Measurement of ammonia volatilization from flooded paddy fields in Vietnam

Nitrogen (N) loss through ammonia volatilization from paddy fields at three sites in Vietnam was measured using the dynamic chamber method. Two sites were located in northern Vietnam and volatilization was measured in the summer and spring. The third site was in the Mekong Delta region in southern Vietnam and volatilization was measured in the dry and wet seasons. Urea was applied at 20-40 kg N ha-1 as a split application and a total of 80-100 kg N ha-1 was applied in the cropping season. Peaks in the NH3 flux were observed at 1 or 3 days after the application of urea, followed by a sharp decline to generally less than 1 mg N m-2 h-1 within 9 days. The estimated N losses by NH3 volatilization during the first 10-day period after fertilizer application and throughout the cropping period were 0.5-19.7% and 1.7-14.6% of the applied N, respectively, indicating that NH3 volatilization was a significant pathway of N loss from these Vietnamese paddy fields.