A Soil Water Balance Model for Subsurface Water Management

Most cropland in the upper Midwest will experience periods of excess water and drought conditions during a growing season. When the objective is to produce high yields, effective use of a subsurface water management system can help provide optimal soil moisture conditions for growth. A subsurface water management system includes draining excess water from the soil profile through subsurface drainage (SSD), managing the water table through controlled drainage (CD), or adding water to the drainage system during dry conditions (Subirrigation - SI). Subsurface water management can become difficult when determining the time and amount needed for SSD and SI, and (or) the optimal water table (WT) depth when using CD due to water movement in both the upward and downward directions. In this study, a 21 ha field with CD, a 17-ha field with CD + SI, and a 16 ha control field (surface drained only) over clay loam and silty clay loam soils were used to evaluate subsurface water management scheduling for corn (2013) and soybean (2014). The Checkbook Irrigation Scheduling method (Lundsfrom and Stegman, 1988) was modified to include an algorithm to estimate the daily water balance contribution due to upward flux (UF) from a shallow water table. For the 2013 growing season, the UF reduction of the daily soil moisture deficit (SMD) was minimal due to deeper WT over the growing season and there was little difference between the modified and original Checkbook methods. For the 2014 growing season, the SMD estimates from the Modified Checkbook method produced closer estimates to the in-field SMD compared to the original Checkbook method. Therefore, adding SSD and shallow WT contributions in the Checkbook method produces similar, if not more accurate, estimations of daily SMD that can be used for subsurface water management.