That's because what you do above ground changes what happens in the soil—and what happens in the soil makes a difference to farm profitability.

When Dr Gupta Vadakutta, a CSIRO microbiologist, began studying soil microbes in Mallee soils for the Grain & Graze program, he found that the less plant diversity and biomass above ground, the less microbial diversity and density below ground.

Microbes are an essential ally for farmers, Dr Vadakutta says.

They are instrumental in the decay of stubble and pasture litter, and converting it into plant-available nutrient.

They suppress soil-borne crop diseases, encourage plant growth, stabilise the soil and hasten the degradation of chemical residues.

All this contributes to better plant yield and quality, and lower input costs.

Dr Vadakutta’s studies in Mallee soils have shown that microbe-friendly management can increase the release of nitrogen held in the soil by 50pc—from about 20 kilograms/hectare to 35-40kg/ha in one study.

Improved microbial biomass was also demonstrated to halve the loss of nitrogen from leaching.

Annual losses of up to 50 kg/ha of nitrogen were measured at a South Australian site.

While there are various practices that encourage microbes, such as time-controlled grazing and no-till farming, they all come back to a single objective—building carbon in the soil.

“Carbon is the energy source for microbes to built their populations,” Dr Vadakutta said.

“Depending on the soil type, increased amounts of carbon will increase the microbial pool, which acts as a sink for nutrients.

"Biota require nutrients, so they accumulate them—and they will accumulate nutrients when they have carbon, because they need energy.”

Recent Adelaide University studies in South Australia have looked at why farmers in the Eyre Peninsular lost up to 90pc of their winter crops to rhizoctonia, but the losses weren’t shared by their counterparts in the mid-north Avon district.

The difference, researchers believe, lies in the higher levels of soil carbon in the Avon, and the disease suppression activities of the microbes that draw on the carbon.

This increasingly important science of soil microbiology is about to get a boost through molecular genetics, which will help researchers better identify and understand the teeming trillions of organisms that live in every spoonful of fertile soil.