THE EFFECT OF PED SIZE, SIMULATED RAINFALL DURATION AND FREQUENCY ON THE LEACHING OF SALTS FROM CLAY TOPSOILS

Aggregates of saline-sodic clay in three size ranges were leached in c olumns using simulated rainfall events of varying size, duration and f requency. Aggregate size, depth of rainfall and duration affected the rate of leaching, although rainfall pattern became more influential as the aggregate size increased. Using the data, a simple empirical mode l was constructed to predict leaching, using as a basis the cumulative depth of drainage, the size of the aggregates, the storm duration and the frequency. The model is capable of accurately predicting the quan tity of salts leached both under laboratory conditions as well as in m ulched restructured topsoils exposed to winter rainfall. However, it o verestimated leaching from a topsoil exposed to raindrop impact becaus e of the development of a surface crust which cracked during drying. I f the rate of leaching of restructured saline-sodic clays is to be acc urately predicted under field conditions it will be necessary to take account of physical changes such as these taking place at the soil sur face. (C) 1998 Elsevier Science B.V. All rights reserved.