Acidity: bigger than salinity?

Soil acidity threatens major losses in productio. Bill Porter, leading WA's Time ti Lime program, shows a map of lime deposit and extension locations

If acid soil is left untreated, it could become the biggest land degradation issue in Western Australia, according to Agriculture Western Australia (AGWEST) researcher Bill Porter.

This season, though WA landholders are using an estimated 400,000 tonnes of lime to reduce the acid problem, it is only half of the one million tonnes required annually to combat soil acidity.

Dr Porter said research showed that if farmers let soil pH drop to around 4.2 or 4.3, they could expect a production loss of between 10 and 15 per cent.

"Farmers only need to recover 1-3 per cent production loss to pay for the lime to manage the soil system. Ultimately lime will pay for itself."

The 'Time to Lime' program in WA, supported by growers through the GRDC, recommends farmers keep the soil pH above 5. If it is allowed to drop to critical levels of about 4.2, it could take 3-4 years for the lime to lift back the pH to sustainable production levels.

A program of regular soil-testing is essential. Dr Porter suggests that soil tests within the 0-10 cm layer should be taken every two years and testing within the 10-20 cm layer every five years.

"Even though the top 10 cm of soil may be well within the accepted levels, the 10-20 cm subsoil layer may be quite acid. The subsoil layer takes longer to fix. The lime applied to the upper layer has to leach down to reverse the acidity and increase the pH."

It is important for farmers to keep accurate pH records, especially with particular crop rotations, which deplete the soil at significantly different rates.

AGWEST's Lime and Nutrient Calculator could be used accurately to calculate the quantities of lime required as crop yields varied and different crop rotations were used.

Program 3.4.3

Contact: Dr Bill Porter 08 9690 2000