Ammonia Volatilization and Nitrogen Utilization Efficiency in Response to Urea Application in Rice Fields of the Taihu Lake Region,China

Ammonia volatilization losses,nitrogen utilization efficiency,and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town,Changshu City,Jiangsu Province,China.The N fertilizer treatments,applied in triplicate,were 0 (control),100,200,300,or 350 kg N ha-1.After urea was applied to the surface water,a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field.Total N losses through ammonia volatilization generally increased with the N application rate,and the two higher N application rates (300 and 350 kg N ha-1) showed a higher ratio of N lost through ammonia volatilization to applied N.Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0% to 16.7% of the applied N.Increasing the application rate generally decreased the ratio of N in the seed to N in the plant.For all N treatments,the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%.Surplus N with the highest N rate resulted in lodging of rice plants,a decreased rate of nitrogen fertilizer utilization,and reduced rice yields.Calculated from this experiment,the most economical N fertilizer application rate was 227 kg ha-1for the type of paddy soil in the Taihu Lake region.However,recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve the N utilization efficiency of rice.