As you have probably guessed from my column over the years, I love soils, partly because they are the foundation of human life and culture, and partly because they are just so fascinating.

They are colourful, diverse, full of history, and teeming with life, so much life in fact that most of the biodiversity in agriculture is in the soil, not above it.

We are just beginning to understand how organisms living in the soil dominate our agricultural production.

A recent paper by Brussaard et al outlines four challenges that are driving research on soil biodiversity:

• Does it make the ecosystem more resilient?
• Does it help us use water and nutrients more efficiently?
• How can we manage it?
• What is its value?

Researchers have found that high biodiversity enables soil organisms to recover more quickly from stresses such as the addition of heavy metals, or overheating.

They also found that in horticulture, organically managed soil had a more stable ecosystem than intensively managed soil.

The mechanism that provides this resilience and stability is not yet understood.

Stress might alter the population of organisms, making the foodweb unstable.

Another benefit of high biodiversity is that it makes soils less prone to pests and disease because the intense competition for carbon and nutrients inhibits the growth of pathogens.

However, to understand this mechanism further, we need more information on the relationship between soil biodiversity and plants, soil type and management.

Research has also found that polycultures (where a variety of plant species are grown together and support a greater range of soil organisms) have greater nitrogen and phosphorus uptake and uptake efficiency compared with moncultures, suggesting that soil nutrient supply is related to soil biodiversity.

And, interestingly, water use efficiency also seems to be greater in species-rich plant communities than in monocultures.

So how do we manage soil biodiversity, something we can’t see and still don’t understand very well, to achieve these benefits on our own farms?

Brussaard et al suggest we need a combination of factors: good choice of crops and trees, enhancement of natural pest and disease resistance of chosen plants, improvement in the quality of residues they produce, management of organic matter and fertilisers into the system, minimum tillage and maintenance of crop residue cover on the soil surface.

Read their paper, Soil Biodiversity For Agricultural Sustainability, in the journal Agricultural Ecosystems and Environment 121, July 2007.