The living soil

Pauline Mele observing isolated bacteria from wheat roots that are capable of fixing nitrogen. These may represent possible candidates for inoculant development,

Hold a teaspoon of soil and what do you see? Perhaps a very small clod or two, lots of fines (fine soil particles) and the odd flake of straw...?

What you don't see is about one million microbes, which is how many Pauline Mele says are present, on average, in a teaspoon of soil.

This Agriculture Victoria researcher says that soil microbes can do much to help farmers and farming - fixation of nitrogen by rhizobia on legumes being the classic example, but there are others which Dr Mele detailed at the recent annual conference of the Wimmera Conservation Farming Association.

She said that a project supported by growers through the GRDC has shown that the total root length of wheat can be increased when inoculated with a mixture of bacteria isolated from around the wheat root - the practical implications being that the bacterial activity leads to increased early vigour in plants and the potential for higher yields and grain quality.

That's good news and so is the increasing use of one microbe species to suppress the growth of another disease-causing microbe. This technology is commonplace in some overseas countries and, in Australian research, a common soil fungus used to protect wheat from take-all has led to wheat yield increases of 8 per cent.

The good news doesn't end there. Certain bacteria, for example, have been found to degrade waxy residues, and improve water retention and yields in non-wetting soil.

What can we do for microbes?

So there are a number of things microbes can do for farmers, but what can farmers do for them?

Dr Mele says many of our main farming practices have an impact on soil microbial resources either, directly or indirectly.

Stubble retention, for instance, generally increases microbial activity and the number of species present which, in turn, leads to improved soil structure and water infiltration.

When combined with direct-drilling, stubble retention has been shown in Rutherglen trials to increase the number of beneficial fungi. Lime applications in acid soils get the microbes moving too, leading to improved nutrient turnover and soil 'wettability', while legumes-based rotations are known to support a larger, more active and more diverse soil microbial community.

Says Dr Mele: "We can exploit the beneficial properties of soil microbes by considering how our current management practices affect their performance, and modify these practices where appropriate."

Program 3.4.2

Contact: Dr Pauline Mele 02 6030 4500