The Mechanism Of Long-Term Different Straw Return Strategies Affecting The Availability Of Phosphorus In Calcareous Soil

As a macroelement for crop growth,phosphorus（P）participates in various physiological and biochemical reactions in plants,and high amount of mineral P fertilizers are applied into soil to achieve high crop yield.The large production of mineral P fertilizers consumes a large amount of phosphate resources,thus the shortage of phosphorus resources may become a great limiting factor for agricultural development.In addition,high application of mineral P fertilizers increases soil P pool,which may result in many environmental problems.Improving the utilization efficiency of phosphorus has become an important way to alleviate the phosphorus crisis in agricultural production.Crop straw contains types of nutrients,and straw returning would also affect the availability of soil phosphorus.In this study,the impact of different types of straw returning strategies on soil P availability,soil bacterial community and P transformation profiling were detected.The long-term filed experiment was located in Yucheng Experimental Base of Dezhou Experimental Station of the Chinese Academy of Agricultural Sciences including four treatments:no straw returning（CK）,single-season return of wheat straw（W）,single-season return of corn straw（M）,and double-season return of wheat and corn straw（D）.The primary findings are as follows:（1）Long-term straw return significantly increased soil total phosphorus and available phosphorus content,and the available phosphorus content and phosphorus activation coefficient（PAC）of W treatment were significantly higher than that in M and D treatment.The three straw return regimes changed the soil phosphorus reservoir composition,increasing the contents of dicalcium phosphate（Ca₂-P）,octacalcium phosphate（Ca₈-P）,and decacalcium phosphate(Ca₁₀-P)in the soil and decreasing the content of occluded phosphate（O-P）.Straw returning also increased the content of labile organic P（LOP）and moderately labile organic P（MLOP）,but decreased the content of highly resistant organic P（HROP）.Compared with M and D,W treatment was more conducive to the increase of soil available phosphorus content.（2）Straw returning greatly impacted phosphorus adsorption characteristics in aquic soil.Compared with CK,straw return treatment significantly reduced soil phosphorus adsorption capacity,which was decreased by 10.7%,7.5%and 5.1%in W,M,and D treatment,respectively.W treatment significantly reduced soil maximum phosphorus uptake（Qm）of soil and significantly increased soil phosphorus adsorption saturation（DPS）,while M and D treatments had little effect on Qm and DPS.The phosphorus desorption rate of soil was W>D≈M>CK,while the soil phosphorus desorption rate was significantly reduced by CK>D≈M>W.The results of correlation analysis showed that soil exchange calcium content was significantly correlated with the soil phosphorus adsorption and desorption capacity.These results show that in calcareous aquic soil,the three straw return regimes reduced soil adsorption of phosphorus and increased soil desorption capacity of phosphorus,thereby improving the phosphorus supply capacity of the soil.And the effect of single-crop straw return of wheat（W）is better than that of the other two straw return regimes.Reducing the fixation of exchange calcium to phosphorus in the soil may be an important way to improve the availability of soil phosphorus by straw returning.（3）Long-term straw returning significantly enhanced soil acid and alkaline phosphatase activity.All the three straw returning treatments significantly changed the structure of soil bacterial community,but only W treatment significantly increased bacterial diversity.Through functional prediction,it was found that the relative abundance of bacterial taxa involved in inorganic phosphorus dissolution and organic P mineralization was significantly increased by straw returning,and W treatment had the greatest impact than that of M and D.The results of culture experiments showed that straw returning increased bacterial solubility of inorganic phosphorus（Ca₃（PO₄）₂）and the mineralization capacity of organic P（lecithin）.Correlation analysis showed that soil dissolved organic carbon（DOC）,ammonium nitrogen,nitrate nitrogen,and soil p H were significantly correlated with soil microbial phosphorus transformation profiling.In summary,in calcareous aquic soil,the three straw return regimes increased the content of labile and moderately labile P in the soil,and reduced the content of ineffective P,thereby improving the availability of soil P.Straw return treatment reduced the immobilization of soil P by reducing soil adsorption of P,increasing soil desorption capacity of P,and improving soil microbial inorganic P dissolution and organic P mineralization capacity,resulting in the increase of soil available P.In all the three regimes of straw returning,single-season wheat straw returning is more effective than M and D in increasing soil P availability.