Grasslands of the World.pdf - Disasters and Conflicts - UNEP

J.G. McIVOR
Australian grasslands 363
Plate 9.5
Sward of Stylosanthes hamata growing under trees in the Northern Territory.
legume pastures are more important on less fertile soils (Walker and Weston,
1990). A special development has been the use of shallow ponds to grow
flood -tolerant grasses (Brachiaria mutica , Hymenachne amplexicaulis and
Echinochloa polystachya ) to provide green herbage during the dry season .
In contrast to southern Australia , fertilizer application has been much less
important in tropical pasture development . This partly reflects the use of
grass -only pastures on fertile soils and also the importance of the Stylosanthes
species (see Plate 9.5) with their low phosphorus requirements and ability to
grow well on soils with low available phosphorus (4–8 ppm) levels (McIvor,
1984; Jones et al., 1997). As for southern Australia, superphosphate dominates
fertilizer usage on pasture, comprising approximately 70 percent of the
total fertilizer applied. However, nitrogen-fertilized grasses have important
specialized roles, including pastures based on temperate species for winter
production on some dairy farms .
There have been no surveys for sown tropical pastures equivalent to those
noted above in temperate areas. However, there are problems with some
sown pastures, with approximately 100 000 ha per year going out of production
during the period 1986/87 to 1989/90 (Walker, 1991) due to a decline in
sown species (Walker and Weston, 1990). Although grass -only pastures on
fertile soils are initially very productive, this phase generally lasts only four
to ten years then plant and animal productivity declines due to reductions
in available nitrogen and sometimes loss of desirable species (Myers and
Robbins, 1991; Jones, McDonald and Silvey, 1995).