Tile Drainage Management Influences On Nutrient, Bacteria and Rhodamine Movement to Surface Water and Groundwater Following Liquid Manure Application.

Controlled tile drainage (CD) is an accepted agricultural water management practice for reducing nutrient losses to surface water, however, the effect of CD on bacteria and nutrient transport to surface water and groundwater following liquid swine manure application (LMA) is currently not well understood. In light of this knowledge gap, this study investigated the influence of CD on bacteria and nutrient loading to surface water (SW) and groundwater from a fall season liquid LMA on four 1500 m2 macroporous clay loam test plots, of which two had CD and two had free draining tiles (FD). Rhodamine WT (RWT) was mixed into the manure and monitored in the tile water and groundwater following LMA. Tile water and groundwater quality were both influenced by drainage management. Following LMA on the FD plots, RWT, nutrients and bacteria moved rapidly via tile discharge to SW; however, at the CD plots, tiles did flow until the first post LMA rainfall, so the immediate risk of LMA induced contamination of SW was abated. Over the 36 d monitoring period, flow weighted average conductivity, redox potential, and turbidity, as well as kjeldahl N (TKN), total P (TP), and RWT concentrations, tended to be higher in the CD tile effluent; as a result, SW nutrient and RWT loading was not proportional to tile discharge volume, which was 60% less at the CD plots. TKN, TP, and RWT concentrations in groundwater also tended to be higher at the CD plots. Bacteria behaved differently than nutrients and RWT, and concentrations of E. coli, fecal coliforms, and C. perfringens tended to be lower in the tile effluent at the CD plots. Based on these results, CD has potential for mitigating bacteria movement to surface water from fall LMA, however, nutrient losses may be enhanced.