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THE IRRIGATION AGE. 



THE PRIMER OF IRRIGATION. 



COPYRIGHTED. 1903, BY D. H. ANDERSON. 



CHAPTER XIII. 



THE SCIENCE AND ABT OF IEBIGATION. 



The main object of irrigation should always be 

 borne in mind; that is: nature having withheld from 

 plants the moisture necessary to their growth, it be- 

 comes necessary to supply the omission. When that 

 object has been attained, the work of the irrigator ends, 

 and to continue farther would be detrimental to the 

 soil, and injurious to plants instead of beneficial. 



Given a certain tract of land, and a water supply, 

 the question which confronts the irrigation farmer is : 

 How shall the water be applied to the best advantage? 

 It must occur to him that there can not be one fixed, 

 rigid system of applying water to the soil, for he can 

 perceive by looking about him that there are widely dif- 

 ferent varieties of plants, and opposite conditions of 

 soil which preclude a uniform system of irrigation. 



Scientific writers, and practical men, those who 

 have studied the subject from the earliest ages, and in 

 every country, have suggested more than a dozen dif- 

 ferent systems, but practical irrigators of modern times, 

 men who have acquired experience by practical experi- 

 ments, some of them costly, in our sixteen arid and 

 sub-humid States, have settled upon four distinct sys- 

 tems of irrigation as amply sufficient for every condi- 

 tion of soil and climate, for economically supplying 

 plants and soil with life-giving moisture. 



Let the reader recall what has already been said 

 on the subject in previous chapters, that except in the 

 case of aquatic plants, it is not water or rather wetness 

 that is essential to the perfection of plant life, but 

 moisture. True, it is from water that moisture is de- 

 rived, but when water is converted into moisture it is 

 no longer water, but plant food. When a man eats 

 meat and vegetables, he is not" eating oxygen, hydrogen, 

 nitrogen, carbonic acid, and the like, he is eating, how- 

 ever, combinations of those chemical substances, com- 

 binations which he, himself, can not create by devour- 

 ing the chemicals themselves in an original state. To 

 attempt to do so would be his speedy death, notwith- 

 standing the theories concerning the value of dieting 

 on certain artificial chemical combinations known as 

 "health foods." 



Water is poured into or upon* the soil; gravity 

 draws it downward; the particles of earth seize upon 

 what they require, and the surplus water continues to 

 descend until it reaches a water table, or is carried off 

 through drainage appliances. Then capillary action be- 

 gins, and the moisture ascends, and it and the nutritive 

 elements it has gathered from the soil is seized upon 

 by the roots of plants and devoured, that is absorbed, 

 and the plant grows and waxes perfect upon the meat 

 with which it is fed. 



The four systems of irrigation referred to are as 

 follows : 



First FLOWING, or ditch irrigation, where the 

 water is run over the land through ditches or furrows 

 intersecting the land to be watered. 



Second FLOODING, where the water is made to 

 cover the land entirely at any desired depth, and is 

 either allowed to remain stagnant, or stationary, or 

 possesses a slight current. 



Third INFILTRATION, or seepage, in which 

 the water is carried to the roots of plants by means of 



open ditches, or through subterranean waterways, in 

 which case it is termed SUB-IRRIGATION. 



Fourth ASPERSION, or sprinkling, in which 

 the water is applied in a shower, or as an imitation 

 rain. Watering with a common garden sprinkling pot, 

 or rubber hose, will give an idea of this system. 



The first of these systems constitutes irrigation in 

 the strict sense of the word, wherever water is utilized 

 as a fertilizer of the soil, or an agent of humidity or 

 moisture. The latter system relates to watering small 

 garden plants, and flowers, and is commonly applied by 

 means of some sprikling apparatus suitable to the size 

 of the garden patch, and the quantity of water to be 

 applied. It is not serviceable in hot dry regions and 

 seasons because of rapid evaporation which makes it 

 less economical than the others. 



The choice of these systems, excluding the last, is 

 subordinated to the nature of the soil, and topography, 

 or "lay" of the land, the species of plants and the kind 

 of culture, the quality and level of the water, and par- 

 ticularly to the disposable volume of the latter. In 

 fact, two principles based upon the volume, or quantity 

 of irrigating waters, regulate their use: The utilization 

 of the maximum quantity of water obtainable to irri- 

 gate a given surface, or an increase of the irrigable sur- 

 face to correspond with the maximum quantity of 

 water. 



The first principle is applicable to the sub-humid 

 sections where there is a certain amount of rainfall in 

 the winter months with dry summers, or a "dry season," 

 like the Pacific Coast States, New Mexico, Arizona, and 

 portions of Texas, or snow in winter as in Colorado, 

 Wyoming, and the other northerly States. 



In these localities, the rain and snow store in the 

 soil a greater or less volume of water, which serves not 

 only to fertilize it, but to keep it in a condition which 

 will enable vegetation to either continue to grow .with- 

 out stopping, or to sprout in the early spring without 

 preliminary irrigation. 



In the warmer regions, however, there are dry 

 belts, where the rainfall is so slight as to be unservice- 

 able to perfect a crop, and in these belts little will grow 

 without irrigation. To these localities may be applied 

 the second principle. 



Between these limits, principles, or conditions, are 

 grouped numerous variations in plant growth, in aid 

 of which irrigation supplies the means of rationally 

 utilizing water for crop growing purposes, These vari- 

 ations will be taken up under the explanation of the 

 four systems alluded to. 



FLOWING, DITCH AND FURROW IRRIGATION. 



On a naked tract of inclined, or sloping land, water 

 follows the heaviest grade with an increasing speed or 

 flow. When the same tract is covered with growing 

 plants, the flow of water is retarded by the resistance 

 of the plants, until an equilibrium is established, which 

 requires more or less time according to the steepness of 

 the grade and the character of the plants, and then the 

 water flows with a uniform velocity, the same as if the 

 land were naked. When that equilibrium has been 

 reached, reason tells the irrigator to stop the water 

 supply or the surface will be cut into gullies. 



When the grade is very slight, the water, being un- 

 able to attain sufficient velocity, is lost in the soil before 

 it can cover the entire tract. 



In the former case, the zone of irrigation must be 

 narrowed, and in the second, the lateral or distributing 



