Evaluating the nutrient reduction and water supply benefits of an on-farm water storage (OFWS) system in East Mississippi

An On-Farm Water Storage (OFWS) system is a structural Best Management Practice (BMP) that prevents downstream nutrient loading by capturing irrigation tailwater and storm runoff from agricultural fields. OFWS systems, as a result, also act as a source of water for irrigation with the potential to recycle nutrients captured in runoff events. A monitoring study was conducted for an OFWS system located on a corn and soybean farm in East Mississippi from June 2014 to August 2016 to analyze the effectiveness of the system for reducing downstream nutrient runoff, supplying water for irrigation, and recycling nutrients in captured water that is reapplied to the field. Nitrate and dissolved phosphorus (DP) concentrations in the storm runoff events captured by the OFWS system storage pond and prevented from going downstream measured as high as 179 mg L−1 and 0.69 mg L−1, respectively. Water can be lost downstream from the storage pond overflow pipe when the pond is at its maximum capacity in March-April of each year, but nitrate concentrations were less than 10 mg L−1 in the storage pond in March-April for both years of the study, and DP concentration was less than 0.053 mg L−1 in the water that could be lost downstream, which showed that OFWS systems can be effective in reducing downstream nutrient loading by capturing storm runoff events. Over three growing seasons, roughly 357,000 m3 of water was used for irrigation from the OFWS storage pond in a region which has traditionally been under dryland production. This shows that OFWS systems can serve a dual purpose of reducing nutrient runoff and providing water for irrigation in East Mississippi, where groundwater is not a cost-efficient source of water for irrigation. Irrigated corn yields were higher than non-irrigated corn yields by an average of 1532; 2285; and 3950 kg ha−1 in 2014, 2015, and 2016, respectively; and irrigated soybean yields were higher than non-irrigated soybean yields over the same years by an average of 302; 1411; and 800 kg ha−1, respectively, demonstrating the importance of irrigation in East Mississippi. Analysis of nutrient concentrations in water samples collected simultaneously from both the irrigation system (sprinkler), which is fed from the bottom of the pond, and the storage pond grab samples showed that nitrate concentrations in the irrigation samples were lower than in the storage pond, but ammonia concentrations were higher in the irrigation water samples. Low nitrate concentrations and variability in nitrate concentration in the irrigation water as compared to the storage pond water showed that some of the nitrogen load is being recycled but not enough for the producer to reduce commercial fertilizer application.