Effect of Row Spacing and Seeding Rate on Forage Production and Chemical Composition of Two Sorghum Cultivars Harvested at Two Cutting Frequencies 1

Experiments were conducted in 1965 and 1966 at Madison, Wisconsin, to determine effects of row spacing and seeding rate on forage production and chemical composition of 'Piper' sudangrass and 'Sudax, SX‐11' a sorghumsudangrass hybrid, harvested three times at a height of 76 cm or twice at later stages. Row spacings were 17.8, 35.6 and 71.1 cm. Seeding rates were 8.4, 16.8 and 33.6 kg per ha in 1965 and 13.5, 26.9 and 53.8 kg per ha in 1966. Herbage yields were greater, nitrogen concentration lower, and lignin concentration higher under the two‐cut system. Yields of the cultivars were similar under three cuttings. Under two cuttings, SX‐11 outyielded Piper when both were harvested at the same morphological stage. However, since SX‐11 is later maturing, Piper's rate of forage production equalled or exceeded that of SX‐11 under both managements. Nitrogen concentration was higher and lignin concentration lower in SX‐11 at any given time. Forage yields in 17.8‐ and 35.6‐cm rows were similar and exceeded that of 71.1‐cm rows. Row spacing had little effect on chemical composition. Forage production increased as seeding rate increased, particularly in narrow rows. Under three cuttings only, nitrogen decreased and lignin increased at first harvest as seeding rate increased. Seeding rate had no significant effect on chemical composition at second harvest.