Abstract
On the heavy montmorillonitic clay soils of the Sudan Gezira a neutron probe was used to study water movement through a dry and saline-sodic profile prior to irrigation and cropping. It was found that the upper 10cm layer can transmit capillary water when it reaches 24mm of moisture. This layer had an antecedent moisture content of 5mm and attained saturation at 49mm after 4h of flooding. The moisture profile showed that the oil continued to take up water so long free water was maintained on the surface and a hydraulic potential existed within the profile. The uptake of water however, slowed down progressively with time. The magnitude of slowing down was highest at 10cm layer and decreased with depth to 30cm which attained an intake rate of 1mm/h after 6h of inundation. Changes in volume weight both before and after watering were measured with a gamma probe. In these swelling clays volume weight decreased considerably after wetting. It is therefore, necessary to report the moisture content of the soil at the time of measurements. Before wetting, the maximum dry volume weight was 1·513g/cm3 (moisture content 18·0 per cent by volume) at a depth of 60cm whereas after watering it was 1·430g/cm3 (moisture content 29·2 per cent by volume) at 80cm.
