Nitrogen Losses from Flooded Rice Field

A field microplot experiment was conducted during the tillering stage of paddy rice to investigate nitrogen (N) Iosses from flooded rice fields following fertilizer application. After application of ammonium bicarbonate, most of nitrogen in the floodwater was present as NH4-N and its concentration varied widely with time. Concentrations of both NO3-N and NO2-N in the floodwater were low due to the weakened nitrification. Under flooded anaerobic reducing conditions, soil solution concentrations of NO3-N and NH4-N were not high, ranging from 0.6 mg L-1 to 4.8 mg L-1, and decreased with soil depth. However, the groundwater was still contaminated with NO3-N and NH4-N. Rainfall simulation tests showed that the N losses via runoff in rice fields were closely related to the time intervals between fertilizer applications and rainfall events. When a large rain fell for a short period after fertilizer application, the N losses via runoff could be large, which could have a considerable effect on surfa