Supply potential and agronomic value of urban market crop waste

Abstract

Garbage is a worldwide problem, particularly in urban areas of sub-Saharan Africa where lots of fresh food stuffs accompanied by non-consumable residues are accumulated. Landfill disposal, which is invariably inefficient and uneconomical, is the primary method of garbage management in this region. Ineffective management has resulted in large piles of garbage spending days to weeks in towns uncollected, thus becoming an environmental problem. Alternative disposal options such as recycling in the form of composts for agricultural use need serious consideration. Studies in Uganda have demonstrated that the bulk of the urban market garbage is of crop origin and, therefore, can be utilised to address the country's degraded soils. Prior to recommendation of these materials for wide farmer use, it is prudent that the supply potential and agronomic effectiveness are evaluated. In light of this and other considerations, three studies were conducted in Kampala City and its environs. The studies included (i) an urban market waste generation survey, (ii) an on-station agronomic effectiveness evaluation, both in the greenhouse and in the field, (iii) a study matching N release from urban market crop waste compost with N uptake by crops. The urban market survey established, through a 12 months period, the garbage quantity and quality of five major markets within Kampala City and its suburbs. Materials were sampled from garbage skips on a monthly basis; sorted into various components, and weights recorded. Those of crop origin were evaluated for the nutrient content. From the survey, 97% of the garbage was crop waste, with the major components being banana, fruit, vegetable and maize residues, representing 34, 16, 14 and 8%, of the total waste, xii