Simulation-Based Approach for Automatic Drainage Water Management and Subirrigation Strategy Considering Field Water Table Depths

The hydrological model, DRAINMOD-NII, has undergone modifications to simulate automatic controlled drainage (ACD) and automatic controlled drainage/subirrigation (ACD-SI) systems based on simulated field water table depths (WTD). The model assesses the predicted daily WTD to ensure it falls within a predefined desired range. The lower limit of this range is set at three times the maximum root depth during the growing season, while the upper limit is 30 cm below the soil surface. The modified model automates the ACD-SI system by eliminating the control structure (weir) entirely when the WTD is shallower than the upper limit. Conversely, it switches to subirrigation mode when the water table is deeper than the lower limit. The model was applied to two US data sets from North Carolina and Illinois, simulating five drainage management systems: Conventional Drainage (CVD), Traditional Controlled Drainage (TCD), Subirrigation, ACD, and ACD-SI. The results demonstrated that the predicted drainage, nitrogen losses, and crop yield are similar for the TCD and ACD systems. However, the ACD-SI system showed lesser simulated drainage and nitrogen losses and greater crop yield when compared to the other systems. The ranges of reductions in drainage losses compared to the CVD system were increased from 25%–41% to 27%–45% for the TCD and ACD systems to 36%–51% and 47%–62% for the ACD-SI system for the NC and IL data sets, respectively. Also, the ranges of reductions in nitrogen losses were increased from 6%–57% to 21%–35% for the TCD and ACD systems to 21%–69% and 36%–52% for the ACD-SI system for the NC and IL data sets, respectively. Furthermore, the ACD-SI system had an economic impact as it increased relative crop yield and reduced the amount of water required for subirrigation compared to the traditional subirrigation system.