A new $48 million co-investment by GRDC and the Western Australian Department of Primary Industries and Regional Development (DPIRD) is expected to 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; and
- water harvesting strategies in heavy soils, particularly those in the eastern wheatbelt.
Part 1 – Compaction
The challenge
Research has shown that compaction affects all soil types, across all locations. This means it has a significant impact 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 grainbelt, compaction levels are now deeper than ever before.
During the past 10 years, he has seen an increase in compaction depths from 300 millimetres to 400mm, and even to 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 wheatbelt, we believe all soil types suffer from some level of compaction, and this compaction is getting deeper.”
The research
Trials established five years ago, through Soil Constraints West, at seven different locations, across seven different soil types, have investigated the value of deep-ripping with and without topsoil inclusion.
These were monitored in the past four year, 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.
Mr Parkers says, while all soils suffer from compaction, sandy soils appear to be the most affected.
He says the only soils that can partially escape 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 wheatbelt.”
The outcomes
The research identified that almost all soils benefitted 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 trials sites showed varying levels of benefit from deep-ripping, with varying levels of yield improvements continuing over the five years.
Take-home messages
- 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.
Part 2 – Water repellency
The challenge
While growers and researchers have known about the problem of water repellency in sandy soils for many decades, it has 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 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 while 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 have staggered establishment.”
Dr Davies says the issue of weeds having staggered establishment on water repellent soils results from a lack of available water, which makes them harder to control.
Then, he says, 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.
The research
Dr Davies and his team divided the research, carried out through the Soil Constraints West initiative, into two main areas of focus.
On one hand they looked at migration strategies – that is, ways to get around the problem without solving it.
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.
The second research focus was on soil amelioration strategies – assessing the best ways to solve the problem in the longer term.
Dr Davies says the researchers looked at a 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 ploughs; and clay spreading, or delving.
He says more than 80 amelioration trials were run across grain growing areas, with 68 of those involving cereals crops.
The outcomes
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 crop 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 onto the furrow, or putting it through the liquid kits down under the soil near the seed,” Dr Davies 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.
He says in the soil amelioration trials, results were mixed, with different soil types responding differently to the various techniques.
“One of our interesting results was in regard to the longevity of these amelioration strategies, where we saw immediate yield increases, and averages of around 50 per cent, from the deep soil mixing strategies in all sandy soils,” he 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 benefits of additional deep-ripping after mould-board ploughing or spading on all soil types.
“On average, this gave an additional 10 per cent (300kg/ha) yield increase across all soil types,” he sayd.
“On some sites, this increase was up to 900kg/ha.”
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 more than 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 repellence.
“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 repellence, 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.
Take home messages
- 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 helps ascertain potential water repellency levels.