Effects of water depth increases on the production and growth of wild rice, Zinzania aquatica L.

Abstract

Wild rice, grown in plastic buckets suspended from specially designed rafts, was subjected to increases in water depth during the submerged-leaf, first floating-leaf, second floating-leaf, and the first aerial-leaf stages. The depth was increased from the initial depth of 45cm by either 0cm (control), 15cm, 30cm, or 50cm. With the exception.of the 15cm treatment, increases in water depth resulted in decreases in the vegetative characteristics of plant height, total and component (root, stem, leaf) dry weights, and the number of tillers on each plant. As water depth increased similar reductions occurred in the reproductive characteristics of the number of inflorescences per plant, the number of pedicels per plant, and the dry weights of the inflorescences. The 15cm treatment had higher production values than the control, possibly because the lower light levels at the greater depth were closer to optimum for the particular seed source used. The final biomass did not seem to be influenced by the phenological stages when these depth increases occurred. The growth of wild rice subjected to increases in water depth was analysed using growth curves and modelling techniques. The growth of the plants in the control treatment was accurately described by the logistic equation. Growth for plants experiencing increases in water depth, for all phenological stages studied, was also described by the logistic equation. The derived parameters of K and r, in each phenological stage, were plotted versus water depth. Equations describing the resultant relationship between r and Increases in water depth was determined to be the same. This suggested that for wild rice the maximum instantaneous rate of growth is constant. Thus, under conditions of optimum nutrient levels, water depth increases have the same effect on wild rice production during all phenologlcal stages.