.Meanwhile,it has been discussed the turnover of soil microbial biomass P?SMBP?and biological effectiveness of four P components.The main results are summarized as follows:?1?From the available P evolution characteristics of three cropping systems in,compared with no P treatments?CP?,P treatment?OP?FP?could significantly increase the content of Olsen-P.The Olsen-P content of 14.3%and 9.5%soil samples in RW,MW cropping system respectively were higher than agronomy threshold of 15 mg/kg,and Olsen-P content of all other treatments were lower than 15 mg/kg,which were much lower than the environmental threshold of 50 mg/kg.Thus,the Olsen-P level of all P treatments in this study is reasonable,which could not only meet the needs of crop,also could not cause the risk of environmental pollution.The fertilization program had the promotion significance.?2?Under the condition of no P application in the RW cropping system,the Olsen-P content decreased by 2.98mg/kg for every 100kg/ha P deficiency in the soil.Under optimized?OP?and high-input P application conditions?FP?,the Olsen-P content increased by 1.33mg/kg and 1.71mg/kg respectively for each 100 kg/ha P accumulated in the soil.Under the condition of no P application?CP?in the MW cropping system,the Olsen-P content decreased by 3.36mg/kg for every 100kg/ha P deficiency in the soil.Under optimized?OP?and high-input P application conditions?FP?,the Olsen-P content increased by1.70mg/kg and 1.95mg/kg respectively for each 100 kg/ha P accumulated in the soil.Under the condition of no P application in the RF cropping system,the Olsen-P content decreased by 3.48mg/kg for every100kg/ha P deficiency in the soil.Under optimized?OP?,the Olsen-P content increased by 1.91mg/kg for each 100 kg/ha P accumulated in the soil.This showed that the accumulation of soil phosphorus under long-term application was the direct cause of the increase of Olsen-P in soil.?3?The biologically-based method?BBP?divided soil P into four components:?1?soluble or interception of rhizosphere?CaCl₂-P?,?2?inorganic combined,organic acid complexation?Citrate-P?,?3?enzyme mineralization of organic P?Enzyme-P?,?4?potential activation of inorganic P?HCl-P?.Olsen-p of RF cropping system mainly came from the addition of soluble and weakly adsorbed inorganic phosphorus and protonation of HCl-P,while Olsen-P of MW and RW cropping systems mainly came from the activation and release of Citrate-P and the addition of protonation of HCl-P.Cropping systems have a great influence on the relationship among the four bioavailable P components,SMBP and Olsen-P.The bio-availability of P components in RF cropping system was realized mainly through SMBP positive effect.However,The indirect path coefficient of four bioavailable P components with SMBP was generally low in MW,RW cropping systems,possibly because dryland rotation and paddy-upland rotation promoted the growth of the soil microorganisms to some extent,and strengthened the biological fixation of soil P,thereby reduced the effectiveness of the P components.At the same time,the reciprocal transformation of the four bioavailable P components under certain conditions could improve the soil P availability to some extent,especially the positive effect relationship in the inorganic P pool?CaCl₂-P,Citrate-P,HCl-P?might have a great impact on the phosphorus availability.