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

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

Ground Cover Radio Podcast logo Audio

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

Photo of Evan Lewis Ground Cover

pH maps cut the cost of tackling soil acidity

Issue #120

Author(s): Clarisa Collis

Date: 18.01.2016

For Victorian grower Evan Lewis, mapping with a focus on soil acidity to guide variable-rate lime applications has allowed him to reduce input costs, lifting the overall profitability of his cropping program, which includes faba beans, wheat, barley and canola.

Photo showing roots of faba bean crops in alluvial soil at Holbrook, NSW Ground Cover

Soil acidity holds back pulse potential

GRDC Project Code: DAN00191

Issue #120

Author(s): Helen Burns

Date: 18.01.2016

Correct paddock selection and timely lime application are important lessons from the 2015 faba bean crops being monitored for a GRDC-funded project aimed at improving the performance of legume crops on the acid soils in the southern region high-rainfall zone.