THE IERIGATION AGE. 



123 



Notes on Practical 

 Irrigation 



D. H. Anderson 



SOIL IN GENERAL. 

 Foundation of Plant Life Power to Absorb Moisture. 



The reader has already discovered that the inorganic 

 elements consist of decomposed rocks and minerals, which 

 have assumed a variety of forms by combining with one 

 another, and now he has reached a point which is the 

 foundation of plant life, being that other essential in all 

 soils, the organic elements, which must exist in a greater 

 or less proportion. This organic matter consists of de- 

 cayed animal and vegetable substances, sometimes in 

 brown or black fibrous particles, many of which, on close 

 examination, show something of the original structure of 

 the objects from which they have been derived; some- 

 times forming only a brown powder intermixed with the 

 mineral matters of the soil, sometimes entirely void of 

 color and soluble in water. In soils which appear to 

 consist of pure sand, clay, or chalk, organic matter in this 

 latter form may often be detected in considerable quan- 

 tities. 



In the table already given, the percentage of humic 

 acid, insoluble humus, and organic substances contain- 

 ing nitrogen, is given as 3.387 per centum, a very small 

 quantity apparently, but really amounting to 124,521 

 pounds or 62J4 tons, in a top layer of soil eight inches 

 deep, covering one acre of land; a quantity sufficient to 

 supply crops with essential matter for plant food dur- 

 ing many years without manuring. 



This vegetable matter is the result of vegetable de- 

 composition, a decay which means fermentation ending 

 in putrefaction, a purely chemical process. Whence it is 

 said: Growth is a living process; death, or decay, a 

 chemical process. Putrefaction is the silent and inward 

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

 turn produces life. The saying of that great physician 

 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 pro- 

 duce an animal, and the seed, or plant germ, must first 

 putrefy before there can be any living plant. 



Three Classes of Soil. 



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 siliceous, 

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

 clay is meant the common clay abounding everywhere, 

 and composed of about thirty-six parts of alumina, sixty-eight 

 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 therefore, 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 dynamite 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 character- 

 istics. 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 always 

 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 gar- 

 den or vegetable mould and arable soil weigh from 102 to 

 119 pounds. The more humus compound soil contains, 

 the lighter it is. 



Why Sand Plains Are Hot. 



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 phyical characteristic, de- 

 pends upon four circumstances: color, dampness, materials, 

 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, or secondly, damp- 

 ness 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 different 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 tempera- 

 ture will be found to be inconsiderable. 



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



