DANGERS OF IRRIGATION

New Zealand Mail, Issue 1666, 3 February 1904, Page 68

DANGERS OF IRRIGATION

1 A <r well-known Government scientist” w&9 recently quoted: in the columns of the *'New York Skin” as stating that irriga>tion is only a temporary expedient for making arid lands productive, andl that genuinely arid countries are always sooner or later ruined by the alkali on the soil, which is brought to the surface by the waters of irrigation aud there deposited. Such a statement, ascribed to one presumably connected with the Department of Agriculture, deserves somewhat miOT© than passing attention, particularly in view of the extensive irrigation carried on in America and in the improvement of which this very department has epent so much money. That the evil was exaggerated there seemed no doubt. An inquiry directed by the Agricultural Department brought ai roply from Professor 321 wood Mead, chief of the irrigation investigations, Who shares our view of the master. The department is well aware of the fact that water dissolves the salts contained in the lower soils or arid regions, and that the water rises by capillary action, and carries these salts in solution u:p to or near the surface, where they are deposited when the water is evaporated. This state of affairs would'be extremely serious, so serious, indeed, thiat further irrigation would be of doubtful value, if not an absolute waste of time and money, ware not the remedy for it, which the unnamed "Government scientist” _ demands, already discovered and put into practice. The investigations of the Department show that the conditions in question are due mainly to over irrigation, that is, flooding of the arid lands; but can be remedied by proper drainage. The soils of arid regions are usually of a sandy and silty nature, in which water and air penetrate to great depths. In consequence of this, the roots of plants in these regions reach down to considerable depths to obtain moisture aud nutriment, instead of spreading along the surface as in humid dl'imates. If, by over irrigation, th|e water level is allowed to rise close to the surface, the layer of soil which supplies the plant with food is shallower, and its nutriment soon exhausted. Furthermore, is the water is within reach of surface -evaporation, the alkali it contains in solution will accumulate to such an extent as to render the soil unfit for estivation. The employment of judiciously disposed drains serves the double purpose of preventing undue rise of the irrigation water and of carrying off the objectionable alkali. The depth to which these drains are laid is a matter of great importance. The limit has been placed at 4 feet from the surface, though greater depths have been recommended. Careful consideration of the source and flow of water sometimes permits the location of a single drain in such a manner as to carry off water which might otherwise injure hundreds of acres of land. The drainage water may be collected in reservoirs, and than redistributed in. the- irrigation ditches. In localities where water is scarce, the economy of such a system is apparent. Such operations have been successfully andl very extensively carried out in Colorado, where it has also been demonstrated that lands already injured by alkali can be restored to productiveness by means of proper subsoil drainage.