THE IRRIGATION AGE. 



211 



ditches must be brought closer together. When the sur- 

 face soil is undulating, or irregular, the water spreads 

 out unevenly, in which case the distributing laterals 

 must be brought still closer together, and arranged to 

 correspond with the irregularities to avoid gullying. 



Flowing is adapted to land the slope or grade of 

 which is between four and two per cent per running 

 yard. On steeper grades, irrigation is effected more 

 economically by arranging a series of levels or plateaus. 



On feeble grades, the quantity of water increases 

 by accumulation and remains longer in a stagnant con- 

 dition, but in general, by this system of irrigation the 

 water is more fully aerated and its fertilizing power 

 increased. 



On large fields, water flowing over steep grades 

 being more rapid, the ditches or water furrows should 

 be more numerous, to enable the soil to gather from the 

 water whatever fertilizing material it holds in suspen- 

 sion. 



Where the grade is very slight, drainage may be 

 necessary to carry off an excess of water. After culti- 

 vation is always necessary as soon as the soil is in a 

 suitable condition, from twelve to twenty-four hours 

 being sufficient time according to the climatic condi- 

 tions of heat and cold. 



In all cases of ditch and furrow irrigation, it must 

 be remembered that the less the number of distributing 

 ditches or furrows, the less the quantity of water turned 

 into the soil. 



IRRIGATION BY FLOODING. 



(Submersion.) 



In the system of irrigation by flowing, whatever 

 method be adopted, running water over the land, or 

 drawing it from ditches through furrows, the best con- 

 ditions for utilizing water are realized, that i^ to say, 

 so far as movement, aeration, double use, and facility 

 of distribution are concerned. It is possible to avoid 

 direct contact of the water with plants, thus retaining 

 essential atmospheric influences, and also regulating 

 the temperature of soil and vegetation. In this latter 

 case, it is reasonable to suppose that even in the arid, 

 hot regions, the application of cold water direct from a 

 mountain stream, or surface well, would check vegeta- 

 tion, an effect which is always deleterious to all grow- 

 ing crops. 



But there are circumstances when flooding or sub- 

 mersion of the soil is not only convenient but more 

 beneficial, inasmuch as it supplies the soil with mois- 

 ture to a greater depth, thus furnishing deep rooted 

 plants with food material. Reference to alfalfa will 

 make this clear. 



Irrigation by flooding is simply submerging a 

 given tract of land, by covering it with a sheet of water 

 more or less deep, and allowing it to remain upon it a 

 certain time, to "soak" into the soil before drawing it 

 off to use on some other tract. 



On flat or level ground, preparations for submer- 

 sion are simple and easy. It suffices to smooth the sur- 

 face by reducing knolls and filling cavities or hollows 

 by means of a plow, cultivator, or road scraper, and 

 then throwing up ridges of earth or dikes around the 

 edge of the tract to retain the water. 



It is an essentially economical method of irriga- 

 tion, and is adapted to land and plants which do not 

 require continuous or periodical applications of water. 

 Its advantages are that it irrigates uniformly; utilizes 

 all the water applied, it being absorbed except the small 



fraction lost by evaporation. Again, it tends to enrich 

 the soil more than any other system by giving the vari- 

 ous organic and inorganic solutions suspended in the 

 water time to be deposited upon and carried into the 

 soil. Lastly, it insures the destruction of insects and 

 their larvae injurious to plants. 



Opposed to its advantages are the following de- 

 fects : 



The plants are submerged either totally or par- 

 tially, and the essential atmospheric influences sus- 

 pended ; the surface of the land is cut into dikes which 

 interfere with adequate cultivation, and the consump- 

 tion of water is much greater in a given time than 

 when the water is flowed upon the land. Exceptions 

 might be made to include alfalfa, sugar beets, and 

 heavy root crops gross feeders the proper flooding 

 of which could not be detrimental, but on the con- 

 trary beneficial. It is, moreover, essential in rice cul- 

 ture, and highly beneficial in vegetable gardens, fruit 

 culture and in vineyards. 



NATURAL SUBMERSION. 



Irrigation by flooding, though produced by arti- 

 ficial means, is effected by the operations of nature in 

 many regions of great fertility and abundant harvests. 

 Countries of immense extent are fertilized by periodi- 

 cal, or rather annual submersions without which the 

 soil would be absolutely barren. 



Such countries are Egypt, which i* fertilized by . 

 the regular flooding of the river Nile; the llamas, 

 pampas, and steppes of South America, which are 

 boundless natural pastures, mafhtained by the periodi- 

 cal overflow of numberless streams and rivers, and 

 whose fertility and plant growth could not be per- 

 petuated by artificial irrigation through ditches, be- 

 cause of the absence of grade to' allow flowing. In the 

 zone bounded by the dikes and river bed of the Rhone, 

 between Avignon and the sea, in France, the lands are 

 submerged through their whole extent during the win- 

 ter months. Cereals, alfalfa, vines, fruit trees and 

 vegetables grow to perfection without other fertiliza- 

 tion and with very little cultivation. The damages 

 from these annual inundations, though not slight, are 

 regarded as of little consequence when compared with 

 the benefits derived from them. 



Other regions might be specified if it were neces- 

 sary to advocate the benefits of land flooding. We 

 might go back into the misty ages of antiquity and 

 point to the wonderfully fertile regions around the 

 Euphrates and Tigris, and depict the glories of ancient 

 dynasties that reached the pinnacle of earthly great- 

 ness through the fertilizing of land by flooding, and 

 show how those powerful dynasties crumbled into dust 

 when the lands were no longer thus fertilized, but this 

 is intended to be a practical work with barely enough 

 sentiment to make it readable. 



ARTIFICIAL FLOODING. 



It is possible for man to imitate or copy nature, 

 even to surpass nature, for he can control his water 

 supply, whereas that of nature is uncontrollable to a 

 great extent and destructive a combination of utility 

 and damage. 



There are two methods of artificial flooding or 

 submersion of land: 



If the irrigation water provided for ditch or flow- 

 ing is not all exhausted by that process, it is run upon 

 land especially prepared for submersion, and allowed 

 to remain upon it stagnant for a certain length of time, 



