Author: Rebecca Thyer
A cropping evolution is gathering momentum across the Mallee region as growers increasingly fine-tune their rotations to increase the role of break crops in lifting productivity and profitability
Michael Moodie addressing growers at a SAGIT trial site.
Driving across the northern Mallee five years ago you may have noticed the occasional crop of canola. Break crops such as canola were not popular, as intensive cereal cropping dominated the landscape.
Mallee Sustainable Farming’s Michael Moodie says that in 2011 barely five per cent of Mallee cropping land was sown to break crops. So when the GRDC-funded Low Rainfall Crop Sequencing Project began in that year, continuous cereal cropping was the norm.
The Low Rainfall Crop Sequencing Project
The Low Rainfall Crop Sequencing Project ran trials from 2011 to 2014 at: Condobolin, NSW, with Central West Farming Systems; Chinkapook, Victoria, with the Birchip Cropping Group; Mildura, Victoria, with Mallee Sustainable Farming; Appila, SA, with Upper North Farming Systems; and Minnipa, SA, with the Eyre Peninsula Agricultural Research Foundation.
At each site, about 15 different break options were used for a one or two-year break in 2011. From 2012, wheat was sown on the one-year break sites, and then in 2013 and 2014 wheat was sown at all sites. A control plot of continuous wheat was planted at each site so that direct comparisons could be made.
Some breaks were used at every site, including canola, peas, pasture and fallow, and some were tailored to the location, for example at the Central West NSW trial lupins were planted to mirror regional grower choice.
Five years later the change has been dramatic, with Australian Bureau of Statistics data showing the area planted to break crops in the Victorian Mallee has increased from two to seven per cent. Michael Moodie attributes this to increasing grower confidence in the crops.
Mr Moodie, who has been completing on-farm trials as part of the project at Mildura, Victoria, says the research has changed people’s thinking, especially in the northern Mallee: “The trials have given growers confidence in the long-term profitability of break crops,” he says. “There is now four years of regionally specific data from the project showing the benefits and reducing the risk of taking on break crops.”
Mr Moodie says the momentum for change was helped by the fact that when the project began, many of the region’s growers were already seeking alternatives to continuous cereal cropping. Intensive cereal cropping had led to declining productivity from agronomic constraints such as grassy weeds, declining soil nitrogen and crop diseases.
Figure 1 Percentage of Mallee (North and South) seeded to different crops.
Mr Moodie’s Mallee Sustainable Farming (MSF) trial assessed nine different break-crop options in 2011, as well as a baseline wheat. In 2012 the break was either continued for a second year, or sown back to wheat. Wheat was grown on all plots in 2013 and 2014.
He found that a one-year break of field peas led to an increase of 0.3 tonnes per hectare in the subsequent wheat crop, or 0.1t/ha from a canola break. However, these benefits lasted only one year.
After a two-year break, wheat yields increased by 0.5 to 1.25t/ha, with a benefit of up to 0.4t/ha observed in the second year of wheat following the break.
Mr Moodie says the key driver for improved performance was brome grass reduction. It accounted for 39 per cent of the total yield increase in 2013 and 80 per cent in 2014. (Increased nitrogen, at 38 per cent and 18 per cent in 2013 and 2014, and less rhizoctonia at 19 per cent in 2013 were the other significant causes of improved wheat performance.)
Previous GRDC-supported research found that brome grass competing early in wheat at a density of 100 plants per square metre can reduce yields by as much as 30 to 50 per cent.
Loxton, South Australia, grower Robin Schaefer says break crops have considerably improved his management of grass weeds on a new property bought by the family, while pulse crops in particular have led to a clear lift in productivity overall.
While on a steep learning curve initially, gross margins from pulses – including chickpeas, field peas, lentils and lupins – were by 2015 markedly better than those from cereals.
He says the key has been “getting the agronomy right” – the soil type and the timing of sowing, chemical applications and harvesting.
In addition to their own performance, Robin says pulses have driven up gross margins in cereals: “We’ve seen significant yield improvements from cereals planted on pulse stubble.”
For James and Robert Stephens, who farm in a low-rainfall zone between Bowhill and Mannum, about 140 kilometres east of Adelaide, controlling brome grass was one of the main motivations for introducing break crops about five years ago.
This year they planted half their farm to break crops – lupins, field peas, vetch and, for the first time, lentils.
James Stephens says the decision was made in order to better control weeds, extend the chemistry available for control and to boost soil nitrogen levels.
“So, with our agronomist, we were keen to look at the big picture and that meant including more pulse crops in our sequences. We now aim to have 30 per cent of the cropping area under pulses each year, and we also know that one year of break crops is not enough.”
This echoes MSF findings, with Mr Moodie saying that in his Mildura trials four out of the five top performers incorporated a two-year break.
“Break crops provide more and different options for growers to work with, such as different herbicides and even different end-uses such as brown manure or grazing. It’s this diversity that is important.”
Crop diversity continues to be a focus of his research and in trials funded by the South Australian Grain Industry Trust (SAGIT) he is aiming to compare the production potential and yield stability of a wide range of break crops across key soil types in the Mallee.
“We are also undertaking trials which establish the effectiveness of alternative weed-control strategies, such as harvest weed-seed control. This information is being employed by local growers and agronomists to use tools such as the Land Use Sequence Optimiser model to identify long-term rotations that successfully manage weeds and improve profitability.”
And now, when he drives across the Mallee, he enjoys seeing the diversity of crops grown (Figure 2). “Five years ago it was over 95 per cent cereals. Now there’s wide-ranging plantings of field peas, and vetch – for manuring, hay or livestock. Here and there you can see chickpeas, lentils and lupins. Growers are really expanding their horizons, using a wider range of crops in their farming system which, as the trials show, is a really positive move not only for soil health and weed control but also profitability.”
Figure 2 South Australian legume crop plantings from 2010 to today.
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