Improvement of soil structure and plant growth by addition of alum sludge

Addition of the alum sludge to soils in pots decreased both slaking and dispersion of soils and resulted in improved aggregation. Water retention between ‐ 10 and ‐1000 kPa was increased and the strength of aggregates and the modulus of rupture of moulded briquettes were decreased by the addition of sludge. The application of sludge to three soils increased the yield of dry matter of maize grown in pots with and without an addition of fertilizer, but high rates of application led to germination problems and decreased phosphate uptake by the maize. It is concluded that alum sludge may be disposed of in soils with beneficial effects on soil structure and plant growth, but requires testing in the field at rates of the order of 2 t ha−1