The Living Soil
“If we have declared a war against the soil itself, then we are literally committing a species level suicide.”Dr. Vandana Shiva (Indian scholar and environmentalist)
One of Earth’s greatest treasures is soil, without which we could not survive. Soil is the mother of nearly all plant life, and ultimately, all animal life on this planet. This living skin of the earth is the interface between biology and geology.
Soil starts with a mineral source—weathered rock, glacial silt, river sediments, lava flows, sand, etc. As each piece of land has its own geological history, the mineral content of soil varies among different pieces of land except the basic silicon oxide. But soil isn’t soil yet until organic matter is added. Organic sources can be living or non-living. Old leaves, dead animals, and tiny living things all enrich the soil with its necessary carbon.
Healthy mature soil is about 50 percent solids and 50 percent air and water, simply teeming with life—mites, nematodes, protozoa, and a whole menagerie of other organisms, most of them smaller than the head of a pin.
Soil microorganisms are so abundant that 70 to 80 percent have yet to be identified. It is estimated that one tablespoon of soil contains about 50 billion microbes. More than 90 percent of land plants are nourished by mycorrhizae, a symbiotic form of fungi that help move nutrients from the soil into the plants’ roots. There are millions other microbes each functioning in special ways to enable the plants to grow healthily. Bacteria eat exudates released through the roots of the plants while nematodes and protozoa swim in the film of water around soil particles and feed on bacteria. Mites eat fungi and fungi decompose soil organic matter. Secretions of some microbes decompose minerals and turn them into plant available form. These soil lives create channels that improve aeration and drainage as they move through the soil, making it unfavorable for anaerobic bacteria to grow. In this way, they help keep the plants healthy as pathogenic bacteria are usually anaerobic. As the C to N (carbon-to-nitrogen) ratio of these creatures is different, different combination of these soil microbes partly determine the kind of plants they can best nourish.
Generally speaking, the once lifeless crustal rock surface of the earth becomes sand, silt and clay that carry various kinds of minerals from their geological origin through physical processes like weathering, glacial grinding, sedimentation, etc. Since the first nitrogen fixing bacteria brings nitrogen from the atmosphere into the soil, biological successional processes result in generation of tens and thousands of variation in species, and equally abundant in variety are the plants and animals these soil microbes nourish. During this process of evolution, certain minerals and elements enter into a kind of cyclic exchange between the rocks and the atmosphere, releasing the energy from organic matter that have completed their life cycle. Besides the basic carbon cycle, nitrogen cycle and phosphorous cycle, other elements like potassium, sulphur, magnesium, calcium, zinc and trace elements like selenium, etc. also circulate in different living things through the immobilization and mineralisation processes of the microbes. But microbes must have a constant supply of organic matter or their numbers will decline. Conditions that favour soil life also promote plant growth.
Soil has its own life cycle. The best place to observe life cycles of soil is in Hawaii. The Hawaiian Islands are formed through millions years of platonic drift almost in the same direction above the same hot spot deep inside the crust. Islands formed by the cooled down lava line up according to their chronological age. Mineral compositions of the topsoil of the islands are similar as they all have lava as their substrate. On the new island like the Big Island of Hawaii, soils as young as 300 years to extraordinarily rich 20,000-year-old soils in which just about anything can grow, to 350,000-year-old soils whose nutrients have been washed out by eons of rainfall can be found. Extremely old Hawaiian soils, like Kauai, reaching four million years, are almost completely devoid of nutrients. These ancient soils are highly compressed and essentially just clay.
Homo Sapiens first appeared on this planet about 0.2 to 1 million years ago. Farming which enables human beings to choose ‘when to eat what’ has a history of merely ten thousand years old. The life cycle of natural soil should be sufficiently long to nourish all of us if not because of the disturbance of the carbon cycle caused by the use of fossil fuel began about three hundred years ago.
Nitrogen fertilizers were produced from nitrification weapons and insecticides and herbicides from poison gas developed during the First World War. That the seemingly impressive upsurge in farming yield came with the price of diminution of soil health was not known until quite recently.
The operation of food chain based upon large scale mechanical, chemical intensive monoculture agriculture that flourished after the Second World War results in excessive leaching of chemicals into land and fresh water resources rendering the waterlogged soil impermeable and easily compacted by heavy machinery. The soil aging process is thus accelerated. World-widely, soils that would have remained viable for millions of years in nature now become more and more vulnerable to weathering and soil erosion with microorganisms poisoned by agricultural chemicals causing decrease of organic matter in soil. The rate at which soils are disappearing from our globe is alarming. The real-time clock in the Worldometers shows that the area of land lost to soil erosion so far this year amounted to 4,987,477 hectares (1.7times the area Belgium) — and of course, the year (as at Oct 2014) isn’t over yet. In addition to the land lost by desertification which has been exuberated by global warming, the world is losing 12 million hectares of land (3 times the size of Switzerland) every year. According to UN statistics, one-third of the world’s arable land has already been lost to soil erosion. Tragically, these soils will take hundreds to thousands of years to recover fully in nature—and not until all agricultural assaults are ceased. The UN predicts that the world population will reach 9 billion by 2050, and 1 1billion by the end of his century.
Can the development of our food supply system focus only on higher yield without pollution? Is it about time that developing healthy soil and rehabilitating degraded soil be given equal importance if we want to survive as a species?
#soil biology reference