Nitrate and Chloride Accumulation and Distribution in Fertilized Tile-Drained Soils
1974
Gast, R. G. | Nelson, W. W. | MacGregor, J. M.
Results of long term continuous corn studies on tile drained Webster loam in southwest Minnesota show that annual N applications up to 70% greater than N removed in grain are required for maximum yields. The object of the reported study was to establish the relative role of N incorporation into the soil organic matter and/or losses through denitrification, downward leaching, or tile drainage in determining the fate of this fertilizer-N added above that removed in corn grain. Nitrate and chloride accumulations and distributions were determined in a Webster loam and Waldorf silty clay loam profiles after long term fertilization for continuous corn. Concentrations in the profiles were determined at 0.3 m depth intervals and at increasing distances from tile lines. Maximum NO₃⁻-N accumulations accounted for less than half of the fertilizer-N added but unrecovered in the corn grain. In contrast, Cl⁻ accumulations in the soil profiles were approximately equal to that added, with little or no effect of distance from tile lines on either amounts present or on profile distribution: i.e. there was relatively little Cl⁻ loss through tile drainage. Assuming Cl⁻ and NO₃⁻ move with water at about the same rate, the results further suggest minimal loss of NO₃⁻-N in tile drainage. Since Cl⁻ and NO₃⁻ concentration are small at depths greater than 3 m, downward leaching losses are apparently minimal leaving denitrification and/or incorporation into organic matter as the mechanisms largely responsible for disappearance of the unused fertilizer-N. Denitrification is probably the main factor involved since similar experiments on well-drained Minnesota soil showed little net incorporation of N into organic matter.
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