Elemental and fibre contents of savanna grasses: variation with grazing, soil type, season and species.
Abstract
Green leaf samples of Cenchrus ciliaris, Chloris roxburghiana, Chrysopogon plumulosus, Digitaria macroblephara, Eustachys paspaloides, Kyllinga alba, Pennisetum mezianum, P. stramineum, Sporobolus nervosus and S. pyramidalis were taken from sites of low herbivore use intensity (HUI), while samples of Cynodon plectostachyus, C. dactylon, Dactyloctenium aegyptium, Eragrostis cilianensis, Setaria verticillata and Urochloa panicoides were taken from sites with high herbivore use in the Kajaido district, S. Kenya in the Nov. 1984-Jan. 1985 growing season. The contents of water, CP, cell contents, cell wall, lignocellulose, hemicellulose, cellulose, lignin, silica, ash and 19 elements, and their variation with season, soil type and grazing intensity, were examined. As the growing season progressed there was a systematic decline in nutritional value at all sites, as indicated by fibre properties. Fibre nutritional values were at all times higher in areas of high HUI than of low HUI. There were few differences in fibre properties between soil types. Element contents varied widely between samples from different soil types, but variation was relatively lower with time and HUI. Much of the between-site variation was due to different plant species compositions. These contrasting patterns of variation resulted in poor correlations between fibre properties and element contents. The data suggested that grazing animals can regulate plant nutritional properties by increasing soil nutrient levels and by changing species composition. Their activities could contribute to the development of localized areas of nutritional sufficiency in the absence of intrinsic soil differences.