A Comparative Study of the Growth of Eichhornia Crassipes Solms. and Pistia Stratiotes L. in Water-Culture

Abstract

Eichhornia crassipes and Pistia stratiotes were grown in water -culture at different pH levels. In one experiment the pH levels, 3.0, 4.3, 5.6, 6.9 and 8.2, were maintained in either a modified Long Ashton solution or in tapwater. In the 2nd experiment pH levels of 4.0, 5.5 and 7.0 were in combination with nitrogen levels of 1, 5, and 25 ppm N. Species performance was measured in terms of total dry-weight yield, number of plants produced and mean dry-weight per plant. Judged in terms of total dry-weight yield the 2 species had very different pH optima; Eichhornia crassipes yielded best at approximately pH 7.0 and Pistia stratiotes at approximately pH 4.0. The former species produced more plants but of approximately the same size under optimum conditions when compared with growth at other pH levels. P. stratiotes produced a considerably greater number of plants at the optimum level than at others but these were smaller. In both species increase in nitrogen level caused a linear increase in both total dry-weight yield and plant number but had little effect upon mean weight/plant. The effect of solution concentration could not be entirely attributed to a nitrogen effect. The results are discussed in terms of growth of Eichhornia crassipes in the Sudan Nile system and elsewhere, and the reported ''antagonism'' between the 2 species.