Grains Research and Development

Date: 29.07.2016

Soil Acidity in WA

Truck in a paddock.

More than 70% of surface soils and almost half of subsurface soils across WA’s south-west are below appropriate pH levels for agricultural production.

Subsurface acidity is a major constraint to crop and pasture productivity right across WA’s wheatbelt, estimated to reduce crop yields by 9–12 per cent.

Some trace elements become more soluble at lower pH, as does aluminium (Al), which is toxic to plants when in solution. If soil pH is too low – below about 4.8 – the concentration of Al in the soil water increases rapidly and reduces root growth. The resultant smaller root systems have limited access to nutrients and water, leading to lower plant biomass and grain yields.

Adding lime to the soil raises the pH. Above pH 4.8 the Al becomes non-toxic in the soil, enabling the plants to develop effective root systems. Research shows that as well as improving crop yields and widening rotation options, liming has a long-term positive impact on the ecosystem by potentially boosting soil microbial activity, improving availability of major plant nutrients and helping to reduce weed seed banks.

DAFWA’s recommended minimum pH levels for WA’s agricultural soils to maintain or achieve yield potential (measured in pH calcium chloride– or pHCa) are:

Surface (0–10 cm) pHCa 5.5

Subsurface (10–20 cm and  20–30 cm) pHCa 4.8, and no less than pHCa 4.5 to avoid Al toxicity.

Wheat yields will not be constrained by acidity when these levels are met.

Lime use is most effective if it is precisely targeted to property areas based on subsurface soil testing during the summer months to a depth of at least 30 cm (in 10 cm increments), and to 40 or 50 cm on sandy soil. Scheduled liming applications are required to maintain the desired pH level in the soil, with priority given to the farm’s most productive cropping areas.

It is important that growers source the best value for money lime based on neutralising value (i.e. the carbonate content of lime determines the capacity of the lime to neutralise acidity) and particle size (i.e. the size of the lime particles determines how quickly the lime can neutralise acid). Lime with a high proportion of finer particles has a larger surface area to react with the acid in the soil.

Mechanically incorporating lime into the subsurface during amelioration with deep tillage, spading or mouldboard ploughing generally achieves more rapid improvements in subsurface pH levels. Variable rate technology can also be successfully applied to lime spreading.


Grains Research Updates

Soil acidity and arresting the impact of this yield thief

GRDC Project Code: RSS00010

Author(s): Brian Hughes (PIRSA Rural Solutions), Tim Herrman (Department of Environment, Water and Natural Resources) and Andrew Harding (PIRSA Rural Solutions).

Date: 07.02.2017

The extent and severity of soil acidity are increasing under high yielding continuously cropped farming systems.
When acidity emerges in high value sensitive crops such as lentils or faba beans, it often follows a patchy distribution which can be diagnosed and treated.
There are some new trials comparing the effectiveness of liming products.
New decision support tools have been developed to assist in comparing treatment options and understanding the economic impacts of acidity. more

Grains Research Updates

Acid soils - is gypsum part of the soluation

GRDC Project Code: GIA00004

Author(s): James Easton, CSBP

Date: 29.02.2016

A survey of south western agricultural soils of Western Australia from 2005 - 2012 showed that 72% of topsoils and 45% of sub surface soils were below the targets pHCaCl2 of 5.5 and 4.8, respectively (Gazey et al., 2013).
Lime sand is applied to improve the pH but crop responses are rare in the first few years following application. Lime use is also limited by high freight costs of transporting quality sources (generally coastal and north of Perth) to far away farms.
Aluminium (Al) toxicity is often a major constraint of acid sub soils.
Field trials in the eastern wheatbelt have previously indicated that gypsum could be used to increase wheat growth in Al toxic subsoils in sandy soils of low rainfall (McLay et al. 1994 I).
Gypsum is used to reduce Al toxicity in countries such as Brazil and South Africa, but is still not generally recommended in Western Australia.
There are several inland gypsum reserves in Western Australia close to cropping land affected by aluminium toxicity.
The aim of this research is to investigate further whether gypsum can be used as an ameliorant of Al toxicity to improve the profitability of crops grown on acid soils in Western Australia.

Grains Research Updates

Local lime results and what you need to consider in buying and applying lime

GRDC Project Code: SFS00026

Author(s): Lisa Miller (Southern Farming Systems)

Date: 25.02.2016

• Monitor the 10-20cm soil depth for soil acidity as this layer could be acidic or likely to become acidic and cause yield penalties
• If surface liming, then keep the topsoil at pH(Ca) >5.5 to allow lime movement down the soil profile
• For a fast lime response, incorporate it and use a high quality lime with a high proportion of particle sizes less than 0.1mm
• There are different calculations that can help you compare limes and effective neutralising value (ENV) isn’t necessarily the best one to use more

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Ground Cover Radio 120: Soil acidity holds back pulse potential

GRDC Project Code: DAN00191

Date: 23.01.2016

Correct paddock selection and timely lime application are important lessons from 2015 faba bean crop trials in the southern region, high-rainfall zone. more