THE IRRIGATION AGE. 



211 



chemical process. Putrefaction is the silent and on- 

 ward march of decay, its goal being humic acid, which 

 in its turn produces life. The saying of that great physi- 

 cian of the past centuries, Paracelsus, may be aptly 

 quoted here: "Putrefaction is the first step to life." 

 Everything travels in a circle in the vegetable as well 

 as in the animal kingdom : The egg, or germ must 

 first putrefy to produce an animal, and the seed, or plant 

 germ, must first putrefy before there can be any living 

 plant. 



It has been said that various names have been given 

 soils, according to the predominating mineral of which 

 .they are composed, but in reality, there are only three 

 great varieties of soil: sand, clay and loam, the latter 

 being a mixture of granite sand and clay. The great 

 distinctions in the scale of soils, may be said to be sand 

 and clay, all other varieties proceeding from mixtures 

 of these with each other. Now, the sand may be silice- 

 ous, or calcareous, that is, composed of silicates or lime. 

 By clay is meant the common clay abounding every- 

 where, and composed of about thirty-six parts of Ahim- 

 ina, 68 parts of Silica, Oxide of Iron, and Salts of Lime, 

 and Alkalies, 6 parts. A sandy clay soil is clay and 

 sand, equal parts; clay loam is three fourths clay and 

 one fourth sand; peat soil is nearly all humus, which 

 we have seen is vegetable matter decomposed, decayed 

 or putrefied; garden, or vegetable mold is eight per 

 cent humus, the rest being silica, and the other mineral 

 substances; arable land is three per cent humus. There 

 are, in addition to these varieties of soil, several special 

 varieties which are fortunately not general, and there- 

 fore, need not be more than referred to. They are those 

 peculiar conditions found in the "black waxy," "bad 

 lands," "hard pan," upon which, nothing short of dyna- 

 mite will make any impression so far as discovered, and 

 the "tules," which are common to California, but are 

 extraordinarily fertile when reclaimed, being similar to 

 peat bogs without the disadvantages of the latter, and 

 that are known as "swamp" or "marsh lands." When 

 it comes to "desert lands" in the sense of the Acts of 

 Congress, they lack only water to make them as fertile 

 as any lands in the world. They will be treated in the 

 chapter on Arid and Semi-Arid Lands. 



Aside from the chemical composition of soils, what 

 equally concerns the farmer is their physical charac- 

 teristics. These may be enumerated under the terms 

 cold, hot, wet and dry land. And these are dependent 

 upon weight, color, consistency, and power to retain 

 water. The relation of the soil to consistency makes 

 it light or heavy; its relation to heat and moisture 

 makes it hot or cold, dry or wet. 



Taking the varieties already specified, sand is al- 

 ways the heaviest part of soil, whether dry or wet; clay 

 is among the lightest parts, though humus has the least 

 absolute weight. . To calculate more closely : a cubic 

 foot of sand weighs, in a common damp state, 141 

 pounds ; clay weighs 115 pounds, and humus, 81 

 pounds, and garden or vegetable mould and arable soil 

 weigh from 102 to 119 pounds. The more humus com- 

 pound soil contains, the lighter it is. 



The power of a soil to retain heat is nearly in pro- 

 portion to the absolute weight. The greater the mass 

 in a given bulk, the greater is this power. Hence, 

 sand retains heat longest, three times longer than 

 humus, and half as long again as clay. This is the 

 reason for the dryness and heat of sandy plains. Sand, 

 clay and peat are to each other as 1, 2, 3 in their power 

 of retaining heat. 



But while the capacity of soil to retain heat de- 

 pends on the absolute weight, the power to be warmed, 

 which is a very important physical characteristic, de- 

 pends upon four circumstances : color, dampness, mat- 

 erials, and fourth the angle at which the sun's rays fall 

 upon it. 



The blacker the color, the easier warmed. In this 

 respect, white sand and gray differ almost fifty per cent 

 in the degree of heat acquired in a given time. As 

 peat and humus are of a black, or dark brown color, 

 they easily become warm soils when dry, for secondly, 

 dampness modifies the influence of color, so that a dry, 

 light-colored soil will become hotter sooner than a dark 

 wet one. As long as evaporation goes on, a difference 

 of ten or twelve degrees will be found between a dry 

 and a wet soil of the same color. Thirdly, the differ- 

 ent materials of which soils are composed exert but very 

 little influence on their power of being heated by the 

 sun's rays. Indeed, if sand, clay, peat, garden mould, 

 all equally dry, are sprinkled with chalk, making their 

 surfaces all of a color, and then exposed to the sun's 

 rays, the difference in their temperature will be found 

 to be inconsiderable. 



Fourthly, the angle at which the sun's rays fall on 

 the land, has much to do with its heat. The more 

 perpendicular the rays, the greater the heat. The effect 

 is less in proportion as these rays, by falling more slant- 

 ing, spread their light out over a greater surface. This 

 point is so well understood that it is not necessary to 

 dwell any longer upon it, further than to add, that there 

 are localities where every degree of heat diminishes the 

 prospect of a good crop, particularly in hot regions, 

 and the circumstance should be taken advantage of to 

 obviate the danger of loss. A northern exposure or 

 an eastern exposure, or a crop on a slope may sometimes 

 realize more benefit than if this knowledge were dis- 

 regarded. 



The relation of soil to moisture and gas, particul- 

 arly moisture, is of great importance in the case of 

 irrigation. All soil, except pure siliceous sand, absorbs 

 moisture, but in different degrees. Humus possesses 

 .the greatest powers of absorption, and no variety of 

 humus equals in its absorptive power, that from animal 

 manure, except those heavily charged arid and semi- 

 arid lands, in which fibrous roots and vegetable matter 

 form a large part of the elements they contain. The 

 others rank in the following order : Garden mould, clay, 

 loam, sandy clay, arable soil. They all become satur- 

 ated with moisture by a few days' exposure. 



It is a very interesting question: Does soil give up 

 this absorbed water speedily and equally? Is its power 

 of retaining water equal? There is no more important 

 question to the irrigator. As a general fact, it may 

 be stated, that the soil which absorbs fastest and most, 

 evaporates slowest and least. Hnmus evaporates least 

 'in a given time. The power of evaporation is modified 

 by the consistency of the soil; by a different degree of 

 looseness and compactness of soil. Garden mould, for 

 instance, dries faster than clay. As it has already been 

 shown, that the power of being warmed is much modi- 

 fied by moisture, so the power of a soil to retain water 

 makes the. distinction of a hot or cold, wet or dry soil. 



Connected with this power of absorbing moisture, 

 is the very important relation of soil to gas. All soils 

 absorb oxygen gas when damp, never when dry. 

 Humus has this power in the highest degree, however, 

 whether it be wet or dry. Clay comes next, frozen 

 earths not at all. A moderate temperature increases 



