Water quality and soil nutrient availability trade-offs associated with timing and duration of managed flooding for migratory waterbird habitat

Controlled fall and winter flooding of cropland for migratory shorebird and waterfowl habitat may reduce nutrients in runoff, but the impact of anoxic conditions under corn (Zea mays L.)–soybean (Glycine max) rotation due to flooding is not well studied. Influences of fall and/or winter flooding on total soil carbon (C), total and inorganic soil nitrogen (N), Mehlich 3-extractable soil nutrients, including phosphorus (P), and soil exoenzyme activities, including aryl sulfatase and β-N-acetyl-glucosaminidase (NAG), were compared before (September) and after (February) flooding. Five flood treatments were distributed across three farms under corn–soybean rotation. Treatments included control or no flooding, passive rainfall capture, fall flood, winter flood, and fall through winter (FW) flooding. Flooding decreased suspended solids (SS), total and dissolved P, and inorganic N concentrations in runoff water during storm events. Soil pH, total soil C and N, and inorganic N increased between pre- and post-flooding time in all treatments. Soil available-P decreased in FW treatments, but remaining P availability was still not limiting for crop production. The magnitude of increased NAG activity was lower in fields experiencing winter flooding. While fall-winter flooding decreased available P, fall or winter only flooding did not induce significant changes in soil nutrient availability, and all three management options provided significant reductions in runoff nutrient concentrations across three different farms in the Mississippi Alluvial Plain.