Effects of agricultural practices and vadose zone stratigraphy on nitrate concentration in ground water in Kansas, USA

Differences in nitrate-N concentrations in ground water in Kansas can be explained by variations in agricultural practices and vadose-zone stratigraphy. In northwestern Kansas, past use of a local stream for tailwater runoff from irrigation and high fertilizer applications for sugar-beet farming resulted in high nitrate-N concentrations (12-60 mg L(-1); in both soil and ground water. Nitrogen isotope values from the soil and ground water range from +4 to +80 parts per thousand, which is typical for a fertilizer source. In parts of south-central Kansas, the use of crop rotation and the presence of both continuous fine-textured layers and a reducing ground-water chemistry resulted in ground-water nitrate-N values of < 3 mg L(-1);. The effects of denitrification in the vadose zone and ground water are indicated by enriched delta(15)N values of +10 to +15 parts per thousand At a site study, irrigated continuous corn was grown on sandy soils with discontinuous fine-textured layers. Here, nitrate-N concentrations were often > 10 mg L(-1); in both soil and grounwater. Nitrogen isotope values of +3 to +7 parts per thousand indicate a fertilizer source. Crop rotation decreased nitrate-N values in the shallow ground water (9 m). However, deeper ground water showed increasing nitrate-N concentrations as a result of past farming practices. Copyright (C) 1996 IAWQ.