Sulfate desorption and mobility in soil can be of both environmental and agronomic importance. This study was conducted to describe the desorption of SO₄ from agricultural soils under experimental conditions applicable to the movement of SO₄ in overland flow and runoff waters. The kinetics of SO₄ desorption from soil were investigated at five different water/soil ratios (10:1–400:1), five time periods (5–180 min), and four SO₄ additions (0–200 mg kg⁻¹). Sulfate desorption (Sd) was logarithmically related to contact time (t) and water/soil ratio (W) and was a linear function of the initial extractable SO₄ content of soil (Sₑ). The kinetics of SO₄ desorption was described by the equation Sd = K Sₑ tᵅ Wᵝ, where K, α, and β are constants for a given soil. This equation has previously been shown to describe desorption of soil P and K. The kinetic constants, K (r² = 0.88), α (r² = 0.83), and β (r² = 0.88), were related to extractable soil Al content for 107 U.S. soils. The uniformity of equation constants for a given soil and the ease with which they can be estimated from extractable soil Al indicate the potential use of the equation in modeling SO₄ desorption from soil and subsequent movement in surface runoff water.
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