Fate Of ¹⁵N In Coastal Saline Soil And The Effect Of Urea Combining With Organic Materials On Conversion And Utilization Of Nitrogen

The coastal light,medium and heavy saline Soil-Winter wheat system in the Yellow River Delta was studied.The ¹⁵N tracer method was used to determine the ¹⁵N abundance of various parts of wheat plant and soil of different levels in the mature stage,and the absorption amount and absorption rate of urea nitrogen in various parts of wheat plant,as well as the residual amount and residual rate in different soil levels were calculated and analyzed;The absorption and residual characteristics of urea nitrogen in different salinized soil-wheat systems were determined;Field in situ training methods,based on the application of urea with straw or organic manure,the determination of wheat during the period of arable layer soil NH₄⁺-N,NO₃^--N content and dry matter at indicators such as quality,plant nitrogen content,analysis of inorganic nitrogen content in saline soil,net nitrogen mineralization rate and wheat nitrogen utilization index,discusses the urea with straw and organic fertilizer rates at different levels of salinization in soil nitrogen transformation characteristics and efficiency.The main research results are as follows:(1)In soil of different salinization degree in the Yellow River delta,the dry matter quality,urea nitrogen absorption ratio and absorption amount distribution characteristics of all parts of wheat plant were grain>sheath>stem>leaf>root,grain dry matter quality,urea nitrogen absorption ratio and absorption amount were significantly higher than other parts.The increase of salinization can promote the absorption of nitrogen and urea nitrogen,and inhibit the accumulation of dry matter and urea nitrogen.(2)The residual urea nitrogen in 0-100cm saline soil decreases with the deepening of soil layer,which is mainly concentrated in 0-20cm soil layer.With the increase of soil salinization,the urea nitrogen residue in 0-40 cm soil layer was significantly reduced,the urea nitrogen residue in 60-100 cm soil layer was increased,and the proportion of urea nitrogen migration to the depth of soil increased.(3)In the coastal saline soil-wheat system,the uptake rate of urea nitrogen in the soil was1.53%?13.96%in the current season,the soil residual rate was 10.05%?48.69%,and the loss rate was 37.35%?88.42%.The absorption and utilization of urea nitrogen in the three kinds of salt-soil were the lowest,with the highest residue in the mild salt-soil and the highest loss in the moderate and severe salt-soil.Soil salinization degree will inhibit urea nitrogen recovery and residue,aggravate its loss.(4)Application of urea and organic materials in different salinized soils during wheat growth period could significantly increase the contents of NH₄⁺-N,NO₃^--N and inorganic nitrogen in soil,and NO₃^--N is the main form of inorganic nitrogen,which has a long accumulation time.Application of urea combined with organic fertilizer can increase the total nitrogen content in salinized soil,while applying straw in mild and moderate saline soil can reduce the inorganic nitrogen content;Inorganic nitrogen content in heavily saline soil was increased when organic fertilizer was applied.Soil salinization increased the content of NH₄⁺-N and decreased the content of NO₃^--N,inorganic nitrogen and total nitrogen.(5)Application of urea and organic materials in wheat growth period can significantly improve the net nitrogen mineralization/fixation rate,and generally is positive in the growth period after fertilization,showing a net accumulation.The net nitrification rate is generally higher than the net ammoniation rate,which is the main process of the net nitrogen mineralization rate.Application of urea combined with organic fertilizer can promote the rate of net ammoniation,but inhibit the rate of net nitrification and net nitrogen mineralization;application of urea combined with organic fertilizer can promote the rate of net nitrogen mineralization.Soil salinization degree will inhibit the net ammonia rate,promote the net nitrification and net nitrogen mineralization rate.(6)Application of urea and organic materials in three saline soils could significantly increase aboveground biomass and nitrogen accumulation of wheat.Application of urea combined with organic fertilizer was beneficial to increase the aboveground biomass,total nitrogen content,nitrogen accumulation and nitrogen fertilizer utilization efficiency of wheat,and the straw application basically inhibited the above indexes.The soil salinization degree will reduce the above ground biomass,nitrogen accumulation and nitrogen fertilizer utilization efficiency,but increase the above ground nitrogen absorption.