Effect Of Long-term Fertilization And Tillage Management On Soil Phosphorous Fractions Under Paddy Cultivation In Different Agroclimatic Regions Of China

Long-term fertilization and tillage management may exacerbate the composition and availability of soil phosphorus（P）under subtropical paddy soils and thus affect long-term plant growth.However,the response of soil P fractions to long-term fertilization and tillage remains elusive.[Objective]The objectives of this study were to investigate the responses of soil P-fractions and its mobility to different chemical fertilization rates under double rice cropping system,to explore the soil P fractions associated with soil chemical properties under long-term fertilization,to research the influence of combined use of chemical fertilizer with wheat straw and manure on rice yield and P fractions distribution,and the effects of tillage management on soil P fractions and the rice yield under different climatic conditions were investigated.[Method]The experiment was based on five long-term fertilization experiments located in Nanchang（NC）,Jinxian（JX）,Ningxiang（NX）,Chongqing（CQ）,Suining（SN）and a long-term experiment consisting of fluvo aquic soil in Lujiang,Anhui province.For tillage,two experimental sites located in Ningxiang and Haerbin were selected for this study.Three treatments were selected from NC,JX,NX,CQ and SN i-e.,CK,NPK and NPKM.Whereas four treatments were selected from Lujiang i-e.,CK,NPK,NPKS and NPKM.For the tillage experiment the treatments selected were conventional tillage（T1）,conventional tillage with straw（T2）,rotary tillage（T3）and no tillage with straw（T4）.Soil physico-chemical properties were analyzed,and soil phosphatase enzyme activities were assayed.The organic and inorganic forms of phosphorus were determined by using the sequential fractionation scheme of Hedley et al.（1982）.[Result]The results showed that chemical fertilizers combined with manure（NPKM）had higher concentration of soil total phosphorus,Olsen P and soil organic matter（SOM）,compared with the NPK and CK treatment.In NPKM,the grain yield was significantly higher compared with CK and NPK at all the sites.Hedley fractionation revealed the predominance of most of the organic and inorganic P（Po and Pi）fractions with long-term fertilization,specifically with the NPKM treatment,at all the sites.The non-labile P pool was decreased,while the moderately labile P pool proportions were significantly increased by the NPK and NPKM treatments,compared to CK.In fluvo aquic soil,NPK（chemical fertilizers）,NPKS（chemical fertilizers plus wheat straw）and NPKM（chemical fertilizers plus fermented wheat straw）.Results showed that combined application of chemical fertilizers with organic amendments significantly increased grain yield,agronomic efficiency of P（AEP）,P recovery efficiency and partial factor productivity of P compared with CK and NPK.Total N and mineral N were also significantly higher in NPKS and NPKM,compared with NPK.NPKS and NPKM significantly changed P fractions distribution and increased most of the labile（NaHCO₃-P）and moderately labile fractions（NaOH-P）and decreased residual P content compared with NPK.In tillage experiments,the results showed that the no-tillage system significantly increased SOM content,total P and Olsen P concentrations at both the sites compared with conventional tillage.Phosphomonoesterase（AcP）and phosphodiesterase（DP）enzyme activities were significantly increased by 39.8%,62.1%and 40.3%,54.6%compared with T1 at both the sites,respectively.The organic and inorganic fractions of P were significantly affected by different tillage systems.Labile and moderately labile P pool was increased by 29.3%and 19.2%in Ningxiang,64.7%and 33.8%in Haerbin with T4,compared with T1,and decreased the nonlabile P by 10.6%and 18.5%,respectively.[Conclusion]Compared with low NPK inputs,long term high NPK addition has significantly increased the soil nutrients availability for plant uptake,increased the P lability,resulting in higher crop yields and improved agronomic P efficiency.The Long-term application of manure or straw with inorganic fertilizer significantly increased the grain yield and labile soil P fractions and decreased the non-labile P pools much more,compared with the inorganic applications.In case of tillage,no-tillage with straw return increased the P availability&lability by enhancing the microbial activities in the topsoil layer more than the conventional tillage systems,thereby improving soil chemical,physical and biological properties over time.Overall,we concluded from our study that the long-term manure application and straw return significantly affected soil P fractions and P availability,ultimately affecting the crop yields and productivity.The organic additions had a significant role in the soil P transformations.The results indicated that Hedley sequential fractionation technique shows a greater ability to determine the bioavailability of soil phosphorus.Future study is required to know that how long-term fertilization affects the chemical structures of various P fractions and their stability under different soil types,in relation to SOC stocks.Like the XANES is effective in distinguishing phosphorus bound by metal compounds.