MINERAL CONCENTRATIONS IN FORAGE SORGHUM GROWN UNDER 2 HARVEST MANAGEMENT-SYSTEMS

Little information is available on the mineral concentrations of forag e sorghum (Sorghum bicolor (L.) Moench] leaves and stems. Our objectiv e was to determine whether commercially available forage sorghum could be expected to supply the minimum mineral requirements for beef cattl e when harvested as simulated grazing of pastures (SP) or as hay. In 1 987 and 1988, 10 forage sorghum entries were grown near Lubbock, TX, i n replicated plantings on a fine, mixed thermic Aridic Paleustolls wit h supplemental furrow irrigation. There were three SP harvests in 1987 and four in 1988. The hay treatments were harvested twice in 1987 and three times in 1988. Entries and managements were different (P less-t han-or-equal-to 0.05) in mineral concentrations, as was the management x entry interaction for Mg, K, Na, Cu, and the K/(Ca + Mg) ratio. Gen erally, for both management systems, leaves had numerically higher con centrations of Ca, Mg, P, and Mn than stems, while the reverse was tru e for K, Na, and the K/(Ca + Mg) ratio. Copper and Zn concentrations w ere not consistent for either harvest schedule or leaves and stems. Mi nerals found most likely to be limiting for beef cattle (Bos taurus) w ere P and Zn, but P would generally be adequate if cattle had daily ac cess to leafy growth. Calcium tended to be low and the K/(Ca + Mg) rat io high in stems of the hay harvests. The levels of the other minerals appeared to meet the minimum requirements for beef cattle for most of the growing season. Overall, the 10 entries of forage sorghum appeare d similar in meeting mineral requirements or beef cattle.