Individual study: The effect of clipping on growth and nutrient uptake of annual plants in semi-arid savanna in the Gourma region of Mali
Hiernaux P. & Turner M.D. (1996) The effect of clipping on growth and nutrient uptake of Sahelian annual rangelands. Journal of Applied Ecology, 33, 387-399
To gain a better understanding of how best to manage semi-arid rangelands in western Africa, growth and nutrient-uptake responses of annual rangeland plants to defoliation (mimicking grazing) were studied at 13 sandy range sites located across the Sahelian zone of Mali between 1977 and 1989.
Experimental sites were near the village of Kanadji (4 sites), the town of Niono (2 sites), and in the Gourma region (7 sites) of southern Mali. The sites differed with respect to average annual rainfall, woody cover and land use history but were all on sandy or loamy-sand soils with the herb layer dominated by annuals.
At each site, exclosures (to keep out grazing stock) between 200-1,000 m² were constructed in areas containing no woody plants. A series of 34 clipping experiments were conducted using identical treatment designs with respect to timing and frequency of clipping. The area inside exclosures was divided into plots (1-4 m²) with 3-8 replicates per treatment. Vegetation was clipped to about 1 cm stubble during the growing season. Plots were clipped either every 15 days or every 30 days throughout the growing season.
Dry weight yielded at each clip date was recorded. The effect of highly variable growing conditions between sites (rainfall and nutrient availability) on vegetation response to clipping was analysed.
About 75% of first clippings at the beginning of the growing season resulted in very low biomass (<15 g dry matter/m²). The growth response of the annual vegetation to clipping was found to be more related to environmental variables associated with rainfall and growing condition than to clipping frequency. However, clipping consistently increased N and P yields in vegetation samples. Reallocation of nutrients from roots to shoots and newly growing leaves was probably occurring immediately after clipping.
Growth response to defoliation was found to be determined more by growing conditions (primarily moisture and nutrient availability) rather than clipping frequency.
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