Long-term impact of dairy lagoon wastewater on shallow groundwater quality

A long term study was conducted using dairy lagoon wastewater as a nutrient source for a multiple cropping system. Screened wastewater was applied at different rates (200, 400, 600, or 800 kg/ha/yr N in the waste) to the four quadrants of a center pivot area from 1991-1997, with a triple cropping system of corn, coastal bermudagrass, and abruzzi rye. In March 1997 the study was changed such that commercial fertilizer was used for two of the quadrants to compare yields and environmental impact between the inorganic nutrient source and the animal waste. Also, from 1497-1999, the study compared the original cropping system with a triple cropping system consisting of corn, tropical corn, and a mixture of rye and clover. A network of 72 shallow groundwater wells was established beneath the center pivot in 1991. Water samples have been periodically collected from these wells for more than eight years and analyzed for nitrogen and phosphorus. This paper reports the impact of the land applied wastewater and inorganic fertilizer on nitrates in shallow groundwater.