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Cadmium Buffering Capacity and Accumulation in Swiss Chard in Some Sludge-Amended Soils

Washington State Univ. Res. and Extension Center, 7612 Pioneer Way East, Puyallup, WA 98371-4998

* Corresponding author.

ABSTRACT

Cadmium sorption by soils could be an important factor regulating the plant availability of soil Cd. Five soils containing varying amounts of Cd resulting from previous sludge application were analyzed for residual Cd availability under field conditions using Swiss chard (Beta vulgaris L.) as an indicator plant. The Cd accumulation was not highly correlated with DTPA (diethylene-triamine-pentaacetic acid)-extractable Cd (R² = 0.53). This result may be explained by a dissimilar response of plant Cd and DTPA Cd to soil pH. However, DTPA extracted 50 to 75% of sorbed Cd, depending on soil type. The recovery was little affected by the quantity of Cd sorbed. As such, DTPA Cd could be used to predict Cd accumulation by converting it to the quantity of Cd sorbed (Cd_s). The Cd_s was combined with the pH-dependent Cd buffering capacity (BC) to obtain Cd_s/BC, an intensity factor for soil Cd. The buffering capacity is defined as the slope of the Cd-sorption isotherm. The Cd_s/BC and plant Cd were highly correlated over all the soils, using the Michaelis-Menten equation as a model (R² = 0.83).

Scientific Paper no. 8901-05. Dep. of Agronomy and Soils, College of Agric. and Home Economics Res. Center, Washington State Univ., Pullman, WA 99164.

Received for publication February 14, 1989.