SOIL, FORAGE, AND SERUM NUTRIENT CHANGES AS AFFECTED BY DEPOSITION OFVOLCANIC SEDIMENTS IN NORTHWESTERN NICARAGUA

A study was carried out to determine the mineral status of grazing cat tle as affected by the eruption of the Cerro Negro Volcano in northwes tern Nicaragua. A total of 14 composite soil and forage samples and 30 blood samples were collected at each collection period, before (Augus t 1991) and after (August 1992) the volcanic eruption. Higher soil lev els of calcium (Ca), sodium (Na), manganese (Mn) (P<0.01), zinc (Zn) ( P<0.05), and lower organic matter (OM) (P<0.01) were found after the v olcanic eruption. Phosphorus (P) was the only macromineral found defic ient with 93 and 71% of the samples below a critical level before and after volcanic eruption, respectively. Forage Ca, potassium (K), magne sium (Mg), P, Zn, copper (Cu), and selenium (Se) concentrations did no t vary between collections. Forage crude protein (CP), in vitro organi c matter digestibility [(IVOMD) P<0.05], cobalt (Go), Mn, and Na (P<0. 01) were lower after the eruption. Iron (Fe) was the only mineral in f orages that increased (P<0.01) after the volcanic eruption. Of the six minerals evaluated in serum only Ca and Mg concentrations were higher (P<0.05) after the volcanic eruption. The macrominerals more likely t o be deficient in this area are P and Mg. Trace elements most likely t o limit cattle productivity are Zn, Mn, Cu, Se, and Co. Special attent ion should be given to supplementation of Cu, since both plant and ani mal tissue samples reflected a deficiency of this mineral.