Comparing grass quantity and quality in sodic and crest patches in the semi-arid granitic savanna of the southern Kruger National Park, South Africa.
Alard, Glynn*,, Scholes, Mary,
ABSTRACT- Sodic and crest patches are characteristic of the South African semi-arid Lowveld granitic savanna. Sodic patches have low herbaceous standing crop and high herbivore density relative to crest patches. The long-term use of standing crop indices to assess grassland productivity in the region has created an impression of low grass productivity on sodic patches. These patch types were compared for grass biomass productivity and forage quality. One square meter plots were placed in both patch types for monthly harvesting of sward production over the growth season (November to May). The study site straddled an exclosure enabling plot placement in areas excluding and including herbivory. Grass clippings collected over three seasons (2002/03 to 2004/5) were dried, weighed, and analyzed for percentage Sodium, Carbon, and Nitrogen. Within and across all seasons, sodic patch grass productivity was not significantly different to crest productivity in exclusion plots. Crest patch standing crop was significantly higher than the sodic sward in plots subjected to herbivory, indicating that sodic patch forage is utilized significantly more than crest forage. Significantly higher percentage sodium (1.06 ± 0.54% in sodic forage and 0.28 ± 0.3% in crest forage) and lower carbon/nitrogen ratios (18.5 ± 5.01 in sodic forage and 27.7 ± 9.02 in crest forage) in sodic patch forage are strongly correlated to sward utilization. Sodic patches are therefore important resource elements in the semi-arid granitic savanna landscape in terms of high quantity and quality forage supply. The use of standing crop is inadequate for the assessment of grass biomass productivity in highly grazed systems.
Key words: savanna, productivity, grass
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