THE IRRIGATION AGE. 



277 



to spread out through open joints of the tiles, or through 

 openings expressly made for the purpose, within reach 

 of the roots, whereas, in drainage exclusively, the 

 drains operated contrariwise by drawing the water away 

 from the roots. By this method none of the land was 

 overlooked and irrigation could be effected at any time, 

 and liquid fertilizers could be introduced whenever de- 

 sirable. The pipes were easily laid in an ordinary fur- 

 row opened by a plow, and could be multiplied economi- 

 cally to any extent. 



Second. The second process was to lay a certain 

 number of drains along the line of the steepest grade 

 and connect them with a transverse collecting pipe or 

 conduit, in the center of which was arranged a vertical 

 tube or well of wood or tile, up which the water ascended 

 and flowed over into a main ditch from which the sur- 

 face could be irrigated in the usual manner. Each 

 transverse collecting drain corresponded with a princi- 

 pal flowing ditch, and to suspend irrigation all that was 

 necessary was to throw open the front or end of each 

 discharge drain where it entered the transverse collect- 

 ing drain. 



The vertical tubes or wells were vent holes pro- 

 vided with sluices which could be worked from the top 

 in any desired convenient manner, whenever it was de- 

 sired to drain without irrigation or irrigate without 

 draining, or whether it was desired to hold the water at 

 a given level in the soil to furnish seepage water or 

 irrigate by infiltration. 



The principle of these methods is identical with 

 that of ordinary irrigation, which, after all is said, is 

 the seepage or filtration of water from above down 

 through the soil, and the absorption by the soil of the 

 elements held in suspension or solution by the water. 

 Carbonic acid is disengaged by flowing over the surface, 

 is partially decomposed by the plants and absorbed by 

 them, and the remainder passes into the soil. Oxygen, 

 after subjecting what it reaches to the phenomena of 

 combustion, which explains the fertilizing effects of 

 irrigation, is less abundant in water filtered through the 

 soil than in that which flows over the surface, while, on 

 the contrary, carbonic and sulphuric acids increase in 

 quantity. By seepage or infiltration from below upward, 

 mineral matters, lime, chalk, potash, etc., are not pre- 

 cipitated mechanically, but deposited in the sub-soil un- 

 less the water be saturated, which is too often the case 

 in the alkali lands, bnt which is more or less obviated 

 by combining this system of drainage with irrigation. 

 At all events it reduces the quantity of the deposit 

 of deleterious mineral salts to a minimum. In 

 addition to that desideratum it is possible to 

 wash the alkali out of the soil by permitting the 

 saturated water to drain off and carry with it 

 ;he alkali in the sub-soil or near the surface, top 

 washing of course carrying the surface alkali down 

 within reach of the drains. It is like cleansing a 

 sponge of its impurities. Dip an impure sponge in a 

 basin of pure water and squeeze. The water becomes 

 impregnated with the impurities of the sponge. Throw 

 away that water and fill the basin with clear water and 

 dip in it the sponge and squeeze as before. By and by 

 the water running from the sponge is clear, showing 

 that the latter contains no more impurities. 



If it be true, as the majority of the scientists main- 

 tain, that the use of irrigating water is all the more 

 beneficial when vegetation is most flourishing and 

 luxuriant, and that the nutritive elements in the soil 

 are directly absorbed by the roots, it is apparent that 



the oxydizing and purifying action of drainage com- 

 bined with irrigation must be the means of supplying 

 vegetation with the necessary plant food, either through 

 the infiltration of the water into the region of the roots 

 or by intermittent flowing over the surface from the 

 vent wells. 



The system is quite simple, expense alone being 

 probably the only disadvantage, bnt even then, if the 

 land must be drained, the laying of tiles, if with a view 

 of also irrigating, will divide the expense. 



By an arrangement of valves or plugs managed 

 from the vertical vent wells, the pipes are closed at the 

 point where irrigation is desired. Then, the water 

 flowing through the drains is stopped at the closed valve, 

 escapes through the loose joints of the tiles, and if per- 

 mitted, will make its way to the surface. When one sec- 

 tion has been sufficiently irrigated in this manner, the 

 valve is opened, and another one further down is closed, 

 and the soil in that section irrigated in the same man- 

 ner. To drain without irrigating, all the underground 

 valves are opened and the water flows through the 

 secondary drains into the main, or transverse collecting 

 drain, to be carried off entirely or into a reservoir for 

 further use unless too alkaline. 



To wash the soil, repeat the process of irrigation 

 and drainage several times successively until tests show 

 a weak solution. 



This system of irrigation and drainage may be 

 adapted to any condition of soil, or to any topography. 

 Indeed, the principle of the siphon may be connected 

 with it. Regard, of course, must be had to the nature 

 of the plants to be irrigated when it comes to regulating 

 the depth at which the tiles are to be placed, or the 

 height to which the water is to be permitted to ascend 

 in the soil. Where the land is flat the tiles may be laid 

 on a light grade, the source of the water supply above 

 the tiles regulating the velocity of the current of water 

 and the height to which it can be raised in the soil. In 

 such cases, a fifty or a hundred-acre tract may be sub- 

 irrigated by infiltration until it is in a fit condition to 

 cultivate for any crop without any flowing over the 

 surface. In sloping land the pipes should be laid paral- 

 lel with the slope to insure uniformity of distribution, 

 at, say. four feet below the surface for ordinary culture, 

 with transverse collecting pipes at intervals, so as to lay 

 out the land in sections, each one of which may be 

 irrigated in turn. Practically, the system means the 

 creation of an artificial water table managed at will. 



A query arises here : Will not the water rising in 

 an upper section of land through the drain pipes also 

 descend to the section below at the same time in obedi- 

 ence to the law of gravity? 



The answer is that water as such certainly will 

 descend and much faster than it rises. But moisture 

 will not. In irrigating the upper section of a tract of 

 land through drain pipes, the water is under pressure 

 which overcomes gravity. Again, the soil will absorb the 

 water as fast as it rises and not until it is saturated 

 will it give any of it up, and then the surplus will be- 

 gin to flow downward, but when that moment arrives the 

 irrigator opens the valve and removes the pressure, suf- 

 fers the saturated land to drain off and moisture alone 

 is left, which, as has been said, does not drain down- 

 ward, but ascends toward the surface in obedience to 

 the law of capillary attraction. 



SURFACE, SUB-IRRIGATION AND DRAINAGE COMBINED. 



It is possible to combine surface, sub-irrigation and 

 drainage by the same system of underground conduits 



