A multi-million-dollar suite of projects investigating innovative solutions to Western Australia's challenging and yield-limiting soils is coming to a close after five years of intensive research.
The Soil Constraints West project, co-invested by GRDC and the Department of Primary Industries and Regional Development (DPIRD), has been a ground-breaking initiative - searching for strategies to combat WA's four main soil constraints of:
- Water repellence
A series of GRDC videos delve into some of the key findings and tactics stemming from research undertaken in these projects and that are being successfully used on-farm.
Soil Constraints West project manager and DPIRD soil science and crop nutrition portfolio manager, Chris Gazey, believes the initiative could prove to be one of the most significant industry investments in recent decades, providing growers with multi-pronged tactics to tackle soil constraints.
Mr Gazey says with the introduction and subsequent almost-total uptake of no-till farming practices over the past 25 years, soil constraints, particularly compaction and water repellency, have been increasing in their severity, impacting significantly on grain yields over the past decade.
He says the hit-and-miss research approach to managing soil constraints is now a thing of the past, with all aspects of the industry recognising the need for a coordinated campaign to manage all constraints.
"In many cases, soils will have more than one constraint and tackling individual constraints in isolation may not provide the most cost-effective or productive solution," Mr Gazey says.
"Under the overarching Soil Constraints West banner, the challenges of the four different soil constraints can be viewed as a total package, with solutions provided to growers as a whole, rather than in isolation."
Soil Constraints West was a $33 million investment in projects that will conclude in June 2019, with trials running across the state's wheatbelt.
Some of the many and varied outcomes have included a focus on inversion tillage, deep-ripping, lime incorporation, gypsum application, water harvesting and improved mapping of soil constraints and the development of decision tools.
Mr Gazey believes growers are now better equipped to understand how and why their soils are restricting plant growth and the focus on soil health, particularly through amelioration strategies, is no longer a foreign concept.
"Through this project, we have talked with hundreds of growers and advisers across the state, and there is now a new focus on re-engineering soils to remove constraints and work towards achieving yields that our soils can be capable of," he says.
While the Soil Constraints West project has ended, a new $48 million co-investment by GRDC and DPIRD will take soil health research to new levels.
Under three separate but coordinated banners, the new research will consider:
- The yield potential of WA soils where all constraints have been removed
- Preserving this potential using agronomic tools such as controlled-traffic farming and crop rotations
- Water harvesting strategies in heavy soils, particularly those in the eastern wheatbelt.
Part 1: Compaction
Research has shown that compaction affects all soil types, across all locations, impacting on plant growth and ultimately on yield. Economists estimate compacted soils are costing WA growers up to $54 per hectare in lost yield potential annually.
For some grain businesses, this could be the difference between making a profit or a loss in any given year.
DPIRD research officer Wayne Parker says after a decade of testing compaction levels throughout the WA wheatbelt, compaction levels are now deeper than even before.
In the past 10 years, he has seen an increase in compaction depths from 300 millimetres to 400mm and even 500mm below the surface.
"You can't ignore the physics," he says. "As machinery gets bigger and heavier, so too are the compaction layers going to get deeper and harder to fix."
"After analysing hundreds of paddocks across the grainbelt, we believe all soil types suffer from some level of compaction, and this compaction is getting deeper."
Trials established five years ago at seven different locations, across seven different soil types, have investigated the value of deep-ripping with and without topsoil inclusion.
The trials have been monitored over the past four years, assessing the longevity of the benefits from this deep-ripping.
Trials were run at Binnu (two trials), Moora, Beacon, Broomehill, Munglinup and Ongerup, on yellow sands, Morrell soil, duplex sand over clay, duplex sand over gravel and clay duplex.
As machinery gets bigger and heavier, so too are the compaction layers going to get deeper and harder to fix.
Mr Parker says while all soils suffer from compaction, sandy soils appear to be the most affected.
He says the only soils that can partially escape the damaging effects of compaction are those that can self-repair through swelling and shrinking across the seasons.
"These soils are the ones with very high levels of clay and we've only seen them in some parts of Queensland and northern NSW," he says.
"These self-repairing soils are not present anywhere in the WA grainbelt."
The research identified that almost all soils benefited from deep-ripping to break through the hardpan layer at depth and the value of deep-ripping continued for several years.
"The only site that didn't see a yield improvement from the deep-ripping was at Beacon in the Morrell red clay with a carbonate base, but we believe we disturbed some sodic soil at depth which restricted root growth in that soil," Mr Parker says.
All other trial sites showed varying levels of benefit from deep-ripping, with varying levels of yield improvements continuing over the five years.
- All soils in WA are likely to have some level of compaction, which restricts root growth and therefore impacts on yield.
- Testing soils for compaction and other soil constraints is important before any deep-ripping begins to ascertain what type and depth of amelioration is right for your soil type.
- Soil constraints can be tested using laboratory services and hardpan compaction can be tested using a push rod penetrometer. Penetrometers are available for purchase at most machinery dealerships or online.
- It is important to protect investments in soil amelioration through future farming practices, particularly the use of controlled-traffic farming (CTF) principles.
- The CTF calculator is now available to help growers shift to a CTF system.
Part 2: Water repellency
While growers and researchers have known about the problem of water repellency in sandy soils for many decades, it's only been in recent years that solutions have been developed to combat this major yield constraint.
Water repellency is caused by hydrophobic particles, such as waxes or oils from organic matter, coating soil particles and preventing water from entering the soil profile quickly and evenly.
Scientists have discovered sandy soils are more prone to water repellency because the soil particles have a smaller surface area than other soil types, allowing the waxes and oils to more readily coat the soil particles.
DPIRD senior research officer Dr Stephen Davies has led the Soil Constraints West Water Repellency project for the past five years, searching for solutions to reduce the impact of this increasing problem.
"Water repellency creates a whole host of problems; obviously the main one being poor crop establishment due to a lack of available moisture and nutrients in the soils," Dr Davies says.
"But following on from that, we have seen weed control becoming a problem because weeds also have staggered establishment resulting from a lack of available water, which makes them harder to control."
Then there are environmental problems such as ineffective water and nutrient use, wind and water erosion and waterlogging, with water running off hills and collecting in valley floors.
Dr Davies says a little over half, or 10 million hectares, of WA's wheatbelt soils are likely to show some level of water repellency.
He says the uptake of minimum-tillage farming practices has meant the hydrophobic organic particles are concentrated in the topsoil, which has seen a greater expression of the problem in recent years.
Dr Davies and his team divided the research into two main areas of focus.
"On one hand, we looked at mitigation strategies, that is, ways to get around the problem without solving it," he says.
Thirty trials were run across the wheatbelt, in the West Midlands region, the southern wheatbelt and along the south coast, looking at the use of banded wetters on crop establishment and yield.
A further 14 trials investigated the impact of paired-row or near-row sowing on both crop establishment and yield.
The second research focus was on soil amelioration strategies assessing the best ways to solve the problem in the longer term.
Dr Davies says researchers looked at range of different amelioration techniques on a number of different soil types, including:
- Deep soil mixing with spaders
- Inversion ploughing with mouldboard ploughs and one-way plough
- Clay spreading or delving.
He says more than 80 amelioration trials were run across grain growing areas, with 68 of those involving cereal crops.
Dr Davies says the paired-row and near-row sowing trials on sandy soils consistently saw a 50 per cent improvement in crop establishment, translating into 20 per cent increases in yield.
Banded wetters also achieved positive responses in forest gravel soils, with up to 15 per cent yield increases, translating to more than 400 kilograms per hectare in some trials.
"There are two ways of placing banded wetters on to the soil; by putting it behind the press wheel on to the furrow, or putting it through the liquid kits down under the soil near the seed," he says.
"Both techniques saw a consistent improvement in crop establishment and yield in these forest gravels, with no clear difference between either strategy."
In contrast, banded wetters were statistically ineffective on deep sandy soils.
Dr Davies says that in these trials there was a slight yield improvement when the wetter was used on cereal crops in a dry sowing environment, but in all other situations the wetters did not prove to be a reliable option for these soils.
In the soil amelioration trials, there was a range of mixed results, with different soil types responding differently to the various techniques.
We saw immediate yield increases, averages of around 50 per cent, from the deep soil mixing strategies in all sandy soils.
"One of our interesting results was in regard to the longevity of these amelioration strategies, where we saw immediate yield increases, averages of around 50 per cent, from the deep soil mixing strategies in all sandy soils," Dr Davies says.
"But, after about three years, these improvements dropped off significantly in the poorer pale deep sands to about 11 per cent.
"In the deeper yellow sands, these yield improvements, while also dropping, are still at around 33 per cent on average three to five years after the amelioration work has been done."
Dr Davies says another interesting finding was the benefit of additional deep-ripping after mouldboard ploughing or spading on all soil types.
"On average, this gave an additional 10 per cent (300kg/ha) yield increase across all soil types. On some sites, this increase was up to 900kg/ha," he says.
These amelioration trials were also run in forest gravel soils in the southern wheatbelt, where yield increases were, on average, about 20 per cent, lasting for over five years.
Separate trials are now suggesting that clay addition to the topsoil, either through spreading or delving, offers a near-permanent solution to water repellency
"This is a high-cost, long-term strategy, best suited to higher-rainfall environments where yield potentials are high and evaporation from the soil surface is low," Dr Davies says.
"The quality of clay subsoils vary and need to be tested. Some are quite fertile and can provide a significant addition of nutrients and improve the nutrient holding exchange capacity of the soil, while other subsoil clays are of lower quality and may have fewer advantages."
Dr Davies says clay addition to topsoil has the advantage of not only overcoming water repellency, but can also help bind and stabilise the surface soil, reducing wind erosion risk.
"Some growers have used an effective strategy of first ameliorating the soil with spading or inversion ploughing and then identifying those parts of the paddock which are still under-performing and add subsoil clay to further improve these," he says.
- Know your soil type and yield potential to know which strategy and level of investment will suit your business.
- Multiple strategies may be needed to combat water repellency and other associated constraints.
- Banded wetters did not prove a worthwhile strategy on sandy soils but were effective on forest gravels.
- Patchy establishment with inconsistent soil wetting, molarity of ethanol droplet (MED) or water droplet penetration time testing can be used to ascertain potential water repellency levels.
Part 3: Acidity
With soil acidity one of the major yield constraints for WA growers, solutions to address this ever-increasing challenge are critical for WA's grain industry, particularly in the central and eastern wheatbelt.
DPIRD research officer Dr Gaus Azam and his team have been working to understand soil acidity, its link to aluminium toxicity and the combined effect on plant root growth.
Dr Azam says soil acidity increases:
- when land is cleared
- when paddocks are continuously cropped, particularly with legumes in the system
- through the regular use of ammonium-based fertilisers.
He says when topsoil pH levels are below 5.5 (CaCl), there is limited improvement in the soil pH in deeper levels and subsurface acidity becomes an issue. When subsoil pH levels are below 4.8, aluminium becomes toxic to plant roots.
Aluminium becomes toxic to more sensitive canola and barley at levels of two to five milligrams/kg, and to most tolerant wheat above 5mg/kg.
In essence, excess toxic aluminium affects root cell division and deforms the root tips, arresting elongation of the roots and rendering them unable to extract water or nutrients from deeper in the soil.
"What we generally see with high aluminium levels in the subsurface is the plant shutting down as the roots reach eight to 15cm below the surface," Dr Azam says.
"This is less of an issue in wet seasons, where water is readily available, but in the drier years and areas with only medium to low-rainfall, a reduced root structure will place a plant under great stress, particularly towards the end of the season."
Eight trials in the central and eastern wheatbelt looked at lime applications on sandy soils with and without incorporation.
Dr Azam says many growers have continued to apply lime, without incorporating it, over many years but have not seen the immediate yield responses they had hoped for.
"Growers have hoped rain events would move lime through the soil profile, but we now know that lime can sit on the surface for many years without moving," he says.
"In fact, with the acidic soil pH levels which growers are now faced with, it is now our understanding that it will take decades for lime to move through the profile without intervention."
Growers have hoped rain events would move lime through the soil profile, but we now know that lime can sit on the surface for many years without moving.
Other research investigated various amelioration methods, in different soil types, to move the lime through to the subsoil to reduce acidity and remove the toxic aluminium.
Trials compared lime application without incorporation and with deep incorporation, one-way ploughing and spading.
A separate set of trials also investigated the interaction between lime and gypsum in these acidic soils.
"Some growers are not comfortable with cultivation of any means, and there is a belief that the addition of gypsum to the lime application will move the product through the soil profile much quicker, so we wanted to test that idea," Dr Azam says.
"Given that gypsum does not increase soil pH (it might slightly acidify some sandy soils if applied at higher rate), this was an interesting trial and something that needed close monitoring."
A trial in Wongan Hills, where a total of 8.5t/ha of lime was applied at the surface in three separate applications over 23 years, showed 40 per cent of the lime was still sitting on the topsoil at the end of this 23-year period.
The unincorporated lime allowed for a slight improvement in the subsoil pH levels, which translated to a wheat yield improvement in 2018 of 750kg/ha after the 23 years.
However, a 250kg/ha additional yield increase was achieved in just one season simply by incorporating the lime that had previously been applied.
Separate trials in Kalannie and Merredin, comparing different incorporation techniques, highlighted that shallow ploughing did not create any significant immediate yield response.
Dr Azam says the best results in these incorporation trials came from deep incorporation, at 250mm or deeper.
Results from the lime and gypsum combination trial at Kalannie showed up to a 30 per cent yield increase when both compounds were applied and incorporated.
Dr Azam says while gypsum can only be used on suitable soils, the trial demonstrated decreased effects of aluminium toxicity in the soil and an increase in the plant's ability to take up water and nutrients.
- If you farm in a low-rainfall area with sandy soils, it is likely your soil will have low pH and high aluminium levels.
- Soil testing is critical to determine soil buffering rates, which will determine lime application rates.
- Invest in lime applications with incorporation; however, be conscious of wind erosion at critical times of the year.
- Consider deep tillage incorporation methods over shallow tillage.
- An application rate of 1t/ha for gypsum is optimum for sandy soils but only in conjunction with a liming program.
Part 4: Sodicity
Found predominantly in heavy soils in lower-rainfall regions, sodicity restricts a plant's ability to access water, thereby reducing yield potential.
According to DPIRD senior research scientist David Hall, sodicity is the accumulation of sodium and salts within the soil profile.
Excessive sodium causes clay to disperse, clogging soil pores and restricting water infiltration, drainage and root growth, while the salts reduce water availability to crops.
While rising water tables as a result of land clearing have long been considered the main cause of salinity in WA soils, scientists are now also acknowledging the widespread impact of transient salinity, or cyclical salt in the soil, caused predominantly by the salts contained in normal rainfall events accumulating in the soil over many decades.
While sodicity can also be a problem in higher-rainfall areas, the biggest yield impacts are experienced in heavy clay soils in lower rainfall regions, particularly during low decile rainfall years.
"Sodicity causes soil structure decline and leads to the development of transient salinity over many years," Mr Hall says.
"Innovative solutions that stabilise these soils are required to ensure plant health in the long-term."
In the past five years, under the banner of the Soil Constraints West project, numerous research trials across the eastern and southern wheatbelt have investigated the impact of innovative solutions to the challenge of sodic soils.
Trials considering the impacts of soil amelioration strategies, such as delving and deep-ripping, focused on breaking up the soil profile to create water and root pathways in these clay soils.
"Heavy clay soils respond very differently to certain soil amelioration techniques when compared to sandy soils," Mr Hall says.
"What we were trying to do with these trials is determine what would happen if we broke through the heavy clay dome and bought that clay up to the top layer of the soil."
Other trials considered the application of gypsum, mulch and the injection of manures into the soils.
While adding organic matter to a broadacre business is an expensive solution, Mr Hall says the project left "no stone unturned" in attempts to find ways to stabilise sodic sols.
Other trials considered water harvesting through the creation of mounds and furrows during the sowing process, while further research compared saline soils resulting from rising water tables to sodic soils as a result of transient salinity.
Mr Hall says the research demonstrated that gypsum is a useful resource for growers with sodic soils that have an exchangeable sodium percentage of 10 or above.
"The simple solution to improve sodic soils is to replace the sodium with calcium," he says.
"Gypsum is predominantly calcium and is very mobile through the profile, which moves the sodium off the exchange sites and improves the structure of the soil."
However, not all soils are responsive to gypsum and growers must test to ascertain their exchangeable sodium percentage in the top 30cm of the soil.
We saw clear yield benefits from both the mulching and the manure injection in higher-rainfall locations, but the cost of application would be prohibitive in a broadacre sense.
This research also considered the impact of acidifying alkaline soils to combat the effects of the sodium through improved soil structure.
"These sodic heavy clay soils are often very alkaline, as opposed to the sandy soils found in the western, northern and central wheatbelt," Mr Hall says.
The application of elemental sulfur, dissolved at a rate of between 30 and 60 per cent, effectively converted the calcium carbonate contained in these soils to gypsum.
Mr Hall cautions that understanding the chemistry involved in this strategy is critical to ensure a stable pH range within the soils.
"In some of the trials, we did see the pH levels change from 8.5 down to 3.9, which will obviously cause different soil constraint problems, but the concept of acidifying these soils, even slightly, to reduce their sodicity was promising," he says.
Between 30 and 90 per cent yield responses were achieved in the trials looking at the creation of mounds and furrows for water harvesting purposes.
In regard to mulching and manure injection, Mr Hall says he believes opportunities exist to improve sodic soil structures if cost effective strategies can be developed.
"In these trials we saw clear yield benefits from both the mulching and the manure injection in higher-rainfall locations, but the cost of application would be prohibitive in a broadacre sense," he says.
"While this was blue sky research, it did demonstrate the value of the addition of organic matter to improve soil structure, and perhaps opportunities will exist in the future through harvest chaff applications on the paddock after weed-seeds have been destroyed."
- Soil testing is imperative to determine your soil type and structure.
- Understanding these soil test results is important to ensure the best strategies are employed to re-engineer your soils.
- When considering gypsum application, you must know the percentage of exchangeable sodium in the top 30cm of your soils.
- Optimal gypsum application rates are 3-5t/ha for clay soils.
- High yield increases from mounds and furrows usually only occur in lower-rainfall years.
- While mulches may see big yield increases, these are potentially uneconomical solutions.
GRDC Research Codes (Soils Constraints West projects): DAW00236, DAW00252, DAW00242, DAW00243, DAW00244 (Soils Constraints West)
GRDC Research Codes (new initiative): DAW1901-006RTX, DAW1902-001RTX, DAW1902-003RTX
More information: Chris Gazey, DPIRD, firstname.lastname@example.org