What’s in a handful of soil?

Soil plays a critical role in the survival of people, plants and animals, yet is vastly underappreciated by the world at large. Victor Roberts, specialist soil scientist at the KwaZulu-Natal Department of Agriculture and Rural Development, explains why this situation must change.

What’s in a handful of soil?
Photo: Dr Jack
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The UN declared 2015 as the International Year of Soils. It is remarkable that this organisation, which deals with so many political and human rights issues, should also focus on the value and health of soil.

If I were to ask farmers what they regarded as their most valuable asset on their farm, most would say it is their soil. However, it is not quite as simple as that. The answer would depend on where the farmer wanted to be in three years’, five years’ or 20 years’ time. It would also depend on his views towards the environment and society.

If a farmer wanted to sell his farm and use the funds to retire comfortably, then perhaps his most valuable asset would not be his farm’s soil, but its agricultural machinery. If he intended to continue farming five to 20 years into the future, or wanted his children to inherit the business and continue farming on the property, his most valuable asset might well be his soil.

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If he wanted to increase the farm’s productivity in a sustainable manner, then the farm’s most valuable asset would certainly be its soil.

Complexity

There are many processes involved in the formation of soil, and these take an extremely long time. A mere 1cm layer of soil can take anything from a few hundred to a thousand years to form, a fact of great concern, considering the extensive soil erosion on the planet.

This complex and all too finite world is found, in varied forms, in every landscape across the planet. Factors such as different parent materials and different climates influence the diversity of our soils. A vast amount of life exists in a mere handful of healthy soil. Take the tardigrade, for example, a harmless and common invertebrate that is difficult to see with the naked eye. It is a micro-animal that measures between 0,2mm and 0,5mm in length and is found on every continent – from the top of Mount Everest to Antarctica – provided it has water to breathe and move in.

Tardigrades can survive temperatures of just 1°C above absolute zero (-273°C) and as high as 121°C. They can withstand crushing air pressure of 1 000 atmospheres, yet also cope with the vacuum of space. They can survive ultraviolet light and are resistant to many toxins as well as radiation hundreds of times stronger than what mammals can withstand.

Scientists have studied tardigrades for more than two centuries, but still have not found any specific medical, commercial or environmental uses for these creatures. They are simply there. Why am I focusing on tardigrades? Because these creatures offer a fascinating glimpse into the wonder and complexity of soil, and point to the fact that we have so much more to study on the subject.

A teeming world
In addition to tardigrades, healthy soil is home to billions of other organisms, many of which are known to be crucial in the balance of life. These include bacteria, fungi, insects, larvae, earthworms and decomposing plant material. A high-powered microscope reveals billions of organisms in a mere handful. And in one way or another, all are linked.

These organisms are not distributed evenly throughout the soil. There are zones of high concentrations of these organisms interspersed with zones that comprise mostly mineral matter, pores, water and few organisms. A single handful of soil contains in excess of 500 species of fungi and potentially more than 50km of fungal mycelium. There are 10 000 species and a staggering 100 billion individual specimens of bacteria.

Tens of species of tiny plants collectively produce over 500m of often invisible root systems. There are hundreds of species of algae and protozoa, and more than 50 species of nematodes comprising 10 000 individual specimens. A single handful of soil is home to more living organisms in a handful of soil than there are people on earth. In fact, there are more living organisms within the soil itself than above its surface.

Global effects
The handful of soil that we are looking at has global implications. For example, in the nitrogen cycle which functions on a global scale, soil is involved alongside the atmosphere and the ocean. Other important global-scale cycles in which soil plays a vital part include the carbon cycle, the sulphur cycle, the oxygen cycle, the phosphorous cycle and the water cycle. About 5,5% of the world’s carbon, excluding fossil reserves, is found in the soil. In addition, 1,7% of the earth’s water reserves are found in the soil.

A new look at soil
On average, 45% of any given quantity of soil comprises mineral matter, about 25% consists of air, about 25% is water, and about 5% is organic matter. Although these different aspects of soil have long been studied, it is only in recent years that scientists have concentrated on the boundaries between them. One of the more interesting boundaries is the rhizosphere, a narrow band of soil that surrounds plant roots. This is where mineral and organic matter intersect: roots give off exudates, making it an area of high activity and high populations of soil life.

Modern technology allows scientists more intensive investigation of the rhizosphere. A research paper published in 2009 in Plant and Soil titled, ‘The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms’, begins by stating: “The rhizosphere is a hotspot of microbial interactions as exudates released by plant roots are a main food source for microorganisms and a driving force of their population density and activities.”

READ: Testing your soil

 

Recent research has found that root exudates are responsible for even more than previously thought. For example, while we previously knew that iron, aluminium and manganese formed reactive soluble complexes and minerals in the soil, we have since found that this process has contributed to carbon sequestration for millennia. It also protects organic matter, which has a relatively quick turnover in the soil.

Intrigued by this new discovery, scientists have begun looking at three root exudates in the rhizosphere. They have found that, contrary to previous understanding, plant roots give decomposer organisms access to what was initially thought to be unavailable carbon. When plant roots exude oxalic acid, the population of soil microbia in the rhizosphere increases by as much as 100% to process the carbon.

Going, going, gone?
Despite learning ever more about the wonders of soil and its enormous value and importance, people have for far too long taken it for granted and treated it poorly. And the result is that, eventually, we may still have to erect a tombstone which reads: “RIP. Here lies my soil. Well, at least it did before I lost it.”

There is a danger that we are losing our soils faster than they can be replaced. One of the problem areas is farming, where it aims for maximum yield and compromises soil’s survival and sustainability. In 1907, renowned US agriculturist, CW Burkett, in his book, Agriculture for Beginners, wrote: “All over the country many soils are worn out, depleted, exhausted – almost dead. But here is comfort: these soils possess possibilities and may be restored to high productive power, provided you do a few simple things”.

This quote still holds true. We need to find and implement the processes needed to both preserve and improve our soils. Soil has an amazing ability to bounce back and keep going – if we treat it correctly. We must continually ask ourselves what we are doing to keep our soil in a good state.

And, if we don’t like the answer, then we need to make the necessary changes. – Lloyd Phillips

Adapted from a presentation given at the Conservation Agriculture Conference 2015, hosted by the No-Till Club at ATKV Drakensville, KwaZulu-Natal, from 1 to 3 September.

Phone Victor Roberts on 033 355 9455 or email [email protected].

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