THE IRRIGATION AGE. 



275 



THE PRIMER OF IRRIGATION. 



COPYRIGHTED, 1908, BY D. H. ANDERSON. 



CHAPTER XV. 



SUB-IRRIGATION DRAINAGE. 



(Continued.) 



Infiltration, or seepage, as a method of irrigation is 

 included in this chapter because it is practically sub- 

 irrigation. 



The drainage here referred to is that system of 

 carrying off the surplus or excess of water through un- 

 derground conveyances, when the same is connected 

 with a system of sub-irrigation. Drainage proper will 

 furnish matter for a special chapter on the subject. 



Irrigation by infiltration, or seepage, is effected 

 through following the configuration of the land, by 

 means of flowing or sleeping water seeping through or 

 into the soil from ditches, canals, or pipes, uncovered or 

 covered, but located below the surface of the ground. 

 The water spreads out, seeps or soaks out from the con- 

 veyance fan-like into the soil from the sides and bot- 

 tom of the ditch, canal or pipe, and, following the law 

 of gravity, descends or ascends in accordance with the 

 law of capillary attraction. 



Infiltration rests upon the principle of the per- 

 meability of the soil, and hence, this method of irriga- 

 tion is not always as beneficial as those already 

 mentioned, for the reason that it consumes a large 

 quantity of water without supplying the soil with a 

 uniform humidity. 



Unless, however, and here are two occasions when 

 infiltration is more economical and beneficial : When 

 .the water in the trench, or ditch, or underground con- 

 veyance is running water, and when it reaches the roots 

 of the plants intended without spreading out where it 

 can not be utilized. 



The advantages of underground or sub-irrigation 

 are too numerous to be ignored. By this system, land 

 too elevated to be reached by water through other means 

 may be transformed into fertile tracts. In the case 

 of hill land it is admirable for cereals, and also on lands 

 where weeds abound. It lends an invaluable aid to a 

 series of special cultures, such as grapes, olives, oranges 

 and citrus fruits generally, likewise in gardening. It 

 enables steep land to be cut into terraces which irriga- 

 tion water generally could not penetrate to a sufficient 

 depth. In addition to these advantages, the application 

 of underground water on arid or waste land covered 

 with sand or gravel, permits the propagation and cul- 

 tivation of profitable productive plants which would 

 otherwise perish through dryness of sub-soil. Finally, 

 a well arranged system of sub-irrigation operates as a 

 drainage system as well as for irrigation. 



The nature of the soil is more important than the 

 configuration of the ground in sub-irrigation. In this 

 respect, hard impenetrable soils should be avoided for 

 irrigation by infiltration. Experience alone can guide 

 the irrigator in establishing his system of deep ditches, 

 the main point being always to provide for moistening 

 the soil uniformly. 



Furrow irrigation applied to cultivated land is 

 similar to infiltration. Eunning water into furrows 

 and then cultivating the soil over them is a very com- 



mon method of irrigating by infiltration, and it is suita- 

 ble for shallow rooted plants, corn, and tubers gen- 

 erally. The pulverized earth forms a mulch which ob- 

 viates rapid evaporation and enables the water to seep 

 into the soil in every direction before drying out. It 

 is also adopted on a large scale in orchards, vineyards, 

 nurseries, for small fruits and in flower and vegetable 

 gardens where deep irrigation or sub-irrigation proper 

 would not be effective. In all such methods of irriga- 

 tion it is well to provide that the water or surface wet- 

 ness be prevented from extending as far as the plant 

 proper, and restrict it to the service of the roots. It is 

 considered more efficacious than direct irrigation, for the 

 reason that the humidity is imprisoned around the roots 

 and evaporation is perceptibly retarded. 



It is in the kitchen garden, applied to the culture 

 of root plants, that irrigation by infiltration attains 

 marvelous results. It is the only system of irrigation 

 that enables plants to obtain the greatest quantity of 

 nutritive matter from a given surface. The soil is never 

 at rest; one crop may immediately succeed another, 

 growth continuing all the year around without interrup- 

 tion. It is, in the hot arid regions, equivalent to hot- 

 house culture, so far as luxuriance of growth is con- 

 cerned, but the crops possess a quality of excellence 

 unknown to forced culture. 



SUBTERRANEAN CONDUITS. 



Although infiltration is sub-irrigation, many per- 

 sons limit the system of sub-irrigation to the conveyance 

 of water through underground pipes, tiles or conduits. 

 This method of irrigation is very ancient in its applica- 

 tion to special cultures, or to utilize liquid fertilizers. 

 When the volume of water is limited, the soil too porous 

 for surface applications, the method of applying water 

 to the roots of plants through subterranean conduits is 

 very successful in its results, but only, let it be said, 

 for very profitable plants. In general, the great ex- 

 pense attendant upon the installation of a system of 

 underground conduits has prevented the common use 

 of this system of irrigation, ordinary infiltration as 

 above described having been found satisfactory. 



But the constant pouring of water upon the soil in 

 many of the older irrigated districts in the arid region, 

 has resulted in creating a water table near the surface, 

 so near in fact that formerly fertile tracts of land have 

 been converted into swamps. Hence, drainage has be- 

 come a problem necessary to be solved if fertile lands 

 and profitable orchards are to be saved from destruction, 

 and it is gradually dawning upon the minds of irriga- 

 tors that where there is a system of sub-irrigation there 

 is also a system of drainage ready at hand. 



The writer advances the proposition founded on 

 long experience in other countries of similar soil, climate 

 and meteorology as the arid and semi-arid lands of the 

 west, that sub-irrigation and drainage may well go to- 

 gether, and that if tiling or other media be so arranged 

 in underground conduits, they will serve a double pur- 

 pose, one highly economical and productive of good 

 results. The conditions, indeed, are identical. The 

 water passing through the drain pipes is surplus water, 

 which may quite naturally be used over again as is the 

 surplus water from a surface ditch, or that from over- 

 flowed land. 



Nearly a hundred years ago the scientist Fellen- 

 berg put in at the agricultural establishment of Hofwyl, 

 near the city of Berne, a system of sub-irrigation 



