Variación estacional de la composición mineral en pastizales de dehesa

The seasonal variations in the concentrations of sahes, N, P, K, Ca, Mg, Na, Fe, Mn, Cu and Zn in the pasture lands of a dehesas in the Pro- vince of Salamanca are studied. The sampling was monthly and took place during the period from September 1978 to October 1979. In general, the contení of ashes, N, P and K evolves in a similar ma- nner, reaching highest valúes in spring and lowest valúes in summer. Ho- wever, the concentrations of Ca, Mg and Mn show sharp oscilations at zone or fasture-type level. Those of Na, Cu and Zn are totally different from eteach other, but while in the Na concentration there are scarce fluc- tuations throughout the seasons, there are marked variations in the other tvvo. The elements Mg and Na are outstanding due to their relatively low concentrations which lie between 0 03 and 0.15% and 0.02 and 0.14% for the former and the latter, respectively. In the pasture land of the dehesa studied, it is usual to find deficien- cies in the elements Na, Cu and Zn throughout the year, while it is only in spring that the concentrations of N, P, Ca and Mg rise above the cri- tical levéis of an adequate nutrition for rumiants.