Effect of controlled drainage on nitrogen losses from controlled irrigation paddy fields through subsurface drainage and ammonia volatilization after fertilization

The effect of controlled drainage (CD) on nitrogen (N) losses from controlled irrigation (CI) paddy fields through subsurface drainage and ammonia volatilization (AV) was investigated by managing water table control levels (WTC) with a lysimeter equipped with an automatic water table control system. Three drainage treatments were implemented, namely, controlled water table depths 1-3. The increases of the WTC resulted in a high proportion of groundwater levels below the WTC, which reduced the subsurface outflow from CI paddy fields by 30.5% during the first week after fertilization. Total N concentrations in the 0-10 cm soil solution and subsurface drain water were higher as the WTC increased. The increase of the WTC during the first week after fertilization could effectively decrease the N losses from CI paddy fields by 9.5%, and the first weekly N losses through subsurface drainage and AV after fertilization were reduced by 17.2% and 9.3%, respectively. The large reductions in subsurface outflow decreased the first weekly N losses through subsurface drainage after fertilization. The retention time of shallow water in CI paddy fields was extended with the increases in WTC, which may reduce the first weekly AV losses after fertilization. Results show that the combination of CI and CD may be an effective water management method for mitigating N losses through subsurface drainage and AV after fertilization from paddy fields.