Crop Yield Summary for Three Wetland Reservoir Subirrigation Systems in Northwest Ohio

Abstract. Wetland Reservoir Subirrigation Systems (WRSIS) are innovative agricultural water management and recycling systems comprised of three main components; a constructed wetland, a water storage reservoir, and cropland containing subsurface drainage pipe systems. Surface runoff and subsurface drainage from cropland are diverted to a constructed treatment wetland to partially remove nutrients and suspended sediment. Water from the wetland is then routed to a storage reservoir and held there until needed during the growing season for subirrigation. With subirrigation, water from the reservoir is added directly to some of the cropland subsurface drainage pipe systems in order to irrigate the crops through the root zone. Three WRSIS were installed in northwest Ohio; within Defiance, Fulton, and Van Wert Counties. These three sites were operated and monitored from 1996 through 2008. Potential WRSIS benefits included: (1) reduced offsite release of nitrogen nutrients and suspended sediment, (2) additional wetland vegetation and wildlife habitat, and (3) enhanced crop yields. With respect to crop production at all three sites combined, the subirrigated fields within WRSIS, as compared to fields with conventional, unrestricted subsurface drainage, were found to have respectively larger corn (Zea mays) and soybean (Glycine max) yields of 28.7% and 25.2% during dry growing seasons, 14.1% and 6.9% during near average or wet growing seasons, and 19.1% and 12.1% overall. Subirrigated field crop yield results varied between sites with the greatest corn and soybean production increases found at the Fulton County WRSIS, followed by the Van Wert County WRSIS, then the Defiance County WRSIS. At the Defiance County WRSIS, which had high clay content, low hydraulic conductivity soils, a shorter subirrigated field drain line spacing distance (half of what is typical) was found to improve the yield of corn, but not soybeans. This study indicates that WRSIS can provide significant crop yield benefits, especially during dry growing seasons.