Effects Of Reducing Nitrogen Application Combined With Microbial Agents On Soil Microbial Characteristics And Rice Root Development

With the contradiction between man and land and the long-term excessive application of chemical fertilizers in China,the effect of large-scale application of chemical fertilizers on grain production has approached the limit of increasing production.At the same time,excessive application of chemical fertilizers,especially nitrogen fertilizers,leading to eutrophication of water bodies and increased greenhouse effect of the atmosphere have become more and more prominent,and also cause soil fertility degradation,such as decreased soil enzyme activity and reduced soil microbial diversity.Therefore,there is an urgent need to find safe alternative fertilization strategies to improve the sustainable of agro-ecosystems.As a new type of fertilizer,microbial agents have attracted much attention because they can synthesize active substances,stimulate the growth and development of plant roots,and improve soil enzyme activities,nutrient bioavailability and soil productivity.Experiments on the use of microbial agents to achieve fertilizer reduction have also appeared,but the effects achieved are different.In order to find out the influence mechanism of microbial agents on soil microbial characteristics and rice root development characteristics under the condition of reducing chemical fertilizer dosage,pot experiment and field experiment were carried out in this study,and 9 fertilization treatments were set in pot experiment:the fertilization level was full nitrogen fertilizer?N₁?and nitrogen fertilizer reduction was 30%(N_0.7);the combined microbial agent was a nitrogen-fixing bacterium?G?and a composite microbial agent?S?field trial.Set 9 treatments:fertilization level is full nitrogen fertilizer?N₁?and nitrogen fertilizer reduction 30%(N_0.7);compounding agent is compound microbial agent?B?and compound microbial agent?S?,soil microbial characteristics,rice root development characteristics And rice yield and other aspects to explore whether microbial agents can be produced Reduction without reducing the amount of fertilizer,and to clarify its mechanism of action and effectiveness,aimed at providing theoretical reference and data support for reduced fertilizer application and maintain the sustainable development of agriculture.The research results are as follows:?1?Compared with full application of N fertilizer,reducing 30%of N fertilizer with compound microbial agent S treatment in pot experiment can increase the shannon index of bacteria and fungi,the number of bacterial OTU,Among them,the enzyme activities reached the highest for reducing 30%of N fertilizer with microbial agents treatment at the 50^thday.Compared with the full application of N fertilizer,the activities of soil urease,sucrase and catalase were increased by 22.7%,16.67%,and 16.35%,respectively.Moreover,the effect of the composite microbial agent S on the microbial properties is better than that of the single microbial agent.In the field experiment,the number of bacteria OTU treated with reducing30%of N fertilizer with compound microbial agent S was greater than that of single application of full N fertilizer;soil urease,catalase,sucrase activities and soil microbial biomass carbon and nitrogen content and the full application of N fertilizer treatment increased by 17.14%,39.07%,31.80%,19.0%and 34.8%,respectively;while the urease treated with the combined application of microbial agents B and N fertilizer reductionwas lower than that of full application of N fertilizer.The effect of the composite microbial agent S on the microbial properties is better than that of the composite microbial agent B.?2?Compared with the full N fertilizer,the root length,root surface area,root mean diameter and total root volume of rice treated with reducing 30%of N fertilizer with compound microbial agent S in the pot experiment were significantly increased;The root biomass under reducing 30%of N fertilizer with microbial agents was increased significantly at 40?50 days.Moreover,the effect of the composite microbial agent S is better than that of the single microbial agent.In the field experiment,the combined application of microbial agent S and N fertilizer reduction can increase rice root length,root surface area,total root volume and root total carbon and nitrogen content in rice tillering stage,heading stage and grain filling stage,and promote rice root growth;Compared with the application of N fertilizer,the yield of rice with reducing 30%of N fertilizer with microbial agent S increased by 686.17 kg hm^-2.It can be seen that the combined application of microbial agent S and N fertilizer reduction can improve soil enzyme activities,thereby promoting rice root growth,increasing rice yield,and finally reducing the amount of chemical fertilizer,increasing crop yield and and improve the sustainable development of the agro-ecosystem.