Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: July 17, 2002
Publication Date: November 14, 2002
Citation: BURKART, M.R., TOMER, M.D., JAQUIS, R.J., KRAMER, L.A. QUALITY OF WATERS FOUND AT DEPTH WITHIN A LOESS-HILLS AGRICULTURAL LANDSCAPE. SOIL AND WATER CONSERVATION SOCIETY. 2002. CD-ROM. ANKENY, IA. Technical Abstract: Concerns about nitrate-N in ground waters of Midwest agricultural watersheds have increased in recent years. We installed a transect of multi-depth piezometers and lysimeters in each of two adjacent first-order watersheds in the loess hills of southwest Iowa, and monitored NO3-N concentrations each month since 1997. Divide, slope, toeslope, and valley bottom positions were included in each transect. The two catchments differ in cropping rotation; watershed 2 has been in a six-year rotation (corn-soybean-corn-3 yr alfalfa) using narrow strips, and watershed 1 has been in a corn/soybean rotation, since 1992. Prior to 1992 both watersheds were in continuous corn, but watershed 1 received 448 kg N/ha annually between 1969 and 1973. Large variations in NO3-N concentrations occurred, and spatial-temporal trends differed with depth and landscape position. Concentrations ranged from non-detectable (<0.1 mg/L) to nearly 130 mg/L, but are usually between 10 and 30 mg/L. Largest concentrations (> 40 mg/L) were in upper (divide and backslope) positions, while the least concentrations were in deep ground waters. Vertical hydraulic gradients within the saturated zone were different between the two catchments. Shallow ground water was perched in watershed 1 in the valley, and the perched water had the greatest nitrate concentrations in either watershed at this position. This was reflected in greater nitrate concentrations in stream waters in watershed 1, which were measured during base (stable) flow conditions. Patterns, while complex, do show an influence of the different agricultural practices applied to these two watersheds.