27 May 2007

Topsoil: It's the Organisms, Stupid!

There is nothing magical about topsoil. For thousands of years, humans have been able to detect when soil was healthy and capable of growing good crops. Although pre-scientific humans knew nothing about the details of decomposition, they could tell a good crop from a bad crop--and quickly learned the external characteristics of good soil.

Now we are being told that the earth is losing its topsoil, and that such a loss can never be recovered. Regular readers of this blog may recognise such claims as "appeals to the pseudo-apocalypse." Which is precisely what they are.

It is certainly true that mining and other industrial processes destroy topsoil. And while conventional methods of remediating soil from mining and from other industry may be effective, they can also be extremely expensive.

Scientists in Russia have developed complex mixtures of micro-organisms that can be placed in situ, to remediate soil from petro-chemical contamination. Canadian scientists have gone farther, creating symbiotic combinations of plants and microbes, to clean contaminants from soil in situ.

Researchers are always looking for new bacteria in the strangest places. Or perhaps, not so strange, if you are looking for assistance for petroleum cleanup.

Here is a short description of the micro-world of soil:
• Bacteria -- Bacteria are the tiniest and most diverse of all soil organisms. A single teaspoon of topsoil typically contains more than 100 million bacteria that belong to over 1,000 different species. Bacteria help to decompose residue in the soil and increase nutrient availability for plants by dissolving phosphorus and fixing atmospheric nitrogen. Some bacteria that live on plant surfaces can also prevent plant diseases, either by antagonizing pathogens or stimulating the plant’s own immune systems.

• Fungi -- Fungi are important in the break down of plant residue, and they can transport nutrients through the soil profile. Because they are tougher than bacteria, they tend to release nutrients more slowly so that plants can have access to them throughout the growing season. Some fungi, called mycorrhizae, develop beneficial relationships with plants that allow for nutrient and water absorption by plant roots. Fungal cells also help to stabilize soil structure by secreting a sticky gel that glues mineral and organic particles together into aggregates. These aggregates allow for natural breaks to occur in soil, allowing for greater aeration and water infiltration.

• Protozoa -- Protozoa are single-celled animals that act as secondary consumers of organic matter. They feed on bacteria, fungi, other protozoa, and organic molecules. Protozoa are believed to be responsible for mineralizing a small fraction of the nitrogen in soils.

• Nematodes -- Nematodes are simple worms that are less than one-tenth of an inch long. They help breakdown organic residues and feed on bacteria, fungi and protozoa. They also convert some nitrogen into usable forms for plants.

• Free-living mites -- Soil mites are arthropods that graze on decomposing organic matter, fungi, algae and nematodes. Mite populations are slow to develop, so their appearance indicates a highly stable soil environment.

• Springtails -- Springtails are arthropods found in decaying material. They are one of several biological agents responsible for the creation of soil, and are considered to be the most abundant of all macroscopic animals living in the topsoil.

• Earthworms -- Earthworms round out the list as important keepers and restorers of soil fertility. While less numerous than nematodes, they account for up to 10 times the biomass of the other secondary consumers. Earthworms feed on bacteria-laden plant residues and organic matter mixed with mineral particles. The resulting material is given off as worm casts, which are generally higher in available nitrogen, calcium, magnesium and phosphorus than the soil itself. Earthworms also constantly bring soil up to the surface, providing anywhere from one to 100 tons per acre of organic-laden soil for plant use each year.

“There are countless other organisms that contribute to the soil community. The variety of soil organisms is so high that even today we don’t have the tools to say what an average community really looks like from a small scale to a large scale,” said Gardener. “But it can be said that a healthy soil is often marked by multiple trophic levels of diverse microflora, microfauna and mesofauna.”

Up until now, most of the microbe-hunting has been done by pharmacology researchers, looking for magic bullets against human infection, cancer, and other disease. More and more, such hunts are being done to find cures for environmental ills.

Plants can certainly be grown without soil, and in certain environments aeroponic crops will be the only source of fresh vegetables and fruits.

But the Earth itself has needs beyond the needs of humans. That is the concern. That is why humans have to learn to care for the health of the planet. Humans can learn to take care of themselves. They can also learn to care for the planet, even when their own welfare is not directly concerned.

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“During times of universal deceit, telling the truth becomes a revolutionary act” _George Orwell

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