HRZ trials investigate new yield-lift tactics
GroundCover™ Issue: 112 | Author: Nicole Baxter
Subsoil manuring and early sowing are showing potential as tactics for improving crop production in south-eastern Australia’s high-rainfall zone.
Research in the high-rainfall zone (HRZ) has revealed two management options that have demonstrated measurable benefits for growers keen to improve their crop production.
Projects coordinator with the Victorian grower group Southern Farming Systems (SFS) Annieka Paridaen says there have been plenty of lessons learnt using subsoil manuring and early sowing in the past eight years.
“We’ve learnt a lot by digging holes to look at the subsoil and in large parts of the HRZ we’ve found dense sodic clay subsoils packed so tightly there is little space for air or water movement,” Ms Paridaen says.
Sodic soils (high in exchangeable sodium) are considered hostile to crop growth because they have a macroporosity of less than 10 per cent, which prevents roots from penetrating the subsoil in search of nutrients and moisture.
Crops grown on these soils typically fail to yield well in dry springs because root growth is restricted to a shallow band of topsoil. In wet winters, crops may also die from lack of oxygen or waterlogging because of slow moisture flow through the soil.
While amelioration works initially focused on raised-bed cropping to increase the depth of soil in which roots could grow, Ms Paridaen says attention turned to subsoil manuring when growers started asking if something could be done to improve their base soils.
In 2005, researchers from La Trobe University and the Victorian Department of Primary Industries (now the Victorian Department of Environment and Primary Industries) teamed up with John Sheehan of ‘Yalock Estate’, near Ballan, half way between Melbourne and Ballarat in Victoria.
Ms Paridaen says the trial used a modified deep-ripper to incorporate a range of different ameliorants into twin riplines 80 centimetres apart.
After three years of trials, a 55 to 60 per cent increase in yield was recorded over the control each year where 20 tonnes per hectare of lucerne pellets or 20t/ha of Dynamic Lifter® were incorporated to a depth of 40cm.
In 2009, with GRDC support, the trials were extended to other locations in Victoria and the best responses were measured after incorporation of 20t/ha of poultry manure.
Ms Paridaen says the addition of poultry manure appears to increase the water-holding capacity of the soil, which delays crop senescence (death) in spring, allowing crops to access more moisture during grain fill.
However, she encourages growers to carry out deep soil tests to determine the depth of the sodic subsoil clay layer and ensure deep-ripping is done carefully to avoid bringing sodic soil to the surface.
Ms Paridaen says a lesson learnt from the research is that although subsoil constraints are costly to crop productivity, they are also costly to rectify.
She says researchers have estimated the cost of treatment at between $800 and $1200/ha, depending on transport, application and manure costs.
Nonetheless, Ms Paridaen says researchers are still seeing yield benefits six years after the first trials were done.
To determine if a less costly approach could be used to ameliorate the sodic subsoils, SFS initiated a further trial as part of the GRDC’s National Water Use Efficiency Initiative.
The small plot-trial tested a range of treatments including:
- no-till with artificial nutrients;
- deep-ripping with artificial nutrients;
- deep-ripping with deep manuring;
- deep-ripping with surface manuring; and
- mouldboard ploughing plus manuring.
To date, the no-till plus artificial nutrients and the mouldboard plough plus manure treatment have shown the best results (Table 1). However, Ms Paridaen hopes to continue the research in large-scale replicated trials to test the longevity of yield response over subsequent years.
Meanwhile, other GRDC-supported research by CSIRO and SFS has been evaluating early sowing as a tactic growers can use to improve crop water use and yields.
Ms Paridaen says modelling by CSIRO’s Dr James Hunt shows that optimal sowing dates are earlier than those currently used by many growers in the HRZ.
“We’re only starting to realise that we may be selling some of our wheat varieties short by not appreciating their different characteristics and missing an opportunity to increase our crop yields when the break comes early or on time,” she says.
“Perhaps we can think outside the square and spread our production risk by diversifying our wheat varieties based on their maturity, and sow early if it rains in late March.”
To test the concept, SFS initiated a trial in 2012 with Dr Hunt to test four wheat varieties – Forrest, Bolac, Derrimut and LongReach Lincoln – all with different maturities.
Ms Paridaen says the research team used time-of-sowing and modelling to calculate the optimum sowing dates for two different locations to ensure the different wheat varieties flowered in the correct window (Table 2).
At Westmere, Victoria, in 2012, the sowing dates for all varieties were 17 April, 27 April, 8 May and 17 May, while at Inverleigh, Victoria, the sowing dates were 1 May, 11 May and 27 May.
|Maturity group||Variety||Sowing date||Anthesis date||Sowing date||Anthesis date|
|Very slow||Forrest||18 April||24 October||1 May||14 October|
|Slow||Bolac||27 April||13 October||11 May||11 October|
|Mid||Derrimut||9 May||13 October||11 May||13 October|
|Fast||LongReach Lincoln||18 May||18 October||28 May||13 October|
|1 At growth stage Z65 or when 50 per cent of ears had flowered.
SOURCE: Annieka Paridaen, GRDC National Water Use Efficiency Initiative meeting, June 2013
Later that year, at the SFS AgriFocus field day on 18 October, Ms Paridaen asked growers to guess the wheat variety that would yield the highest at harvest.
Ms Paridaen recalls that many growers picked Forrest to produce the most grain because it “looked amazing”, with plenty of biomass and long heads.
But it was a case of all show and no substance when the season turned dry from that point, with no rain until the end of November.
When the harvest results were analysed, Ms Paridaen says there were plenty of lessons learnt (Figures 1 and 2).
At Westmere, when the treatments were sown dry on 17 April, establishment was compromised when the sowing rig passed through the soil and pulled up large clods that were thrown back over the seeds.
“We made sure we gave the other treatments a tickle before sowing to improve the tilth,” she recalls. “We also had a few issues with Septoria tritici the first time of sowing.”
At Inverleigh, the early-sown Bolac yielded the best, with Derrimut performing a close second. By contrast, Forrest – the pick of many of the growers at the AgriFocus field day – failed to survive the dry finish.
After looking specifically at the performance of Bolac at Westmere (and discounting the first time of sowing because of the establishment problems), Ms Paridaen says she calculated a nine per cent difference in yield when the variety was sown on 27 April, its optimum sowing date, compared with the fourth time of sowing on 11 May.
“The best thing about this development of growing wheat in the HRZ is that it is achievable,” she says. “You don’t need the latest equipment, you don’t need to spend heaps of money, you have the tools already; you just need to be prepared.”
Dr Hunt also believes early sowing has huge potential in the HRZ because it helps growers to overcome constraints such as waterlogging and damage by invertebrate pests as well as lifting yield potential.
After testing the concept in 2012, SFS, CSIRO and the Foundation for Arable Research (FAR) Australia established a larger experiment at Inverleigh in 2013 as part of a new GRDC project investigating early sowing.
Constrained by the dry autumn in 2013, the researchers used 15 millimetres of irrigation applied to press-wheel furrows to establish seed at each time of sowing.
Dr Hunt says winter and spring were favourable at the site (the water-limited yield potential was 8.2t/ha) and Yield Prophet® was used to match nitrogen inputs to yield potential (with 300 kilograms/ha of nitrogen applied in total). Although the trial was planted on pea-hay stubble, significant take-all was observed within the treatments. S. tritici was also present despite in-furrow flutriafol treatment and three foliar applications of fungicide.
Even with the disease pressure, Dr Hunt says the yield results were exceptional, with the highest yields (more than 9t/ha) coming from the slow-maturing red wheat variety SQP Revenue, with its winter growth habit, and LongReach Beaufort, a slow-maturing spring wheat sown at the end of April (Table 3).
He says defoliating SQP Revenue at GS30 (to simulate grazing) increased the yield so much that it out-yielded LongReach Beaufort (Table 4).
“There is some evidence that this could have been related to the effect that grazing had on the severity of S. tritici,” he says.
Of the milling wheats, Forrest was the highest yielding, particularly at the early sowing dates.
Preparation the key
From two years of results, both Ms Paridaen and Dr Hunt say that careful preparation is the key to taking advantage of early sowing opportunities.
If sowing dry, Ms Paridaen encourages growers to try to sow into a carefully prepared seedbed to ensure effective establishment when rain does arrive.
“Paddocks earmarked for early sowing also need to be weed and disease-free,” Dr Hunt adds. “A double break, such as a pulse crop or a pasture hay crop followed by a canola crop, is an ideal set-up for early sown wheat in the HRZ.”
He also suggests deferring nitrogen until GS30 to avoid excessive early growth unless grazing. “If initial soil nitrogen levels are high, use low sowing rates,” he says.
Ms Paridaen says growers keen to adjust their sowing dates also need to remember to change the timing of fungicide sprays.
“You can’t expect a crop to yield well if there’s no green leaf left,” she says. “That’s what happened to our early-sown LongReach Lincoln wheat in 2012.”
What about frost?
Understandably, plenty of eyebrows are being raised in the HRZ when early sowing is discussed, with frost the chief concern.
Dr Hunt says one lesson learnt from the black frost of 18 October 2013 was that delaying sowing (or flowering) was not an effective way to manage frost risk: “All varieties in our trials at Temora, New South Wales, suffered about 60 per cent frost damage, but the varieties that flowered on time (or early) yielded the most,” he says.
Dr Hunt says that knowing the optimal flowering period and how to achieve it from different sowing dates, with a range of varieties for the appropriate environment, can allow early sowing opportunities to be taken as they arise.
He suggests keeping two to three varieties (one winter and one or two spring wheats) so a wheat crop can be sown any time over a three-month period (Table 5).
“Some tactical thinking is required, but the potential yield benefits far outweigh the logistical hassles.”
0439 339 433
Dr James Hunt
02 6246 5066
Watch GCTV episode ‘Subsoil manuring’s positive impact on crop yields’ or visit www.grdc.com.au/GCTV12-SubsoilManure to watch the episode on YouTube
GRDC Project Code CSP00111, CSP00178
Region South, North