| OCR Text |
Show j . '.illlW44wW'W' I J DRAIN IRRIGATED LAND I AJLA4-4mM.-H , More than 10 per cent of the j irrigated lands in the United J States which have had water for ! any considerable period of time are now either absolutely unproductive un-productive or given over to poor pastures and unprofitable crops, according to the United States department of agriculture- Waterlogging Wa-terlogging and the accumulation of harmful mineral salts are responsible. re-sponsible. Even in some of the most recent irrigation projects serious injury from these causes caus-es has been wrought. Methods of reclaiming land which has fallen into this condition condi-tion forms the subject of a new bulletin of the department "The Drainage Of Irrigated Land " Drainage supplemented by proper prop-er methods of cultivation; cropping, crop-ping, and irrigation, will restore these waterlogged areas to a condition in which they can be farmed with profit, the bulletin points out Proper drainage will accomplish four objects: (1) the lowering of the groundwater ground-water table to a depth where the moisture and air within the root zone will be properly balanced, (2) the creation of an outlet for . percolating water, so that the ground-water table will not fluc- tuate excessively; (3) the rapid y " ' removal of excess moisture following fol-lowing spring thaws; and (4) the creation of an outlet for the downward moving water used to dissolve out the injurious salts. Incrustations of alkali salts and the presencc-of highly alkali-resistant plants are frequently frequent-ly indications of overirrigation. v.. lit some cases ponds, bogs, and marshes are also found, but in ? others there are no visible signs l of .excessive wetness and its ex- ; istence can only be inferred from ; j its effects upon vegetation- The l bulletin culls special attention .to lVe difference in drainage practice between the arid and the the need, for thorough knowl edge of underground condition To drain areas of this char acter will cost, it is estimated, on the average farm from $10 to $20 an acre except under unusual un-usual conditions when the cost may run as high as $50 an acre. Both open canals and covered conduits are in general use. The open canals, however, are intend ed primarily the main outlet out-let systems In which provision nrust be ma . for a considerable of wa-er- The covered drains arc cor farm drainage proper, although, except for the additional expense., they could be used equally well for the main outlets- As a matter of fact, although they cost more than the open c?.nals, the maintenance main-tenance charges are usually lower, low-er, much valuable space is saved, sav-ed, and cultivation and irrigation irriga-tion are much easier with them than with open canals. Where covered conduits are employed they are usually made either of valient or ciay tile- In some localities lo-calities lumber box drains are used, but this is usually advantageous advan-tageous only in isolated places where lumber is cheap and transportation trans-portation rates high- The life of such a drain is reasonably long if the lumber is continuously continu-ously wet, but if alternate wetting wet-ting and drying takes place, the material may last only a few tcrial activity is increased and years. T . . - - in properly drained land bacterial bac-terial activity is increased and more plant food provided by the admission of air into the soil to take the place of the excess water wa-ter which has been removed. The downward movement of water through the soil also leaches out the excess of harmful salts, and this is one of the most important import-ant functions of drainage in the irrigated sections- The water . - removed by the drainage system may be employed for the irrigation irriga-tion of other areas, thereby increasing' in-creasing' the available irrigated i area- Furthermore, drained land may be plowed earlier than un-drained, un-drained, and in consequence may be irrigated earlier. This is an obvious advantage in that it makes it possible for the land to be irrigated before the supply of water becomes reduced. Various forms of drainage systems and the best methods of constructing them arc discussed in the bulletin- o |
