THE IRKIGATION AGE. 



173 



is this susceptibility to change, and the constant as- 

 sumption of new forms by vegetable products which is 

 the foundation of tillage, and the essence of the knowl- 

 edge of irrigation. 



HOW PLANTS FEED. 



We do not know and we may not understand what 

 life is, nor how plants grow, but it is a knowledge which 

 comes to the most superficial observer, that all plants 

 feed upon various substances their roots find in the 

 soil, which substances are called "salts," and they arc 

 prepared for the uses of the plant by the action of or- 

 ganic matter on the inorganic or vice versa. That is to 

 say, vegetable matter combines with decomposed rocks 

 or minerals and forms a plant food without which the 

 plant cannot live. We know as a fact that the silicates 

 OT rock elements and minerals or metallic salts compose 

 all the earthy ingredients of soil, and are always found 

 i.u plants, the ashes of any burned vegetable or plant 

 showing this. But these silicates and salts do not make 

 fertility in soil. Fertility depends on the presence in 

 the soil of matter which has already formed a part of 

 a living, structure, organic substances in fact. It is 

 this matter which causes constant chemical changes in 

 which lies the very essence of fertility. To make this 

 quite clear, it will be sufficient to refer to the fertility 

 in the valley of the Nile in Egypt caused by the over- 

 flow of the river and the deposits, upon the silicates 

 and minerals or metallic salts, which in plain language 

 means the sands of the desert, of a layer of mud con- 

 taining decomposed vegetable or organic matter. The 

 consequence is, chemical action takes place and a rich 

 harvest follows. The result would be the same in our 

 arid plains where the soil contains all the ingredients 

 necessary to plant life, but the element of moisture to 

 dissolve and unite them is absent. Here, irrigation 

 creates fertility. The oxygen and the hydrogen in the 

 water supplies the soil with the elements it lacks to man- 

 ufacture plant food. 



There is a curious, not to say mysterious, fact con- 

 nected with the transformation of the organic and inor- 

 ganic elements in the soil into plant food, and that is, 

 the chemical change does not take place except through 

 the intervention or agency of the living plant itself. 

 It is life that is necessary to the process and this life 

 of the plant gives life to the inert elements around it. 

 The. mere presence of a living plant gives to the ele- 

 ments power to enter into new combinations, and 

 then these combinations occur in obedience only to the 

 well-known, established, eternal laws of chemical 

 affinity. , 



If, on a dry day, a wheat or barley plant is care- 

 fully pulled up from a loose soil, a cylinder of earthy 

 particles will be seen to adhere like a sheath around 

 every root fibre. This will be also noticed in the case of 

 every plant. It is from these earthy particles that the 

 plant derives the phosphoric acid, potash, silicic acid, 

 and all the other metallic salts, as well as ammonia. 

 The little cylinders are the laboratories in which nature 

 prepares the food absorbed by the plant, and this food 

 is prepared or drawn from the earth immediately con- 

 tiguous to the plant and its roots. This demonstrates 

 the importance of the mechanical tillage of the ground. 

 Cultivated plants receive their food principally from 

 the earthy particles with which the roots are in direct 

 contact, out of a solution forming around the roots, 

 themselves. All nutritive substances lying beyond the 



immediate reach of the roots, though effective as food, 

 are not available for the use of the plants, hence the 

 necessity of constant tillage, cultivation of the soil, to 

 bring the nutrition in contact with the roots. 



FORMATION AND USE OF EARTH SALTS. 



A plant is not, like an animal, endowed with spe- 

 cial organs to dissolve the food and make it ready for 

 absorption; this preparation of the nutriment is as- 

 signed to the fruitful earth itself, which in this respect 

 discharges the functions performed by the stomach and 

 intestines of animals. The arable soil decomposes all 

 salts of potash, of ammonia, and the soluble phosphates, 

 and the potash, ammonia, and phosphoric acid always 

 take the same form in the soil, no matter from what 

 salt they are derived. 



It is essential that these "salts," as they are called, 

 should be understood, for without them there can be no 

 fertility,. Unless these "salts" exist in a soil in certain 

 quantities the organic elements, or what are known as 

 "humic acids," are insoluble and cannot be absorbed into 

 the plant through its roots, and so there can be no fruit 

 or vegetable. Yet there is such a thing as an excess 

 of these same salts, and then there is barrenness. A com- 

 mon illustration of which may be seen in what are termed 

 "alkali lands," which will be treated in detail in another 

 chapter. 



To simplify an acquaintance with these various 

 salts, we shall divide them into three general classes 

 depending upon the acids formed from them, all of 

 them nutritious to plants. 



First Carbonates. 



Second Nitrates. 



Third Phosphates. 



The carbonates compose a very large portion of 

 the salts used in agriculture, and include limestone, 

 marble, shells. These salts are set loose from tire rock, 

 that is the decomposed rock already alluded to, by the 

 action of the -living plant, and their business is to dis- 

 solve, or render soluble, the organic matter in the soil, 

 so that the plant may absorb it through its roots. When 

 there is an excess of these salts, or of lime or alkali, 

 the organic matter is rendered insoluble, that is, the 

 plant cannot absorb it, and then the soil is barren. 

 There are, however, certain plants known as "gross 

 feeders," which flourish in such soils, but of them more 

 will be said in another chapter. 



The second class of nourishing salts is the nitrates, 

 and includes saltpeter, nitrate of potash, nitrate of 

 soda, and all composts of lime, alkali and animal matter. 

 This class of salts produces ammonia which hastens the 

 decay or decomposition of the organic matter, and pre- 

 pares it for absorption by the plant. All the nitrates 

 act under the influence of the growing plant and yield 

 nitrogen which is essential to its life, indeed, if there 

 are any salts which can be called vegetable foods, they 

 are the nitrates, and they hold the very first place among 

 salts in agriculture. 



The third class of plant nourishing salts is the 

 phosphates. They are found in bones, liquid manure, 

 and in certain rocky formations which are abundant in 

 the United States, and around up, are largely used upon 

 land to add to its fertility and increase the supply of 

 plant food. 



The phosphates act much like the nitrates, their 

 acid forming a constituent of the plant. 



The proper, proportionate quantity of all these 

 salts in the soil, is generally in the order already given : 



