Drying climate turns research spotlight onto heavy soils
GroundCover™ Issue: 119 | Author: Janet Paterson
There is increasing focus on removing physical and chemical soil constraints to productivity across the Western Australian wheatbelt as growers strive for more profitable crops with less and less rainfall. Here we look at how two eastern wheatbelt growers are dealing with the same problematic soil type in very different ways (Part 1).
Merredin grower Ian Sutherland does not need a shovel to find where the worst of his ‘Morrell’ soil is located on his heavy land. It usually shows up as completely bare patches in crops, despite having been seeded and treated exactly the same as the rest of the paddock.
“Across an 80-hectare cropping paddock of heavy soils we can have half a hectare of poor Morrell soil show up as totally bare and about 30 hectares of other Morrell underperforming,” Ian says.
So-called for the gum trees that grew on it pre-clearing, Morrell soil ranges in quality. It is situated low in the landscape and covers five to 10 per cent of WA’s agricultural area – mostly in the eastern and central wheatbelt.
Morrell soil is heavy with good natural fertility but is alkaline, often saline and sometimes sodic. About 150 to 200 millimetres of seasonal rainfall is needed to leach enough salt away for the soil to achieve its yield potential.
Sodicity (caused by an oversupply of sodium in the soil) causes the clay particles in Morrell soil to disperse, which destroys soil structure, curbs water penetration and concentrates salt near the surface.
“Morrell soil is a heavy loamy-clay so it needs more rainfall to fill its soil water bucket than a sandier soil, but once it has enough moisture Morrell can perform really well,” Ian says.
He describes the Morrell soil type as a “0.3 to 3.0 tonne” soil because yields can pivot between terrible and fantastic, depending on seasonal rain. “But in our low rainfall area it’s a rare season that delivers us three tonnes … unfortunately.”
While a drying climate and poor crop yields have caused some growers to consign the worst of the soil type to the too-hard basket, preliminary success with a mulching trial aimed at conserving soil moisture has spurred Ian and members of his local grower group to investigate whether Morrell soil can be better managed.
“In the past growers have grazed sheep on the worst Morrell soil, but now with many going out of livestock the soils are being abandoned, which is a big shame in my opinion.”
While the Sutherlands have only a relatively small area of Morrell soil on their property, Ian has done a lot of thinking about how to make it more productive. “A neighbour has 1000 hectares of Morrell and the soil type is common right across the eastern wheatbelt so finding ways to make it consistently productive is important.”
Ian says in a good year (200mm growing-season rainfall) Morrell soil can be profitable because its good fertility makes it cheaper to crop and manage than the sandier, acidic soils in the region. “We can spend just half a tonne of yield on a three-tonne barley crop, which makes the soil very attractive economically in a good year.”
Barley is Ian’s preferred crop choice on Morrell soil because it can tolerate salinity and frost better than wheat – characteristics important in the low-lying landscape where Morrell is located.
Department of Agriculture and Food, WA (DAFWA) researchers have joined forces with the Merredin and District Farm Improvement Group (MADFIG) to trial a range of amelioration methods on the Sutherlands’ Morrell soil over the next five years.
“The bulk of the trials are ‘proof of concept’ in nature. We want to see what might work and then hopefully the researchers can develop an economical solution to make these soils more viable,” Ian says.
He says the aim is to develop management systems to make the worst of the Morrell soil cost neutral and the underperforming Morrells more profitable.
“It’s about finding ways to improve soil structure and chemistry so that crop roots can access more soil moisture and therefore yield more.”
Ian was alerted to the possible benefits of mulching the soil by old header trails showing up as waves of higher-yielding crops on the Morrell soil. “I wondered whether the better growth on the header trails might be to do with the chaff so in 2013 I set up some small mulching and seeding depth demonstrations on a high-salt patch of Morrell to determine their effect on germination.”
The theory was that mulching would help the soil retain its moisture, which would in turn dilute the salt content and enable the barley crop to germinate.
Ian says the results were amazing, with mulched soil delivering high germination rates. “While mulching large areas with straw is probably not a profitable option, the trial did provide confidence that we might be able to treat the worst of the soil type to get some ground cover on it and set it up to start self-mulching with its own biomass in time.”
In 2014 Ian repeated the mulching trial by rolling straw bales out across a larger area of recently seeded Morrell soil. “With 30mm of rain immediately following sowing we got a fantastic response to the mulching, with all the mulched area germinating while the unmulched area remained bare.”
DAFWA development officer Caroline Peek says up until about 15 years ago the Morrell soil type did not present a production constraint because seasonal rainfall was reliable enough to deliver good yields on the heavy soils.
“But June rainfall has dropped off by about 40 per cent in the eastern wheatbelt, which has made it more difficult to get a crop out of the ground on the heavier soils and in particular the Morrells, which need moisture to wash salt down the soil profile.”
Caroline says the drying climate has stolen about 45mm of seasonal rainfall from eastern wheatbelt areas such as the Sutherlands’ Merredin property.
“Heavier soils in the eastern wheatbelt have traditionally been the most productive because they hold more moisture and are more naturally fertile – but the drying climate has seen the region’s sandier soils generate more profit in recent times.”
However, these soils have their own issues such as acidity and compaction at depth thwarting root growth. “About 25 to 30 per cent of the central and eastern wheatbelt contains Morrell soils so it is important that we investigate ways to manage them more productively,” Caroline says.
The five-year amelioration project will eventually be spread across seven on-farm sites in the central and eastern wheatbelt along with another at Katanning in the Great Southern, which also contains Morrell soils.
“We are working with grower groups at each site to translate their management ideas into trials – the Sutherlands’ is the first trial site up and running and we will have the others in place by 2016.”
Part 2 of this story – the Nixon family: Problem soil becomes a surprise bonusCaroline Peek, DAFWA,
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