Tropical Grasslands (2003) Volume 37, 129150
Effects of sown grasses and stocking rates on pasture and animal production from legume-based pastures in the seasonally dry tropics
CSIRO Sustainable Ecosystems, Davies Laboratory, Townsville, Queensland, Australia
pasture was oversown with a legume mixture [Macroptilium atropurpureum
cv. Siratro (siratro), Stylosanthes hamata cv. Verano (verano)
and S. viscosa] together with Urochloa mosambicensis cv.
Nixon (sabi) or Chloris gayana cv. Callide (rhodes) or with no
sown grass (native). The 3 treatments were stocked continuously at 3
stocking rates (SR) of 0.65, 0.95 and 1.25 steers/ha with 2 replicates.
In addition, unreplicated paddocks of the 3 grass treatments stocked
at 1.25 steers/ha were fertilised with ammonium nitrate at 100 kg N/ha/yr.
All paddocks were fertilised with 100 kg/ha of single superphosphate
every 2 years (≈5 kg P/ha/yr). The experiment was sown in 1977
and terminated in 1993.
grasses decreased with increasing SR and were virtually eliminated at
high SR with sabi. Rhodes established rapidly and was the most dominant
grass for the first 5 years. Thereafter (except with N fertiliser),
it declined through years of drought. Sabi established slowly but after
the 5th year became dominant. After 1984, Bothriochloa pertusa
(not recorded in the original native pasture) increased and became the
dominant grass at high and medium SRs on the native and rhodes grass
treatments. It was less invasive at low SR.
Verano was the
most successful legume, becoming the dominant species at high and medium
SRs until B. pertusa invaded and reduced legume contribution.
Siratro persisted only at low SR, mainly with sabi grass.
With N fertilisation, rhodes grass was the most prominent
species and N-fertilised native and sabi treatments contained significant
levels of annual grasses and dicot weeds, especially Sida spp. and Alternanthera
yields declined linearly with SR. Overall, pasture yields at low SR
were similar for all grass treatments but at medium and high SRs, yields
on the native treatment were lower than for the sown grass treatments.
N-fertilised treatments gave higher yields than the legume-based treatments
at the same SR, especially with rhodes grass where mean yields were
double those on the native grass treatment (7250 vs 3360 kg/ha).
(July–June) varied from 293–1316 mm over the period but there was no
relationship (P>0.05) between annual liveweight gain (LWG) and annual
rainfall. Annual LWG/head was, however, linearly related (P<0.01) to
‘green days’/yr. SR had more effect on annual gain/head than did the
grass treatments, with a mean linear decline of 40 kg/unit increase
in SR. In only 2 years did a sown grass treatment (sabi) give higher
(P<0.05) LWG than the native pasture control. Overall, however, gains
on sabi were 14% higher than those of the other treatments (P<0.01).
Mean gains/head/yr were 143, 125 and 125 kg for the sabi, rhodes and
native treatments, respectively.
treatments gave mean LWGs of 126, 121 and 86 kg/head/yr for the sabi,
rhodes and native treatments.
supplementation nor a full mineral supplement improved liveweight gain
on any treatment despite low Cu concentrations in rhodes grass of <4