Raised beds are becoming an accepted system for broadacre crops in irrigation areas. A combination of raised beds within traditional rice bays is proving to be a "one size fits all" system, allowing a more flexible cropping option for farmers in the Murrumbidgee Irrigation Area of NSW. Alec Nicol reports
[Photo (left): Barley growing on beds inside an irrigated rice field]
Initially trialled as a means to improve the water-use efficiency of rice, a system of raised beds within a bankless channel layout is emerging as an option for taking advantage of changing irrigation systems.
A CSIRO report on water management in the Murrumbidgee Irrigation Area (MIA), is recommending spreading peak summer crop demand to improve seasonal river flows by encouraging the growth of winter crops.
This ushers in the option to increase wheat and other crop areas in the rice rotation.
This new push towards winter cropping in irrigation areas is enthusiastically supported by researcher Geoff Beecher from the NSW Department of Primary Industries.
Although his work at the Murrumbidgee Shire Community Demonstration Farm (begun in 2002) shows that any small reduction in water-use derived from growing rice on the lateral raised-bed system is swallowed up by reduced yield, he urges farmers not to focus just on rice.
"The lateral raised beds within the bays system allows us to grow three crops in two years and to react quickly to any change in irrigation allocation," he says. The lateral raised beds even open up the opportunity for broadacre farmers to diversify into rotations that include high-value horticulture crops.
Since the summer of 2002-03, country under traditional flat irrigation has produced a rice crop and two wheat crops. The area under lateral raised beds has produced two crops of barley and two crops of soybeans as well as the rice crop.
Mr Beecher is enthusiastic about the new system because it gives growers a relatively low-cost option to increase flexibility and react to changes in water allocations. "It means that we can switch quickly from crop to crop without an expensive reworking of the layout," he says.
"We can use the bay system to irrigate the rice on raised beds conventionally, with the advantages that we can get water on more quickly than the traditional siphon system, and carry out mid-season draining more efficiently.
"Plus, the bankless channel system and terracing allows improved water management; there"s less drainage water at the end of the system and less recycling is required. It"s a less labour-intensive, more efficient system."
But he says the key advantage is being able to get on to the ground quickly after a summer crop and sow a winter crop to take advantage of the residual moisture: five crops on the beds-in-bays compared to three crops on the traditional layout in the same period.
Researchers now say that sub-surface drip irrigation could be used to "tweak" the system even further. Although expensive to establish at about $4000 to $5000 per hectare, the drip irrigation system reduces water use in rice crops by about a third. However, in trials, the decision not to protect the rice with ponded water at panicle initiation saw very disappointing yields, from just over eight tonnes a hectare in 2003-04 down to 3.5t/ha in 2004-05 due to cold conditions.
It was a different story with soybeans, where drip irrigation out-performed furrow irrigation in yield in 2004-05 and had similar water productivity.
"That doesn"t mean that sub-surface drip is an economical system for broadacre crops," says Mr Beecher. "The small increases in yield and water-use efficiency don"t compensate for the high establishment cost. Sub-surface drip only comes into its own with high-value crops, such as vegetables, where yield is much more dependent on irrigation efficiency.
"The future of the system probably depends on looking outside the square and introducing a high value crop into the rotation. In this case the broadacre crops would act as a disease break-crop."
Mr Beecher suggests that the drought has curtailed the adoption of the bedsin- bays system, but says a number of paddocks have been developed and that maize is a popular crop.
"What was initially investigated as a technique to improve water-use efficiency of a particular crop will probably be adopted because it"s so adaptable to a range of crops; it increases cropping flexibility, reduces costs and increases cropping system productivity."
GRDC Research Code DAN00002
For more information: Geoff Beecher, 02 6951 2725, email@example.com
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