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Influence of Trace Metals on Some Soil Nitrogen Transformations¹

ABSTRACT

An investigation to evaluate the influence of trace metals on N immobilization, N mineralization, and nitrification was conducted. Samples of Yolo silt loam amended with 100 ppm NH₄-N, 1% sewage sludge, and 1% ground alfalfa (Medicago sativa L.) were treated with solutions to provide 100, 200, and 400 ppm of Cd(II), Cr(III), Cu(II), Mn(II), Pb(II) and Zn(II), and incubated for 2, 4, 8, and 12-week periods. Metals were determined by extracting with water, KNO₃, DTPA (diethylenetriaminepentaacetic acid), and HNO, at the end of each incubation period.

All metals reverted quickly to more insoluble forms. Quantities of metals extractable with water + KNO₃ + DTPA decreased with time, while corresponding increases in HNO₃-soluble forms occurred. Nitrogen immobilization was measured during the 2- to 4-week period, and N mineralization and nitrification during the 4- to 12-week period. At low levels of metal addition Mn and Pb stimulated N immobilization, but at 400 ppm all metals were inhibitory to all N transformations. Among the six metals studied the sequence in order of decreasing inhibition was Cr > Cd > Cu > Zn > Mn > Pb. it was concluded that N transformation rates may be affected by trace metals in soils receiving heavy sludge applications.

Key Words: trace mental toxicity • N immobilization • N mineralization • nitrification

¹ Contribution of the Department of Land, Air and Water Resources, University of California, Davis, CA 95616.

² Former Research Assistant and Professor of Soil Microbiology, respectively. Senior author is now Postdoctoral Associate, Department of Agronomy, Cornell University, Ithaca, NY 14853.

Received for publication September 2, 1980.