Biological management of water hyacinth waste in Uganda

The recent biological invasion of water hyacinth (Eichhornia crassipes (Mar t.) Solms) into lakes and rivers of East Africa has forced the implementati on of mechanical harvesting around key harbours and dams, resulting in subs equent difficulties of waste disposal. Utilization of these wastes would as sist in deferring costs of control, currently covered by international agen cies. This paper reports the nutrient contents, mineralization patterns and potential for ensiling water hyacinth wastes. Whole chopped plants and tis sues separated into leaves, petioles and roots were placed into litter bags , deployed as surface mulch or submerged in water and recovered over 16 wee ks. The wastes consisted of 45% leaves, 26% petiole and 29% roots and conta ined 92% moisture. Decomposition was greater under surface mulched conditio ns and significant differences were observed between plant tissues. The tim e to 50% decomposition of whole plants was 21 and 74 days for mulched and s ubmerged conditions, respectively. Mineralization of N and P was significan tly 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. With out additives, the pH of water hyacinth alone was 7.33, suggesting poor sil age quality. Addition of 15% maize bran or molasses resulted in silage of p H 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 h yacinth silage prepared with maize bran and molasses was readily accepted b y goats and young steers. Waste disposal problems may be related to poor ae ration within mounds and an alternative exists for use of the wastes as org anic inputs to soils or as livestock feed.