Study On The Behaviors And Absorbing Utilization Of Nitrogen Fertilizer In Latosol Of Dryland In Tropical Zone

In order to find out the behaviors of fertilizer-N and the N-utilization of vegetables after nitrogen fertilizer was applied in soils under the tropical climate, and offer theoretic basis for adequately applying nitrogen fertilizer, reduce losses of nitrogen, enhance the utilization ratio of nitrogen fertilizer, improve vegetables quality and protecte the environment, the 15N tracer and ordinary fertilizer-N experiments were carried out to study the behaviors of nitrogen fertilizer at different application rates of nitrogen with two leaf-vegetables. The main results were as follows:1. In summer , ammonia volatilization of urea was detected one day after its application and reached the peak 3-5 days , it took 20 days to cease . in winter, ammonia volatilization of urea was detected 5 days after urea was applicated and reached the peak 10-17 days, it was remained 40 days after its application.2. The recovery efficiency of fertilizer-N was between 60% and 70% at different application rates of nitrogen. The utilization ratio of nitrogen fertilizer was ranged from 22.5% to 43.84% (33.32% on average), the residual-N in soil were from 24.25% to 47.28% (32.68% on average), more than 80% of residual-N was distributed in the soil layers of 0-40cm, the main form of residual-N was ammonium-nitrogen.3. The nitrogen losses of fertilizer-N were in the range of 30-40% (34% onaverage), ammonia volatilization was in the range of 0.72%-28.1% (19.11% on average) in summer, and they were 11.4-22.94%(13.9% on average) in winter. The 15N content of soil layers lower than 40cm depth was increased with the increase of applied-N amount, and 15N was traced in percolated water, but the rate of it was too small to negligible.4. The utilization ratio of nitrogen fertilizer was decreased with the increase of applied-N amount both difference method and 15N tracer, the utilization ratio of nitrogen fertilizer was measured by difference methods, it was39.85% on average, and 6.53% higher than by the method of 15N tracer.5. Under this experiment, the optimum applied -N amount of two vegetables was 300Kg/hm2, the dry-weight, total-N and economic efficiency was decreased, the utilization ratio of nitrogen fertilizer was declined significantly when applied -N amount was more than the optimum applied -N amount.6. When applied -N amount was more than 300Kg/hm2, the contents of some cations, which effect on key enzymes of nitrogen assimilation, was declined significantly, thus, total-N decreased in leaves of swamp cabbage.7. Between the content of ammonium-N +amide-N and the nitrate reductive activity (NRA) in leaves of vegetables were negative correlation. When the content of ammonium-N + amide-N in leaves of vegetables lied in high level, they inhabited the nitrate reductive activity, therefore, the content of nitrate increased in leaves of vegetables.