Tropical grasses studied

Lester McCormick with Denevan Ellis
NSW DPI pasture specialist Lester McCormick with Denevan Ellis from the property "Maryvale", Duri, discussing the performance of tropical grasses at a recent field day.

With the ability to use water efficiently to provide increased feed as well as controlling recharge, tropical grasses are almost certain to play an increased role in grazing systems.

Now, research near Tamworth shows they can also outperform other forage crops, especially in difficult conditions.

NSW Department of Primary Industries (DPI) is comparing water use and forage production for tropical grasses and traditional forages in a project funded by the Cooperative Research Centre for Future Farm Industries.

Despite an extremely dry start to the 2006-07 summer, good falls occurred in late February and early March, lifting the total to 364 millimetres over the eight month growing period compared to the longterm average of 479mm.

The tropical grasses showed an excellent growth response to the late season rain, with Premier digit grass producing 16.1 tonnes per hectare (t/ha) of dry matter, Katambora Rhodes 11.4t/ha, and Swann forest bluegrass 6.8t/ha.

Forage sorghum produced 12.89t/ha.

The early performing tropical grasses started to produce strong growth by late September and by early December growth rates were as high as 140kg DM/ha per day for the Premier digit.

By comparison forage sorghum crop achieved just 18kg DM/ha per day in early December but at that time it was still too young to graze.

Expressed as dry matter, Premier digit produced 50 per cent more forage than sorghum for the season.

With a rooting depth of 1.3m, Premier digit took 175mm of water out of the soil and had a water use efficiency of 32kg of dry matter per mm of soil moisture and rainfall.

During drier parts of the season, Premier tended to wilt and become dormant rather than continue chasing moisture, while Katambora chased every drop of moisture it could get.

That’s reflected in data which shows Katambora extracted 213 mm from the soil with a rooting depth of 1.7m, but it only produced 22.7kg of dry matter per mm of water.

Katambora took longer to respond to rain because it had completely dried out the soil profile. There were also plant losses.

Meanwhile, Swann had a root depth of 1.2m, extracted 139mm of water, and produced 13.7kg/mm of water.

Lucerne was also grown in the trial and it produced 11.6t/ha of dry matter with a water efficiency of 23.3kg of dry matter per mm of moisture.

While lucerne produced quality forage, the level of ground cover has only once exceeded 75 per cent, the threshold above which soil erosion is minimized.

The tropical grasses, however, have maintained groundcover levels above 80 per cent, substantially reducing the risk of soil erosion.

In addition, they can produce large quantities of forage, at very efficient rates, which can be used at the time of growth or later in the season as bulk to fill the autumn feed gap.

Separate research will determine the optimal rates of nitrogen fertiliser required to increase forage quality and quantity so producers will have a better guide to match stock numbers with pasture growth rates.