THE IKRIGATION AGE. 



15 



Notes on Practical 

 Irrigation 



D. H. Anderson 



SOIL IN GENERAL. 



Its Formation, Characteristics and Uses Fertility and 

 Sterility. 



The mere planting of a seed in the ground is not 

 sufficient to insure its growth or development into a 

 useful or profitable plant. This fact is well known to 

 everybody, but what is not so well known is, the reason 

 or cause why a seed grows up into a vigorous plant cap- 

 able of reproducing seed similar to the one from which 

 it sprang, and how it does it. 



There are certain- elements which are essential to 

 the growth of every plant, the development of every 

 germ, for without them it cannot live; these are heat, 

 light, air and moisture. A few grains of wheat discov- 

 ered in the coffin of an Egyptian mummy after three or 

 four thousand years' deprivation of the four essential ele- 

 ments, were found inert, that is, they were not alive, 

 neither were they dead, for upon giving them the essen- 

 tials above referred to, the wheat sprang into life and 

 produced a plentiful supply of grain. 



Still, notwithstanding the necessity of heat, light, air 

 and moisture, plants cannot flourish without proper food. 

 In this respect plants are similar to animals. Among 

 animals there is no universal specified diet, some eating 

 one kind of food, others another. We see many that eat 

 flesh exclusively, others whose sole diet is insects. Cer- 

 tain animals eat herbs and grass, others grain, and when 

 we reach man we find an animal that will eat anything 

 and everything; hence we call man "omnivorous." 



It is the same with plants, some devouring in their 

 fashion a certain kind of food, some another, and so on 

 all along the list. Plants are substantially like animals 

 that possess a stomach; they eat and digest, absorb and 

 assimilate the food they obtain. If the plant is not fur- 

 nished with its proper food, or if it is prevented from 

 obtaining it, it shrivels, droops, withers and dies just like 

 an animal that starves to death. 



Plant Instinct for Food. 



There is another striking resemblance between plants 

 and animals, which is the instinct and power 'to seek food. 

 The plant being a fixture in the soil, cannot, of course, 

 "prowl" about in search of food, but it throws out roots, 

 fibers and filaments in every direction, its instincts reach- 

 ing in the direction of food as surely and with as much 

 certainly as the nose of an animal scents its prey of the 

 eye of an eagle sees its quarry. Not only does the plant 

 seek food beneath the surface of the earth, but it thrusts 

 shoots, branches and leaves up into the atmosphere for 

 the purpose of extracting nourishment there also. 



It is, however, from the soil that plants receive the 

 principal supply of food necessary for their development, 

 hence an acquaintance with its chemical and physical 

 properties is important in helping us to understand the 

 nutritive processes of plants and the operation of agri- 

 culture. 



Volumes of books have been written on the general 



subject of agriculture, but they are more adapted to soils 

 upon which falls sufficient rain to dissolve the salts neces- 

 sary to produce a crop. In a book devoted to irrigation, 

 the principles of agriculture and' the adaptation of the 

 various elements of plant food in the soil are all the 

 more important, as the water employed in irrigation 

 which is nothing but artificial rain -is absolutely within 

 the control of man, and not dependent upon meteorolog- 

 ical uncertainties. One fact should, however, be con- 

 stantly borne in mind by the practical irrigator, that pure 

 water is absolutely sterile so far as plant food is con- 

 cerned, and if poured upon a pure soil, which is also 

 sterile, there can be no crop of any sort raised. A rem- 

 edy for supplying a defect of plant food in irrigating 

 water will be given in detail in another chapter, the scope 

 of this chapter being limited to soils that contain plant 

 food, or are arable, in which case the quality of the water 

 is of secondary importance. 



Origin of Arable Soil. 



Arable soil owes its formation to the disintegration 

 of minerals and rocks, brought about by mechanical and 

 chemical agencies. The rock may be said to stand in 

 about the same relation to the arable soil resulting from 

 p its disintegration as the wood or vegetable fiber stands 

 to what is called the humus resulting from its decay. To 

 be fertile, however, the soil must contain disintegrated 

 vegetable matter. There is no fertility in a heap of saw- 

 dust, nor is there in a heap of powdered rock; indeed, 

 the two might be combined and still remain sterile, it is 

 only after both have been disintegrated by chemical or 

 mechanical action that they become plant foods capable 

 of nourishing and maintaining plant life. 



From this it results that soil consists of two grand 

 divisions of elements: inorganic and organic. The in- 

 organic are wholly mineral; they are the products of the 

 chemical action of the metallic or unmetallic elements of 

 rocks. They existed before plants or animals. Life has 

 not called them into existence, nor created them out of 

 simple elements. Yet these inorganic mineral elements of 

 soil become part of plants, and under the influence of the 

 principle of life they no longer obey chemical laws, but 

 are parts of a living structure. Through the operation of 

 the laws of the life of the plant, these mineral elements 

 become organic and so continue until death comes and 

 decay begins, when they return to their mineral form. 



Organic elements are the products of substances once 

 endowed with life. This power influences the elements, 

 recombines them in forms so essentially connected with 

 life that they are, with few exceptions, produced only by 

 a living process. They are the products of living organs, 

 hence termed organic, and when formed, are subject to 

 chemical laws. The number of elements in the inorganic 

 parts of soil is twelve: Oxygen, sulphur, phosphorus, 

 carbon, silicon and the metals: potassium, sodium, cal- 

 cium, aluminium, magnesium, irori and manganese. 



The number of elements in the organic parts of soil 

 does not exceed four: Oxygen, hydrogen, carbon and ni- 

 trogen. 



The great difference between these two divisions is, 

 that while the inorganic elements are combinations of 

 two elementary substances, the organic are combinations 

 of three or four elements, but never less than two. These 

 three elements, however, are variously combined with the 

 other elements to form salts which enter into the great 

 body of vegetable products, in fact they are continually 



