A field day inspecting various break options at Minnipa in 2012. 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.
Minnipa, in the north of the Eyre Peninsula, was one of the five sites selected for the trial. With 324mm annual rainfall and sandy loam over light clay, the average yield of wheat at the site is historically around 1.7t/ha.
Prior to the trials, at least five consecutive seasons of wheat had been grown, with key challenges developing in control of the grassy weeds barley grass, brome grass and annual ryegrass, as well as high levels of rhizoctonia inoculum levels.
Seasons 2011 and 2012 were mostly sown to breaks, with the exception of the one-year break plots which were sown to a break in 2011 but back to wheat in 2012. These two years, particularly 2011, were mild, with relatively high rainfall.
“The results were strong from the break years at Minnipa,” Dr Wilhelm said. “In particular, a medic pasture grew 3-4 tonnes of dry matter per hectare, which was great. Because we had a control plot of continuous wheat, it didn’t matter to the results of the trial that the break years were good, as the control plot had a couple of good years too.”
The effect of the first two years’ crop choice on the third year wheat performance is shown in Figure 1. The wheat yield (depicted as grey bars) was lowest for the control (wheat/wheat) option, with grazing options giving the highest yields. Grassy weed control followed a similar trend, though it should be noted that while a one year vetch hay break appeared to give strong weed control (third point from the right), this effect was short lived, and did not persist into 2014.
Figure 1: 2013 wheat yields (grey bars, t/ha) and grass weed counts (black line, plants/m2) taken 20 August 2013 following treatments imposed in 2011 and 2012. Source: Nigel Wilhelm
Rhizoctonia levels were similarly beneficially affected by break crops.
“In 2013 roots were collected and scored for rhizoctonia wheat root damage. The continuous cereal treatments had significantly higher root disease incidence compared to all other treatments. At these levels nutrient uptake can be reduced and could help explain the poor yields recorded in these treatments,” Dr Wilhelm said.
In terms of profitability over four years, the most profitable sequences were two years of fallow and two years of wheat, or canola cut for hay, peas harvested for grain and two years of wheat.
Nigel Wilhelm, 08 8303 9353, firstname.lastname@example.org
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Break crops deliver profit in low rainfall regions
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