Nitrate, Phosphorus, and Sulfate in Subsurface Drainage Water
1975
Baker, J. L. | Campbell, K. L. | Johnson, H. P. | Hanway, J. J.
Measurements made over a 4-year study of flow and NO₃-N, PO₄-P, total P, and SO₄-S content of subsurface drainage water from tile-drained cropland indicate that annual nutrient losses are highly variable. Annual losses of phosphorus, SO₄-S, and NO₃-N ranged from 0 to 0.04, 0 to 32, and 0 to 93 kg/ha, respectively, being very dependent on the amount of water lost. Because of low concentrations of phosphorus, losses with subsurface drainage water were insignificant when compared with losses associated with surface runoff. Concentrations of SO₄-S and NO₃-N were seemingly inversely related. Tile drainage water with consistently high NO₃-N content relative to surface runoff (> 10 ppm even under the low-fertility management of this study, 224 kg/ha of N over 5 years) is believed responsible for the high NO₃-N content sometimes found in a river draining central Iowa. The nitrate content of water from the saturated and unsaturated zones of the soil profile indicates that waves or pulses of water, with different NO₃-N concentrations, moving through the soil profile cause the observed variation of NO₃-N content of subsurface drainage water with time and flow rate. Such variations illustrate the difficulty of identifying water-quality trends from limited data.
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