The effect of clipping on growth and nutrient uptake of Sahelian annual rangelands.
Growth and nutrient-uptake responses of annual rangeland to defoliation were studied at 13 sandy range sites located across the Sahelian zone of Mali between 1977 and 1989. 34 cutting experiments (site-years) were conducted using identical treatment designs with respect to the timing and frequency of cutting. The effect of highly variable growing conditions (rainfall and nutrient availability) on the response to cutting was analysed through a series of regression analyses. The growth response of vegetation to cutting was more related to variables associated with rainfall and growing conditions than to cutting frequency. Total yields were lowered most during periods of rapid growth. N and P yields were not affected by growing conditions while cutting consistently increased N and P yields. Greater sink strength in cut plants better explained the observed stimulation of N and P yields than did the increased nutrient availability that could result from modified soil water status after cutting The significance of these results for the ecological grazing management of Sahelian rangelands is discussed.