Soils of high acidity are a major limitation to crop productivity in much of the world. In Australia acid soils covers about 40% of the total land area. Although soil acidification is a natural process but modern agriculture practices have accelerated acidification of soils compared with natural ecosystems in southern Australia (Bromfield et al 1983; Lewis et al 1987). Approximately 30 million hectares of acid soils have developed after land clearing since European settlement. Among various soil acidifying processes, leaching of nitrate produced by legume nitrogen fixation and from the application of ammonical fertilizers, and removal of bases in crop harvests, are the most important factors in increasing soil acidification rates in Australia. Heavy clays, predominantly used for growing cotton in northern NSW, are generally alkaline and contain some free calcium carbonate in subsoil. Therefore, presently there appears to be no cause for concern from soil acidification in such soils. Other soils particularly, lighter textured Red Earths and Red Brown Earths characterised by neutral or slightly acidic pH, are also used for cotton production. These soils may have a potential acidification problem.