POTENTIAL INFLUENCE OF DRAINAGE WATER RECYCLING ON CROP YIELD, STREAMFLOW, AND WATER QUALITY IN INDIANA

Subsurface tile drainage systems are essential to productive agriculture in low-gradient regions with poorly drained soils, but water drained from these landscapes carries dissolved nutrients (e.g. nitrate) which contribute to downstream hypoxic conditions. Indiana is one of the top four states in terms of subsurface drainage extent, approximately 42% (5.6 million acres) of all cropland has subsurface drainage and only 3% (<500,000 acres) of all cropland is irrigated. Drainage water recycling (DWR) is a water conservation practice in which subsurface drainage is stored on site in a pond, reservoir, or ditch to be used as a source for supplemental irrigation during periods of water deficit. This study investigates how wide spread adoption of DWR could influence streamflow, water quality and crop yields in a traditionally drained and rain-fed agriculture system. The Variable Infiltration Capacity (VIC) macroscale hydrology model, with a subsurface drainage algorithm, coupled with the Cropping Systems Simulation Model (CropSyst) dynamic crop growth model is used to simulate corn and soybean yields and hydrology across the state of Indiana from 1984 to 2013. Simulated subsurface drainage is evaluated using observed drainflow from five field sites. Simulated routed streamflow is evaluated using observed streamflow from eight watersheds ranging from 476 to 12,265 mi². The VIC-CropSyst model is calibrated using observed county-level yields (2004 - 2013) and state average irrigated yields reported by the National Agricultural Statistics Service. Two scenarios are simulated, one with conventional drainage and the other with DWR adopted in all areas with subsurface drainage where 1% of the drained area is retired from crop production and used as a storage pond. The differences in simulated corn and soy crop yield, annual volume of captured drainflow (load reduction) and streamflow patterns between the two scenarios for eight large watersheds across Indiana will be presented.