Grains Research and Development

Date: 29.11.2013

Soil Acidity in WA

side-view of a vertical slice of soil, showing the results of a lime trial.

Subsurface acidity is a major constraint to crop and pasture productivity right across WA’s wheatbelt.

It is estimated to erode potential crop yields by 9 to 12 per cent, worth $500 million annually.

About 14.25 million hectares of WA wheatbelt soils are acidic or at risk of becoming acidic to the point of restricting crop yields.
Lime use has increased in recent years to address acidic soils with low pH.

Soil pH is a measure of the concentration of hydrogen ions (acid) dissolved in the soil water.

Some trace elements become more soluble at lower pH and so 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.

Poorer root systems restrict uptake of nutrients and water and lead to lower plant biomass and grain yields.

When lime is added to soil, it neutralises hydrogen ions.

As the pH is raised, Al becomes less soluble and plants are able to develop effective root systems.

WA growers apply about one million tonnes of lime each year. But the Department of Agriculture and Food, Western Australia (DAFWA) has set a target of 2.5 million tonnes per annum for the next decade to halt further soil acidification and recover pH to levels where cereal yields will not be constrained.

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 seedbanks.

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 30cm (in 10cm increments).

Regularly scheduled maintenance liming is needed for paddocks with soil pH profiles that meet DAFWA pH targets.

Strategic applications can then be used for highly productive cropping areas where pH needs to be recovered to recommended levels.

Many WA growers and research trials are finding there are faster subsurface pH improvements if lime is mechanically incorporated into the subsurface during amelioration with deep tillage, spading or mouldboard ploughing.

Another tool is to lime with variable rate technology using paddock ‘zones’.

The key to liming success is to apply sufficient lime to achieve soil pH targets.

To find out more about DAFWA’s soil pH targets and lime incorporation methods follow the Read More link below.

Read more...

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