Chemical composition, in vitro digestibility, leaf:stem ratio, HCN potential and dry matter production of forage sorghums in south-east Queensland

Abstract

Quality and dry matter production data are presented for 13 forage sorghum cultivars grown in a two-year trial on the Darling Downs of southern Queensland. Dry matter production ranged from 10.8 to 16.5 t/ha. Generally, forage hybrids (Sorghum bicolor x S. sudanense) produced more digestible dry matter than cultivars from the sweet sorghum group. There was a wide range in leaf:stem ratio; the highest were the late maturing cultivars Magic (2.12) and Jumbo (1.36) and the lowest the sudangrasses Trudan (0.57) and Piper (0.43). This was not strongly reflected in in vitro dry matter digestibility (55. 7 to 62.5%) or crude protein (9.2 to 12.1 %) although the correlation between leaf:stem ratio and crude protein was high (r=0.7). Sodium contents were consistently low and varied little from O.Q1 %. The HCN potential of sample leaves of sweet sorghums averaged 745 ppm compared to 485 ppm for all other cultivars.