To Prevent Aridization, Combat Salinity

Abstract

With some 8% of the world's land-surface occupied by absolute desert, and up to another 40% estimated to be covered or threatened by less-extreme deserts or semideserts, it is clear that still-increasing desertification imposes one of the most critical situations and hence important considerations for the future of Man and Nature. All the inhabited continents are involved to varying degrees, with Australia (80% desertified) the worst-hit areally. And yet the area of the world that is affected by desertification, soil-degradation, erosion, and/or recurrent droughts, continues to increase at a rate of 5–7 million hectares annually in the face of ever-increasing overall human population. This survey warns again of foreseeable dangers for the future.Aridization and more advanced desertification of land result from the combined action of natural tendencies and ecological mistakes made by Man in the course of his manifold activities. Most alarmingly, the velocity of what is mainly anthropogenic aridization is commonly measured in terms of a few years or at most a single human generation. But help should come from the maintenance of rain-fed farming in less arid areas, and especially from the widespread establishment of irrigation systems which now involve some 250 millions of hectares. There are, however, very serious problems engendered by continuing irrigation, which is apt to be wasteful of fresh water. To begin with, river-water resources are becoming increasingly limited and artesian waters are too-easily depleted or become brackish. Worse still, with the high rate of evaporation in arid regions, salinization of the surface and the uppermost soil horizon commonly ensues, and gradually penetrates to lower strata in which plants mainly root. Most existing irrigation systems lack the piping or consistent lining of water-bringing canals and the deep (2.5–3 m) horizontal drainage-ducts that are needed to evacuate excessive soluble salts. The ultimate disposal of the salt, moreover, still causes problems when the sea cannot be used or salt-lakes be created for fish and waterfowl. Meanwhile, revegetation is becoming more and more widely practised and some success is attending efforts to develop salt-resistant crops in USA, India, and USSR.