Variations in nutritional quality and biomass production of semiarid grasslands

The effect of the growing season and topographic zone on biomass production, protein content, cell content (CC), lignin, cellulose, hemicellulose, digestibility (DMD), and mineral element concentrations (P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn) were studied in herbage samples collected from semiarid grasslands in Central-Western Spain. Protein and mineral contents decreased as the growing season progressed whereas fibre properties tended to increase. Topographic gradient significantly affected peak biomass production, fibre properties, protein and mineral contents. Stepwise multiple regression showed that the prediction of biomass production on these areas was related to cellulose, Na, Fe, and Mg contents in the grassland community whereas fibre properties were mainly predicted by Ca, Na,and Cu. Principal component analysis indicated that the temporal evolution (component II) of the organic variables determined pasture quality whereas most of the variation in mineral content was related to the topographical gradient (component I). Some organic and inorganic parameters may cause deficiencies in cattle grazing on the upper and middle zones, mostly at the end of the growing season. The data suggest that information about the temporal and spatial variations of the production and nutritional quality of semiarid grassland is necessary for making correct management.