| Corn（Zea mays L.）and soybean（Glycine max Merr）are important food crops in China.Straw returning under corn and soybean rotation can improve soil ecological environment and benefit to crop growt.Crop straw contains C,N,P,K and other microelements,direct straw return carries a variety of nutrient elements into soil,supplies the nutrient source,and lays the foundation for the continuous high yield of crops.Based on the location experiment of soybean-corn rotation under straw returning combined with phosphorus fertilizer application since 2016,the characteristics of soil phosphorus supply and crop phosphorus accumulation were studied,so as to provide reference for rational application of phosphorus fertilizer under straw returning.The experiment adopted frame planting method and split zone design,the two factors were straw returning and phosphorus application amount.The main plot was straw returning with no straw returning,direct straw returning and straw burning,expressed as S0,S1 and S2,the soybean straw returning amount was 33 g/frame(4677 kg·ha-1),and the corn straw returning amount was84 g/frame(12 t·ha-1).The sub-plot were four phosphorus application levels with no phosphorus,low,medium,and high amonut,expressed as P0,P1,P2,P3.Phosphorus fertilizer application amount converted to heavy superphosphate（P2O5:44%）was 0,78.4,156.8,235.2 kg·ha-1.To investigate the changes of soil available phosphorus,soil phosphorus content,soil phosphatase activity,soybean and corn phosphorus accumulation,and the effects of straw returning and phosphorus fertilizer on the utilization rate and yield of soybean and corn phosphorus fertilizer.The results showed:Straw returning and phosphorus fertilizer application increased soil available phosphorus and total phosphorus content in soil.After 4 years soybean and corn rotation under different phosphorus application levels,direct straw returning（S1）increased soil total phosphorus content on average by 4.50%,the content of available phosphorus increased by 4.43%,the differences were all extremely significant.After 5 years soybean and corn rotation,straw direct returning（S1）increased soil total phosphorus content on average by 2.16%,the content of available phosphorus increased by 2.61%,the difference reached significant level.The content of soil available phosphorus and total phosphorus increased with the increase of phosphorus application.Straw returning had no significant effect on dry matter of soybean and corn,straw burning（S2）significantly increased the phosphorus content of corn at three-leaf stage by 7.39%,straw burning（S2）significantly increased the phosphorus content of soybean pod skin by 6.67%at harvest.Phosphorus application significantly increased the whole plant phosphorus accumulation of soybean at harvest stage,and increased with the increase of phosphorus application.At the level of P2,the phosphorus accumulation of the whole corn plant was the highest in the straw burning treatment（S2）.Under the condition of direct straw returning（S1）,the phosphorus content of corn plant in P1,P2 and P3 treatments were increased by 15.86%,14.30%and 13.91%compared with those in P0 treatment,respectively.Under the condition of direct straw returning（S1）,the phosphorus content of corn plant in P1,P2 and P3 treatments were increased by 6.13%,8.91%and8.90%compared with those in P0,respectively.Phosphorus utilization rate,phosphorus fertilizer partial productivity and phosphorus fertilizer agronomic productivity of corn and soybean decreased with the increase of phosphorus fertilzer application,and the straw returning had no significant effect on phosphorus utilization rate,phosphorus fertilizer partial productivity and phosphorus fertilizer agronomic productivity.Soil acid phosphatase activity was significantly higher than neutral and alkaline phosphatase activity,and straw returning significantly increased soil acid and alkaline phosphatase activity;In the fourth year of soybean and corn rotation,soil acid phosphatase activity at the P1 level was the highest and reached 17.44μmol·d-1g-1under direct straw returning（S1）treatmen.The phosphatase activity of direct straw returning（S1）and burning straw returning（S2）was 36.55%and 12.26%higher than that of no straw returning（S0）,respectively.Soil phosphatase activity was significantly increased by phosphorus fertilizer application,but there was no significant relationship between phosphorus fertilizer application and soil phosphatase activity.Straw returning and phosphate fertilizer apllication significantly increased soybean and corn yield,and straw returning had no significant effect on soybean and maize yield under the same phosphorus application level.After 4 years soybean and corn rotation,the corn yield was the highest when direct straw returning（S1）at P2 level.After 5 years soybean and corn rotation,the soybean yield was the highest when direct straw returning（S1）at P3 level. |
