Agricultural Drainage and Hydrologic Variability in the US Corn Belt.

Subsurface (tile) drainage is an important water management practice for agricultural watersheds in the Midwest because it lowers seasonally high water table levels and enables the land to be utilized for row crops. At the same time this practice poses problems for the environment because it increases the concentration of nitrates entering local bodies of water and alters streamflow patterns. Drainage water management offers the potential for increased water conservation in some years, but may have a negative impact on greenhouse gas emissions by increasing the presence of reducing conditions.  The Variable Infiltration Capacity (VIC) model is a large-scale hydrologic model that was recently updated to simulate subsurface tile drainage. The VIC model calculates water and energy balances using meteorological data, such as temperature and precipitation, for individual grid cells. As part of this study we tested the new subsurface drainage algorithm within the VIC model to determine its ability to adequately simulate subsurface tile drainage from individual fields. The calibrated and evaluated VIC model was then used for a simulation across the US corn belt to evaluate  how climate variability will impact the quantity and seasonality of water held in the soil under different management practices including drainage water management.   Results from this study will be used to evaluate strategies for long-term sustainability of corn and soybean cropping systems, considering nitrate pollution from subsurface drainage and greenhouse gas emissions in the face of climate variability and change.