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Leaching of Calcium and Magnesium from Soil Columns as Affected by Form of Nitrogen in Applied Sewage¹

ABSTRACT

Three laboratory column experiments utilizing calcareous and noncalcareous soils from the Central Valley of California were conducted to assess the impact of secondary sewage application on the transport of calcium and magnesium in the soil profile. Synthetic sewage containing 3 meq/liter of N in either the ammonium or nitrate form was applied to columns of Salado sandy loam and its subsoil at the rate of 7.5 cm/week for 41 weeks. Concentrations of Ca and Mg in the column effluents were higher with NH₄⁺ sewage than with NO₃^- sewage. In a similar experiment with treatment plant sewage augmented by the addition of ammonium or nitrate to bring the level to about 4 meq/liter applied to columns of five different soils, similar results were obtained. On the average, NH₄-amended sewage removed 1.32 meq more Ca and 0.84 meq more Mg per liter of effluent than did NO₃-amended sewage. This was attributed at least in part to proton generation during nitrification of the input NH₄⁺. However, in a third experiment, secondary waste water that was not augmented in its N level was applied to columns of two different soils, one lot prior to nitrification and the other after nitrification had been allowed to proceed to completion. In Panoche clay loam, Ca elution was the same whether the sewage was nitrified or not, whereas Mg was eluted to a greater extent by the nitrified sewage. In Columbia fine sandy loam, somewhat more Ca and slightly less Mg were eluted by nitrified sewage. We concluded that the nitrification process does not significantly influence Ca and Mg mobility at practical levels of waste water application.

¹ Contribution from the Dep. of Land, Air & Water, Resources, Univ. of California, Davis, CA 95616.

² Formerly Postgraduate Research Soil Scientist, and Professor of Soil Microbiology, respectively. Senior author is presently at the Dep. of Biological & Agricultural Engineering, North Carolina State Univ., Raleigh.

Received for publication February 29, 1980. Accepted for publication October 6, 1980.