Brassica plants such as canola release chemicals which can kill some soil organisms. This is one good reason why canola boosts following wheat yields, especially in areas where the take-all fungus thrives.
But does the chemical affect only the 'nasties' in the soil and leave good organisms such as vesicular arbuscular mycorrhizal (VAM) fungi alone?
VAM form an association with a majority of plants and act as an extension to the root system by helping the nutrient uptake.
Canola's effect on VAM is under the microscope of CSIRO's Megan Ryan. At sites in NSW and Victoria, Dr Ryan found that VAM numbers were consistently lower following brassica crops. However, in the soil types examined to date, this did not affect wheat yields because wheat is among the species that do not depend on VAM.
It may be a different story for VAM-dependent crops — among them most legume plants, plus linseed and sunflower.
And that is the next phase of Dr Ryan's research — to find out the extent of yield loss, if any, when VAM-dependent crops are grown following a brassica.
Contact: Dr Megan Ryan 02 6246 5387