Simulated water quality and irrigation benefits from drainage water recycling at two tile-drained sites in the U.S. Midwest

Drainage water recycling, the practice of capturing and storing water drained from fields and using the stored water to irrigate crops when there is a soil water deficit, has been proposed to increase the resiliency of drained agriculture, but the potential benefits have not been quantified. This study determined irrigation and nutrient reduction benefits of drainage water recycling for various reservoir sizes at two tile-drained sites in the U.S. Midwest with differing climates and soils. Field and reservoir water budgets were developed using ten years of measured tile drain flow and weather data. The calculated volume of drain flow that could be captured by the reservoir was combined with measured nitrate-nitrogen and soluble reactive phosphorus concentrations to determine nutrient load reductions. At the Indiana site, a reservoir size representing 6% of the field area (3.05 m depth) would provide water storage for meeting irrigation requirements in all ten years. This reservoir would capture 37% of annual tile drain flow on average, resulting in average annual load reductions of 11 kg ha−1 yr−1 (37%) for nitrate-N and 0.05 kg ha−1 yr−1 (39%) for soluble reactive phosphorus. At the Iowa site, a reservoir size of 8% was necessary to meet the irrigation requirements, which were zero in most years but were higher than at the Indiana site for the three years in which irrigation was needed. This larger reservoir would capture 23% of annual tile drain flow on average, with average annual load reductions of 9 kg ha−1 yr−1 (24%) for nitrate-nitrogen and 0.02 kg ha−1 yr−1 (21%) for soluble reactive phosphorus. Quantifying nutrient load reductions and irrigation potential at these two sites showed that drainage water recycling is a promising practice for the tile-drained landscape of the U.S. Midwest, providing a strategy to manage water-related risks while also contributing to water quality goals.