Organic waste materials for soil fertility improvement in the border region of the Eastern Cape, South Africa

Sixteen organic wastes with potential for enhancing soil productivity were identified in the Border region of the Eastern Cape, South Africa and were analysed for elemental composition. Pineapple waste (Pw), tobacco waste (Tw), poultry manure (Pm), pig dung (Pd) and commercial compost (Cp) were further analysed for their lignin, polyphenol and cellulose contents. The nutrient release patterns and carbon mineralization of these organic wastes were, investigated in laboratory incubation studies in which the organic wastes were mixed with 100 g of soil at rates that supplied 100 kg N ha(-1) and incubated for 12 weeks. Incubation of the four organic wastes and Cp resulted in the release of N, P, K, Ca, Mg, Zn, Fe and Cu indicating the potential of the materials to supply these nutrients to crop plants. The mineralization of N was highest during the, first four weeks of incubation and the rate of release followed the order Cp > Pd congruent to Pin > Pw congruent to Tw. The N mineralization rate was positively correlated with total N and lignin content and negatively related to the C:N ratio, cellulose, polyphenol and polyphenol:total N. All organic materials had a positive influence on soil microbial biomass but Tw had the least effect, possibly due to the toxic effects of nicotine. With the exception of Pm, organic wastes that had P contents above the critical value of 0.2% released considerable amounts of P especially towards the end of the incubation. Compared with the other micronutrients studied, Zn was released by the organic materials in larger quantities and in proportion to the Zn content of the materials. Based on N mineralization, nature and cost of the materials, Pm, Pd, Pw and Tw were found to be suitable for the improvement of soil productivity. Poultry manure and Pd could be applied directly to soils as sources of N for annual crops while Tw and Pw could be mixed with inorganic fertilizers or used as raw materials in composting.