Effects Of Maize Soybean Rotation,straw Returning And Phosphorus Fertilizer On Soil Phosphorus Components And Related Enzyme Activities

Maize and soybean are important grain crops in China.Heilongjiang Province is the main producing area of spring maize and soybean in China.In 2020,the output of Heilongjiang Province was 36.466million tons and 9.32 million tons,accounting for 14.0%and 40.7%of the national output.Due to the lagging development of straw returning technology,straw open burning seriously pollutes the environment.In recent years,the No.1 central document has repeatedly proposed to strengthen the comprehensive utilization of crop straw,further increase the intensity of straw returning in Northeast China to promote high-quality straw returning.Straw is directly returned to soil to improve the absorption and utilization of phosphorus by crops and supplement basic nutrients,so that crops can achieve yield increase.Excessive application of phosphorus fertilizer will increase the economic cost resulting in a decline in utilization rate of phosphorus fertilizer.Therefore,the research and promotion of maize and soybean straw returning production technology has important theoretical and production significance for agricultural sustainable development.The experiment was carried out in the experimental base of Northeast Agricultural University in2021,using the continuous positioning method of frame planting.Under the conditions of no straw returning（S0）,straw burying returning（S1）and straw burning returning（S2）,four phosphorus fertilizer application rates were set up.The application rates of calcium superphosphate（P₂O₅:44%）in P0、P1、P2 and P3 treatments were 0、0.55(77 kg·hm^-2)、1.10(155 kg·hm^-2)、1.65(232 kg·hm^-2)g/plant,respectively.The changes of soil phosphorus components,soil phosphatase activity,phosphate content of maize plants,phosphorus accumulation in maize plants,phosphorus fertilizer utilization rate and yield of maize were measured.The experimental results show that:（1）Straw burying,burning and combined application of phosphorus fertilizer significantly increased soil total phosphorus and available phosphorus content,soil total and fast-acting phosphorus content and increased with increasing phosphorus application,available phosphorus content increased significantly with the increase of phosphorus application rate,soil total phosphorus and available phosphorus content showed P3>P2>P1>P0,soil total phosphorus and available phosphorus content increased by 23.38%and36.99%compared with no phosphorus fertilizer treatment.There was no significant difference in the content of soil total phosphorus and available phosphorus between the two straw returning methods;straw return and phosphate fertilization increase soil total and fast-acting phosphorus content.（2）The return of straw to the field,the return of burning to the field and the application of phosphorus fertilizer affected the phosphorus component content of the soil,and the phosphorus application increased the soil phosphorus component content,and the soil active phosphorus content,medium active phosphorus content and stable state phosphorus content increased with the increase of phosphorus application,which was P3>P2>P1>P0.Under the condition of straw not returning to the field,the application of phosphorus fertilizer significantly increased the contents of H₂O-P、NaHCO₃-P、NaOH-Pi and Residual-P;Under the condition of straw burying and returning to the field,the application of phosphorus fertilizer significantly increased the contents of H₂O-P、NaHCO₃-Po、a OH-P、HCl-P and Residual-P;Under the condition of straw burning and returning to the field,the application of phosphorus fertilizer significantly increased the contents of H₂O-P、NaHCO₃-Po、NaOH-P、HCl-P and Residual-P;phosphorus fertilization increases soil active,moderately active and steady state phosphorus content.（3）Soil alkaline phosphatase activity was highest in the high phosphorus application before spring sowing and in the medium phosphorus application after autumn harvest under the three straw return conditions;the pattern of change in soil neutral phosphatase activity was consistent before spring sowing and after autumn harvest,highest in the medium phosphorus application under the no straw return and straw return conditions,and highest in the low phosphorus application under the straw return conditions;straw return by turning and burying affected soil phosphatase activity.Soil acid phosphatase activity was highest under the three types of straw return,with the highest phosphorus application before spring sowing and no consistent pattern of change after autumn harvest;straw buried and returned to the field increased soil alkaline phosphatase activity and acid phosphatase activity before spring sowing and after autumn harvest,while straw burnt and returned to the field increased soil neutral phosphatase activity before spring sowing and after autumn harvest.（4）Phosphorus accumulation in maize plants was affected by straw burial,burning and fertilizer application.Phosphorus application significantly increased maize plant phosphorus accumulation,while high phosphorus application significantly increased maize plant phosphorus accumulation under no straw return and straw burn return conditions,medium phosphorus application significantly increased maize plant phosphorus accumulation under straw bury return conditions,and both straw bury return and burn return increased maize plant phosphorus accumulation compared to no return;phosphorus fertilisation to increase phosphorus accumulation in maize.（5）The combined analysis of maize and soybean yields in the three crop rotation cycles（6 years）showed a gradual increase in yield with increasing phosphorus application,with no consistent pattern of change in the effect of straw burying and burning on maize and soybean yields;Phosphorus application to improve maize and soybean yields.