Key points

• Soil constraint amelioration is site and season-specific
• Diagnosing soil constraints is challenging
• Controlled environment and extensive regional trials build data sets to inform soil constraint management
• Decision support is required to inform soil constraint management

Australia's soils are one of its most valuable natural resources and play a fundamental role in primary production, as well as the country's environmental, economic and social sustainability. However, our soils are among the oldest in the world, extremely variable, highly eroded and frequently nutrient-poor.

Many of the soils under crop production suffer from one or more primary constraints to plant growth (salinity, sodicity, acidity, alkalinity, compaction, poor water infiltration and retention), which require expert management.

Challenging decisions

Soil constraints are challenging to diagnose as they can exist simultaneously and are often highly variable across paddocks and within soil profiles. Seasonal performance of crops and crop type can further confound identification of constraints.

Once identified, deciding how to manage the most important soil constraint is often fraught and challenging. Do you quarantine badly constrained areas and use them for more appropriate enterprises, or return them to natural vegetation? Do you mitigate the constraint and try to minimise its adverse effects, or do you invest in a more radical soil amelioration program to change the soil's properties for the medium to long term? What amendments do you use and how should they be applied? What are the costs, benefits and risks of adopting each management option?

The science of soil constraints and mechanisms of amelioration are now being unravelled through detailed controlled environment studies using soil cores and analysing soil and crop responses to a suite of amendments.

Some options might require significant investment in terms of knowledge and data, skills, labour, amendments and machinery to provide long-term solutions.

Building knowledge and skills from data

GRDC brings a national focus to investment in grower priorities and is able to take a broad view of the issues across Australia while understanding the regional differences in climate, farming systems, soil types and constraints. The science of soil constraints and mechanisms of amelioration are now being unravelled through detailed controlled environment studies using soil cores and analysing soil and crop responses to a suite of amendments.

These controlled-environment studies are then cross-referenced with extensive multi-location field trials across Australia to design solutions specific to each location. More recently, GRDC has invested in synchrotron scanning technology, which will provide further insights into interactions between root and water distribution and nutrient availability in soil cores collected from field trials.

As climate and farming practices continue to change, we have seen an increase in the prevalence of some soil constraints. This means amelioration approaches need to be dynamic to address evolving constraints and improve productivity while ensuring the sustainability of farming systems.

One area of research is focusing on the importance of soil microbes, the fungi and bacteria, particularly in their role in promoting soil aggregation and improving structure in dispersive clay subsoils.

Amelioration approaches need to be dynamic to address evolving constraints and improve productivity while ensuring the sustainability of farming systems.

The latest analytical methods are now being applied at this frontier to determine how the best combinations of microbes and organic matter might be incorporated into customised amelioration plans.

As the inventory of data from field trials continues to grow over time, our scientific understanding expands, enabling researchers to predict the size of yield benefits in different soil types and seasons, and the longevity of different amelioration practices. This data will also inform more sophisticated economic analysis considering risk.

Although researchers are making inroads into managing soil constraints, it is equally important to improve grower confidence in diagnosing constraints and devising economic solutions at paddock and farm scales.

In this respect, several of the recent GRDC investments include action learning groups where small groups of growers identify their own soil constraint issues and test amelioration options, developing creative, flexible and successful strategies.

More information: Stephen Loss, stephen.loss@grdc.com.au; Rowan Maddern, rowan.maddern@grdc.com.au; John Rochecouste, john.rochecouste@grdc.com.au