DEEP PERCOLATION DURING PROLONGED PONDING OF A SWELLING SOIL, AND THE EFFECT OF GYPSUM TREATMENT

A sodic clay soil (a Vertisol) was instrumented from a 5 m deep pit to avoid the problems of preferential cracking around surface installations. Infiltration rates and changes in water content and vertical swelling at a number of depths in the soil profile were measured during prolonged ponding (139 and 160 days on separate plots). Essentially no deep percolation in one plot contrasted with a substantial amount (6.6 mm day-1) in the second, gypsum-treated plot, with obvious consequences for changes in ground-water level. A method of calculating deep percolation is presented which takes into account the effects of swelling. © 1979.