Fertilizer nitrogen transported via agricultural drainage has caused eutrophication of nearby surface waters. In the Lower Mississippi River Valley region, periods of drought are occurring more frequently. The impacts of drought on nutrient loss from agricultural lands of this region have not been reported. Field studies were used to evaluate the impact of climate (rainfall) on nitrate loss from agricultural fields in both normal (1996) and drought (1999) periods at the Ben Hur Water Quality Site in Baton Rouge, Louisiana. Four replicates of two treatments, surface drainage only (SUR) and surface drainage + deep controlled drainage (DCD), were initiated on 0.21 ha plots planted to corn (Zea mays L.). After each rainfall/runoff event, the volumes of runoff and subsurface drainage were analyzed for soluble nitrate concentration and loss. No significant drainage treatment impacts were found on runoff volume and nitrate loss in runoff. Nitrate loss in runoff was impacted by climate, with a four-fold decrease in nitrate loss during the drought, caused by decreased volume of runoff. Conversely, the mass of nitrate loss in leachate increased two-fold during the drought. Diverting subsurface drainage effluent (DCD) to surface receiving waters increased nitrate transport to these waters by 2.6 times in the normal climate, and over ten-fold during the drought, compared to SUR management. In either climate, but particularly during drought, subsurface drainage could potentially accelerate eutrophication of receiving waters of this region. When compared to DCD, these results suggest that SUR should be the water management practice in this region.
