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Copper and Cadmium Effects on Potassium Adsorption and Buffering Capacity

Dep. of Plant and Soil Science, Montana State Univ., Bozeman, MT 59717

*Corresponding author.

ABSTRACT

Trace metals have accumulated in many soils from application of mine wastes, sewage sludges, and other residues. Toxic effects of heavy metals on plants growing in contaminated soil have been well documented, but related effects of heavy metals on nutrient availability, e.g., K, are limited. This research was conducted to investigate influences of Cu or Cd added as Cl salts on K adsorption kinetics, K buffering capacity, and relative distribution of K between solution and solid phase. Amsterdam silty clay loam (Typic Haploboroll) was equilibrated with H₂O (Soil/H₂O = 1:10) containing seven levels of K and three levels of Cu or Cd at 5 and 20 °C for 0.25 to 336 h. The major species of K, Cu, and Cd were K and Cu in the K-Cu system, and K, Cd, and CdCl in the K-Cd system as calculated by GEOCHEM. The kinetics of K adsorption was best described by the Elovich equation. Potassium adsorption was rapid, occurring in less than 15 min, followed by a gradual continuous adsorption. The amount of K adsorbed decreased more from Cu than from Cd additions. Reaction rate constants decreased with increasing Cu and Cd. Potassium buffering capacity decreased 20 to 32% and 7 to 20%, respectively, from addition of 400 mg Cu or Cd kg^–1 soil. Copper and Cd changed the distribution of K, Ca, and Mg between soil and solution. Soil-selectivity order for these cations was Ca > Mg > K. Additions of Cu and Cd increased exchange-site selectivity for K more than that of Mg or Ca, in that order. Potassium-Ca distribution was influenced more by Cu and Cd than was K-Mg distribution. Results suggest that trace-metal contamination of the soil might influence soil K availability by changing K adsorption kinetics, buffering capacity, and distribution.

Contribution no. J-2383 from Montana Agric. Exp. Stn.

Received for publication August 28, 1989.