Water requirements for salt control in rice schemes in the Senegal river delta and valley

Abstract

The paper estimates the water requirements for salt control in rice schemes located on saline soils in the Senegal river delta. When the fields are not cultivated, salts are transported to the top soil by capillary rise from the very saline and shallow ground water table. During the irrigation season, the large quantity of irrigation water adds additional salt to the fields. If the percolation rate of the soil is small, salts will have to be removed from the schemes by flushing the standing water from the fields when the salinity of the water reaches the threshold value of 1.5 ds m−1. The results indicate that if the schemes are located on the river banks (fonde), flushing at the beginning of the season and the percolation losses throughout the season may be sufficient to keep the salts out of the root zone. On the less permeable soils in the depressions (hollalde), an extra flushing is required to evacuate enough salts from the fields during the irrigation season. In total about 2,300 m3 ha−1 of water may be needed for flushing. If flushing is not practised, the schemes have to be abandoned after a few years of cultivation due to build-up of soil salinity.