Water hyacinth (Eichhornia crassipes (Mart.) Solms) grows very vigorously and has a high content of nutrients. Cultivation experiments were conducted on water hyacinth to check whether it is worth using for water purification and to obtain guiding principles for the practical use of water hyacinth grown in natural water channels or ponds.

The average dry weight, nitrogen and phosphate content in the biomass were 5.0%, 2.5% and 0.57%, respectively. The growth rate of the water hyacinth was higher from May to June than in other seasons. The logarithmic regression equation between the growth rate (Y) and solar radiation (X) was expressed by Ln (Y) = 0.0042X-4.92 with a coefficient of correlation of 0.768. The relationship between the concentration of nutrients in water (X) and in water hyacinth (Y) is expressed by Y = Cmax.X/(Ks+X). The relationship between the relative growth rate and the concentration of nutrients was also expressed by the same type of equation. The relationship between a harvesting interval and the total yield of the water hyacinth within a given period was expressed by a mathematical model. It was made clear from the model that the shorter the harvesting interval was, the more the total yield of the crop increased.