This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Soils are classified in various ways, according to their texture and mechanical composition. Thus such terms as poor, hungry, cold, hot, wet, heavy, light, sour, sweet, are used to denote various conditions; while the terms sandy, clayey, loamy, chalky, marly, and peaty indicate the predominating constituent of a particular soil.
Several of these terms really mean the same thing to the cultivator. A poor, hungry, light, or hot soil, as a rule, indicates one of a sandy or gravelly nature. Such a soil is " poor" because it is impoverished of plant foods; it is "hungry" because it eats up enormous quantities of organic manures; it is "light", not because of its actual weight, but because it crumbles and falls to pieces easily, and its particles will not cohere and retain sufficient moisture or food; it is "hot" because its gritty particles absorb so much heat during the day that moisture is driven away from the roots of the crops. A "hot" soil also has great variations and fluctuations of temperature, being generally too hot by day in the summer and too cold by night in winter. A hot soil, however, that is well manured and supplied with sufficient moisture is valuable for the production of early crops.
On the other hand, a cold, wet, heavy soil usually denotes one of an ill-tilled, clayey nature. Such a clayey soil is "cold" because of its "wetness", the heat of the sun being used to dry up the superfluous water instead of being available to warm the soil particles and promote root action. It thus follows that a wet and cold soil is also a "heavy" one, that is, one very difficult to lift, owing to the cohesiveness of its particles, and not so much on account of its actual weight.
When a cold, wet, and heavy, clayey soil is also full of decaying organic material, and is never deeply cultivated, it then becomes "sour". This sourness is due to the fermentation and decomposition of the organic refuse, which liberates the carbonic acid gas so freely that oxygen is driven out of the soil. A good loamy soil even may be brought into a sour condition by overdressing with stable manure, and by not digging deeply to allow the fresher air to enter and the water to pass away freely to the lower strata.
To test a soil for sourness or acidity, place a small portion into a clean Florence flask, adding enough distilled or filtered rain water to cover it. Boil over a lamp for about fifteen minutes, afterwards allowing the solid matters to settle. Then pour off the clear liquid, and test with a slip of blue litmus paper. If the paper turns red, it is a sign that the soil is sour. To remove the acidity, the soil should be deeply dug, and lime or basic slag added.