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Extractable Chromium as Related to Soil pH and Applied Chromium¹

ABSTRACT

The objective of this study was to evaluate the soil chemistry of added Cr(III), Cr(VI), and sludge Cr as affected by initial soil pH. Treatments of 0 and 500 ppm Cr as CrCl₃ and CrO₃, and sludge Cr at a rate of 1,400 ppm Cr were applied to Rubicon sand (Entic Haplorthod, pH 4.7), Morley clay loam (Typic Hapludalf, pH 6.0), and limed Morley clay loam (pH 7.5). Pots were sampled at 24 hours, 1, 2, 4, 8, and 16 weeks of incubation. Soil samples were extracted in succession with distilled water, 1M NH₄Cl, 0.1M CuSO₄, 0.3M (NH₄)₂C₂O₄, and citrate-dithionite-bicarbonate.

Chromium(III) addition reduced soil pH while sludge raised soil pH. Chromium(VI) treatment initially lowered soil pH but then raised it above the pH of control soils after a short time period. Water-soluble Cr(III) decreased with time, though more rapidly as soil pH increased. When added as Cr(VI), water-soluble Cr also decreased with time but less rapidly as soil pH increased. Exchangeable (1M NH₄Cl extractable) and organic-bound Cr (0.1M CuSO₄ extractable) were negligible. Oxalate and dithionite extractions removed large quantities of Cr from all treatments. Water-soluble Cr compounds appeared to convert to insoluble compounds of Cr(III) in soils. Sludge Cr is probably a colloidal precipitate prior to incorporation.

¹ Contribution of the Crop and Soil Sci. Dep., Michigan Agric. Exp. Stn. Journal Article no. 8750. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the M.S. degree at Mich. State Univ. Presented in part before Div. A-5, Am. Soc. of Agron., Nov. 1976, Houston, Texas.

² Former Graduate Assistant (now Graduate Assistant, Agron. Dep., Univ. of Georgia, Athens, GA 30602) and Professor, respectively, Crop & Soil Sci. Dep., Michigan State Univ., East Lansing, MI 48824.

Received for publication October 12, 1978. Accepted for publication November 26, 1979.