Waterlogging and Salinity in the Indus Plain: Comment

Abstract

Not only does Ghulam Mohammad's contribution on waterlogging and salinity in the Indus Plain [5] reflect a wide understanding of the agricultural problems of Pakistan but the clarity of his presentation is commendable. My comments all have to do with water quality and drainage problems in this vast irrigated area with the future rather than the immediately present problems primarily in mind. I trust that all statements will be regarded as constructive rather than critical. The changes now occurring with irrigation in the compositions of the initially high-quality canal waters of the Indus Plain as these waters become groundwaters, appear to be little different from the past changes which occurred more slowly but which are responsible for the diverse compositions of the present groundwaters. Many of these present-day groundwaters were left be hind by the flood waters which deposited the valley alluvium. The flood waters left on the land surface underwent concentration by evapotranspiration with precipitations of CaCO3 and losses of Mg in the form of compounds of salica. As a result of these precipitations there were increases in the proportions of Na.