Effects Of Microbial Agents On Nitrogen And Phosphorus Nutrition Of Crops And Rhizosphere Microenvironment In High Phosphorus Soil

Irrational application of chemical fertilizers causes soil nutrient imbalance,reduced microbial diversity,soil diseases,and other soil quality problems and is one of the main sources of non-point pollution.The application of microbial agents can improve the soil environment and crop growth to reduce problems caused by irrational application of chemical fertilizers.In this study,the high phosphorus soil in the main grain producing area of Huanghuai sea was selected as the object.Field in situ experiments were carried out for two consecutive years.The effects of six different microbial agents combined with conventional fertilizer on the growth of crops,available nitrogen and phosphorus and the community structure of rhizosphere microorganism in different stages of high-phosphorus soil were compared.Meanwhile,the changes of nitrogen and phosphorus in different forms of soil profile were analyzed.The microbial agents applied in this study were(1)fungal microbial agents,Trichoderma compound agent(TC)and(2)bacterial microbial agents,namely,soil remediation agent(SR),anti-repeat microbial agent(AM),microbial agent(MA),plant-rhizosphere growth-promoting bacteria agent(PG),and biological fertilizer agent(BF).Short term application of microbial agents was conducted to compare the effects of microbial agents on wheat growth,soil nitrogen,soil phosphorus and microbial community composition in different stages,to explore the effects difference of microbial agents and its reasons.Continuous application of microbial agents was conducted to compare the accumulation of different forms of nitrogen and phosphorus in high phosphorus soil,to evaluate the stability of microbial agents in promoting growth and increasing yield,to reveal the influence of microbial agents on rhizosphere bacterial community and the abundance of nifH,AOA-amoA,and AOB-amoA genes.The main conclusions were as follows:(1)Effects of microbial agents on crop growthThe short-term application of PG significantly increasesd the wheat yield by 33.4%,the spike number,and the grain weight,and PG was beneficial to the growth of wheat at the regreening stage.Continuous application of PG,BF increased the yield by 30.05%,32.51%.The results show that PG has the greatest advantage in increasing wheat yield steadily.With the increase of application years,the effect of BF on increasing production is gradually obvious.(2)Effects of microbial agents on the available nitrogen and phosphorus in soil surfaceShort-term application of microbial agents significantly increased the content of alkali-hydrolytic nitrogen(AN),but had no significant effect on available phosphorus(AP)in soil surface,the microbial agents(MA,BF,PG)which promote the growth of crops had better effect on the improvement of AN in the topsoil.From the different growth stages,microbial agents were beneficial to increase the content of AN in the topsoil at the regreening stage and flowering stage of wheat.After the continuous application of TC and PG,they significantly increased the content of AN,but there was also no significant difference in the content of AP.The results show that TC and PG have the stable activation effect on the content of AN in the topsoil.(3)Effects of microbial agents on structure of soil bacterial communityShort term application of microbial agents did not significantly change the diversity of rhizosphere bacterial community.The Shannon index of rhizosphere soil was significantly increased by the continuous application of PG and MA,indicating that increasing the application years is conducive to improving the diversity of microbial community structure in rhizosphere soil.LefSe analysis results showed that the short-time application of five bacterial agents caused the beneficial rhizospher bacteria enrichment in the rhizosphere soil.After continuous application of microbial agents,the enrichment of SR agent disappeared,and four agents containing Bacillus subtilis stably enriched the beneficial rhizosphere bacteria.(4)Accumulation of different forms of nitrogen and phosphorus in soil profiles with the application of microbial agentsThe continuous application of PG agents increased the content of AN in topsoil,but had no significant change in AP.The continuous application of PG agent significantly reduced the content of AN at 20?40 cm and 40?60 cm,and the content of AP at 40?60 cm.Meanwhile,PG significantly promoted the contents of H2O-Pi,NaOH-Po and NH4+-N at the 0?20cm soil,significantly reduced the contents of H2O-Pi,NaOH-Pi and HCl-Pi at the 20-40cm soil,and significantly reduced the content of NaOH-Pi at the 40?60cm soil.The results shows that the application of microbial agents affects the content of N and P in different depths of soil,and PG is benificial to activate the available N in the surface layer and reduce the accumulation of N and P in the middle and deep layers.(5)Abundance of AO A-amoA,AOB-amoA and nifH genes in rhizosphere soilQuantitative analysis of AOA-amoA,AOB-amoA and nifH genes in rhizosphere soil by qPCR showed that the application of SR,PG and MA significantly increased the abundance of AOA-amoA gene,MA significantly increasesd the abundance of nifH gene,indicating that MA significantly improved the nitrification and nitrogen fixation ability of soil,and SR and PG significantly improved the nitrification ability of soil.In conclusion,the application of PG in the high-phosphorus soil has the best effect,which can be recommended as the best bacterial agent to reduce the amount of fertilizer and increase fertilizer efficiency.