Ammonia Volatilization under Different Nitrogen Application Rates in Paddy Soil in the Nnorthern ErHai Lake Area

An enclosed vent method was used to measure the ammonia(NH3) volatilization from a paddy soil of rice system under different application rates of urea in the northern ErHai Lake region. Concentrations of NH4 +-N and NO3-N, and pH value in the surface water were determined. The results showed that ammonia volatilization flux(AVF) peaked on the 3rd day after the basal fertilizer application, and decreased afterwards. The ammonia volatilization stopped after 9 d of basal fertilizer applicaion. However, AVF peaked on the 1st or 2nd day after the basal fertilizer application, and decreased rapidly afterwards, and then stopped after 5 days of the booting fertilizer application. There was a significant positive correlation between the nitrogen application rates and ammonia volatilization accumulation(AVA) in different growth stages of rice(correlation coefficients were above 0.839). AVA in the basal feertilizer stage was generally greater than that of the booting fertilizer stage. The total AVA losses varied from 15.23 to 55.45 kg N /hm2, and the loss rates of ammonia volatilization(LRAV) ranged from 11.28 % to 15.40 % in the N treatments during the whole growth period. The NH4 +-N concentrations in the surface water peaked 1 d earliler than that of AVF. Ammonia volatilization in the surface water was prohibited when the concentration of NH4 +-N was less than 10 mg/L. AVF was significantly positively correlated with NH4 +-N concentration in the surface water(the correlation coefficient was 0.624). However, there were no significant correlations between AVF and pH value or NO3--N concentration in the surface water. Therefore, around 5~9 days after fertilizer application were the key period for controlling the NH3loss from the paddy fields,while the nitrogen application rates and the changes in NH4 +-N concentration in the surface water were one of the key factors to determine ammonia volatilization loss.