Des Moines River Nitrate in Relation to Watershed Agricultural Practices: 1945 Versus 1980s

Concern for nitrate (NO 3 -N) contamination of surface waters in Iowa has brought much speculation with regard to the source of NO 3 -N. It is frequently assumed that the large percentage increase in fertilizer N use over the last 50 yr is the primary cause of high concentrations of NO 3 -N in surface waters of central Iowa. We performed an analysis of data relating flow and NO 3 -N concentration for the Des Moines River to identify the effect of agricultural practices on NO 3 -N in the river.