Bioproductivity and Decomposition of Waterhyacinth in Uganda

The biological invasion of the waterhyacinth (Eichhornia crassipes (Mart.) Solms) into lakes and rivers of East Africa forced the implementation of mechanical harvesting around key harbours and dams, resulting in subsequent difficulties of waste disposal. Utilising these wastes assists in minising the costs of waste management. Estimates of waterhyacinth biomass were made by randomly deploying 1 m2 buoyant sampling frames across four sites on the Ugandan shores of Lake Victoria and determining the weight within the frame. Single plants ranging from 0.3 - 0.9 kg were placed within similar buoyant frames and their productivity monitored over a period of 16 weeks in a sheltered bay at Bugiri and a pond at Kajjansi. Nutrient contents and mineralisation patterns of harvested waterhyacinth wastes were characterised. Whole chopped plants and tissues were separated into leaves, petioles and roots, placed into litter bags, deployed as surface mulch and recovered over 16 weeks. Fresh biomass at the four sites was between 300 to 610 t ha-1. Productivity ranged from 58 to 228 t ha-1 yr-1 resulting from rapid production of daughter plants (108 to 237 plants m-2 yr-1). Decomposition of the waterhyacinth was rapid but with significant differences between plant tissues. Time to 50% decomposition of whole plants, leaves and roots was 21, 31 and 45 days, respectively. Waterhyacinth applied as surface mulch to fields may offer opportunity as an organic input to soils because of the relatively rich nutrient contents and rapid decay pattern but the large bulk of fresh plants (92% water) may offset these advantages.L\u2019invasion de l\u2019eau par la jacinthe (Eichhornia crassipes (Mart.) Solms) dans les lacs et rivi\ue8res de l\u2019Afrique de l\u2019Est a forc\ue9 l\u2019application des recoltes m\ue9caniques au tour d\u2019entr\ue9es importantes et de digues r\ue9sultant aux difficult\ue9s cons\ue9quentes des ordures. L\u2019utilisation de ces ordures aide \ue0 differer les co\ue9ts de contr\uf4le. Les estimations de la biomasse vivante ont \ue9t\ue9 faite al\ue9atoirement par des cadres flottables d\u20191m2 d\u2019\ue9chantillonnage dans 4 sites sur les rives du lac Victoria en Uganda et le poids des mauvaises herbes a \ue9t\ue9 d\ue9termin\ue9 \ue0 l\u2019interieur du cadre. Des plantes individuelles d\u2019environ 0.3-0.9 kg ont \ue9t\ue9 plac\ue9es \ue0 l\u2019int\ue9rieur de cadres semblables flottables et leur productivit\ue9 suivie pour une p\ue9riode de plus de 16 semaines sous l\u2019abri de baie \ue0 Bugiri et dans un \ueatang artificiel \ue0 Kajjansi. Le contenu nutritif et la tendance de min\ue9ralisation des d\ue9chets de la jacinthe recolt\ue9c ont \ue9t\ue9 caracteris\ue9s, toutes les plantes d\ue9coup\ue9es et tissus ont \ue9t\ue9 s\ue9par\ue9s en feuilles, p\ue9tioles et racines; plac\ue9es dans des sacs de d\ue9tritus \ue0 la surface comme fumier et r\ue9cuper\ue9 apr\ue8s 16 semaines. La biomasse fr\ue8che dans les 4 sites a \ue9t\ue9 estim\ue9e \ueatre de l\u2019ordre de 390 - 610 t ha-1. La productivit\ue9 variait de 58 - 228 t ha-1 yr-1 venant de la reproduction de 108 - 237 plantes ha-1 yr-1. Ces donn\ue9es sugg\ue8rent que la performance \ue9tait associe\ue9e aux differentes qualit\ue9s de syst\ue8mes aquatiques. La d\ue9composition de la jacinthe \ue9tait rapide mais avec de differences significatives entre les tissus des plantes. Le temps de d\ue9composition de 50% de toutes les plantes, feuilles et racines \ue9tait de21, 31 et 45 jours respectivement. La jacinthe utilis\ue9e comme paille de couverture en champs est avantageuse comme une resource organique aux sols \ue0 cause du contenu nutritif relativement riche et de sa d\ue9composition rapide