RESEARCH ARTICLE In Situ Nitrogen Mineralization, Nitrification, and Ammonia Volatilization in Maize Field Fertilized with Urea in Huanghuaihai Region

Nitrogen (N) fertilization potentially affects soil N mineralization and leaching, and can en-hance NH3 volatilization, thus impacting crop production. A fertilizer experiment with five levels of N addition (0, 79, 147, 215 and 375 kg N ha-1) was performed in 2009 and 2010 in a maize field in Huanghuaihai region, China, where> 300 kg N ha-1 has been routinely ap-plied to soil during maize growth period of 120 days. Responses of net N mineralization, in-organic N flux (0–10cm), NH3 volatilization, and maize yield to N fertilization were measured. During the growth period, net N mineralization and nitrification varied seasonally, with higher rates occurring in August and coinciding with the R1 stage of maize growth. Soil NO3 −-N contributed to more than 60 % of inorganic N flux during maize growth. Cumulative NH3 volatilization increased with N additions, with total NH3 volatilization during maize growth accounting for about 4 % of added N. Relative to the control, mean maize yield in the fertilizer treatments increased by 17 % and 20 % in 2009 and 2010, respectively. However, grain yield, aboveground biomass, and plant N accumulation did not increase with added N at levels> 215 kg N ha-1. These results suggest that the current N rate of 300 kg N ha-1 is not only excessive, but also reduces fertilizer efficacy and may contribute to environmental problems such as global warming and eutrophication of ground water and streams