Cattle manure and grass residues as liming materials in a semi-subsistence farming system

A field experiment was conducted on an acid soil in a semi-subsistence farming area of KwaZulu-Natal, South Africa to investigate the possibility of using organic amendments as liming materials within a minimum tillage (strip cultivation) system to produce maize. Amendments (cattle manure, grass residues and dolomitic lime) were incorporated to a depth of 20 cm in bands 15 cm wide down plant rows at rates of 10 and 20 t ha−1 (in the amended area) for organic materials and 2.5 and 5.0 t ha−1 for lime. The remainder of the field remained untilled. Additions of cattle manure rapidly increased soil pH, and concentrations of exchangeable K, Ca and Mg and extractable P were also greatly elevated. Grass residue additions increased pH progressively and increased exchangeable K and Mg and those of dolomitic lime increased pH, exchangeable Ca and Mg. Addition of each of the amendments decreased concentrations of exchangeable Al; the effect was greatest for animal manure after 6 weeks and for lime and grass residues at harvest. At harvest, addition of all three amendments had significantly reduced concentrations of both phytotoxic monomeric and total Al in soil solution. The system not only resulted in an increase in pH and extractable nutrients in row soil compared to that in the inter-row but also an increase in the size and activity of the soil microbial community. Maize yields were increased by additions of amendments under both unfertilised and fertilised conditions and yields were generally greatest at the higher rate of addition. Under unfertilised conditions, cattle manure treatments gave the greatest yields. Fertiliser additions increased yields greatly particularly in the control, grass residue and lime treatments. It was concluded that the strip tillage system used is a practicable way of applying high rates of organic materials to soils, that cattle manure has a rapid liming effect as well as being a nutrient source and that grass residues from rangeland decompose slowly and, therefore, have a slow liming effect.