Diverse tactics for soil constraints

Photo of Elizabeth Petersen, DAFWA

DAFWA economist Dr Elizabeth Petersen is undertaking GRDC-funded research into the costs and benefits of ameliorating soil constraints in WA.


Economic analysis of options for managing Western Australia’s main subsoil constraints has uncovered the most cost-effective long-term solutions that can boost profits by up to $174 per hectare per year in some areas.

The best returns to address subsoil acidity came from liming; optimum results for dealing with subsoil compaction came from deep ripping/working coupled with controlled-traffic farming (CTF); and use of gypsum was the most economic tactic for subsoil sodicity.

The analysis was conducted through the GRDC’s Soil Constraints – West initiative by Department of Agriculture and Food, WA (DAFWA) economist Dr Elizabeth Petersen.

At the GRDC Grains Research Update, Perth, earlier this year she suggested that across WA’s agricultural zones, acidity is the most costly subsoil constraint faced by grain growers.

Grappling with subsoil acidity

Dr Petersen estimates that subsoil acidity cuts average returns for individual growers by about $140/ha/year due to lost production.

“For industry, this represents a loss of about $1.6 billion annually across an affected area of 11 million hectares,” she says.

“Yield penalties caused by acidity occur in about 94 per cent of seasons, average losses for barley and canola are about 46 per cent and average losses for wheat are about 13 per cent (lupins are not susceptible to acidity).”

Dr Petersen studied the long-term economics (based on 20-year discounted cashflow analysis) of top-dressing and deep-banding lime to address subsoil acidity on the main WA soil types affected by this constraint.

This took into account lime source, freight costs, potential yields and optimal application rates. Liming increased average annual profits across all zones by $63/ha/year – or $11 for each $1 invested.

This ranged from $13/ha/year in the region from Moora to Kojonup, up to $174/ha/year in the region from Mullewa to Morawa.

“If we top-dressed and deep banded in year one and four, the break-even point in most areas was in the second year, after which there was a profit hit from (the cost of)a reapplication of lime – before profit rose again,” Dr Petersen says. “Without liming, crop yields and profits fell in the long term due to ongoing acidification of the soil.”

Costs of subsoil compaction

Dr Petersen says about 12 million hectares of WA’s agricultural area is affected by subsoil compaction, costing the average grower about $55/ha/year in lost production and the industry about $880 million/year.

She says compaction causes yield penalties of 10 to 30 per cent in WA in about 67 per cent of seasons.

Her 20-year discounted cashflow analysis shows the most profitable amelioration strategy is deep ripping and deep working in conjunction with CTF.

This lifted average profits by about $35/ha/year – or a $9 return for every $1 spent – ranging from $20/ha/year in the central and northern grainbelt, up to $78/ha/year on the south coast.

Dr Petersen says the response from deep ripping/working with gypsum, but without using CTF, was more uncertain and marginal.

“Many WA growers appear to be unconvinced about the benefits of CTF, but our analysis shows it can be really profitable,” she says.

Managing subsoil sodicity

About 10 million hectares of WA is estimated to be susceptible to subsoil sodicity, costing the average grain grower about $50/ha/year in lost production from 10 to 30 per cent crop yield penalties occurring in most years.

Dr Petersen’s analysis showed that applying gypsum in year one and year 15 to ameliorate this constraint had widely variable profit benefits across the state. But there was an average $9/ha/year profit gain – or about $1.40 returned for every $1 spent.

Where to next

Dr Petersen says this type of economic analysis is important in guiding GRDC investments into subsoil constraints. She says the study will continue and use updated underlying assumptions as new information is generated by GRDC-funded research on the ground.

“Going forward, we anticipate there will be more work into the economic feasibility of dealing with multiple subsoil constraints occurring in major WA soil types, as the initial analysis treated each constraint in isolation,” she says.

“We also aim to look at the seasonal impacts on each soil constraint, rather than assuming an average season, and potentially the impact of when the management strategy is used in the crop rotation.

“The result will be practical and valuable information to help boost grower confidence in adopting soil-amelioration strategies.”

More information:

Dr Elizabeth Petersen, DAFWA,
0404 077 194,

Useful resources:

DAFWA’s Economic analysis of the impacts and management of subsoil constraints – report
Ground Cover Supplement – 'Soil constraints'
GRDC Hot Topic – Soil Acidity in WA


Time fungicides for powdery mildew control


Profits count in nutrition calculations

GRDC Project Code DAW00242, DAW00243, DAW00236

Region West