Decline in canola yields due to 'soil constraints'

Canola plants showing symptoms of manganese toxicity.
Canola plants showing symptoms of manganese toxicity.

Canola yields in southern Australia decreased by ten per cent during the 1990s, and grain growers fear that acid and saline soils could be partly to blame.

Sub-soil constraints on canola performance, along with increased disease pressure, are thought to be the two main reasons for the yield decline.

A new three year $900,000 research project funded by the Grains Research and Development Corporation (GRDC) is to look at the relative contribution of subsurface soil constraints to the poor performance of canola.

Project leader Dr Mark Conyers from the NSW Department of Primary Industries (DPI) says the popularity of canola – invaluable as a ‘break’ crop – could have led to it being grown on less suitable soils.

A cash crop in its own right, canola is used to break the cycle of cereal root diseases and to improve the performance of wheat.

Research in southern NSW has found that wheat grown after canola yields 20 per cent more than wheat grown after wheat, and the gross margin for canola-wheat is 25 per cent higher than for wheat-wheat.

Dr Conyers says increased use of canola could have led to increased disease pressure, and that disease is a key factor in yield decline in some areas.

“The decline in relative canola performance could also be due to its increased popularity in the 1990s and the consequent spread of canola onto less suitable soils.”

Researchers have found that the depth that canola roots grow to varies greatly according to soil type, and this affects how much water the plants can access.

A CSIRO survey of 130 paddocks from Corowa to Canowindra in southern NSW found that root depth in heavier sodic (sodium-affected) clay soils was about 100 cm - half that for friable red loams.

At sowing time, water stored in subsoil can significantly improve yields – and the amount of stored water available to a crop is strongly influenced by root depth.

Dr Conyers said research undertaken south of Wagga Wagga found that the development of roots of canola plants in about 60% of paddocks were severely restricted, often resulting in ‘J-rooting’.

The study aims to identify key sub-soil constraints such as hardpans, salinity (osmotic effects or toxicity), acidity and sodicity.

“This will enable us to provide ‘best bet’ management strategies for ameliorating sub-soil constraints.”

“Our goal is to improve canola performance so that its important role in the farming system is maintained”, Dr Conyers said.

GRDC has awarded the Graham Centre – a partnership between NSW DPI and Charles Sturt University – funding to lead a consortium to carry out the research.

Consortium partners include CSIRO, Farmlink, Victorian DPI and the University of Melbourne.