David Mutetikka

Biological management of water hyacinth waste in Uganda

ABSTRACT The recent biological invasion of water hyacinth (Eichhornia crassipes (Mart.) Solms) into lakes and rivers of East Africa has forced the implementation of mechanical harvesting around key harbours and dams, resulting in subsequent difficulties of waste disposal. Utilization of these wastes would assist in deferring costs of control, currently covered by international agencies. This paper reports the nutrient contents, mineralization patterns and potential for ensiling water hyacinth wastes. Whole chopped plants and tissues separated into leaves, petioles and roots were placed into litter bags, deployed as surface mulch or submerged in water and recovered over 16 weeks. The wastes consisted of 45% leaves, 26% petiole and 29% roots and contained 92% moisture. Decomposition was greater under surface mulched conditions and significant differences were observed between plant tissues. The time to 50% decomposition of whole plants was 21 and 74 days for mulched and submerged conditions, respectively. Mineralization of N and P was significantly delayed under anaerobic conditions. Shoots of fresh water hyacinth were chopped into 2 to 4 cm pieces, maize bran or molasses added at rates of 0, 10, 15, 20 and 25% on a fresh weight basis and fermented for 21 days. Without additives, the pH of water hyacinth alone was 7.33, suggesting poor silage quality. Addition of 15% maize bran or molasses resulted in silage of pH 4.1 and 4.2, respectively. Silage prepared with 15% maize bran contained 20% dry weight with 13% crude protein and 20% acid detergent fibre. Water hyacinth silage prepared with maize bran and molasses was readily accepted by goats and young steers. Waste disposal problems may be related to poor aeration within mounds and an alternative exists for use of the wastes as organic inputs to soils or as livestock feed.