葡聚糖改性尿素在潮土中的转化特征OA

[Objective]Sugars regulate the nitrogen transformation process in soil.However,the effects of different polymerization degrees of dextran on nitrogen conversion were not clear.This study focused on investigating the transformation characteristics of dextran-modified urea with varying degrees of polymerization in calcareous fluvo-aquic soil,analyzing the relationship between the polymerization degree of dextran and nitrogen efficiency,and revealing its functioning mechanism.It aimed to provide a solid theoretical basis for the application of different polymerization degrees of dextran in urea.[Method]Four types of modified urea were prepared by incorporating 1%glucose(monosaccharide,GU),maltose(2-poly,MU),oligomeric dextran(≈5-poly,OU),and polydextrose(≈20-poly,PU)into molten urea.Six treatments were designed:no fertilization(CK),conventional urea(U),and four dextran-modified urea treatments.A soil incubation experiment was conducted to evaluate nitrogen transformation,and 13C nuclear magnetic resonance(13C-NMR)spectroscopy was used to characterize the chemical structures,to uncover the urea conversion mechanism affected by dextran polymerization degree and structural changes.[Result](1)Dextran-modified urea contained a Schiff base structure.(2)Compared with U,dextran-modified urea slowed urea hydrolysis and increased soil amide N content by 15.3%-37.1%,with the highest value in OU.(3)After the application of nitrogen fertilizer,the urease activity of the U treatment peaked at 1 d,whereas the urease activity of the dextran-modified urea treatment peaked at 2 d of incubation.(4)Ammonia volatilization accumulation of dextran-modified urea was reduced by 2.2%-12.9%compared with U.With the increase of the degree of polymerization of dextran,the accumulation of ammonia volatilization showed a gradually increasing trend.(5)At the end of the incubation,NO3--N content of dextran-modified urea was increased by 14.1%-30.5%.As the degree of polymerization of dextran increased,the nitrate nitrogen content first increased and then decreased.When the degree of polymerization was 3.35,the nitrate nitrogen content was the highest.[Conclusion]Dextran-modified urea effectively delayed urea hydrolysis,reduced ammonia volatilization,and enhanced soil NO3--N content.GU had the best impact on reducing ammonia volatilization,while dextran with a medium polymerization degree(3.35)had the best effect on improving the NO3--N content in the soil.