The growth of three tropical pasture grasses on the mid-north coast of New South Wales

The yields and seasonal growth curves of kikuyu grass, (Pennisetum clandestinum) setaria,(Setaria anceps cv. Kazungula) and broadleaf paspalum (Paspalum wettsteinii), were determined over a three year period at Taree (lat. 32°s) New South Wales with or without irrigation and under nil, 170 or 680 kg N ha-’ yr-’ (nil, low and high N). Annual forage yields averaged 1300, 51 00 and 13,000 kg DM ha-l at nil, low and high N respectively.Kikuyu grass yields were significantly less than setaria or broadleaf, especially at low N. Both the apparent recovery of nitrogen and the efficiency of dry matter production by kikuyu grass were less than the other grasses. Yields from the irrigated plots were similar to the dryland plots due largely to a generally favourable rainfall pattern. During short dry periods the extra yieldfrom irrigation was less than from the application of nitrogen. The patterns of seasonal growth were similar for each species at any one nitrogenrate and irrigation treatment. The growing season (>5 kg DM ha-’ day-') without nitrogen, was only four to six months, commencing in late spring. This was increased to eight months at low N (October to May) and nine months (September to Mdy) with high N. The mean period of high growth rates (>60 kg DM ha-’ day-')over summerwas nil at nil N, only six days at low N but increased to 154 days at high N. Winter growth was negligible.