Irrigation and water-supply : a practical treatise ... / by John Scott.

  • Scott, John.
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Irrigation and water-supply : a practical treatise ... / by John Scott. Source: Wellcome Collection.

    18/216 (page 4)
    an essentially aquatic nature, for ordinary grasses and meadow herbage are principally watered. But it is performed that growth may be stimulated and fed through certain agencies which the water brings to bear upon the vegetation in question. Effects on Soil.— The immediate effect of irrigation upon the consistence of the soil is to soften it and render it more easily penetrable by the plough and by the roots of the plants. Hence, in dry climates, water is frequently applied before ploughing, at the rate of about 400 to 500 cubic yards per acre, or barely enough to loosen the earth to the depth of a foot M'ith- out drenching it. But it is most important to observe that the ultimate effect of long-continued irrigation is to condense and harden the surface to a very inconvenient degree. Irrigation affects the quality of the soil by intro- ducing into it common air and other gases, and vege- table and mineral matter held in suspiension or solution by the water. In most cases the substances so ixitro- duced are beneficial to vegetation; but in some they are highly noxious. Even the water of large rivers sometimes, as has been observed in India, deposits on the surface, or introduces into the texture of the soil, salts, which in the course of time render it wholly sterile. It likewise acts upon arable soil by facilitating the decomposition of soluble organic and inorganic matter contained in it, and carrying off such matter from it. The extent of this latter action is disputed; but it must be considerable, for constituents of vegetable growth have been found in under-drain water from cultivated fields ; and large tracts of ground, impreg- nated with salts to such a degree as to make them