Wheat yields were generally higher following a range of break crops in Grains Research and Development Corporation (GRDC) funded trials in the higher rainfall area of Katanning.
But continuous wheat treatments were still more profitable than nearly all the other sequences, except those containing oaten hay.
The trials were initiated and conducted by the Department of Agriculture and Food (DAFWA).
Katanning-based DAFWA research officer Raj Malik said the GRDC supported ‘Dynamic Crop Sequence trials’ were in their fourth year at Katanning and in their third year at Wongan Hills.
The Katanning trial had 200 treatments in 2011 and the Wongan Hills trial 100.
Dr Malik said that in 2010 - the third year of the trial at Katanning - wheat was sown over all the plots.
“Lupin grown as a 2009 break crop increased 2010 wheat yields significantly above wheat following wheat – the wheat yield after lupins was 26 and 28 per cent higher than after wheat with and without the fungicide treatment,” he said.
Dr Malik said another important finding from the Katanning trial was that, in most rotations, wheat treated with the fluquinconazole fungicide Jockey® – an effective seed treatment – consistently outyielded wheat treated with the conventional seed treatment flutriafol fungicide Vincit®.
He said that although the wheat yields were higher after lupins, the most profitable three-year crop sequences all included wheat and oaten hay in either 2009 or 2008.
“Continuous wheat had a higher gross margin over three years than all other sequences except those containing oaten hay,” Dr Malik said.
He said weeds had been a relatively minor issue at the Katanning site prior to the fourth year of continuous wheat in 2011 when weeds including brome grass and barley grass increased to high levels.
Dr Malik said seasonal conditions meant that disease levels, which might normally constrain yields in continuous cereal rotations, had been relatively low during the trials.
He said the Katanning trial results indicated that growers looking at building soil quality and sustainability should consider using break crops such as lupins.
“But if they are looking just at the short term financial returns, they can look at continuous wheat treatments, or sequences including wheat and oaten hay,” Dr Malik said.
“However, in the long run these continuous cereal sequences may not be sustainable – for example, weeds have been shown to be a problem in the Katanning plots where four years of continuous wheat was grown.”
At the Wongan Hills site, researchers were this year seeing quite big crop growth responses to crop rotations where lupins or serradella was grown two years ago in 2009.
DAFWA senior research officer Bob French said that due to dry conditions in 2010, fallow in 2009 produced large growth responses in 2010.
“But in 2011 there were also big growth responses to fallow in 2010, despite it being a much better rainfall season,” he said.
“This is likely to be due to improved nitrogen nutrition since we measured very high levels of mineral nitrogen in plots after fallow in 2010.”
Dr French said trials at the Wongan Hills site had also revealed that a ryegrass blowout in one year took at least two years to fix.
“However, it is possible to reduce ryegrass numbers to very low levels using fallow; cutting hay; crop topping lupins; or burying weed seed by mouldboard ploughing before seeding,” he said.
Dr French said researchers had found very low levels of cereal root disease at the Wongan Hills trial site since the research began.
“However, while leaf disease – mainly septoria – levels were low in 2010, there are obvious differences between treatments in 2011,” he said.
“Wheat following broadleaf crops or fallow have the lowest levels of leaf disease.”
DAFWA senior research officer Mark Seymour said work was under way to provide the Katanning and Wongan Hills trial results in a user-friendly, online format which would allow growers to readily compare the yield and gross margin returns from crop rotations they were interested in.