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Dirt In general there are two types of soil, or dirt, on this planet, what we may call mountain soils and meadow soils. Although this is an over simplification, it will serve as a basis for discussion. What happens in the mountains is that the rain water
washing through the rotting organic matter at the surface of the
ground picks up carbon dioxide to form carbonic acid which tends
to dissolve the calcium carbonate as it washes through the underlying
rocks. This dissolved calcium, as calcium bicarbonate, goes down
in the ground water to lower elevations. During the summer months this ground water, laden with calcium bicarbonate, evaporates at the surface of the meadows and re-precipitates the calcium as calcium carbonate, tending to make the surface dirt more alkaline. Rhododendrons, azaleas, camellias and
many other plants apparently prefer what we may call upland forest
soils where the fertility of the surface dirt depends largely on
the ability of the acids to release the minerals of which the dirt
is made. Most of our orchards, including apples, pears, cherries etc. from the rose family, and most of our vegetables, beans and grains like what we may call valley or meadow soils where the fertility depends largely on the ability of the calcium carbonate to hold the necessary minerals in the surface dirt where they are available to the plant's roots. Plants have a limited ability to select what they need from their available resources by putting out more roots in the areas where they find what they want. The fertility of garden soils may sometimes be gauged by dripping hydrochloric acid on a sample. If the acid fizzes, the dirt has enough calcium carbonate to hold the necessary nutrients. The fertility of garden soils may be greatly improved
by digging in organic matter, leaves, manure and whatnot, and allowing
it to rot, then treating it with hydrated lime, fertilizer and whatever
minerals may be needed. The hydrated lime will be caught as calcium carbonate by the carbon dioxide from the rotting organic matter. Then the phosphates of the fertilizer will be caught by the calcium carbonate. Since calcium ammonium phosphate is insoluble in water, even some of the nitrogen may be caught. If, after digging-in the organic matter,
the soil is allowed to dry before sprinkling-in a 'light snowfall'
of hydrated lime, the calcium will be caught. And if, after liming,
the soil is allowed to dry, before watering-in the fertilizer, the phosphate
will be caught and be available to hold most of the needed minerals where
the plants can get at them. Some of the rules you learn in chemistry are that all nitrates are soluble, and that most sodium, potassium and ammonium salts are soluble. But there are a few exceptions. Potassium calcium sulfate is only sparingly soluble, so you can even precipitate potassium if you have some sulfates in your fertilizer. Also, magnesium ammonium phosphate is only sparingly soluble, and calcium ammonium phosphate is insoluble, so you can precipitate nitrogen as ammonium salts, and let the nitrifying bacteria oxidize the nitrogen to nitrate for the plants. One of the advantages
of letting the soil dry before sprinkling it with lime and watering
it in is that it allows the earthworms to go down out of harms way. If you don't happen to live on a delta, where the mineral base of your dirt is silt, brought down by the river from various sources, and if you don't happen to live in south China, where the mineral base of your dirt is thirty feet deep, brought down by dust storms from the Gobi Desert, you may want to up grade the mineral base of your garden. Powdered granite from the aspirator at the tombstone cutter's shop, which splashes in the bucket like water, is probably as good as you can get. Failing that, you might try fine granite sand from the quarry. Or you might add some dolomite number ten, or some oyster shell meal. (In the nineteen sixties,
when I was grinding telescope mirrors against a cast iron tool, with
granite sand for my abrasive, I poured the wet slurry around the
plants at night, and by morning I could see that they loved it.) There are quite a number of minerals that are used in small quantities by plants, magnesium, iron, manganese, copper, zinc, boron, and even molybdenum. Salts of these minerals, dissolved in extremely dilute sulfuric acid, may be sprinkled into the surface dirt occasionally to up grade the mineral base of poorer soils. John Dobson July 4, 2002 4135
Judah Street, San Francisco CA 94122 (415) 665-4054
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