Focus Paddocks show WA crop rotations are on the money
Author: Melissa Williams | Date: 23 Mar 2015
Use of canola at the expense of legumes as the major cereal break in WA crop rotations has not hampered wheat productivity in a five-year study of 184 paddocks.
The oilseed is helping to keep the soilborne diseases rhizoctonia bare-patch and fusarium crown rot in check, but is having a negative impact on Root Lesion Nematodes (RLN) levels.
These are major findings from the State’s Focus Paddock project for the cropping seasons 2010 to 2014.
This GRDC-funded Department of Agriculture and Food (DAFWA) research is assessing the productivity of long-term crop and pasture sequences in 184 Focus Paddocks from Yuna in the north to the south coast.
Reflecting changes in WA farming systems, the cropped area in monitored paddocks is increasing and there is a big shift away from grain legumes to canola as the break crop of choice in all regions.
Despite this, DAFWA’s researchers found the Focus Paddocks were maintained in good condition to grow wheat – which is by far the main game.
But changes were identified in paddock biology – including soil pathogens, pasture productivity and nitrogen (N) levels – and these should be considered in long-term paddock planning.
Weed control was generally found to be sufficient to support wheat-dominant cropping systems and soilborne disease levels appeared to be under control, although RLN incidence was increasing.
DAFWA economist James Hagan told the March West Midlands Group GRDC-DAFWA Regional Crop Update that 90 per cent of Focus Paddocks achieved gross margins (GM) of between $100 and $600 per hectare in the period 2010-14. The average was $235/ha/year (see Table 1).
Highlights of DAFWA’s Focus Paddock economic analysis for 2010-14 include:
- Three years of cereals-one year of canola was the most popular and profitable rotation across the State with an average GM of $360/ha
- Continuous cereals for four years produced an average GM of $280/ha in all regions, but were more common in the north (which did not have as good a result 2013 as southern parts of the state)
- In the northern region, two years of cereals-one year of lupins-one year of canola had an average GM of $280/ha
- Rotations with two years of canola and two years of cereals (W-C-W-C) were popular in the southern agricultural region and had an average GM of $340/ha
- Three years of cereals-one year of pasture had a GM of $280/ha in central and southern areas
- Two years of cereals-two years of pastures had a GM of $240/ha in southern areas.
High wheat and canola prices during the past five years underpinned the dominance of wheat-canola rotations and this was at the expense of pastures and sheep.
James says in years where there are excellent cropping results, such as 2013, it would be expected that gross margins for rotations that include pastures would be lower than crop-based results due to the different abilities to scale-up production between cropping and livestock enterprises.
He says a sustained sheepmeat price of $5.50-$6.00/kg is needed to start swinging the pendulum back the other way.
On average, over four years, 75 per cent of Focus Paddocks had weed numbers below 20 plants/m2 and half had less than five plants/m2.
Canola was the stand out break crop for weed management and, in some cases, reduced burdens from 24 plants/m2 at three to four weeks after crop establishment to three plants/m2 at maximum biomass.
Herbicide resistant weeds were common. Testing of annual ryegrass (Lolium ridgidum) found populations in 90 per cent of Focus Paddocks survived application of one herbicide mode of action, 64 per cent survived two modes of action and 4 per cent survived three modes of action.
DAFWA research officer Martin Harries says about 90 per cent of Focus Paddocks had no - or low - levels of soilborne diseases based on visual scores and these had remained relatively constant from 2010-14.
Detections of RLN - using the pre-seeding DNA soil assay PreDictaB® test - did increase during the four-year period, which DAFWA researchers say could be a future threat to canola’s dominance as the preferred WA break crop.
Martin says crop sequences will need to be planned carefully to avoid a build-up of RLN numbers, especially for Pratylenchus neglectus.
Canola is a host for this nematode and has replaced non-hosts, such as lupins and field peas, in the rotation.
But for rhizoctonia (Rhizoctonia solani (AG8)), Martin says research shows canola is the only species to give suppression of this pathogen – both in soil inoculum and disease levels during the growing season.
Canola is also a good option where there is high risk of crown rot in 2015.
PreDictaB® can help to identify crown rot and other soilborne diseases prior to seeding.
It is accessed via agronomists accredited by the SA Research and Development Institute (SARDI) to interpret the results and provide advice about management options to reduce the risk of yield loss.
PreDicta B® samples are processed weekly from February to mid-May (less frequently at other times of the year).
To date this season, SARDI is observing a much larger proportion of PreDicta B® paddock samples with medium to high crown rot risk.
This trend is reflected in the Focus Paddocks, which have had an increased incidence of crown rot detections from PreDictaB® testing in recent years across all regions.
DAFWA researchers say this highlights the importance of sowing wheat varieties with the best available resistance ratings in WA (check the 2015 Wheat Variety Guide) or using barley or canola in high risk areas.
Other management tactics to reduce the impact of crown rot include:
- Inter-row sowing to separate new cereal crops from standing cereal stubble
- Planting crops at the start of the sowing window for the variety selected (reducing potential moisture and heat stress later in the season)
- Matching fertiliser and seeding rate to season potential
- Considering the newly registered fungicide seed dressing for crown rot suppression.
Increased reliance on canola in the crop rotation will also require monitoring of diseases such as sclerotinia stem rot in coming years, as the Focus Paddocks project has identified this as a potential future weakness in WA farming system agronomy.
The Focus Paddock research found expansion of canola plantings across WA meant this crop was now being sown in areas with sub-optimal pHca levels, posing risks of yield loss due to aluminium (Al) and manganese (Mn) toxicity.
WA’s first case of Mn toxicity was discovered in canola in 2014 and typical symptoms to look for during this growing season are a yellowing rim around the leaf, followed by spotting around the edge of the leaf and yellowing between the veins.
A guideline for suitability of sowing canola is that pHca should be above 5.5 in the topsoil (0-10cm) and above pHca 4.8 in the subsoil (below 10cm).
GRDC is funding a range of projects investigating ways to manage acidity and identifying varieties with better tolerance to Al.
Martin says soil nutrient levels, such as for phosphorus (P), were at or above levels required in the vast majority of Focus Paddocks in 2010-14.
Soil profile N was high across the sites and, as expected, the amount of fallow season rainfall had a big impact on levels at seeding.
On average, soil inorganic N at a subsoil depth of 90cm prior to sowing ranged from 41 to 127kgN/ha across the period 2010-14 and was highest after seasons that had good summer/fallow rainfall.
There was an increased N response (up to 14kgN/ha in some years) where legumes were grown the previous year, but this was hit and miss across regions.
The Focus Paddock research is part of the GRDC-DAFWA Putting the Focus on Profitable Crop and Pasture Sequences in WA project and involves a collaborative effort with the WA grower groups: Liebe Group, Facey Group, WA No Tillage Farmers Association and Mingenew Irwin Group.
Monitoring of Focus Paddocks will continue during seeding this year and the project finishes in mid-2015.
2015 Agribusiness and Regional Crop Updates reports from this project are available at the GIWA website.
Martin Harries, DAFWA
08 9956 8553
Melissa Williams, Cox Inall Communications
0428 884 414
- 2014 Agribusiness Crop Updates and Regional Crop Updates
- DAFWA AGWEST Plant Laboratories
- DAFWA root disease and testing service information
- 2015 Wheat Variety Guide
GRDC Project Code DAW00213