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Past analyses of Florid8 range plants have been hand-plucked, whole-plant samples and have been limited to a few major species sampled at a few times during the year. The objective of this study was to determine if mineral concentrations in hand-plucked samples and the boluses of esophageally f&dated steers: changed from summer to winter; changed on different range areas; could be improved by more frequent grazing. Concentration of P and K in diets collected from steers grazing pine-palmetto, transition, and pond areas were not significantly different, but Ca, Mg, and Mn were usually lower on the pond areas. Concentration of Zn was similar in diets from the 3 areas in summer, but was lower on pine-palmetto and transition areas in winter. Concentration of Fe in diets was greater on pond areas than on pine-palmetto areas, while transition areas were intermediate. Concentrations of P, K, Mg, and Mn in diets of fistulated steers declined from summer to winter. Concentrations of P,K, Fe, and Zn were not different between pastures regrazed in winter and grazed only in winter. Most hand-plucked forages declined in mineral concentration from summer to winter. Florida range must be supplemented with complete minerals regardless of season, range site grazed, or grazing management. S,outh Florida flatwoods range sites are made-up of three subsites: pine-palmetto (75%), maidencane (Panicum hemitomon) ponds (150/, and their intergrading areas, referred to as transition areas (10%) (Hilmon 1964). Pine-palmetto area soils are usually sandy Spodosols, and their low organic matter (a%), together with high rainfall (>I20 mm annually) result in plants with low mineral concentration. Wiregrass (Aristida stricta) (Hilmon and Lewis 1962, Kirk et al. 1974); chalky bluestem (Andropogon capil&es), lop-sided indiangrass (Sorghastrum secundum) (Lewis 1970), and creeping bluestem (Schizachyrium stoloniferum)(Kalmbather and Martin 1981) were found to be below the mineral level necessary for dry, pregnant cows. Large portions of Florida range are grazed from October to March, and native forage that has accumulated from the previous growing season is weathered and senescent, which further adds to the deficiency problems. Soils of the ponds are often Histosols or other soils with high organic matter content, which is responsible for higher dry matter yield and crude protein characteristics of maidencane. Pond vegetation, because of better soils, may have greater mineral supplying potential than pine-palmetto areas. Previous plant-mineral research has been based on handAuthors are associate agronomist, Ona Agricultural Research Center, Ona, Fla. 33865, former graduate assistant, Dept. of Agronomy, and associate statistician University of Florida, Gainesville 3261 I. This article is FlorIda Agr. Exp. Sta. Pap. No. 3676. Manuscript received March 20, 1982. collected whole plant samples from a few species on pine-palmetto areas. However, range pastures and cattle diets are very diverse. One Florida range pasture contained 109 different species, 42 of which were known to have been eaten by esophageally fistulated steers (Kalmbacher et al. 1984). A total of 26 species were eaten on the pine-palmetto area, 13 species on pond areas, and 15 species were eaten on the transition areas. This complex diet mixture and the variation that occurs within a plant (Kalmbacher 1983) make it difficult to characterize range-plant mineral concentration. Use of esophageally fistulated animals is an accepted practice to estimate crude protein, digestibility, botanical composition, etc., of cattle diets (Van Dyne and Torrell 1964, Vavra et al. 1978, Lesperante et al. 1974). Use of fistulated cattle to predict the concentration of P in forage (Hoehne et al. 1967, Langlands 1966, Mayland and Lesperance 1977); and Zn (Little 1975, Mayland and Lesperante 1977), is unreliable because of salivary contamination. Smaller increases due to saliva were found for K, Mn, and Fe (Little 1975, Mayland and Lesperance 1977), while Ca and Mg could be predicted with reasonable error (& 9%) (Little 1975). Objectives of this research were not to predict absolute plant mineral concentration, but to determine if pine-palmetto, maidencane pond, and transition areas were different in their mineral supplying potential by monitoring bolus P, K, Ca, Mg, Fe, Mn, and Zn concentrations. We also wanted to determine if summerwinter grazing improved mineral supplying potential over winter grazing alone. Materials and Methods A 16.2-ha native pasture in good-to-excellent condition was divided into two 8.1 ha pastures, each containing 5.7 ha of pinepalmetto area; 1.6 ha of maidencane pond; and 0.8 ha of transition area. Both the available forage and species selected by cattle on all 3 sites have been described (Kalmbacher et al. 1984). Major soils on the pine-palmetto areas were Ona and Smyrna fine sands (sandy, siliceous, hyperthermic Typic and Arenic Haplaquods, respectively). Soil on the pond was a Samsula muck (sandy, siliceous, silicdysic, hyperthermic, Terric Medisaprist), and on the transition area, a Basinger fine sand (sandy, siliceous, hyperthermic, spodic Psammaquent). Flatwoods, transition and pond soils are ranked lower to higher, respectively, in fertility primarily because of an increase in soil organic matter content. Both pastures were burned in January 1980. One pasture was grazed from 16 June to 26 August 1980 (referred to as ‘summer pasture’), the re-grazed between 15 January and 18 March 1981 (referred to as ‘winter-regrowth-pasture’). The second pasture was grazed between 12 January and 15 March 1981 (referred to as 36 JOURNAL OF RANGE MANAGEMENT 37(l), January 1984 ‘winter-only-pasture?. Results and Discussion Four esophageally fistulated, Brahman cross steers (325 kg) were used on the summer grazed pasture, and 5 steers were used on the winter-only and winter-regrowth pasture. Steers were hazed to a different area on each collection day and allowed to graze only in that area. Screen-bottom collection bags were used to hold the forage (1 .O to 1.5 kg) selected by steers during a 15-minute collection period. Collections were made at 0800 hrs, every other day in summer (35 different days) 1980, when 47 samples were obtained by steers on pine-palmetto area; 37 on pond area and 17 on the transition area. During winter 1981 collections were made with steers alternately on the winter-only, and winter-regrowth-pastures. All areas were grazed on one pasture, then during the next 3 days, all areas were grazed on the other pasture. There were 38 samples collected through steers on the pine-palmetto of the winterregrowth-pasture, 36 samples on its pond, and 37 samples on its transition area (24 different days). On the winter-only-pasture there were 36 samples collected on each of the 3 areas over 24 days. Effect of Season and Previous Grazing Diets of cattle grazing the summer pasture had higher (m.01) K concentrations than diets of cattle grazing winter-only or winterregrowth pastures (Table 1). Concentrations of P in diets were greater (EO.01) on the summer than the winter-regrowth pasture, but there was no (EO.05) difference in P concentration in diets from the summer vs winter only pasture. There was no difference in concentrations of P and K when the winter-regrowth and winteronly pastures were compared. During winter, frost is common in sub-tropical Florida (26ON), and the winter of 198 1 was colder than normal. Mean low was 1.8OC vs. 9.5’ C for the 36-year average (Dantzman and Hodges 1980). Grass was weathered and senescent, and grazing of regrowth from previously grazed summer pasture (3-month-old regrowth) did not enhance P and K concentration over the pasture grazed only in winter (IO-month-old forage). Two nonfistulated steers (375 kg) were placed on each pasture to assure uniform grazing and provide additional grazing pressure. Stocking rates (includes all cattle) for the summer, winterregrowth, and winter-only-pasture were 55,45, and 53 animal unit grazing days/ha, respectively. All cattle were given free-choice minerals. Diet samples collected from fistulated steers were spread on screen trays, dried overnight at 50°C, ground (40 mesh screen), and wet-ashed. Plant P was determined by the vanadomolybdate method (Jackson 1958), and K, Ca, Mg, Fe, Mn, Zn, and Cu were determined by atomic absorption. Standard reference materials (fruit orchard 1eaves)from the National Bureau of Standards were used to check analytical accuracy. Deficiency of P has been reported and recognized in Florida (Kirk et al. 1974, Lewis 1974), but deficiency of K has not received much attention. Creeping bluestem (Kalmbacher and Martin 1981) was reported as being deficient in K for dry-pregnant cows. Fistulated steers in this study received no K in their mineral supplement, yet values for K from the forage collected from steers in winter were still deficient in K (NRC 1976) (Table 1). Hand-collected samples of major forages consumed by fistulated steers were collected weekly to provide trends on mineral concentration which could be used to compare with concentration in the boluses. Forages were collected on the area where cattle were grazing in each pasture, and the parts collected were similar to those eaten by steers. Hand collected samples were dried at the same temperature and duration, ground, and analyzed for the same minerals as diet samples collected from fistulated steers. All data were presented on an oven-dried (SOOC) basis. Iron, Ca, and Zn concentrations (main effect means) were not significantly different in diets eaten on the summer, winter-only, or winter-regrowth pastures (Table 1). However, there were two significant pasture (season) x area interactions for Ca (Table 2), which will be discussed. Because main effect means for the pastures were not different, and since cattle graze all 3 areas in the same pastures on commercial ranches, it is expected that seasonal and regrazing effects on

Seasonal Mineral Concentration in Diets of Esophageally Fistulated Steers on Three Range Areas