'Lime bank' deposits a good investment

Author: Bill Ryan | Date: 13 Dec 2013

GRDC western regional panel member Bill Ryan

For years farmers understood the concept of a ‘super bank’ and applied phosphate as a resource for the future, much like you would put money into a savings account.

My challenge to the Western Australian grains industry is to adopt a ‘lime bank’ mentality, in which regular and targeted lime application becomes a regular part of farm operations, delivering long-term yield benefits through reduced acidity.

The Grains Research and Development Corporation (GRDC) western regional panel and Regional Cropping Solutions Networks (RCSNs) have identified soil acidity as a priority for research, development and extension (RD&E).

As outlined in the GRDC External Investment Plan 2014-15 (www.grdc.com.au/Investment-Plan), the GRDC is increasing its western region investment into understanding and managing subsoil constraints, including acidity and compaction.

The Department of Agriculture and Food (DAFWA) now estimates that soil acidity costs up to $500 million annually in lost production across WA’s grainbelt.

Estimates for the financial opportunity loss from acidic soils in WA have increased dramatically in recent years as new and more detailed data have become available.

Researchers including DAFWA’s Chris Gazey estimate that 2.5 million tonnes per year of lime is needed for the next decade to recover soil pH to the targets of 5.5 in the surface and 4.8 in the subsurface layers and address ongoing soil acidification.

Farmers can be reluctant to apply lime as its cost and application might not be fully recouped in the first year.

But the response from lime application is ongoing, while yield penalties from soil acidity are substantial.

Research has provided clear evidence about the long-term potential yield losses from soil acidity.

The long-term average loss is 9 to 12 per cent per year, but individual losses can be much greater where the soil pH is well below the target when sensitive crops are grown.

If you are growing a 2 tonne per hectare wheat crop at $300 a tonne, this represents losses of $50-70 a hectare if soil pH is low.

So the investment in lime needs to be considered over a number of years. 

This type of investment is usually evaluated using an internal rate of return. 

An investment in lime provides an internal rate of return of 10 to 20 per cent, depending on the amount applied and yield response.

This is a very good return on the investment.

Acidic soils impact on plant growth in a number of ways.

The key problem in WA is that as the soil gets more acidic, the solubility of highly toxic aluminium increases, stunting root growth.

In addition, as pH decreases, phosphorus and nitrogen in the soil become less available to plants.

When soil pH is at the right level plants have access to more water and nutrients, resulting in better yields.

Research has highlighted the importance of subsoil pH and applying lime not just at the surface, but at depth.

If topsoil pH is improved but subsoil pH is low, yields will still be penalised.

This means that soil sampling needs to be not only just to a depth of 0 to 10cm, but to 30cm in 10cm increments to get an accurate picture of soil health.

Researchers are investigating practices which combine liming with soil amelioration

techniques like deep ripping or mouldboard ploughing.

These practices can cause big yield responses to occur quickly, but to maximise the benefit the lime incorporation technique needs to distribute lime well through the subsurface layers.

Researchers also stress that the additional cost of the amelioration technique needs to be weighed up with any potential additional benefits.

More information about lime can be found in Soil Acidity: A guide for WA farmers and consultants, available by searching ‘acidity’ on the DAFWA website www.agric.wa.gov.au, or www.limewa.com.au

 which can be used with the www.soilquality.org.au online lime comparison

ENDS

Region West, National, North, South