Key points

• Complex soil constraints require an integrated approach
• Machinery needs to be selected for constraint and ameliorant
• Computer models can guide machinery selection and design

Ever since the development of the stump-jump plough in 1876 to open up Mallee country for cropping, Australians have had a flair for developing innovative machinery to deal with constraints to farm productivity.

In recent decades, Australian grain growers have benefited from increased mechanisation efficiency and economies of scale, enabling them to expand their individual land holdings.

This increase in demand for land has seen prices in many areas reach an all-time high, considered unaffordable by many growers.

So rather than expand the farm area, many are now examining their soil resources and considering novel ways to tackle constraints to improve crop productivity and increase profits.

Because of high land values, growers are now investing in soil amelioration options that would have been too expensive a decade ago.

Nature of constraints

Constraints relate to the chemical, physical and biological properties of the soil, which limit fertility and the soils' ability to produce profitable crops.

In many regions, the constraints are a natural characteristic. But in others they may result from land degradation and even, paradoxically, from soil conservation practices, such as long-term no-tillage.

Across Australia, GRDC has invested about $10 million per year in current projects to improve its understanding of soil constraints and cost-effective ways to ameliorate these.

These constraints include:

1. acidity;
2. sodicity and poor soil structure;
3. waterlogging;
4. compaction and high soil strength;
5. water repellency and low water-holding capacity; and
6. nutrient deficiency and stratification.

These constraints rarely occur in isolation, so soil amelioration plans must consider the interacting nature of multiple constraints, the cost-effectiveness of potential interventions and wider implications for the farming system.

Soil amelioration

Mouldboard ploughing. Photo: Evan Collis

Once the soil constraints have been identified, growers and their advisers can consider different management options.

Many people think of a physical disruption and engineering solutions at the mention of soil amelioration.

But a combination of approaches may be worthwhile, including plant genetic tolerance and the application of chemical or organic ameliorants.

In some cases, the soil constraint may not be addressed profitably and the best approach is to accept low production and reduce inputs accordingly, or return that area to native vegetation.

Adding to the complexity of soil amelioration is the spatial variability of constraints both across the paddock and with increasing depth.

Amelioration plans, therefore, need to be customised not only to the constraint but also the available ameliorant and specialised machinery may be required as part of the plan.

Insights into the way in which machines operate can aid appropriate choice and set-up of a machine and machine design.

New computer modelling software is now available and can be adapted to investigate machine design and soil movement during operation.

For physical constraints, strategic tillage can be beneficial, but this must be practised judiciously on appropriate soil types to ensure benefits are maximised and the risk of soil erosion is carefully managed.

For chemical constraints, application machinery needs to be matched to the available ameliorant and where in the soil it is needed.

Some ameliorants, such as lime, benefit from being incorporated into the soil, while others, such as organic materials, can be most effective when placed in the subsoil to increase rooting depth and the uptake of water and nutrients.

It may, therefore, be more cost-effective to apply multiple ameliorants and fertilisers at different depths.

The deeper the placement, the more energy and expense required, so it makes sense to address constraints in the topsoil first.

More information: Stephen Loss, Stephen.Loss@grdc.com.au, 0408 412 453; Rowan Maddern, Rowan.Maddern@grdc.com.au, 08 9230 4600; John Rochecouste John.Rochecouste@grdc.com.au, 07 4571 4800.