Effect Of Wheat And Maize Straw Continuous Incorporation On Phosphorus Apparent Balance And Phosphorus Forms Transformation In Lime Concretion Black Soil

Straw is rich in organic matter and nutrient elements such as nitrogen,phosphorus andpotassium.Straw returning to field is one of the important ways to input nutrient elements into soil,and it also has an important impact on the transformation and availability of soil nutrients.At present,the effects of long-term straw return on soil phosphorus apparent balance and phosphorus forms transformation under the wheat-maize rotation system are still unclear in lime concretion black soil of North Anhui province.Based on statistical yearbook data and literature survey parameters,this study clarified the phosphorus resources of wheat and maize straw in North Anhui province and its impact on the balance of soil phosphorus pool.At the same time,five treatments selected from long-term field experiment located in North Anhui province for exploring the effects of straw returning on phosphorus conversion and availability in lime concretion black soil,and analyzing the change rules of soil phosphorus components in different growth stages of wheat under the condition of long-term straw returning,so as to provide reference for the rational application of chemical phosphorus fertilizer and the optimal management of phosphorus.The five treatments included no fertilization（CK）,conventional fertilization（F）,conventional fertilization plus wheat straw return（FWS）,conventional fertilization plus maize straw return（FMS）,and conventional fertilization plus wheat and maize straw return（FWMS）.The main results are as follows:（1）In 2019,the total output of wheat and maize straw phosphorus（P₂O₅）resources in North Anhui was 51 thousand tons,of which the proportion of wheat and maize straw phosphorus nutrient was 60.9%and 39.1%,respectively.In 2019,the contribution of wheat straw returning to soil phosphorus（P₂O₅）input was 14.1-19.8 kg·hm^-2,and the phosphorus removal from wheat grains was 54.4-75.9 kg·hm^-2.The contribution of maize straw returning to soil p input was 16.9-21.8 kg·hm^-2,and the P removal from maize grains was37.8-48.9 kg·hm^-2.In 2019,the annual loss of soil phosphorus（P₂O₅）was 126.2-166.6kg·hm^-2,under the condition that wheat and maize straw were not returned to the field.And the annual loss of soil phosphorus decreased to 110.7-146.9 kg·hm^-2 under the condition that wheat straw was returned to the field in a single season.When maize straw was returned to field in a single season,the annual loss of soil phosphorus decreased to 105.0-148.3 kg·hm^-2.The annual loss of soil phosphorus decreased to 89.5-128.6 kg·hm^-2 when wheat and maize straw were returned to the field.（2）Long-term return of wheat and maize straw significantly increased the contents of total phosphorus and available phosphorus in lime concretion black soil and soil phosphorus activation coefficient.The contents of soil inorganic phosphorus（Ca₂-P,Al-P and Fe-P）and organic phosphorus components（labile,moderately labile,and moderately resistant organic phosphorus）were significantly increased by straw return.The soil Ca₂-P contents of FWS,FMS and FWMS treatments increased by 32.3%,28.5%and 43.7%,respectively,compared to the F treatment.And the soil Al-P contents of three treatments increased by 15.2%,10.6%and 13.3%,respectively.Wheat and maize straw incorporation had no significant influence on soil O-P contents in lime concretion black soil.Furthermore,in comparison with the F treatment,the soil Ca₈-P contents under FMS and FWMS treatments significantly increased,while the contents of Ca₁₀-P and highly resistant organic phosphorus decreased.Besides,the proportions of Ca₂-P in lime concretion black soil were significantly elevated by wheat and maize straw return,and the proportions of O-P,Ca₁₀-P and highly resistant organic phosphorus decreased.Correlation analysis showed that soil Al-P,Fe-P,Ca₂-P and moderately labile organic phosphorus were significantly positively correlated with the content of soil available phosphorus.And path analysis indicated that soil Al-P,Ca₂-P and moderately labile organic phosphorus were the major direct contributors to soil available phosphorus.On the basis of these results,it can be concluded that wheat and maize straw incorporation is an effective way to promote the conversion of unavailable phosphorus into available phosphorus and slowly available phosphorus in lime concretion black soil.There were no significant differences among single-season and double-season straw return treatments in terms of soil phosphorus activation.（3）During the growth period of wheat,soil available P content decreased from seedling stage to jointing stage and booting stage,reached the lowest point at booting stage,and increased significantly and reached the highest point from booting stage to flowering stage.The change rule of soil Ca₂-P content was highly consistent with that of soil available P.It was relatively low at jointing and booting stage,and increased significantly and reached the peak at flowering stage.The contents of Ca₈-P,Al-P,Fe-P,O-P and moderately labile organic phosphorus decreased significantly from jointing stage to booting stage,and increased significantly from booting stage to flowering stage.Highly resistant organic phosphorus decreased at jointing and flowering stage,while Ca₁₀-P did not change significantly during the whole wheat growing season.In quarterly or double season straw counters-field set conditions for a long time,the different development stages of the wheat season of soil effective phosphorus content were significantly increased,and the jointing stage to booting stage and booting stage to the flowering period,long-term single or double cropping straw returning increased the contents of Ca₂-P,Al-P,Fe-P,labile organic phosphorus,moderately labile organic phosphorus and slow available phosphorus source Ca₈-P,but decreased the contents of slow available phosphorus source O-P and ineffective phosphorus source highly resistant organic phosphorus.In the wheat-maize rotation system in North Anhui province,the long-term return of single or double season straw could inhibit the transformation of available phosphorus source to slow and ineffective state,promote the transformation and decomposition of ineffective phosphorus source,and promote the accumulation of available phosphorus source from jointing stage to booting stage and booting stage to flowering stage,and improve the availability of soil phosphorus.