An evaluation of the use of organic amendments to ameliorate aluminium toxicity and phosphorus deficiency in an acid soil. MSc (Agric

The effects ofthe additions ofsome commonly-available organic residues to an acid, P-deficient soil (typical of those used by small-scale farmers in KwaZulu-Natal) on soil pH, exchangeable and soil solution AI, P availability and maize yield response was investigated in a number of laboratory and glasshouse experiments. The organic amendments used were ground-up grassveld residues, household compost, filter cake (a waste product from a sugar mill) and layer poultry manure. The soil used was a Hutton form (Farmingham series) (Rhodic Ferrasol, FAO). In an initial laboratory study, addition ofall ofthe organic residues, at rates equivalent to 10 and 20 Mg ha-l, raised soil pH significantly and as a result there was a marked reduction in exchangeable Al concentrations. The increase in pH and decrease in exchangeable Al was more pronounced at the higher rate ofaddition and followed the order: poultry manure> filter cake> household compost> grass residues. The major mechanism responsible for the increase in pH was thought to differ depending upon the type of organic residue being considered. Whilst the relatively high content ofCaC03 was probably the main mechanism in the case ofpoultry manure and filter cake, the proton consuming ability of humic material probably predominated fo