Effects Of Straw Returning Combined With Phosphorus Fertilizer On Nutrient Accumulation Of Maize And Soil Nitrogen And Phosphorus Fractions

Maize is the main food crop.In 2021,the yield of maize in Heilongjiang has reached 41.49million tons.According to the ratio of grain to straw 1:1.2,the amount of straw will reach 49.79million tons.Straw contains abundant nutrients such as carbon,nitrogen,phosphorus,which is a renewable biomass resource for development and utilization.Straw returning can release nutrients,improve soil structure,increase soil water retention capacity,reduce the application of chemical fertilizers,and increase crop yield.Phosphorus is an essential nutrient for crop growth and development.Phosphorus application can increase soil phosphorus content,but excessive application of phosphorus fertilizer will lead to soil compaction and cause pollution to the environment.Studying the rational application of phosphorus fertilizer under straw returning can provide theoretical reference for maize straw returning in the south-central Songnen Plain and provide technical support for scientific and rational application of phosphorus fertilizer.In this experiment,under the condition of continuous cropping of maize in the south-central Songnen Plain from 2021 to 2022,the frame planting continuous located test were used to set up the split zone test.Three straw returning methods were used as the main factors:no straw returning（S0）,straw burying（S1）,straw burning（S2）,four phosphorus application levels（P0,P1,P2,P3）were used as the secondary factors,and the phosphorus fertilizer was heavy superphosphate（44%）,calculated by P₂O₅:0,34.50,69.00,103.50 kg·hm^-2.A systematic study was conducted to investigate the effects of different straw returning methods and phosphorus application rates on nutrient accumulation in maize plants and maize yield,as well as the changes in soil nitrogen and phosphorus fractions and related enzyme activities and correlations.The results showed that:（1）Phosphorus application increased the nitrogen,phosphorus and potassium accumulation of maize plants.Returning straw to the field reduced nitrogen accumulation in maize plants and potassium accumulation in maize grains and spike-stalk during harvest,and increased phosphorus accumulation and potassium accumulation during the three-leaf stage and jointing stage.Straw burning to the field reduced nitrogen accumulation during the jointing stage and harvest stage and potassium accumulation in maize plants at harvest,and increased phosphorus accumulation of plants at each growth stage.（2）The application of phosphate fertilizer reduced the content of non-acid hydrolyzable nitrogen and acid hydrolyzable amino acid nitrogen,and increased the contents of other organic nitrogen fractions,total nitrogen,available nitrogen,total phosphorus,available phosphorus and phosphorus fractions in soil.The contents of total nitrogen,ammonium nitrogen,acid hydrolyzed total nitrogen,acid hydrolyzed ammonia nitrogen,total phosphorus,available phosphorus,and phosphorus fractions（excluding Residual-P）were positively correlated with phosphorus application amount,while the content of nitrate nitrogen reached the maximum(36.31 mg·kg^-1)when the medium amount of phosphorus fertilizer was applied.Straw returning reduced the content of acid hydrolysis amino sugar nitrogen,and increased the contents of other organic nitrogen fractions,total nitrogen,available nitrogen,total phosphorus,available phosphorus and phosphorus fractions（except H₂O-P）in the soil.Among them,the contents of total nitrogen,ammonium nitrogen,Na HCO₃-Po and Na OH-Po were increased more obviously by straw burying,and the contents of nitrate nitrogen,total phosphorus,available phosphorus,Na HCO₃-Pi,HCl-P and Residual-P were increased by straw burning.（3）Application of phosphate fertilizer increased the activities of soil nitrate reductase,N-acetyl-β-D-glucosidase,alkaline phosphatase and neutral phosphatase.The activities of nitrate reductase,nitrite reductase and alkaline phosphatase showed a single peak curve change,and the peak value appeared at the application of medium amount of phosphate fertilizer.Application of phosphate fertilizer reduced soil urease and leucine aminopeptidase activities.Compared with no straw returning,straw returning increased the activities of N-acetyl-β-D-glucosidase and phosphatase of soil by more than 12.09%,and decreased the activities of leucine aminopeptidase,nitrite reductase,nitrate reductase and urease of soil.Straw burning increased the activities of nitrate reductase and nitrite reductase of soil by 39.10%and 5.34%,and decreased the activities of N-acetyl-β-D-glucosidase,leucine aminopeptidase,urease and phosphatase of soil.（4）There was a correlation between soil nitrogen and phosphorus fractions.TN was significantly positively correlated with TAHN,NHN,ANH,AAN,HUN,Na HCO₃-Po and Na OH-Po.AN was significantly positively correlated with TP,AP,H₂O-P,Na HCO₃-Pi,Na OH-Pi,Na OH-Po and HCl-P.TAHN was significantly positively correlated with AAN,HUN,TP,Na HCO₃-Po and Na OH-Po.There was a correlation between soil enzymes and nitrogen and phosphorus fractions of soil.S-NR was significantly positively correlated with Na OH-Pi,H₂O-P,HCl-P,AN,NO₃^--N,Residual-P,AP,TP and NaHCO₃-Pi.S-NAG,S-AKP,S-ACP and S-NP were positively correlated with NH₄⁺-N,TN,Na HCO₃-Po and NHN.S-LAP was negatively correlated with H₂O-P,HCl-P,AN,NO₃^--N,AP,TP and Na HCO₃-Pi.S-UE was significantly negatively correlated with HCl-P,AN,NO₃^--N,Residual-P and TP.The total nitrogen,available nitrogen and organic nitrogen fractions of soil can regulate maize yield directly or indirectly through soil enzymes related to nitrogen transformation.The total phosphorus and available phosphorus of soil negatively regulate maize yield,while soil phosphorus fractions and enzymes related to phosphorus transformation positively regulate maize yield.（5）Phosphorus application had a highly significant effect on dry matter accumulation of maize.The yield of maize increased with the increase of phosphorus application.The treatments of high phosphorus,medium phosphorus and no phosphorus reached a significant level of difference within2 years,while the treatments of low phosphorus and no phosphorus only reached a significant level of difference within 1 year.Straw returning had a tendency to increase yield,and the effect of increasing yield by straw burying was greater than that of straw burning,but there was no significant difference in maize yield compared with no straw returning.