Yield, yield distribution, and nutritive value of intensively managed warm-season annual grasses

The annual grasses pearl millet [Pennisetum glaucum (L.) R. Br.] and sorghum-sudangrass [Sorghum bicolor (L.) Moench] are alternatives to warm-season perennials in forage systems for lactating dairy cows (Bos taurus) in the southern USA. Large fluctuations in forage production during a short growing season, however, make their management difficult. During 2 yr, seeding date and cultivar effects on dry matter (DM) yield, yield distribution, and nutritive value of these grasses were measured, and treatments were replicated four times. There were four seeding dates in 1996 starting on 10 May and six in 1997 starting on 20 March. Seeding dates were 3 wk apart. Three millet ('GK 600', 'Millex 32', and 'Tifleaf 2) and two sorghum ('Hygrazer' and 'SX 15') cultivars were tested. Soils were a loamy, siliceous, thermic Grossarenic Paleaquult and a hyperthermic Grossarenic Paleudult. Total DM yield, averaged across cultivars, decreased from 7.4 to 5.6 Mg ha(-1) from the first to the fourth seeding date in 1996 and from 7.4 to 4.4 Mg ha(-1) from the first to the sixth seeding date in 1997. Leaf percentage generally was above 70% and often greatest for Tifleaf 2. Seasonal distribution of DM was affected by planting date but not by cultivar. In conclusion, choice of species or cultivar had less impact on the responses measured than did planting date. Seeding at two dates approximately 3 to 6 wk apart is a good strategy for improving yield distribution of these cultivars and providing high nutritive value forage for nearly 5 mo.