Nitrate-nitrogen Movement through Soil as Affected by Soil Profile Characteristics
1976
Devitt, Dale | Letey, J. | Lund, L. J. (Lanny J.) | Blair, J. W.
The contribution of agricultural practices to pollution of ground and surface waters by nitrogen is not completely known. Six tile systems installed on commercial farms with differing soil profile characteristics were selected for investigation. Soil solution samples were extracted from 61-, 91-, 122-, and 183-cm depths and analyzed for nitrate-nitrogen, manganese and chloride concentrations, and electrical conductivity. Redox potential measurements were made at 91- and 183-cm depths. Tensiometers were installed at 61-, 91-, and 122-cm depths to measure hydraulic gradients. Tile effluent samples were also collected and analyzed. Data on redox potential, manganese concentrations, and nitrate-nitrogen concentrations indicated that there was very low denitrificetion potential in coarse-textured profiles and that the nitrate-nitrogen concentration and movement were dependent on water movement and amounts of nitrate available for leaching. Irrigation management to provide low leaching fraction resulted in relatively higher nitrate-nitrogen concentration in the tile effluent but smaller amounts of total nitrate lost as compared to irrigation management for high leaching fractions. Redox potentials and the chloride to nitrate-nitrogen ratios indicated that subsurface layers of high clay content promote denitrificetion. With one exception, a smaller fraction of the applied nitrogen was lost in the tile effluent from profiles containing layers of high clay content as compared to the coarse-textured profiles. The one exception was a profile having high clay content throughout which was recently brought under cultivation. Extremely high residual nitrate-nitrogen was found in this profile which would account for the high concentrations in the tile effluent.
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