Mechanism Of Phosphorus Fertility Affecting Phosphorus Utilization Efficiency In Winter Wheat And Summer Maize Systems

The study on the relationship between fertilizer phosphorus use efficiency and soil phosphorus fertility is of great significance to the construction and optimization of phosphorus management strategies.In this paper,the field experiment of phosphorus fertilizer amount set on Lou soil with different phosphorus fertility gradients was used to study the mechanism of soil phosphorus fertility affecting phosphorus fertilizer utilization from two aspects of root distribution and mycorrhizal colonization,so as to provide a theoretical basis for improving phosphorus fertilizer utilization.In this study,four different phosphorus fertility soils(F1,F2,F3 and F4)were selected to set five phosphorus application rates(0,30,60,90 and 120 kg P2O5/ha)in the representative area of winter wheat-summer maize double cropping system in Guanzhong Plain of Shaanxi Province.The relationship between soil phosphorus fertility and phosphorus fertilizer utilization rate,(biologically based P,hereinafter referred to as “ BBP method ”),root distribution and mycorrhizal colonization was analyzed to further study how phosphorus fertility affects phosphorus fertilizer utilization rate.The main research results are as follows:(1)Under the condition of low phosphorus fertility level(F1),the application of phosphorus significantly increased the yield of winter wheat,but there was no significant effect under other fertility levels.The four-year test results further determined that the agricultural threshold of available phosphorus for winter wheat obtained by long-term fertilizer test in this area was 19 mg/kg.However,during the experiment,phosphorus fertility and phosphorus application rate had no significant effect on the yield of summer maize.(2)The results of four years showed that the application of phosphorus fertilizer significantly increased the content of available phosphorus in topsoil,but had no significant effect on total phosphorus.When the fertilizer application rate reached 90 kg P2O5/ha,the soil at the four P levels had phosphorus surpluses,with each surplus of 100 kg P/ha,the total P content in the topsoil increased by 33 mg/kg,and the available P content increased by 6 mg/kg;The four phosphorus fractions of BBP method had a significant linear positive correlation with available phosphorus content.Path analysis showed that only Ca Cl2-P,enzyme-P and citriate-P had a significant direct effect on soil available phosphorus,and had a significant positive correlation with soil phosphorus activation coefficient.Therefore,among the four phosphorus components,only Ca Cl2-P,enzyme-P and citriate-P contributed significantly to soil phosphorus activation.(3)In this experiment,the wheat phosphorus fertilizer utilization rate calculated by the balance method increased with the increase of soil available phosphorus content,and the soil available phosphorus content reached 21.33-27.05 mg/kg gradually stabilized.The annual phosphorus use efficiency of maize and wheat-maize increased with the increase of soil available phosphorus content.When the phosphorus application rate was 60 kg P2O5/ha,the phosphorus carrying capacity of wheat and maize was basically the same as the phosphorus application rate.At present,the optimum phosphorus fertilizer application rate of wheat and maize was 60 kg P2O5/ha,and the optimum range of soil available phosphorus(Olsen P)was 21-27 mg/kg.(4)Phosphorus application in low phosphorus fertility soil can promote crop root growth,but more than a certain amount will not affect root growth,or even inhibit it.The root length density and root weight density of wheat and maize increased first and then decreased with the increase of soil available phosphorus content,and the critical values of available phosphorus were 25.68 mg/kg and 20.71 mg/kg,respectively.28.40 mg/kg and 24.31 m/kg.The increase of root length density and root weight density of wheat in low fertility soil can promote the absorption of phosphorus.Root length density had no significant effect on phosphorus uptake at high fertility level,while root weight density had less effect on phosphorus uptake than low fertility level.The increase of root length and root weight of maize can promote the absorption of phosphorus at both fertility levels.On the soil with low fertility,the mycorrhizal colonization rates of wheat and maize can be increased by appropriate phosphorus application.However,when the soil fertility is high,phosphorus application will inhibit the mycorrhizal colonization of wheat and maize.Moreover,the mycorrhizal colonization rates of wheat and maize are the same as those of roots with the change of available phosphorus,and the critical values are 17mg/kg and 13 mg/kg,respectively.Moreover,only under high fertility conditions,the increase of mycorrhizal colonization rates of wheat and maize can significantly promote the utilization rate of phosphorus.Therefore,when soil phosphorus is extremely deficient,crops mainly promote phosphorus absorption by increasing root weight density and root length density.When soil phosphorus is high,the role of arbuscular mycorrhizal fungi is highlighted.