Abstract
Waterlogging and salinity are the major threats to the sustainability of irrigated agriculture in Pakistan. About 50% of the Culturable Command Area (CCA) in the Fordwah Eastern Sadiqia South (FESS) is affected by waterlogging and 12% by surface and profile salinity. A sample of 26 watercourses was selected in the project area to evaluate the individual and combined impacts of waterlogging and salinity on the yields of cotton, wheat, sugarcane and rice. The crop yields were measured separately for waterlogged fields and those affected with salinity and waterlogging simultaneously. The extent of yield loss as result of a rise in the water table from 1β2 m to less than 1 m was 27 and 33% for wheat and sugarcane crops, whereas it was 7 and 6% in the case of a drop of the water table to more than 2 m. For cotton, a rising water table from 2β3 m to 1β2 m and less than 1 m gave a yield decrease of about 11 and 60% respectively. The rice crop preferred waterlogging, and in contrast to other crops, gave about 7% less yield with a lowering of the water table from less than 1 m to 1β2 m. The wheat and sugarcane yields had decreasing trends with salinity in excess of 4 dS m^β1^ and had complete failures with salinity greater than 12 dS m^β1^ at water table depths of less than 1, 1β2 and 2β3 m. The cotton crop demonstrated relatively higher salinity tolerance under a water table deeper than 1 m. However, this crop could not survive at salinity levels in excess of 12 dS m^β1^ at water table depth of less than 1 m. The rice crop was a complete failure at salinity level of greater than 12 dS m^β1^ under water table depths of less than 1 and 1β2 m. The combined impact of waterlogging and salinity was more harmful to crop yields when compared with the individual effects of waterlogging. The combined analysis of waterlogging and salinity on crop yields provide a good sensitivity of the salinityβyield relationships and indicated the importance of subsurface drainage. Copyright Β© 2002 John Wiley & Sons, Ltd.