Experimental study on water-saving and emission-reduction effects of controlled drainage technology

Field experiments and laboratory analysis were carried out to determine the effects of controlled drainage (CTD) and conventional drainage (CVD) technologies on drainage volume, concentrations of NH4+-N, NO3−-N, and total phosphorus (TP), nitrogen and phosphorus losses, rice yield, and water utilization efficiency. Results show that CTD technology can effectively reduce drainage times and volume; NH4+-N, NO3−-N, and TP concentrations, from the first to the fourth day after four rainstorms decreased by 28.7%–46.7%, 37.5%–47.5%, and 22.7–31.2%, respectively, with CTD. These are significantly higher rates of decrease than those observed with CVD. CTD can significantly reduce nitrogen and phosphorus losses in field drainage, compared with CVD; the reduction rates observed in this study were, respectively, 66.72%, 55.56%, and 42.81% for NH4+-N, NO3−-N, and TP. Furthermore, in the CTD mode, the rice yield was cut slightly. In the CVD mode, the water production efficiencies in unit irrigation water quantity, unit field water consumption, and unit evapotranspiration were, respectively, 0.85, 0.48, and 1.22 kg/m3, while in the CTD mode they were 2.91, 0.84, and 1.61 kg/m3—in other words, 3.42, 1.75, and 1.32 times those of CVD. Furthermore, the results of analysis of variance (ANOVA) show that the indicators in both the CVD and CTD modes, including the concentrations of NH4+-N, NO3−-N, and TP, the losses of NH4+-N, NO3−-N, and TP, irrigation water quantity, and water consumption, showed extremely significant differences between the modes, but the rice yield showed no significant difference.