Effects Of Different Phosphorus Application Levels On Phosphorus Availability In Wheat-Maize And Pea-Maize Rotation Soils In Guanzhong Plain

As an essential element for crop growth and development,phosphorus（P）plays a very important role in stabilizing grain yield and maintaining the stability of agro-ecosystem.Guanzhong Plain is the main grain producing area of Shaanxi Province,and the phenomenon of excessive phosphate fertilizer input is very serious,which will not only reduce the utilization rate of P fertilizer,but also cause a large amount of P accumulation in the soil,resulting in waste of resources.Therefore,in order to compare the effects of different P application rates in a single season on soil P availability of different crop rotation systems in Guanzhong Plain,two typical annual crop rotation systems,winter wheat-summer maize and pea-summer maize,were selected in this study.Five different P application levels（0,75,150,225,300kg P₂O₅/hm²）were applied to winter wheat and pea before sowing.Soil samples were collected at different growth stages of winter wheat,pea and summer maize to analyze the variation of available and potential P sources in rhizosphere and non-rhizosphere soil under different P application levels.Further explore the effect of P application on soil P availability under different crop rotation systems,the utilization of P fertilizer in the current season,and the difference in the aftereffects of P fertilizer application in summer maize season.It provides a theoretical basis for strengthening the scientific management of P fertilizer in the Guanzhong Plain from the perspective of crop rotation and improving the utilization efficiency of P fertilizer.The main research results are as follows:1.The content of soil available P changed with the growth period,and the maturity period was significantly reduced in the two rotation systems.The content of available P in the non-rhizosphere soil during the jointing,flowering and maturity stages of winter wheat was higher than that in the rhizosphere soil.The content of available phosphorus in rhizosphere soil and non-rhizosphere soil was significantly positively correlated with P application rate.Under the condition of continuous high amount of soil phosphorus accumulation reached equilibrium,the change of available phosphorus content in maize season was not significant,but under the condition of no phosphorus application,the content of available phosphorus in soil decreased significantly after four seasons of planting.2.Under the winter wheat-summer maize rotation system,the soil P activity at seedling,joining and flowering stages of winter wheat was negatively correlated with the amount of P application rate,and the phosphatase activity in rhizosphere soil was higher than that in non-rhizosphere soil.Under the pea-summer maize rotation system,the changes of phosphatase activity in pea rhizosphere and non-rhizosphere soil had different performances in different growth stages.Phosphatase activity in summer maize season was lower than that in winter wheat and pea season,and there was no significant difference in non-rhizosphere soil at different growth stages.Generally,it was positively correlated with available P in non-rhizosphere soil,while negatively correlated with available P in rhizosphere soil.3.The amount of P application significantly affected the soil microbial biomass content of winter wheat,pea and summer maize at harvest.The soil microbial P content under 225 kg/hm² and 300 kg/hm² high P application treatments was higher than that under 75 kg/hm² and 150 kg/hm² low P application treatments,which increased the potential of soil microbial phosphorus supply.4.The content of organic phosphorus in the rhizosphere and non-rhizosphere of winter wheat and pea in the two rotation systems at maturity had no significant difference among different treatments,but the soil p H tended to increase with the increase of P application.The organophosphorus in the non-rhizosphere soil was higher than that in the rhizosphere soil under the same treatment.In the mature stage of summer maize,soil p H and soil organophosphorus content were lower than those of winter wheat and pea,and the organophosphorus content of non-rhizosphere soil was higher than that of rhizosphere soil.5.Phosphorus application has the potential to increase crop yields in winter wheat-summer maize rotation.P application increased winter wheat yield,and 225kg/hm² P application increased winter wheat yield.Compared with no P application,summer maize yield of winter wheat rotation and 75 kg/hm² treatment was significantly increased in 2019,and that of 225 kg/hm² treatment in 2020 was significantly higher than that of no P application and 225 kg/hm² treatment.However,there was no significant difference in crop yield between 150 kg/hm² annual P application and 225 kg/hm² and 300 kg/hm² annual P application.The agronomic efficiency of winter wheat-summer maize rotation was also high.In two years,the phosphorus application level of 150 kg/hm² in the test winter wheat season met the fertilizer demand for the rotation year,which was the optimal application rate for economic yield.6.Phosphorus application increased the crop yield of pea-summer maize during the two years of the experiment,but the potential yield increased with different phosphorus application levels showed inter-annual differences.From 2018 to 2019,the pea yield under 150 kg/hm² P application was the highest,which was significantly higher than that under 225 kg/hm² and 300 kg/hm² P application.There was no significant difference in pea yield between 150 kg/hm² and 225 kg/hm² and300 kg/hm² treatments in 2019-2020.The 75 kg/hm² treatment significantly increased the summer maize yield with pea-rotation,but had no significant difference with high P application.The P agronomic efficiency of pea reached the highest when P application rate was 150 kg/hm²,and the P agronomic efficiency of pea-summer maize rotation system reached the highest when P application rate was75 kg/hm².With the increase of P application rate,P partial productivity of pea and winter wheat-summer maize and pea-summer maize rotation systems showed a decreasing trend during the two years of experiment.