Influence of Controlled Drainage on the Groundwater Nitrogen and Phosphorus Concentration at Jointing-Booting Stage of Wheat

The effect of controlled drainage on nitrogen (N) and phosphorus (P) emission at jointing-booting stage of winter wheat was studied in 2007-2008. The conventional subsurface drainage was taken as the control (T5). The groundwater depth was naturally drained to 400 mm and 800 mm below the soil surface within 3 days at the jointing-booting stage, after the water level was kept at 100 mm for 1 day (T1, T2) and 3 days (T3, T4) from the soil surface. Results showed that controlled drainage could significantly reduce the concentration of P and N in groundwater. Compared to T5, the four controlled treatments could significantly decrease the concentration of TP, NH4+-N, and NO3--N. The highest concentration reduction for TP and NO3--N was observed under T4 and T1, which reached 64.9% and 73.2%, respectively. As for the concentration of NH4(+)-N, the highest reduction was obtained under T2. The change of TP concentration was significantly affected by the interaction of submergence time and drain depth, while the influence of controlled drainage on NH4+-N concentration was not significant. The submergence time, drain depth, and the interaction of submergence time and drain depth had significant effect on the change of concentration of NO3--N.