Nitrogen Losses in Paddy Field Drainage Modified by Different Water Level Regulations

摘要

Nitrogen losses from farmland, through improper drainage and rainstorm runoff, cause non-point source pollution and limit sustainable agriculture development. We determined the effects of controlled drainage (CTD) and conventional drainage (CVD) on migration responses, the transformation of nitrogen, and NH4+-N and NO3--N losses. The results showed that four days after a rainstorm, compared with day one, NH4+-N and NO3--N decreased by ranges of 28.7-46.7% and 7.5-47.5% in CTD, which was significantly higher than CVD. CTD also significantly reduced NH4+-N and NO3--N losses in field drainage compared with CVD. NH4+-N was reduced by 66.72% and NO3--N reduction was 55.56%. NH4+-N contributed most to nitrogen losses, while NO3--N contributed less. Following rainstorm events, varying the water level using CVD and CTD had significant effects on NH (+)(4)-N and NO3--N concentrations. The DRAINMOD-II model was used to simulate NH4 (+)-N and NO3--N levels. It indicated that the observed and simulated values of NH4+-N and NO3--N concentrations in both CVD and CTD were fitted better. Lastly, the innovation of this study was that it focused on nitrogen concentrations and load changes in paddy field drainage after rainstorms, firstly using the DRAINMOD-N II model to simulate NH4+-N and NO3--N concentration changes under field scale. It further validated the pollution-reduction effect under water level control in the paddy field. Also, it improved the irrigation-drainage system of paddy rice and provided a scientific basis for optimizing irrigation-drainage project design in rice irrigation district.