Adding a sweetener to acid soils

Getting lime applications on acid soils right


Cropping
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Liming acidic soils is a proven yield booster, but there are interesting findings on how best to apply the lime. Are you doing it right?

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Lisa Miller, Southern Farming Systems (SFS), uses a soil pit to explain how lime moves through the earth at SFS's AgriFocus event last month.

Lisa Miller, Southern Farming Systems (SFS), uses a soil pit to explain how lime moves through the earth at SFS's AgriFocus event last month.

LIMING of acid soils is an accepted practice to boost productivity – but are growers getting the maximum benefit from their lime inputs when only spreading the ameliorant on the surface?

A Southern Farming Systems (SFS) project into improving acid soils has found that many soils have an acid layer starting at a depth of around 8cm.

Lisa Miller, Southern Farming Systems project coordinator, said at a number of trials through Victoria’s Western District researchers had been surprised at how slow lime particles were to pass through the soil profile.

“Even fine grade lime needs up to two years to fully react and that is with full incorporation,” Ms Miller said at SFS’s AgriFocus event at Westmere last month.

Ms Miller said much of the research at present suggested lime needed to be incorporated to work effectively.

She said farmers looking to keep acidity at bay were best served by constantly working to keep pH up, which meant a high rate, high intensity liming program.

“Keeping the surface (0-10cm) pH rate at 5.5 is the aim,” she said.

“This may mean putting on higher rates than the traditional 2.5 tonnes of lime a hectare.”

She said while it may seem more costly to put on heavier and more frequent rates in the long term it is cheaper than trying to bring up the pH of a really acidic subsoil.

“Addressing an acidic subsoil is more costly and difficult.”

Ms Miller said farmers needed to have a long term view in regards to sweetening soils to make them better for acid sensitive crops, such as pulses.

“Surface applied lime movement is slow, so consider earlier applications of lime before sowing acidic sensitive crops such as faba beans or barley.”

She said farmers should look to apply lime at least two years before sowing acid sensitive crops.

Ms Miller said even with incorporation the process of changing pH was slow.

Using a Speedtiller machine at Holbrook in the Riverina in NSW researchers found the majority of pH change was in the top two centimetres in spite of the incorporation.

She said in terms of dealing with an acid layer, typically at 8-20cm, it was best to put the lime directly in that layer, although this required substantial horsepower to work and farmers also had to be careful when deep ripping not to go below the acidic zone.

No-till farmers are also reluctant to use tillage within their system, although many researchers now say a ‘strategic tillage’ has no ill effects on the overall farming system, provided it does not occur more than once every four years.

The story Adding a sweetener to acid soils first appeared on Farm Online.

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