Show DRAINAGE NEEDED FOR IR LANDS more than 10 per cent of the irrigated lands in the united states which have had water for any considerable period of time are now either absolutely unproductive or given over to poor pastures and unprofitable crops according to the united states deportment department of agriculture Wate flogging and the accumulation of f harmful mineral salts sait j are ae responsible even in soma of the most recent irrig irrigation atio an ejects serious injury irom these causes has been wrought methods of reclaiming land which has fallen into this condition forms the subject of a new bulletin of the department no 10 the drainage of irrigated land drainage supplemented ted by proper methods of cultivation cropping 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 groundwater table will not fluctuate spring thaws 3 the rapid removal of excess moisture following spring thaws and 4 the creation of an outlet for the downward moving water used to dissolve out the injurious salts in stations cru of alkali salts and the presence of highly al kali resistant plants are frequently inc indications of income cases ponds bogs and marshes are also found but ili in others there are no visible signs of bf excessive wetness and its existence can only be inferred from its effects upon vegetation the bulletin calls special attention to the difference in drainage practice between the arid and and the humid regions and emphasizes the need for thorough knowledge of underground der ground conditions to drain areas of this character will cost it is estimated on the average farm from 10 to 20 an acre except under unusual 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 intended primarily for the main main outlet systems in which pro must be made for a considerable sid erable flow of water the covered drains are for farm drainage proper although except for the additional expense they could be used equally well for the main outlets asa matter of fact although they th ey cost more than the open canals the maintenance charges are usually lower much valuable space is is saved and cultivation and irrigation i are much easier with them than with open canals where covered conduits are employed they are usually made either of cement or tile some localities lumber box drains are used but this is usually advantageous vant ageous only in isolated places where lumber is cheap and transportation rates high the life of such a drain is reasonably long if the lumber is continuously wet but if alternate wetting and drying takes alace the material may last only a fua years tri tn 1 properly land anc aerial al activity is increased ani and more plant food provided by the admission of air into the soil to take the place ot the excess water which has bec p r remo remove td the downward movement of water through the soil also leaches cut ut the excer afi i maul eriq and this is one of the most important funch functions ions of drainage in the irrigated sections the water removed by the drainage system may be employed for the irrigation of other areas thereby increasing the available irrigated area furthermore drained land may be plowed earlier than 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 are discussed ed in the bulletin |