Gunasegaran Chelliah, Robert Myer, Jeffrey Carter, and Lee McDowell. University Of Florida, "Nfrec, 3925 Highway 71", Marianna, FL 32446, United States of America
Concentrations of selected macrominerals (Ca, P, Na, K, Mg) were determined from annual pasture forages over four consecutive winter-spring grazing seasons (2001-2005). Forage samples were taken from 8 experimental pastures used in beef cattle grazing trials. Two, 2 yr studies were done; animal and pasture data were reported previously (Myer et al., 2003 and 2006). Each study was of a similar 2x2 design comparing tilled vs. sod-seeded pastures with two different forage combinations (Study 1, rye + oats vs. rye + oats + ryegrass; Study 2, oats + ryegrass vs. ryegrass only). Pastures were planted in Oct or Nov, and grazed (and sampled) starting Nov, Dec, Jan or Feb and ending Apr or May. The overall mean concentrations (range) for Study 1 and 2, respectively were (% of DM): Ca, 0.31 (0.25 to 0.44) and 0.31 (0.10 to 0.46); P, 0.42 (0.28 to 0.54) and 0.35 (0.27 to 0.52); Na, 0.03 (0.02 to 0.05) and 0.04 (0.02 to 0.05); K, 3.2 (2.0 to 5.4) and 2.6 (2.0 to 4.3); and Mg, 0.26 (0.18 to 0.42) and 0.16 (0.11 to 0.22). Year affected (P<0.05) P, K and Mg concentrations within each study, but not Ca or Na. Pasture planting method affected (P<0.05) Ca and P in Study 2 and Mg in Study 1. Forage treatment affected (P<0.05) Ca, K and Mg in Study 2. Sampling month affected (P<0.05) all minerals evaluated in both studies except Na in Study 1. Results indicate that forage type, pasture planting method, year and especially month within year can affect concentrations of macrominerals of annual cool season pastures in the southeastern USA.
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