Currently at least 20 per cent of the world's irrigated land is salt-affected. However, projections of global population growth, and of an increased demand for food and fibre, suggest that larger areas of salt-affected soil will need to be cropped in the future. About 60 per cent of salt-affected soils are sodic, and much of this land is farmed by smallholders. Ameliorating such soils requires the application of a source of calcium (Ca 2þ ), which replaces excess sodium (Na þ ) at the cation exchange sites. The displaced Na þ is then leached from the root zone through excess irrigation, a process that requires adequate flows of water through the soil. However, it must now be recognized that we can no longer conduct sodic soil amelioration and management solely with the aim of achieving high levels of crop productivity. The economic, social, and environmental impacts of different soil-amelioration options must also be considered. A holistic approach is therefore needed. This should consider the cost and availability of the inputs needed for amelioration, the soil depth, the level to which sodicity needs to be reduced to allow cropping, the volume and quality of drainage water generated during amelioration, and the options available for drainage-water disposal or reuse. The quality and cost of water available for post-amelioration crops, and the economic value of the crops grown during and after amelioration should also be taken into account, as should farmers' livelihoods, the environmental implications of amelioration (such as carbon sequestration), and the long-term sustainable use of the ameliorated site (in terms of productivity and market value). Consideration of these factors, with the participation of key stakeholders, could sustainably improve sodic soil productivity and help to transform such soils into a useful economic resource. Such an approach would also aid environmental conservation, by minimizing the chances of secondary sodicity developing in soils, particularly under irrigated agriculture.

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A subfactor-based regression technique for estimating hydraulic roughness coefficients for shallow overland flow was developed from simulated rainfall/runoff plots originallycollected for erosion studies. The data were collected from 14 different native rangeland areas in the western United States. Rainfall was appliedat a constantintensity of 65mm/hrfrom a rotating-boom rainfall simulator. Surfaces evaluated ranged from smooth bare soil to gravelly bare soil and sparsely to densely vegetated rangeland areas. A reference table of "effective roughness" coefficients for shallow overland flow is presented with a description of site char acteristics. The derived roughness regression equations predict an "effective Darcy-Wiesbach roughness coefficient" for nativerangeland (r2 = 0.70)that incorporates the effect of raindrop impact, soil texture, random roughness, rocks, litter, and canopy and basal plant cover. The sites evaluated in the paper covered a wide range of vegetation types and included short-, mid-, and tallgrass prairies; desert shrubsand sagebrush; and oak and pinyon-juniper woodlands. No trend in effective roughness coefficient associated with type of vegetation (grass or shrub) or soil texture was apparent.

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