SEASONAL-VARIATION OF SOIL AND FORAGE MINERAL CONCENTRATIONS IN NORTH FLORIDA

A two-year study was conducted in north Florida on two farms located near Bronson and Williston for beef cattle grazing bahiagrass pastures. Soil concentrations of Ca, P, Mg, Na, and Cu were similar for both locations and seasons for either year. At Bronson soil, Se was higher than at Williston in 1988, but in 1989, soil Se at Williston was higher in the late than in the main grazing season. All soil samples analyzed were deficient in K and Se, and over 63% of samples were found deficient for Mg, Zn, P, Cu, and Mn. Acidity did not appear to be a problem in soil mineral availability, since mean pH was 5.5 and higher. Forage concentrations of Ca, Na, Fe, Co, Mo, and protein were similar for all seasons and locations during 1988; however, greater (P < 0.05) concentrations of P, K, Cu, and Zn were found in June than in October. In 1989, forage concentrations of Ca, K, Na, Zn, Co, Mg, and Cu were higher in the early grazing season (March-May) than during the rest of the year; however, concentrations of K, Mg, Cu, Mn, and Co were higher in the main grazing season (June to August) than in the late grazing season. Forage protein was higher in the early grazing season (March-May) than during the rest of the year. Forage Se was higher at Bronson than at Williston in 1988, and in 1989, forage Se was higher in the late (October) than in the main grazing season (June-August). Mineral deficiencies in 76% or more of the forage samples were found for Cu, Zn, and Co, with all samples being deficient in Na, P, and Se. Consequently, grazing cattle at these locations need continued mineral supplementation of these elements to prevent deficiency diseases from occurring and to support optimum animal productivity.