Effects Of Phosphorus Application Level On Soil Nutrient And Enzyme Activities In Maize/soybean Intercropping System

Phosphorus fertilizer is essential nutrient element for crop growth,which is closely related to soil nutrient and agricultural sustainable production.As an important grain crop,maize is planted in large area in Guanzhong Plain,and soybean affects the national economy lifeline because of its importance in our country.Therefore,maize/soybean intercropping has been widely concerned as a model to improve soil nutrient availability and promote crop production.In order to explore the effects of different phosphorus fertilizer levels and cropping patterns on soil nutrient and crop growth,three phosphorus fertilizer levels were set for maize and soybean（P0:no phosphorus application;P60:60 kg P₂O₅/ha;P180:180 kg P₂O₅/ha）and three cropping patterns（M:maize monoculture;S:soybean monoculture;M/S:maize/soybean intercropping）in our study,to analyze the effects of phosphorus application rates on soil nutrient content under three cropping patterns.Meanwhile,combined with soil microbial biomass,extracellular enzyme activity and its vector characteristics,we explored the restriction characteristics of microbial metabolism on soil nutrients,in order to provide theoretical basis for scientific phosphate fertilizer management.The main research results are as follows:1、The contents of total nitrogen,total phosphorus,dissolved organic carbon,ammonia nitrogen and available phosphorus in soil were increased by applying phosphorus fertilizer.The contents of dissolved organic carbon and ammonia nitrogen under P60 treatment were significantly higher than those under P0 and P180.Soil organic carbon content of soybean monoculture and maize/soybean intercropping was higher than that of maize monoculture.The soil dissolved organic carbon was affected by phosphorus rate and growth period:under P180,the soil dissolved organic carbon of maize monoculture was higher than of soybean monoculture and intercropping;in R1 period,dissolved organic carbon content was higher in soybean monoculture,while in R6,it was higher in corn/soybean intercropping.The soil total nitrogen content of soybean monoculture was higher than that of maize monoculture and intercropping;and the ammonia nitrogen and nitrate nitrogen of soybean monoculture and maize/soybean intercropping were higher than of maize monoculture.On the whole,total phosphorus content was higher in maize/soybean intercropping than in monoculture,and available phosphorus content in soybean monoculture and maize/soybean intercropping was higher than that in maize monoculture.2、The input of phosphorus fertilizer significantly increased the dry matter accumulation and yield of maize and soybean,and the yield of soybean increased with the increase of phosphorus application in soybean monoculture,and P180 treatment significantly increased by 7.0%and 19.1%compared with P60 and P0,respectively.Besides,compared with monoculture,intercropping increased dry matter accumulation and yield of maize,but decreased dry matter accumulation and yield of soybean.3、Phosphorus addition increased soil microbial biomass carbon,nitrogen and phosphorus content,and under P180 treatment is higher than under P0 and P60 generally.Compared with monoculture,intercropping increased soil microbial biomass carbon content,and the microbial biomass nitrogen and phosphorus of soybean monoculture and maize/soybean intercropping was higher than that of maize monoculture.4、Phosphorus application increased soil extracellular enzyme activities,especially for C-acquiring and P-acquiring enzymes.In the V12 and R1 periods in 2021 and R1 periods in2022,the N-acquiring enzyme activity of P0 was higher than that of P60,but in other treatments,the application of phosphorus fertilizer increased the activity of soil N-acquiring enzyme.In addition,the activity of soil C-acquiring enzyme in intercropping was higher than that in monoculture.However,the N-acquiring enzyme activity was higher without phosphorus application and in early growth stage,and lower in P180 treatment and late growth stage in monoculture than in intercropping.The P-acquiring enzyme activity was higher under monoculture than intercropping.5、Stoichiometric scatter plots of extracellular enzyme activity showed that soil microorganisms were limited by relative N in 2021 and relative P in 2022.In monoculture,P180 showed obvious P limitation,while P0 and P60 showed obvious N limitation.In intercropping,P0 showed strong P limitation and P60 showed obvious N limitation.And there was strong C limitation in P180 treatment.On the other hand,compared with monoculture,intercropping soil microorganisms were subject to stronger N limitation and weaker C and P limitation.In addition,the relative P and C limitation of microorganisms showed a significant positive linear relationship,and the nutrient limitation of microorganisms was closely related to soil physical and chemical properties,nutrient content and microbial biomass.