Biomass Production and Nutrient Status of Three Range Grass Species In Awash National Park
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Date
1997-12
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Addis Ababa University
Abstract
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.
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Biology