Biomass Production and Nutrient Status of Three Range Grass Species In Awash National Park

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Addis Ababa University


Three range grass species namely, Chlysopogon plumulosus Hochst, Bothriochloa radicans (Lehm.) A. Camus and Ischaemum afrum (J.F. Gemel.) Dandy were studied at IIIala-sala grassland plain to asses their nutrient status and productivity as influenced by season and simulated grazing. Seasonal and annual biomass production of the grasses, seasonal effects on grass moisture content and on accumulation of N, P, K and Na were studied. The effect of grazing, simulated by clipping, was followed under glasshouse condition. Seasonal and annual biomass production was estimated from four 6 x 6 m fenced quadrates, the grass stand of which was mowed at the beginning to a height of two cm. The three quadrates were systematically selected and placed such that each species had one quadrat where it homogenously covered the entire quadrat, whereas the fourth quadrat was established in such a way that it included mixed stands of the three species. In each quadrat, there were a total of 36, 50 x 50 cm sub-quadrates. Biomass production was estimated from nine subquadrates within each quadrat after allowing the grass to grow for 3, 6, 9 and 12 months. Moisture and nutrient content of grasses was determined seasonally (every three months) from six plant samples for each species collected randomly from the area. All the data were statistically analyzed by one way Analysis of Variance using Tukey's Family Error Rate test. Nine clipping treatment combinations, differing in cutting height and cutting frequency, were applied. The grasses were clipped to 4, 8 and 12 cm every 15, 30 and 45 days interval. Twoway Analysis of Variance was performed to test for significant effects of cutting frquency and cutting height on shoot and root biomass production and nitrogen content of the cpecies The biomass production showed significant seasonal variation following rainfall. Peak biomass was obtained during the wet periods, April-June and July-September. It ranged from 116 g m-2 to 409 g m-2 for B. radicans and I. afrum stands, respectively. There was very little growth in the dry period (October-December). The annual biomass production ranged from 397 to 792 g m-2 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. The clipping experiment showed that both cutting frequency and cutting height affected biomass accumulation and nitrogen content of the three grass species. For all the three species, increasing cutting frequency and decreasing cutting height decreased shoot and root biomass accumulation but increased nitrogen content. In general, clipping decreased shoot and root biomass production but increased the nitrogen content of the species. Except for two values obtained with B. radicans, root/shoot ratio was generally lower in clipped plants; and no consistent effect of clipping on tillering was observed. The experiment indicated that low intensity grazing may improve the nutritional quality of the grasses without reducing biomass production.