Hostile subsoils limit crop returns

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By Phil Price, Consultant to the GRDC Agronomy, Soils and Environment Program

Much of the Australian continent is geologically very old and highly weathered. Soils in most cropping regions share these characteristics, without the influence of renewal processes such as volcanism, glaciation or alluvial deposition that have formed the younger soils found elsewhere. Our long period of relative aridity has also influenced the physical structure and chemical composition of our soils. As a result, many of the soils used to grow grains in Australia contain in their subsoil layers (defined here as deeper than 20 centimetres) a range of factors that limit or "constrain" crop growth and yield.

Growers, agronomists and researchers are increasingly reporting that "hostile subsoils" are a major limiting factor to crop returns. Abundant moisture in the subsoil at harvest after a dry finish, big yield differences between soil types found in the same paddock and root growth restricted to the surface soil layer are all indications of subsoil barriers to crop growth. These effects are seen in particular soil types in all cropping regions, and the impact overall on the grains industry nationally is substantial in terms of forgone yield and profit.

These constraints are generally associated with one or more of the following:

In many situations these subsoil factors interact to effectively deny crop roots access to the soil moisture and nutrients needed for commercial returns. Different crops and cultivars are affected by these constraints to different degrees, and the season has a large influence on their impact. For example, in a season when rainfall is above average and well-spread it may be possible to grow a good crop on the moisture available in the top 60cm of soil, so salinity at 80cm has little effect. But in a dry year, the crop may need to use the water at 80cm to make a reasonable yield, so the saline layer becomes a major limiting factor.

In response to the growing recognition of widespread subsoil constraints, in 2002 the GRDC established a national research initiative with the aim of enabling the grains industry to better understand subsoil constraints and how to manage or avoid them.

A single, large, integrated project, involving several research organisations in New South Wales and Queensland (DNR0004, described on page 3) was funded in the northern region, followed the next year by further investments in the west and south. The nine projects (eight reported here) currently funded within the Combating Subsoil Constraints initiative (SIP08) are managed as a group to help optimise the benefits to be gained by sharing skills and information across research groups and across cropping regions.

SIP08 projects aim to provide a mix of the following outputs:

The GRDC is encouraging links between SIP08 and its other strategic initiatives.

As you will read in the following reports, all the SIP08 projects are tackling the different aspects of subsoil constraints and are working closely with growers in different cropping regions. Information and workshops/field days about subsoil constraints and how to manage them are already being provided in most regions, and this delivery of new knowledge and new management methods will accelerate as the initiative continues.

More information: Dr Phil Price, 02 6251 4669,

Region North