Sward height: a tool for measurement of available herbage

摘要

It is possible to estimate the amount of available herbage in a pasture by measuring the height of the sward. In order to determine the factors responsible for the variations of this amount for a given sward height, we used the data from four measuring arrangements related to the effects of the conditions of management (frequency, intensity, date) on cocksfoot leys or on various other pastures types (leys or permanent pastures). Sward heights were measured with a sward stick. The amount of herbage per cm of height reflects the 'density' of the sward; it always decreases from bottom to top. Moreover it is in the layer nearest to the soil (7 cm in this study) that the variations are most sensitive to the conditions of management and to the types of pasture. These variations derive mostly from the pasture's establishment (permanent pastures or recently sown leys) and from the density of tillers. In the upper layers, herbage density is greater when the sward is constituted by a mixture of species. When assessing the amounts of herbage available for grazing, it is reasonable to use this method, since the layers nearest to the soil, which are responsible for the largest variations in the relation height x biomass, are generally not eaten. A more stable relationship can then be obtained between the amount of available herbage (> 7 cm) and sward height (H - 7 cm). The main factor for the variation in available herbage for a given height is then the number of species constituting the sward.