Effect of soil fertility, weed competition, defoliation and legume seeding rate on establishment of tropical pasture species in south-east Queensland

Abstract

An experiment was sown at two contrasting sites in south-east Queensland to study the response of tropical pasture species in the establishment and second year to treatments imposed during the establishment year. Sowing was into fully prepared seed-beds on a nitrogen deficient low humic gley at Beerwah and a fertile prairie soil at Samford. Limiting nutrients, other than nitrogen, were supplied by fertilizer. The treatments were: two pastures (Macroptilium atropurpureum cv. Siratro/Setaria anceps and Desmodium intortum cv. Greenleaf/setaria anceps), three legume seeding rates, two defoliation systems in the establishment year, and presence or absence of severe annual grass weed competition. In the establishment year there were large treatment effects on the yields of sown pasture species. Sown weeds had a great effect, particularly on the high fertility site where they reduced setaria, desmodium and siratro yields by factors of approximately 50, 10 and 2 respectively. Legume yields increased with legume seeding rates. The sum of legume yields from the regularly cut treatments was only one-half to one-quarter that of the single end of season cut, whereas total grass yields were similar in both treatments. However, all first year treatments had much less effect in the second year, when legumes comprised about 70 per cent of mixtures at the low fertility site and 30 per cent of mixtures at the high fertility site. Some comments are made about this role of soil fertility in the dynamics of pasture establishment and about future lines of research. Results from this and other experiments suggest that pasture establishment problems on fully prepared seed-beds are not a major limitation to the wider use of tropical pastures in south-eastern Queensland.