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Influence of Different Defoliation Systems on the Regrowth of Pearl Millet, Hybrid Sudangrass, and Two Sorghum-Sudangrass Hybrids from Terminal, Axillary, and Basal Buds¹

Stubble heights of 8, 10, 15, and 25 un were imposed on ‘Gahi-1’ pearl millet (Pennisetum typhoides [Burm.] Stapf. and C. E. Hubb.), ‘Haygrazer’ and ‘Sudax SX-12’ sorghum-sudangrass hybrids (Sorghum vulgare Pers. x Sorghum sudanense Stapf.), and ‘Trudan II’ sudangrass hybrid (Sorghum sudanense Stapf.) at either the first, second, or third harvest with other harvests being cut to a uniform height. Considering all cultivars tested, marked reductions in yields were obtained when they were defoliated to 8 cm as compared with 25 cm for 21 out of 24 harvests (87% of the harvest). Net gains in yield ranging from 1,203 to 2,039 kg/ha were realized within a 30-day growth period by raising the stubble height from 8 to 25 cm at a single harvest. Dry matter production was influenced more by variation in stubble heights at the second harvest than when these same variations were imposed at the first or third harvest.

Gahi-1 pearl millet showed a different regrowth pattern than sorghum-sudangrass or sudangrass hybrids, as regrowth was more dependent on terminal buds and less on tillering. Regrowth from terminal buds increased for all the summer annual cultivars as the height of defoliation was raised from 8 to 25 cm. Basal and axillary tillering increased as the height of defoliation was lowered from 25 to 8 cm for the sorghum-sudangass hybrids. The nitrogen content of the forage was not reduced when the harvest height was lowered from 25 to 8 cm at the first or second harvest.

Key Words: Pennisetum typhoides • Sorghum vulgare • Sorghum sudanense • Regrowth • Terminal buds • Axillary buds • Basal buds • Summer annual grass

² Assistant Professor, and Professor of Crop Science, respectively, North Carolina State University, Raleigh, N. C. 27607.

Received for publication November 7, 1969.