Why do healthy soils have such a delightful aromatic whiff?
That is the question micro biologist at the University of Tasmania Dr Shane Powell is tackling in a three-year project in conjunction with Soil CRC, eight Universities and many agricultural organisations including state governmental agencies.
Focusing on high performing soils is critical for the survival of landscapes, animals, plants and ultimately human life and Dr Powell said future understanding of the nature of soil is the basis of her current research.
"I am fascinated by microbes, they are all around us and we should not be freaking out about bacteria, it is all around us and essential," Dr Powell said.
"We wouldn't be breathing oxygen if not for the bacteria in healthy soil."
It is important to understand soil is complicated.
A shovel full of soil is a series of integrated systems, and Dr Powell pointed out they cannot really be understood in isolation.
"Soil is variable, even within one paddock different soil types can be seen," she said.
"Soil is exposed to many external influences such as weather and farming practices."
Dr Powell noted a healthy soil is a conduit for the exchange of nutrients between plants, bacteria and the atmosphere, and all dependent on the other.
"There are always inputs and outputs and they must be balanced," she said.
"Even if you don't think you are putting something in, if you have nitrogen fixing bacteria in your soil they are grabbing nitrogen from the atmosphere."
The diversity and complexity of soil is another level again and Dr Powell said the below ground biology includes insects, worms, nematodes, protoza, microbes, fungi and bacteria all in various stages of influence upon the ultimate health of the soil.
"Many we can't see but they are all incredibly important," she said.
"In a random handful of soil you can have several thousand different types of bacteria all contributing as living organisms are vital for soil to operate at its optimum."
Dr Powell said scientific research has shown soil biota enhance agricultural sustainability by improving crop and pasture yields, lifting nutrient uptake and reducing nitrogen leaching losses.
"It was vital evidence living organisms are vital to the soil to function at its most optimum," she said.
"Soil is a life support system and without it nothing would really function very well."
It aids in the decomposition of organic matter, nutrient recycling, increasing the availability of nutrients, it can cause disease but the bacteria and microbes within the soil can suppress disease.
"Healthy soils stimulate plant growth, suppress levels of disease and they work best when you have a group of organisms which reduce the effect of pathogens," Dr Powell said.
So how do we measure the odor of healthy soil?
Dr Powell said it is a bit like smelling coffee.
"It just smells good, we can't define the smell but we know it is healthy soil," she said.
"And we know the smell of soil after rain is fresh and nice, and we know the sharp sulfurous smell of rotting vegetation so why can't we measure the smell?"
Dr Powell said we can recognise the smell without being able to identify each compound in the soil but the odor does indicate something about the biological activity in the soil.
"The smell is a result of a whole lot of compounds associated with the decomposition of the organic matter in the soil and it will depend on the type of organic matter to start with and what organisms are breaking it down," she said.
"It's not only produced by bacteria in the soil but the fungi and bacteria in the plants also produce compounds which emit smell."
Dr Powell said research is looking at what the bacteria is doing not simply evaluating the different types.
"It is not possible to identify the definitive smell because each soil type is different," she said.
"What happens on a grain farm will be different to what is happening on an apple orchard but we don't know if the same healthy soil smell applies to all types of soils equally."
