Effects Of N Fertilizer Combined With Straws At Different Rates On Amino Sugars In Paddy Soil

Straw returning,as an effective measure to improve the soil physical and chemical properties,improve soil fertility,has been paid great concern and applied extensively.On the one hand,straw with high ratio of carbon and nitrogen can increase the nitrogen demand of soil microbes and enhance the immobilization of inorganic nitrogen by soil microorganisms so that more fertilizer nitrogen can be preserved in the soil with easily decomposed organic transition pool,which be helpful for higer rate of nitrogen utilization.On the other hand,straw incorporated with chemical fertilizers provides a lot of energy and nutrition for soil microbes,which will inevitably have a dramatic effect on soil microbes and further affect the soil carbon and nitrogen cycle related to microbes.In this study,we studied the ¹⁵N enrichment of of "amino sites"in soil and aggregates under the condition of straw returning by pot experiment in order to further understand microbial transformation of nitrogen in soil,and then to reveal the mechanism of effect of straw returning on the microbial transformation process of nitrogen fertilizer in paddy soil,and to provide the theoretical basis for the efficient management of nitrogen fertilizer in farmland fertilizer.The main conclusions are as follows:?1?Compared with non-fertilization,nitrogen fertilizer combined with straw increased soil TN and TN content in soils.Compared with single application of nitrogen fertilizer,the addition of straw not only enhanced the immobilization of ¹⁵N in soil,but also led to more accumulation of fertilizer ¹⁵N in less size than 2000?m of aggregates.?2?Both single application of nitrogen fertilizer and along with straw had accelerated the accumulation of amino sugar,especially the more obvious promotion effect in treatment applied with high level of straw.Compared with single application of nitrogen fertilizer,the inorganic fertilizer combined with straw significantly increased the content of new synthesized amino sugar in soil,which was beneficial to the microbial fixation of ¹⁵N in soil.?3?Soil aggregates,especially>250?m aggregates,are important reservoirs for amino sugars in paddy soil.Straw with nitrogen fertilizer resulted in the transition of amino suger from microaggregate?53-250?m?to small macroaggregates;Nitrogen fertilizer along with low amount of straw strengthen the relative contribution from silt + clay to amino sugar in bulk soil while the application with high amount of straw made the distribution of soil amino sugar to large macroaggregate.?4?As is shown by isotopic analysis that the application of medium and high levels of straw promoted the microbial synthesis of ¹⁵N-amimo sugar in each size of aggregate and the newly synthesized amino sugar was mainly stored in>250?m aggregates.?5?In different particle size of aggregates,the response of microorganisms to fertilization was different.The application of nitrogen fertilizer with high amount of straw was beneficial to the accumulation of amino sugar originated from fungi in large aggregates.In<250?m aggregates,the trend was reversed.?6?The same amount of ¹⁵N fertilizer was applied in different growth stages of rice,the accumulation of ¹⁵N was in the order:basal fertilizer>tillering fertflizer>jointing and booting fertilizer,indicating the ¹⁵N applied as basal fertilizer into the soil is easier to be relented by microorganisms.With the growth and development of rice,the late application of ¹⁵N was easier to enrich in large macroaggregate at expense of the decrease in enrichment of ¹⁵N in 53?2000?m aggregates.In the review,>250?m aggregates in soil are the main reservoirs of soil fertilizers N and amino sugars,which indicates that large aggregate are important place for soil C and N microbial tansformation and play an important role in maintaining soil fertility.In addition,application of N fertilizer increases the immobilization of ¹⁵N in>53?m soil fraction while it fails to enhance the retention of ¹⁵N in bulk soil.In the long run,it may have positive effects on the retention of fertilizer N and then gradual mineralization to be used by next crop.