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Alkali Soils and Soil Solutions

Nature volume 100, page 292 (13 December 1917) | Download Citation



IN any attempt at agriculture in arid or semi-arid regions, considerable trouble is likely to arise from accumulations of soluble salts at the surface of the soil. The trouble is often intensified by irrigation, and it may become so serious as to counteract the advantages of a reclamation scheme that may be satisfactory in other respects. In a recent issue of the Journal of Agricultural Research, Dr. Breazeale estimates that the losses from this cause have already amounted to one hundred million dollars in the United States alone, and the evil is by no means checked. The soluble salts arise from two causes. Some come direct from the weathering of soda feldspars, diorite, etc.; much, however, arises from the circumstance that the area was once largely covered by marine lagoons or landlocked seas, the water of which evaporated, leaving the salts behind. When the soils are first brought under irrigation, the water applied to the higher levels. is usually excessive in amount, and drains through the lower ground, carrying with it in solution considerable amounts of the chloride, sulphate, carbonate, and bicarbonate of sodium. Calcium carbonate is almost invariably present in the soil, and both sodium chloride and sodium sulphate react with this to produce sodium carbonate, which is much more harmful to vegetation than the other salts. The action is, however, reversible, and the addition of calcium sulphate to the soil has long been a recognised method of reducing the amount of sodium carbonate. The method, however, has not always succeeded, and Dr. Breazeale is able to furnish an explanation from his curves showing the amount of carbonate formed from the various sodium salts. If the carbonate is arising from the interaction of sodium chloride or sodium nitrate with calcium carbonate, then calcium sulphate is effective in bringing about the reversal; if it arises from sodium sulphate, then calcium sulphate is without effect.

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