Extractable Iron and Manganese as Related to Soil pH and Applied Chromium

Abstract

AbstractMetal‐metal interactions in soils can be very important in determining the composition and yield of plants. Chromium application has been shown to affect plant Mn concentrations and uptake, and Fe deficiency symptoms have been associated with Cr toxicity by some workers.The objectives of this study were to evaluate the changes in soil Mn and Fe resulting from added Cr(III), Cr(VI), and a high Cr content sludge. 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, a sandy, mixed, frigid Entic Haplorthod (pH 4.7); Morley clay loam, a fine, illitic, mesic Typic Hapludalf (pH 6.0); and limed Morley clay loam (pH 7.5). Pots were sampled after 24 hours, 1, 2, 4, 8, and 16 weeks of incubation. Soil samples were extracted in succession with deionized‐distilled water, 1M NH4Cl, 0.1M CuSO4, 0.3M (NH4)2C2O4, and citrate‐dithionite‐bicarbonate.Water‐soluble Fe was reduced on all soils by Cr(III) and sludge amendment. Sludge amendment increased oxalate‐soluble Fe. Chromium (VI) initially lowered water‐soluble Fe, later raising this fraction above control soil levels.Water‐soluble Mn increased as incubation time increased on all soils treated with water soluble Cr(III). Chromium (VI) initially raised water‐soluble Mn, later lowering this fraction to levels not significantly different from control pots. Sludge‐amended soils produced more water‐soluble Mn with longer incubation times.Addition of inorganic Cr compounds to soils induced changes in soil pH subsequently affecting the soil chemistry of Mn. A Cr‐Fe coprecipitation reaction was indicated by the data.