ALLOCATING part of the farm budget to soil amelioration practices has significant benefits for farm businesses across the Western Australian grainbelt with research showing it to be worth an average of about $124 per hectare per year, depending on location, soil type and crop type.

With the average cost of soil amendment across grain growing regions in WA about $41/hectare, the benefit:cost ratio is 3:1 and there is a net benefit of about $83/ha/year.

A new decision-making tool has been developed to help producers prioritise the spend on amelioration tactics to address soil constraints to get the best ‘bang for buck’.

The ROSA model, developed with GRDC and DPIRD investments, can analyse the benefits and costs of addressing water repellence, as seen on this Moora soil. (Photo: GRDC)

With a limited budget and often multiple soil constraints in different areas of a farm, the Ranking Options for Soil Amelioration (ROSA) model is able to provide a ranking of the return on investment from a range of strategies.

ROSA has been developed with investments through GRDC’s Soil Constraints West group of projects and the WA Department of Primary Industries and Regional Development (DPIRD).

It draws on key data from the 2016 DPIRD report ‘Economic analysis of the impacts and management of subsoil constraints’.

DPIRD economist and ROSA project leader, Elizabeth Petersen, said the tool provided a ranking of the cost-effectiveness of a range of common soil amendment options to address one or more soil constraints on a property.

Mouldboard ploughing and deep tillage economics can be analysed using the ROSA model. (Photo: GRDC)

It considers short and long-term budget implications of the costs and benefits at a paddock or farm scale – for single amendment options and combinations.

These are accrued at different points in time across a 10-year period and calculations are made about likely returns for each dollar spent.

Dr Petersen said the return to investment in ROSA modelling was based on comparing a Benefit Cost Ratio (BCR) for each soil amelioration option or combination.

This is a ratio of benefits over costs that have been discounted over time and represents the dollar return for each dollar spent.

Dr Petersen said ROSA could estimate the value of lost grain production from soil constraints by calculating the gap (for each crop type) between actual yield (in the presence of soil constraints) and potential yield (in the absence of soil constraints considered in the model).

This yield gap is multiplied by farm-gate price and the estimated average area sown to each crop type by agricultural soil zone.

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Figure 1: Indicative potential yield responses (tonnes/ha) to soil amelioration by crop type and Western Australian agricultural soil zone. (Source: Estimates from Elizabeth Petersen, DPIRD.)

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Dr Petersen said ROSA estimated WA croppers lose $4.3 billion each year from soil constraints – dominated by losses in the central and northern grainbelt.

She said the weighted average loss from soil constraints across all WA crop areas was about $330/ha and the south coast had the highest weighted average loss at about $490/ha. This is due to the higher yield potential in this zone (on the back of more rainfall).

After growers and advisers have trialled ROSA, feedback will be used to help fine-tune and update the model by mid-2018. To receive a copy of ROSA, contact DPIRD senior development officer Jeremy Lemon at [email protected]

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Figure 2: Estimated indicative weighted average value of amelioration of soil constraints by crop type and WA agricultural soil zone ($/ha) (within Zones, losses due to constraints are a weighted average for each crop type and response to amelioration by area). (Source: ROSA modelling results, DPIRD. )

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Source: GRDC, DPIRD,

More information: http://mail.grdcsubscribers.com.au//lz/lz.aspx?p1=0530411S2848&CC=&p=0

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