Too much of a good thingWhy filling one gap may create another
GroundCover™ Issue: 54
Helen Olsen looks at solutions to waterlogging
What a difference a drain makes: (far left) a wet headland after 50mm of rain in 2001, and (middle) the same headland in 2003, also after 50mm of rain but with a collector drain installed underneath. Pipe being installed in collector drain (right). Photos: Brad Collis
In high rainfall zones, excess surface water can be as big a headache as too little water in the more established wheatbelt regions. It is one of the reasons why it has taken the development of raised-bed cropping to establish cereals on the farming landscape in southern and coastal districts.
However, raised beds alone are often not enough to manage the problem of waterlogging. Excess water in the furrows between the beds needs to go somewhere; and not in an uncontrolled flood to the nearest low-lying area.
One answer is to install underground plastic drainage pipes that run along a paddock"s headland and drain into a nearby dam. Bruce Wightman, from Victoria"s Department of Primary Industries at Geelong, says headland drains are an important innovation for helping growers in southern regions overcome waterlogging issues.
"The underground collector drainage system gives growers much more control over water use and management than they previously had," he says. "For example, it allows nitrogen and herbicide applications to be done when the grower decides, rather than having to be postponed because of a recent downpour and subsequent wet headland drains."
Over the past two years, Mr Wightman has been overseeing trials of different types of collector drains. These have led to the current version of an underground plastic pipe in a 450 millimetre-deep slot, placed in the centre of a V-shaped ditch or collector drain and backfilled with gravel to the surface.
The pipe runs to the nearest dam, which needs a pump to allow the controlled release of water and to keep the water level below the drain outlet.
Large gravel screenings (40 to 50mm) on top of the collector drain"s filtering system are important for stopping erosion that would otherwise occur around the Vshaped ditch, and also to support the weight of tractors and other farm machinery.
Mr Wightman says the current focus is on developing a filter which will allow quick clearance of water but stop clay or particulate matter blocking the drain.
"We"re trying to find out whether a stocking material is necessary in the filter. Some people believe it becomes blocked with clay too easily."
Mr Wightman says that a collector pipe is not suitable if the paddock gradient is more than one percent. If the headland itself is flat, then the pipe can be installed at an angle underground to allow water flow.
As with most farm equipment, another consideration is cost. "The average price is $10 a metre, which for a 25-hectare square paddock works out at $5,000. It depends on a grower"s recent profit margins as to whether he or she will be able to put this system in."
GRDC Research Code: SFS4.
For more information: Bruce Wightman, 03 5229 0566, mobile 0419 586 891, firstname.lastname@example.org
Adding a cereal crop to the farming mix in high rainfall country is seen as a way to fill a feed gap and potentially generating extra income from the crop.
However CSIRO Plant Industry scientist Dr Libby Salmon says that forage crops can create, as well as fill, a feed gap. She advises growers in higher rainfall zones to look carefully at the integration of all feed sources on the farm and to take a long-term view.
Dr Salmon has been working with a computer modelling system using 30 years" collected weather data to simulate the risks and advantages associated with changing the feed mix. While the results are preliminary, she is advising that good grain yields and livestock prices are needed to offset the cost of removing permanent pasture to sow a cereal crop.
She examined the impact of sowing five percent of the farm to winter wheat on a second cross lamb enterprise on the outskirts of Canberra, and Wagga Wagga between 1973 and 2002. In each case, the grazing pressure was eight ewes per hectare.
Lambs were marketed either in mid-December or were drafted, with the heavier 50 percent being sold then and the remainder fed until the end of the following July. To take advantage of a slightly higher annual rainfall at the Canberra site, a grazing brassica crop was introduced preceding the winter wheat.
According to Dr Salmon, stocking rate is the key profit driver in a pasture-based grazing situation, and higher stocking rates mean that feed gaps become more pronounced. Growing a grazing crop is only one option for filling the gaps.
Growers can just as easily buy feed supplements, which is why she suggests it best to take a whole-farm approach in managing the risks associated with the options. At Wagga Wagga, for example, it was found that introducing a winter cereal crop only lifted the livestock gross margin by $3 a hectare across the farm. At Canberra the results were more pronounced, with a lift of $15/ha when the winter wheat crop was introduced.
Adding the brassica crop pushed up the gross margin by a further $29/ha, but that is only part of the picture.
The average gross margin from pasture alone was $355/ha and from the combination of pasture, winter wheat and a brassica crop it was $400/ha. The best years returned as much as $650/ha for the pasture alone and $850/ha for the combination.
The more pressure put on the system by introducing the brassica crop, the more variability there was in returns between years.
This is seen as demonstrating that risk management needs to be over a long term, not on the basis of a single season.
GRDC Research Code: CSP00009.
For more information: Dr Libby Salmon, 02 6246 5417, email@example.com