IRRIGATION 942 IRRIGATION

IRRIGATION

942

IRRIGATION

every stream in the arid states, and works of considerable magnitude constructed for the storage of floods and the diversion of rivers, irrigating in the aggregate over 7,500,000 acres.

It is estimated that 90 per cent, or more of the irrigated land in the United States is supplied, mostly by gravity, with water from surface streams. The application of water is mostly done by flooding, by furrows and by subirrigation, and for best results skill and judgment are required as to how, when and in what quantities it should be used, which is governed largely by the quality of the soil and the kind of crops raised.

California leads in the number of irrigators and the value of produce from irrigated land, although Colorado has the greatest irrigated area. Of the annual productions on the irrigated farms of the United States forage-crops constitute over one third of the total. Fruits and vegetables are important items, largely grown in favoring localities for winter marketing. The benefits of irrigation are seen in such yields as ten tons per acre of alfalfa per season, five tons of clovers and timothy or the 400 to 500 bushels of Irish potatoes per acre, with the element of uncertainty as to moisture supply practically eliminated. Unless, however, scientific cultivation is given, the best results are not obtained, which applies equally where irrigation is not practiced; and after a field has been watered, following proper cultivation, the top soil should be stirred to aerate the ground and provide a loose, finely pulverized surface, by which excessive evaporation is prevented.

Dry Farming. In this the same principles are involved as in the so-called dry farming so widely exploited in recent years; but these principles are as old as they are excellent and simply mean good tillage, the mode of procedure depending on the requirements of the soils, seasons, climates and crops. It contemplates cultivation of the ground in such manner and at such intervals as will best improve its physical condition and prepare it for the reception and retention of the natural precipitation. By maintaining the surface soil in a proper condition capillary attrac tion with the moisture beneath is broken, lessening the loss of water — in short such methods of tillage as best promote rapid percolation into and prevent evaporation out of the soil. The conclusions from experiments made in Utah by the United States_ government are that "under such conditions, with a rainfall averaging 12 inches per annum, dry farming is feasible," although it is claimed that good results have not been infrequent where the precipitation has been even less. Its value is manifest and important to the husbandmen of the semiarid region where irrigation

is impracticable or impossible, as with the natural rainfall profitable yields are obtained that otherwise have been impossible, and its increasing adoption is proving most beneficial. Its general principles mean much to every farming community, but are vital to the agriculture of regions deficient in rainfall.

The following table shows the areas and cost of such portions of current government irrigation projects as it is expected to complete by 1911 :

The accumulation of alkali on the surface of irrigated lands, which was at first thought a serious detriment, is remedied by underdrainage, and, strange as it may seem to the uninformed, tile drainage appears likely to become not uncommon in many irrigated districts. In fact, irrigation and drainage go hand in hand, and most of the government's irrigation projects provide for elaborate drainage systems. It is anticipated that the advocates of national drainage works for the reclamation of the vast swampland areas of the United States will look to Congress and the Reclamation Bureau to extend the service to include the reclamation of these areas.