14 February 2014
Matthew Cawood
Farmonline
AUSTRALIA could add up to 30 per cent to its northern irrigation zones by opening up the Flinders and Gilbert basins in north Queensland, a CSIRO study has found.
A two-year assessment of the basins identified about 10 million hectares of soils suitable for arable agriculture across the two basins.
With the potential to irrigate up to 50,000ha of that 10 million ha, and to dryland farm other areas, the region represents a rare opportunity to expand agriculture in a world where the availability of agricultural land is mostly shrinking.
The region could grow a wide-range of crops, the study found, from vegetables to sorghum and maize, and agro-industrial crops like sugar and cotton.
CSIRO’s finding emerged after a two-year assessment, part of the $10 million North Queensland Irrigated Agriculture Strategy (NQIAS) that began in 2012.
The key word throughout CSIRO’s assessment is “potential”. Farming these areas will demand new skills and expectations.
“The average rainfall across the Flinders catchment is around 500 millimetres,” said Dr Peter Stone, deputy director of CSIRO’s Sustainable Agriculture Flagship.
“If you go to any part of the world that has 500mm annual rainfall, you’d be hard-pressed to find a place that had more variable year-on-year rainfall than in the Flinders catchment.”
The same applies to the Gilbert catchment’s annual average rainfall of 800mm.
Dams and irrigation have been humanity’s age-old solution to climate variability, and CSIRO thinks it will be no different in these basins.
In the flat Flinders catchment, in-stream water storages are not viable, Dr Stone said.
Instead, CSIO has assessed more than 100,000 sites for on-farm storage dams and concluded that there is potential for 350 gigalitres of storage along these lines in 70-80 per cent of years.
After storage and transmission loss, 350GL of storage could translate to 175GL delivered to crops, Dr Stone said.
In the more northern Gilbert catchment, CSIRO looked at 15 potential in-stream dam sites, and identified two prospects based on yield and cost: at Dagworth on the Einasleigh River, and Green Hills on the Gilbert River.
Combined, these storages could store 750GL of water with 85pc reliability, delivering 250GL to crops.
The prospects for dryland farming across the remaining millions of hectares of viable soils are mixed, Dr Stone said.
For the most part, dryland croppers could expect a break-even yield in 2-3 years out of 10 – strictly opportunity cropping, along the lines of lake-bed cropping in western NSW.
But in these basins, chance is less of a factor than in other risky dryland cropping zones, Dr Stone added.
That’s partly because in seasonal forecasting, the zone has a higher degree of predictive skill than anywhere else in Australia.
It also happens that planting in these areas would happen in February, when there is a good chance that the state of the annual monsoon has already been established.
Future climate change scenarios have been modelled for the next 40 years out, and found that rainfall changed little in those decades.
How agriculture develops in the region – if it develops – depends strongly on the development model chosen, Dr Stone said.
Crops like sugar and cotton need processing facilities close to hand to be viable; for other crops, markets and transport routes have to be mapped out.
There are also potential impacts, like those on the Gulf fisheries, that have to be properly quantified and considered.
Western Australia’s Ord River scheme, the only comparable irrigation area, generates $100 million in produce from about 14,000ha of irrigated land.
The Ord River’s annual average discharge is about 3.8 m megalitres. The Gilbert’s discharge is about 5.3 m ML.
Courtesy of Farmonline