BIOMASS PRODUCTION AND NUTRIENT STATUS OF THREE TROPICAL RANGE GRASS SPECIES

Abstract

Three range grass species namely, Chrysopogon plumulosus Hochst, Bothriochloa radicans (Lehm.) A. Camus and Ischaemum afrum (J. F.
Gemel.) Dandy were studied at Illala-sala grassland plain in Awash National Park, Ethiopia to asses their nutrient status and productivity. Annual and seasonal biomass pr&iuction of these grasses, seasonal effects on grass moisture content and on accumulation of N, P, K and Na were studied. Seasonal and annual biomass production was estimated from four 6 x 6 m fenced quadrates. The grass stand was mowed, at the beginning of the study, to a height of two cm. The biomass production showed marked seasonal variation following rainfall. Peak biomass was obtained during the wet periods, April-June and July-September. It
ranged from 116 g mo2 for B. radicans to 409 g mo2 for I. afrum stands. There was very little growth in the dry period (October-December). The annual biomass production ranged from 397 to 792 g mo2 for B. radicans and mixed species stands, respectively. The biomass production of B. radicans stands were significantly lower than I. afrum and the mixed species stands. Significant seasonal changes in the amount of moisture and nutrient (N, P, and K) content were observed in relation to the amount of rainfall. The moisture and N, P and
K content of aU the three species decreased with the dry season. The crude protein content of the grasses fell below the maintenance level required for ruminants during dry periods, indicating that herbivore populations may be limited by shortage of nutritionally adequate food during the dry season. The relative importance of each species as pasture is discussed.