Cotton production in Australia occurs mainly in cracking clay soils. In the past, it was widely assumed that deep drainage was negligible in these soils (Hearn, 2000). Recently, however, several researchers have contradicted this view. Deep drainage rates between 9 and 146mm/yr, nitrate and chloride fluxes of 227 and 3272 kg/ha/yr, respectively, have been reported from southern Queensland and my New South Wales(Moss et al 1999; Zischke and Gordon, 2000). Willis and Black (1996) reporting from central-western New South Wales observed that deep drainage was 17 mm/yr when a soil had 53% clay, whereas when it had 35% clay drainage increased to 202 mm/yr. These soils tended to have shallow water tables, and they suggested that drainage and Ieaching of salts from the profile could increase the salinity and decrease the depth to the watertable, with associated capillary rise resulting in salinization of productive soils