Problem soil becomes a surprise bonus
GroundCover™ Issue: 119
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 2).
An on-farm ‘lime’ pit has cut liming costs on the Nixon family’s eastern wheatbelt property in Western Australia by a third and provided enough alkalinity to ameliorate the 50 per cent of the farm’s area that is constrained by acidity.
Sourced from one of the Nixons’ poorest paddocks, the domestic ‘lime’ comes in the form of the highly alkaline and problematic Morrell soil type, which Bob Nixon says he was close to pulling permanently from production due to increasingly dry and variable seasons. “The paddock yielded just a third of a tonne per hectare in 2013,” he says.
With calcium-magnesium carbonate rocks visible on the soil surface, the Nixons had suspected for some time that the Morrell soil might be a potential liming resource.
“We soil tested extensively and discovered the soil had a neutralising value averaging 50 per cent of calcium carbonate and at that point we realised we had a significant on-farm liming supply.”
As the Morrell lime has a lower neutralising value than coastal limesand, the Nixons need to use it at double the rate (4t/ha) to achieve the same pH change. However, with lime transport costs as high as $25 to $50/t to the eastern wheatbelt, Bob points out that even a moderately neutralising lime source on-farm becomes a valuable alternative.
“Purchasing and carting limesand from the west coast costs us about $33 a tonne but we can get the equivalent amount of Morrell lime from the pit and on to the paddocks for about two-thirds of this.”
The Morrell lime also has the added advantage of containing calcium (at 12.5 per cent) and magnesium (4.5 per cent) along with significant potassium.
Since 2013 the Nixons have mined about 20,000t of the Morrell and they estimate they have about 250,000t at their disposal. In 2015, Bob says they spread 12,000t of the Morrell lime over 3000ha using excavating and screening equipment available to them through a family business.
The Morrell lime is used in conjunction with gypsum to treat acidity and its associated aluminium toxicity. It has usually been spread and left on the surface, but the Nixons are now ploughing the Morrell to 10 to 13 centimetres in selected paddocks using offset discs.
As dedicated no-till farmers since 1994 it took time to become comfortable with ploughing their most fragile soil types, but incorporating the lime to depth has accelerated the pH recovery of the Nixons’ worst acid soils.
“We’ve increased yields by 600 to 700 kilograms a hectare by incorporating the lime into some paddocks and I think about half of this yield has come from the improved pH and the other half from the plough effect,” Bob says.
Lighter soils turn-around
The Nixons’ heavier soils have usually been their most productive, but with a drying climate they now rely more on their lighter soils to make a profit.
“The lighter soils need less rain than the heavier soils to germinate a crop so with the decline in autumn rainfall we really need to make sure our lighter acid soils are managed correctly to optimise yield,” Bob says.
The long-term drying trend has caused average crop yields to drop by 250kg/ha since the end of the 1990s across the Nixons’ mixed property. By keeping a careful eye on inputs and generating efficiencies of scale Bob says the business has remained profitable.
“In the ’90s it was about producing more but now our focus is on producing the same yields with fewer inputs,” Bob says.
Liming using imported limesand from the west coast has been a major focus for the Nixons since the mid-1990s, with the original pH 4 of the farm’s acid sands having been lifted to above pH 5 following 3 to 5t/ha of limesand over the past 20 years.
“Our longest limed paddock originally had a pH of 4.3 and contained toxic aluminium levels, but it is now at pH 6 after about six tonnes of lime per hectare since 1994.” The goal is to raise pH of the lighter country even further to pH 5.5 to 6 using the Morrell lime.
“Following years of over-fertilisation we have a large phosphorus soil bank and by correcting our soil pH we can make use of this while lowering our phosphorus rates to maintenance and redirecting savings into lime.”
Bob says he does not know how much of the Morrell lime might be in the eastern wheatbelt, but he would be surprised if there were not other deposits of the alkaline soil type. The Nixons do not plan to mine the Morrell commercially, but believe their supply will meet their liming needs for decades to come.
“Even a suitable soil at 25 per cent neutralising value would be a viable lime source in the eastern wheatbelt where transport costs are $35 to $50 per tonne for limesand,” Bob says.
In 2014, Bob Nixon completed a Nuffield scholarship in which he investigated techniques and crop rotations to help cope with a drying climate.
Part 1 of this story – the Sutherland family: Drying climate turns research spotlight onto heavy soils
GRDC Project Code NUF00010