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Effect of Nitrification on Movement of Trace Metals in Soil Columns¹

ABSTRACT

Soil column experiments were conducted with sludge-treated and untreated samples of two soils, Omni silty clay and Delhi loamy sand, to determine whether protons generate during the nitrification process would affect the mobility of the trace metals Cd, Cr, Cu, Mn, Ph, and Zn. Columns 5 cm x 100 cm were leached bi- or tri-weekly with 7.5-cm applications of solutions of CaCl₂, NH₄Cl, or KCl. Trace metals in effluents from the columns were analyzed after each application of leaching solution. After 11 applications over a period of several months the columns were sectioned and the vertical distribution of 2N HCl-extractable metals determined.

Average concentrations of metals in column effluents were well below 1 ppm in all cases except Zn eluted from untreated Delhi loamy sand where 20 mM NH₄Cl or KCl leaching solutions produced effluent concentrations slightly above 1 ppm. There was evidence of nitrification affecting movement of several of the metals, particularly in the cases of Mn, Zn, Cu, and Cd in the untreated Delhi soil. The presence of sludge had a pronounced stabilizing influence of Cd and Zn, and to a lesser degree on other metals, probably as a result of organo-metal complexes.

Much of the input labeled NH₄-N was denitrified, as shown by recoveries of N ranging from 14 to 20% in the Omni soil and 40 to 78% in the Delhi soil. Proton generation during nitrification was, thus, partially offset by neutralization during denitrification. It was concluded that nitrification had relatively little effect on metal mobility under the conditions of the experiment.

Key Words: metal mobility • denitrification • sludge

¹ Contribution from the Dep. of Land, Air, and Water Resour., Univ. of California, Davis, CA 95616. This research was supported by a grant from the Kearney Foundation of Soil Science.

² Former Research Assistant, presently in the Dep. of Agronomy, Cornell Univ., Ithaca, N.Y.; and Professor of Soil Microbiology, Univ. of California, Davis; respectively.

Received for publication January 23, 1980.