Latest agronomic information from recent research into
managing non-wetting soils in Southern Western Australia.
Glenn McDonald (DAFWA, Albany), Stephen Davies (DAFWA, Geraldton).
Key messages:
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Use of a mouldboard plough or modified one-way plough continues to provide higher
yields than other amelioration options when addressing non-wetting soils.
Yield responses to wetting agents are uncertain and depend on the products suitability
to the soil types, application method, crop rotation and season. Therefore products
should be evaluated for efficacy with test strips before wide scale application.
For severely non-wetting soils, where wetting agents have been shown to work,
positive responses have been observed in “wet” starts to the season, such as 2016.
The profitability of management options has not yet been assessed with these results
and the cost of these options should be determined by individual businesses.
Introduction:
Non-wetting soils, or water repellent soils, are a significant problem in farming rotations
throughout Western Australia. Non-wetting soils (NWS) can cause significant reductions in
plant establishment and crop vigour leading to reduced yield. Alleviating the effects of NWS
can be achieved through either applying clay, burying the repellent soil and bringing deeper
wettable soil to the surface, or the application of liquid wetting agents and other products.
None of these options for addressing NWS are without risks and in order to provide better
information to the farm businesses, the research in this paper has focussed on ploughing
methods, the use of wetting agents and the comparison between these options.
Method:
A series of ongoing trials was established in 2015 and 2016 on various gravel soil types in
Southern Western Australia. Treatments ranged from mouldboard plough, one-way plough,
clay and lime applications, wetting agent products, and wetting agent application methods.
Many of these trials are designed to cover more than one season and therefore cover several
crop rotations. These trials were sown in small plots and any wetting agent treatments were
applied at the time of seeding. Any tillage or ameliorant treatments were applied before
seeding. A selection of the results is outlined in this paper.
Results and Discussion
Kojonup agronomy trial
For both 2015 (barley) and 2016 (canola) mouldboard plough (MBP) treatments resulted in
higher yields than any of the wetting agent treatment. This yield advantage was more than 0.5
t/ha for the barley and more than 0.2 t/ha for canola. The one-way plough (OWP) treatment
also had higher yields but these were not as high as using the MBP. At this site the
application of pre-emergent herbicides after both plough treatments caused a small but
insignificant reduction in barley yields in 2015, and had no effect on the canola yield in 2016.
The application of wetting agents had a positive effect on barley yield in 2015 compared to
the untreated control, but during the 2016 season there was no consistent effect on the canola
yield. This is not surprising given the reduced moisture stress in 2016 during crop
establishment and the potential for canola to compensate for a reduction in plant
establishment.
Darkan wetting agent placement trial
The in-furrow placement of wetters at Darkan in 2016 resulted in 0.2 t/ha yield increase for
one product tested above the corresponding on-furrow treatment and the untreated control.
For the other product tested, there was no difference in yield between the placement methods
or the control.
Darkan agronomy trial
During the 2016 season there was no clear yield advantage of using any of the five wetting
agent products tested compared to the control treatment. All wetting agents were applied
either in-furrow or on-furrow. In some cases, there was a significant yield reduction from
using the wetting agent compared to the control, but not all products are recommended for
using with both application methods tested.
All of these wetter treatments were also applied over largescale MBP treated areas. At this
site in 2016 there was little effect of MBP on yield. Although one product applied at a higher
rate had a significantly higher yield of more than 0.5 t/ha when applied over the MBP area
compared to the unploughed area or the untreated control.
Field observations (2016)
It was observed in the bulk sown paddock of barley surrounding one set of trials south of
Kojonup that even with a more favourable start to the season in 2016, where a wetting agent
was not used when finishing seeding the paddock, there was inconsistent growth and uneven
crop development. The soil in this paddock is severely non-wetting and has been shown to
respond to applications of wetting agents in previous years. It was a surprise to both the
grower and the research team that there was such a visual response to the applied wetting
agent. It is estimated at tillering, up to 20% of the area that didn’t receive any wetting agent
application was either bare or had significantly less vigour.
This is a good illustration of the value of conducting test strips or wetting agent evaluations
on farm. For this grower, it has highlighted that the wetting agents work for them and that he
can probably alter his application rate to suit the season. That is, when favourable sowing
conditions, use a lower rate than if conditions are less favourable.
Conclusion:
The use of strategic tillage to address NWS, such as mouldboard plough, or modified oneway plough, continues to show positive yield results. This is consistent with research
conducted in the Northern cropping areas.
Results to date indicate that some wetting agent products are more effective when applied
using a particular method, and some products can be applied using any method. This ongoing
research will help growers to understand the implications of using different application
methods.
It is known that wetting agents do help address NWS but predicting the efficacy of wetting
agents in different soils is very difficult. Results from research trials are complex and
sometimes contradictory. In order to determine the suitability of any product, individual
growers should conduct their own product test strips.
Research into other agronomic management decisions to address NWS is ongoing. This
includes how long wetting agents are active in the soil, interactions of herbicide efficacy with
tillage and effects of product placement.
Acknowledgments:
The project wished to thank the grower hosts that support the research trials; Jono Clifton,
Justin Elliot, Tim Harrington, Ben Sprigg, Kim Oliver.
Also thankyou to Walco Lime for providing lime with short notice for the research trials.
References
GRDC Project Number: DAW00244
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