1(5 



THE IRRIGATION AGE. 



changing, the mere change of one element, or its ab- 

 straction, forming a new product. It is this susceptibility 

 to change and the constant assumption of new forms by 

 vegetable products which is the foundation of tillage, and 

 the essence of the knowledge 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 are prepared 

 for the uses of the plant by the action of organic 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 or rock elements 

 and minerals or metallic salts compose all the earthy 

 ingredients of soil, and are always found in 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 overflow 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 

 containing 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 

 necesary to plant life, but the element of moisture to 

 dissolve and unite them is absent. Here irrigation cre- 

 ates fertility. The oxygen and the hydrogen in the water 

 supplies the soil with the elements it lacks to manufacture 

 plant food. 



Plants Induce Chemical Changes. 



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 elements 

 power to enter into new combinations, and then these com- 

 binations occur in obedience only to the well-known, es- 

 tablished, 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 fiber. 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 contiguous to the plant 

 and its roots. This demonstrates the importance of the 

 mechanical tillage of the ground. Cultivated plants re- 

 ceive 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 sub- 



stances 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, cul- 

 tivation 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 special 

 organs to dissolve the food and make it ready for ab- 

 sorption; this preparation of the nutriment is assigned 

 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 pot- 

 ash, 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 vegetble. 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 argriculture, and include limestone, marble, 

 shells. These salts are set loose from the rock, that is 

 the decomposed rock already alluded to, by the action 

 of the living plant, and their business is to dissolve, 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 mat- 

 ter is rendered insoluble, that is, the plant cannot absorb 

 it, and then the soil is barren. There are, however, cer- 

 tain plants known as "gross feeders," which flourish in 

 such soils, but of them more will be said in another chap- 

 ter. 



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 prepares 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. 



Fertilizers Contain Phosphates. 



The third class of plant nourishing salts is the phos- 

 phates. They are found in bones, liquid manure, and in 

 certain rocky formations which are abundant in the 

 United States, and ground up, are largely used upon land 

 to add to its fertility and increase the supply of plant food. 



(Continued on page 48.) 



