Improving the Chemical Properties of Acid Sulphate Soils from the Casamance River Basin

Abstract

The anoxic conditions produced after the reflooding of acid sulphate soil (ASS) can reduce sulphate and/or Fe(III) with a consequent rise in pH. This study aimed to compare the effect of different amendments on ASS remediation and to analyse the effect on soil pH and exchangeable aluminium. Two mid-term incubation experiments were carried out to analyse the effect of amendments and water management on ASS. Soil samples were taken in the Santak Valley from four agricultural plots. During the first experiment, each soil sample was subject to two water management systems (flooded and non-flooded) and three amendment types (rice straw, manure, and lime). During the second experiment, the flooded condition was performed with three organic amendments (rice straw, manure, and biochar). In the first experiment, the amendments with organic matter (rice straw, and manure) increased the pH more under the flooded conditions, and manure was effective in reducing exchangeable aluminium (Alex) to 45% in the control soil. In the second experiment, all the organic amendments reduced soluble Al, but whereas straw increased soluble Fe, biochar diminished it. The amendment addition increased the soil pH and reduced Alex. The Alex reduction was greater for the stabler organic amendments: manure and biochar.

Keywords

• iron toxicity
• acid sulphate soils
• exchangeable aluminium
• redox potential
• organic amendments