R.M. JONES and G.A. BUNCH

CSIRO Division of Tropical Crops and Pastures, Brisbane, Queensland, Australia

Abstract

Measurements of pasture attributes and animal production were made for 22 years on unreplicated pastures based on Kenya clover (Trifolium semipilosum cv. Safari) and Leucaena leucocephala cv. Peru in coastal south-east Queensland. Safari persisted over this period but its presence and productivity fluctuated between years. There was a trend towards lower pasture and animal production towards the end of the 22-year period. Liveweight gains averaged c. 460 kg/ha/yr in the first 10 years, but declined to just under 400 kg/ha in the last 3 years. The variable growth of Safari in this environment will limit its commercial acceptability.
Animal production from the leucaena pasture in the last 13 years (400 kg/ha) was higher than in the first 10 years (3 10 kg/ha). This was despite a decline in the density of leucaena bushes from c. 8650 plants/ha (1969) to 7000 (1980) and 4120 (1993). Infestation by psyllids was first noticed in 1988, but on this pasture, grazed on a 2 weeks on: 6 weeks off rotation, damage was less serious than on other pastures with a longer rest. Clinical signs of mimosine toxicity and low serum thyroxine levels were measured only in 1981 and 1982 and then only in some animals. No DHP was detected in urine after dosing animals with DHP-degrading bacteria in 1986.