Eeffect of Different Nitrogen Application Types on Nitrogen Utilization Efficiency and Fate of Fertilizer for Sugacane

A pot experiment in greenhouse was conducted with 15N-labeled urea 5g/pot(equal to 450kg·hm-2) total nitrogen by three kinds of treatments of disposable bottom application nitrogen before sowing(T1),50% nitrogen before sowing and 50% nitrogrn during tillering stage(T2),and 30% nitrogen before sowing,30% nitrogen during tillering stage and 40% nitrogen applied during elongation stage(T3) to investigate the use efficiency and fate of fertilizer nitrogen using the sugarcane cultivar ROC22.Results showed that almost 18%~29% of total N uptake by sugarcane was supplied by fertilizer,and 71%~82% N derived from soil and seed-stem.Nitrogen use efficiency ranged from 21.0% to 34.52%,with 15N-fertilizer residue of 37.61%~44.13%,and 15N-fertilizer loss of 21.35%~41.39% among three treatments.Under the three levels of nitrogen application,residual was 15N-fertilizer was mainly distributed in 0~20cm top soil.The uptake of nitrogen and the proportion of total N from fertilizer in sugarcane plant,the yield of stalk and sugar after the nitrogen applied,and the use efficiency and residue ratio of 15N-fertilizer increased significantly over time,while loss rate of 15N-fertilizer decreased significantly with a slight decline trend of nitrogen distributtion and sucrose accumulation in stalk.The results also indicated that after the nitrogen applied the amounts 15N-fertilizer residue in 0~20 cm top soil showed a rising trend,but dropped in 20~40cm soil profile.From the viewpoints of economic benefit and ecological benefit,the nitrogen fertilizer applied of T3 could be optimal treatment.