Effects Of Potassium Fertilier Application On Soil Nitrogen Transformation Processes And Associated Microbial Community Mechanisms

Potassium?K?is one of the most cationic nutrients that required in plants,and it interacts with many nutrients in plants.Currently,research on K fertilizers is more focused on the effect on yield and quality,but less on environmental impact,especially on soil nitrogen cycle.In view of the high loss rate of nitrogen and the general lack of K in arable soil in China,it is necessary to deeply study the transformation process of soil nitrogen in the soil-plant system,and further understand the effect of K on soil nitrogen transformation.Therefore,pot experiment was carried out to analyze the regulation of K on soil nitrogen transformation process through the methods of aeration method and static box experiment,as well as soil microbial metagenome De novo sequencing and other technologies.The results will provide a mechanism basis for regulating the nitrogen balance of farmland ecosystem and reducing nitrogen loss to environment.The main results obtained are as follows:?1?Effects of different K supply levels on soil nitrogen transformation processStudies showed that the addition of K fertilizer had a very significant effect on the content of NH₄⁺and NO₃^-in soil,net ammonization rate,net nitrification rate,and net mineralization rate.At the seedling stage,K fertilizer application significantly increased soil NH₄⁺content,net ammonization rate,but reduced soil NO₃^-content,net nitrification rate and net mineralization rate.At the growing period,the application of K fertilizer reduced the soil NH₄⁺and NO₃^-content and increased net nitrification rate and net mineralization rate of soil.During the harvest period,K fertilizer addition reduced the soil NH₄⁺content and net ammonization rate,and increased the soil NO₃^-content and net nitrification rate.?2?The effect of K on the intensity of soil biochemical actionK application had a very significant effect on the intensities of soil nitrogen fixation,denitrification and nitrification.At the seedling stage,the additional of K fertilizer reduced the ammoniation intensity when combinated with ammonium nitrogen source fertilizer.During the crop harvest period,the application of K fertilizer increased the intensity of soil ammoniation,nitrification,nitrogen fixation,but reduced the intensity of soil denitrification.?3?Effects of different K supply levels on soil nitrification and denitrification microbial communitiesK application had no significant effect on the composition of soil nitrification and denitrification microbial communities,but changed the relative abundance of dominant populations.For nitrification,K fertilizer had a significant effect on the microbial population abundance of Candidatus Kuenenia,which possibly participated in the complete nitrification process,followed by the ammonia oxidation process,and followed by the nitrite oxidation process in which nitrite oxidizing bacteria participate.In the ammonia oxidation process,K fertilizer resulted in higher relative activity of archaea ammonia oxidation archaea?AOA?than ammonia oxidation bacteria?AOB?.Nitrososphaera and Nitrosopumilus were the main dominant microorganism populations of AOA,while Nitrosomonas and Nitrosococcus of Proteobacteria are the dominant microorganism populations of AOB.Under the action of K fertilizer,Nitrospira is the main microbial population involved in nitrite oxidation process.In denitrification,the relative abundance of denitrifying bacteria in different nitrogen sources fertilizer treatments have different response to K fertilizer.Under nitrate nitrogen source fertilizer,K application decreased the relative abundance of total denitrifying bacteria,among which the relative abundance of Paracoccus,Rubrivivax and Geobacter decreased most significantly,while under ammonium source nitrogen,K application increased the relative abundance of denitrifying bacteria,among which Streptomyces of Actinomycetes was the dominant population with the largest increase in relative abundance.?4?Effects of different K supply levels on crop growth and nitrogen absorption and utilizationK fertilizer significantly improved crop biomass,yield,nitrogen absorption,and nitrogen utilization.Under the application of nitrate nitrogen source fertilizer,K application decreased the yield,nitrogen absorption and nitrogen utilization rate,and the extent of reduction increased with the increase of nitrogen application rate.Under the application of ammonium source fertilizer,only the nitrogen utilization rate decreased under K applied,also decreased with the increase of nitrogen application rate.?5?Effect of different potassium supply levels on soil nitrogen lossThe application of K fertilizer significantly increased the cumulative NH₃ emissions from the soil,significantly reduced the residual amount of nitrogen in the soil and the cumulative emissions of N₂O throughout the growing season.At low nitrogen levels,K fertilizer significantly reduced N₂O cumulative emissions in ammonium treatments compared that in nitrate treatments,but at high nitrogen levels,the addition of K fertilizers had no significant effect on cumulative N₂O emissions in ammonium treatments,but reduced cumulative emissions of N₂O in nitrate nitrogen fertilizers treatment.The above results show that K fertilizer can significantly affect the intensity of soil nitrification and denitrification through the regulation of nitrification and denitrification microbial community abundance and the absorption and utilization of nitrogen by plants,thus reducing N₂O cumulative emissions and loss of environmental nitrogen,and playing an active regulatory role in farmland nitrogen management.Especially in K-deficient soil,K application is of great significance for improving nitrogen use efficiency and reducing environmental nitrogen emission.