SOIL: did you know?

• An average soil sample is 45 per cent minerals, 25 per cent water, 25 per cent air and 5 per cent organic matter; the organic portion can rise to 10 per cent in a well-maintained garden soil.
• The mineral portion of soil is made up of weathered rock.
• Many soils have been transported over long distances by glacial movement, water flows and wind, settling far from their original ‘parent rock’.
• Central and South American rain forests get most of their mineral nutrients from the Sahara, as soil dust from North Africa is transported across the Atlantic.
• It is the size of the mineral particles that gives the soil its texture, from very fine clay to coarse sand. Fine clay is used to make porcelain.
• Volcanic soil is among the most fertile on the planet.
• A healthy soil reduces the risk of floods and filters out pollutants from water.
• Red and yellow soils contain iron and are low in organic matter.
• Dark brown to black soils are high in organic carbon and are good for agriculture.
• Blue to purple soils suffer waterlogging.
• Rainforest soils contain little organic matter because the heat and humidity break it down too quickly for it to penetrate below the soil surface. This is why such soils degrade so quickly after deforestation, making them inappropriate for conversion to agriculture.
• Humus is organic matter that has reached a point of stability where it will break down no further if conditions do not change. A high humus content improves soil structure, promoting moisture retention and aeration.
• Bacteria and fungi secrete sticky substances that help bind the soil together.
• Soil classification is extremely complex: scientists have identified more than 10,000 soil types in Europe and more than 20,000 in the USA.

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