Comparison of the effectiveness of mined and by-product South African gypsums and other calcium sources for soil sodicity remediation

Abstract

Studies evaluating the effectiveness of South African gypsum sources are scarce or outdated because of newly introduced products, such as granulated and liquid gypsums. The efficacy of calcium (Ca) nitrate and micro-fine (MF) calcitic limes in comparison to gypsums has also never been evaluated. The aim of this study was to compare the effectiveness of mined and by-product gypsums and other Ca sources in terms of soil sodicity remediation and saturated hydraulic conductivity (K_sat) improvement. In a controlled laboratory study, 12 mined and by-product gypsums sources, MF calcitic limes and calcium nitrate were surface-applied to a sodic, sandy loam soil to achieve an exchangeable sodium percentage (ESP) of 5%. The soils received 300 mm simulated rainfall, and then soil chemical properties and K_sat were determined. Finer by-product gypsum sources (particularly liquid and flue gas desulphurisation (FGD) gypsums) exhibited faster dissolution rates and superior performance in lowering soil ESP to 4.2–4.7% and pH by 0.5–0.7 units compared to Class A mined gypsums (ESP 9.0–11.1% and 0.2 pH units). Only the liquid, phospho-, FGD gypsums and calcium nitrate significantly increased soil hydraulic conductivity (123–130%) compared to the control. The MF calcitic limes had no effect on the sodic soil properties.