Leaching of tile-drained saline soils

Abstract

Leaching experiments were conducted on three tile-drained saline soils, each soil having a different average hydraulic conductivity. The experimental plots consisted of the area between two parallel lateral drains and the main disposal drain. Fresh irrigation water was alternately ponded to a depth of 15 cm and drained to slightly above tiledrain depth. Chloride removal was measured on soil samples taken after completion of each draining cycle and, independently, from frequent sampling of the tile effluent. The quantity of drainage water and chloride removed through the drains was smaller than the total drainage water, estimated from the water balance and total chloride loss from the soil profiles, indicating that all seepage water did not discharge through the tiles. Analysis of results shows that during the ponding stage desalinization proceeds more rapidly near the drains than midway between, while during the falling water-table stage desalinization is more even over the whole area. This is explained by the difference in surface inflow rates across the area between drains during the two stages. Comparison of continuous ponding with alternate ponding and draining shows that in the latter case complete desalinization is achieved with considerably less leaching water. The leaching efficiency is not very high under conditions of continuous ponding.