SARDI researcher Nigel Wilhelm has found that break crops can increase profitability in low rainfall farming systems. Source: Nigel Wilhelm
A major GRDC-funded project has assessed the profitability of many different break options in five different low rainfall sites across southern Australia over the last four years.
Low Rainfall Crop Sequencing Project leader Nigel Wilhelm says a common finding across all trial sites is that incorporating break crops provided a more profitable outcome over four years than continuous wheat.
The project ran trials from 2011 to 2014 at Condobolin, NSW with Central West Farming Systems; Chinkapook, Vic, with Birchip Cropping Group; Mildura, Vic, 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.
Dr Wilhelm, who is a research scientist at the South Australian Research and Development Institute (SARDI) the research arm of PIRSA, said the break options were selected based on the local region.
“Some breaks we used at every site, including canola, peas, pasture, fallow, and some were tailored to the location, for example at the Central West trial we planted lupins (both narrow leafed and white), which growers use in that region. We also used some crops in different ways, for instance peas were either cut for hay or harvested, to check the different profitability outcomes,” he said.
The key agronomic outcome from the trials was that the break crops had a ‘spectacular’ impact on subsequent cereal performance.
“We chose sites which had a long history of cereals. Many growers in the low rainfall zone are reluctant to stray away from wheat, which was served them so well in the past, and so it is fairly common for paddocks to have this long history of cereals,” Dr Wilhelm said.
“What we found was that a break crop brought a completely new lease of life to these ‘tired’ paddocks, with the yield in the first year of cereals up to 1t/ha higher than the continuous wheat control plot.”
Dr Wilhelm suggests the major reason growers should consider a break crop is for the benefit it delivers in following wheat yields.
Figure 1 shows the benefit in yield from a one or two year break in the first and second years of wheat following a break, incorporating the average of all break options.
“After a one year-break, there was a median increase of around 0.25t/ha, and that benefit flowed through into the second year with a 0.1t/ha benefit compared to the control. The real winner though was after a two-year break where the median benefit was 0.75t/ha, and in 25 percent of cases, the benefit was over 1t/ha. The second year wasn’t quite so dramatic, but there was still a 0.2t/ha improvement,” he said.
The cumulative benefit of a two-year break over two years of wheat was on average 1.2t/ha, compared to growing continuous wheat. This benefit is in addition to any profit obtained from growing the break crop.
Figure 1: Benefit of break options on subsequent wheat yields across experiments at four locations in the low rainfall zone of south-eastern Australia, compared to continuous wheat. The plot displays the median (—), 25th to 75th percentiles (n), 10th (┴) and 90th (┬) percentiles and the <10th and > 90th percentiles (◌). The median is the middle value in the range of outcomes. Source: Nigel Wilhelm.
Breaks as a cash crop
One key finding from the trials was the effectiveness of some break options as a cash-crop.
“A finding that we believe would surprise a lot of growers was that some of the break options were not much more expensive to grow than a wheat crop. Where wheat has been grown continuously, the cost of maintaining yield has been gradually increasing due to higher fertiliser rates and herbicides. Combined with improved management practices around break crops, this meant that despite perceptions that breaks are expensive, there wasn’t necessarily much difference in cost,” Dr Wilhelm said.
Changes to management practices include recommendations for reduced sowing rate in many break crops compared to guidelines in higher rainfall areas. For example, seed for hybrid Clearfield canola varieties can cost up to $80/ha when sown at rates suitable for higher rainfall, and as such reducing sowing rates to a rate more suitable to the LRZ can significantly reduce costs, especially if combined with retained seed from open pollinated varieties. Growers are advised to see their local agronomist for the most up-to-date agronomic recommendations for particular crops in their region.
“The performance of some of the break crops was also better than a lot of the local growers expected. For instance peas occasionally yielding almost as much as the wheat, because of the low baseline wheat performance as well as new pea varieties having improved adaption to the lower rainfall environments,” he said.
The research team has put together gross margin outcomes for each of the scenarios tested. At all sites, there was always at least one break option which increased the overall gross margin over four years. In some cases two year breaks were even more profitable.
The study found that providing at least one of the break years resulted in a profit then the overall outcome of a two-year break could be more profitable than wheat alone. For example, a failed canola crop, followed by a profitable pea crop and then two years of wheat was more profitable than four years of wheat.
“This is fantastic news for growers. It is a mitigating factor to some of the risks of break crops,” Dr Wilhelm said.
“For instance, canola had some real challenges in 2014. However, growers who put in a canola crop last year, and who get a profitable break this year, could still better off in the long run than if they’d stuck with wheat over the last two years.”
The analyses conducted in the trial do not include the costs of development of herbicide and pesticide resistance. It’s well understood that use of the same modes of action year after year lead to selection for resistance, so a further significant benefit of break crops, which cannot be easily quantified, is the opportunity to rotate chemicals and open up new options for weed and insect control, which will delay the onset of resistance.
Break crop choice
Trial plots at Minnipa in 2012 comparing a range of break options compared to wheat. Source: Nigel Wilhelm
After studying 15 different break options, what was Dr Wilhelm’s advice in selecting a break type?
“The key is to choose a break that will address the cause of a tired paddock. In many low rainfall environments, grassy weeds are a key cause of declining wheat yields. In this case, we found canola had a strong effect on the weed seedbank for multiple years, because not only can grass selective herbicides be used, canola also competes very strongly with any escape weeds from grass control operations. However vetch tends to be a poor competitor early in the season and a few grassy seed escapes can still set a lot of seed,” he said.
Where nutrients are the limiting factor, canola is less likely to be beneficial compared to crops such as pulses, which fix their own N from the atmosphere and can build soil reserves.
The options available after a crop has been planted are also a consideration.
“Seasonal conditions are always a risk factor. If a grower chooses a crop that can be cut for hay or harvested for grain, this might reduce the risk level. For instance if a grower plants peas they can choose to go through for grain, or else if the season turns dry and its unlikely to get through to a strong yield, they can cut it for hay and still make a reasonable return,” Dr Wilhelm said.
The low rainfall zone crop sequencing project has been extended by one year for 2015 so that the effect of break crops on wheat yield can be assessed three years following the break.
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