C.K. McDONALD, R.M. JONES and J.C. TOTHILL¹

CSIRO Tropical Agriculture, St Lucia, Queensland, Australia
¹Present address: 405 Pullenvale Rd, Pullenvale, Queensland, Australia

Abstract

Six grass species were oversown into speargrass (Heteropogon contortus) (low fertility) and speargrass-siratro (Macroptilium atropurpureum cv. Siratro) (high fertility) pastures on granite soils in south-east Queensland in 1979 and 1980.
Establishment from both sowings was very poor for all species; however, sabi grass (Urochloa mosambicensis cv. Nixon) and digit grass (Digitaria eriantha cv. Premier) persisted, increased in density and gradually spread into adjacent plots. For both species, spread was greater in the high fertility pasture than in the low fertility pasture.
After 16 years, the yield of digit grass was significantly less than that of speargrass or sabi grass at the low fertility level, and this grass showed a higher response to application of N.
Both sown grasses were highly competitive and reduced the number of native species where they were sown. Digit grass caused a far greater reduction than sabi grass, and the amount of bare ground in digit grass plots was 3 times that in speargrass areas.
On low fertility granite soils, neither species offers any benefits in productivity over good speargrass. The potential dominance of digit grass suggests it should not be sown on these soils, whereas sabi grass may have a role for oversowing into badly degraded native pastures.