FarmTalk #8 – Identifying subsoil constraints on Mallee farms

Fact Sheet #8 – Feb 2004

Dr Garry O’leary – CSIRO Land and Water, Mallee Research Station, Walpeup

What’s the issue?
Physical and chemical subsoil constraints are known to reduce crop growth and yield in Mallee soils. Such constraints limit root growth, water use, nutrient uptake and ultimately grain yield.

Yield losses of around 20-25% (typically 0.5 t/ha = $50/ha) have been reported. Not only yield and profit are reduced but losses of water and nutrients also occur, and significant losses of water can contribute to increased salinity in the Murray basin.

What do we know about subsoil constraints?
Significant chemical subsoil constraints to cereal cropping were first identified in the Mallee region. The problem of chemical subsoil constraints in this region is a serious problem requiring attention from both plant breeding and agronomic management.

The major constraint appears to be predominantly high salt, often NOT associated with a shallow watertable.

Physical or Chemical?
• Chemical constraints appear to be geographically more widespread than physical constraints, such as compaction.
• Physical constraints are significant in some places (e.g. some mallee sandhills), however it is not clear if this issue is widespread.