Use of vermicompost extract as an aluminium inhibitor in aqueous solutions

Abstract

Vermicompost extract (VCE) demonstrated the ability to raise the measured pH level of an acid soil thus showing a potential to limit aluminium toxicity. The relatively high proportion of humic substances (60% of VCE solid matter) suggested the possibility of formation of stable chelates with aluminium ions. A rate‐based colorimetric method was utilised measuring at 585 nm the aluminium‐pyrocatechol violet complex (Al‐PCV₃) after 60 seconds ("toxic”; Al index) and 2 hours ("total”; Al). By artificially altering the pH levels of various VCE:Al solutions, in the absence of soil, the relative and combined effects of pH and chelation on Al level reduction were observed. Inferences were drawn to predict the efficacy of VCE applied to acid soils displaying Al phytotoxicity. These are to be tested in subsequent work. In solutions above pH 6, a 98% reduction of total Al was obtained due to pH effects, whereas at pH 4, a 90% reduction was obtained due to chelation. The trends were similar for “toxic”; Al indices.