Amelioration strategies for saline soils: A review

Soil salinization is one of the major causes of declining agricultural prod uctivity in many arid and semiarid regions of the world. Excessive salt con centrations in soils. in most cases, cannot be reduced with time by routine irrigation and crop management practices. Such situations demand soil amel ioration. Various means used to ameliorate saline soils include: (a) moveme nt of excess soluble salts from upper to lower soil depths via leaching, wh ich may be accomplished by continuous pending, intermittent pending, or spr inkling; (b) surface flushing of salts from soils that contain salt crusts at the surface, a shallow watertable, ol a highly impermeable profile; (c) biological reduction of salts by harvest of high-salt accumulating aerial p lant parts, in areas with negligible irrigation water or rainfall available for leaching; and (d) amelioration of saline soils under cropping and leac hing. Among these methods, cropping in conjunction with leaching has been f ound as the most successful and sustainable way to ameliorate saline soils. Cropping during leaching or between leachings causes an increase in salt-l eaching efficiency because a decrease in soil water content occurs under un saturated water flow conditions with a concurrent decrease in large pore by pass and drainage volume. Consequently, anaerobic conditions in soil may oc cur during leaching that can affect crop growth. Thus, in addition to the e xisting salt-tolerant crop genotypes, research is needed to seek out or dev elop genotypes with increased tolerances to salinity and hypoxia. Since sal t leaching is interacted by many factors, evaluation of the traditional con cepts such as the leaching requirement (LR), the leaching fraction (LF) and the salt balance index (SBI) demands incorporation of a rapid, efficient a nd economical way of monitoring changes in soil salinity during amelioratio n. Besides this, numerous models that have been developed for simulating mo vement and reactions of salts in soils need evaluation under actual field c onditions. Copyright (C) 2000 John Wiley & Sons, Ltd.