Effects of Agricultural Drainage on Water Quality in the Lower Mississippi Valley and Gulf Coastal Region

Sediment and nutrient (N, P, K) losses were measured from research plots with surface drainage only and from plots with both surface and subsurface drainage for all or part of the decade, 1982-1991. During the 1987 growing season, losses of pesticides (atrazine and metolachlor) were also measured. Subsurface drainage was effective in reducing surface runoff by an average of 35%, and thus reduced soil loss 31%, nitrogen loss 17%, phosphorus loss 31%, and potassium loss 27%. For the 1987 season, losses of preemergent applied herbicides from the plots with subsurface drainage were less than one-half that from plots with surface drainage only; 1.4% vs. 3.2% of applied for atrazine, and 1.1% vs. 2.4% of applied for metolachlor.