J.G. McIVOR¹, V. SINGH², J.P. CORFIELD¹ and R.J. JONES¹

¹Division of Tropical Crops and Pastures, CSIRO, Townsville, Queensland, Australia,
²G.B. Pant University of Agriculture and Technology, Pantnagar, India

Abstract

Seed production by native and naturalised perennial grasses was measured over 3 years in plots grazed at 3 stocking rates at Lansdown, near Townsville in north-east Queensland. The 2 naturalised grasses, Bothriochloa pertusa and Chloris inflata, produced many more seeds (360–2990/m²) than the native tussock grasses, Chrysopogon fallax, Heteropogon contortus, Sorghum nitidum and Themeda triandra (1–110/m²). Seed production by B. pertusa and C. inflata was highest at the medium stocking rate (0.6 steers/ha), with small decreases at both higher (0.9 steers/ha) and lower (0.3 steers/ha) rates. The other species produced most seed at the lowest stocking rate, and seed production declined at higher rates. Flowering patterns varied widely both between species and between years. C. fallax flowered earliest in the growing season, followed by T. triandra, C. inflata, H. contortus, S. nitidum and B. pertusa. If perennial plants of the tussock grasses are lost from pastures, they are likely to be replaced by free-seeding species such as B. pertusa and C. inflata, which are tolerant of grazing.