Spatial Relations between Row Crops and Nitrate Contamination in Groundwater

Nitrogen management practices associated with row crops arewidely considered as an important contributor to nitrate pollution in water resources. We studied the relations between row crops and nitrate concentration in groundwater in an agricultural basin of Iowa, U.S.A., from a spatial perspective. Nitrate concentration and row crop area wereanalyzed on a section scale (a square mile, or 2.56 km2)for three different years. Their section values were standardized to remove the effects of precipitation and non-constant sample variances in different years. The between-year differences in individual section values werecollectively analyzed as an indication of changes in the spatial distribution from year to year. Contingency table analysis was applied to test for relations of spatial changesbetween nitrate and row crops. During the study period, thenitrate concentration and row crop area on a per section basischanged considerably from one sampling year to another.However, no significant changes were found in their spatial distributions. As a result, no significant relations betweennitrate and row crops were found in terms of changes in theirspatial distributions.