Pace setting growers look at green manure by Bernie Reppel
GroundCover™ Issue: 34
What did the old song say — "Everything old is new again"? The practice of green manuring — growing a crop, usually a legume, for its benefits to the soil and to following harvestable crops — is traditional in long-established farming systems, but it hasn't been done much in Australia's northern grains region.
In north-west New South Wales, members of the go-ahead Walgett Sustainable Agriculture Group (WSAG) thought they'd give it a try with faba beans. Andrew and Hugh Ball planted 80 hectares in 1999, with Mark Evans (350 hectares) and Paul Duncan (200 hectares) following on in 2000.
WSAG's 16 grower members have been innovation pacesetters in the northern region in recent years,
with a strong commitment to developing sustainable long-term rotations. WSAG's agronomist/manager Greg Rummery says faba beans as green manure is a relatively rare practice in the northern grains region.
But "all the evidence in the north suggests that wheat yields are superior after faba beans, even if you take off a grain crop," Mr Rummery says. "We als6 know that, while faba beans produce a large biomass, they are very vulnerable to disease and frost in northern conditions and you can't be sure of getting a crop successfully through to the podding stage.
"As well, black oats and other grass weeds are difficult to control properly in faba beans, which is a weakness in their full rotational benefits.
"We reasoned that green manuring is something professional farmers are going to have to do in the north, by planting some type of short-term ley crop, and faba beans might fill that need."
Mr Rummery says initial plans to spray out the crop faltered due to difficult seasonal conditions and the difficulties inherent in spraying out a lush legume crop. They decided to plough in the total area.
One crop of faba beans had all been double-cropped out of sorghum and its standing dry stalks added to the challenge of incorporation.
"In that situation, a chisel plough is the last thing you would want, so we used a set of offsets," Mr Rummery
says. "You could say we were breaking the rules, but you have to be flexible. There's nothing wrong with using offsets if the conditions are right.
"It's only if they are your primary tillage implement that you have got a problem."
Mr Rummery says the two growers involved in the 2000 trial were most likely to work the green-manured paddocks once more and then spray them through into wheat in 2001. WSAG will monitor the short- and longer-term nitrogen and other benefits of the green manure crops.
"On straight economics, the sums point to nitrogen left behind by such a green manure crop costing around the same as bagged fertiliser or gas," he says. "But that does not account for the other benefits of legume N over bagged N, like soil structure improvement through root growth.
"Organic N is also released more slowly, in tune with the seasons, and so is better able to supply a wheat crop over the season, instead of in a big rush at planting time."
Program 3.5.1 Contact: Mr Greg Rummery 02 6828 1882 Mr Tom Howard 02 6828 1228