In many countries of the dry areas irrigated agriculture and horticulture are exposed to increasing pressure to expand the use of brackish and even high-saline waters for crop production, as water resources of good quality are required for human consumption and industrial development. But experience shows that successful and sustainable application of lower quality waters such as brackish or saline waters requires special management practices, which need to be improved. The adaptation of irrigation management to saline growth conditions is often unsatisfactory, as our understanding on the process of water uptake by roots from saline soils and factors affecting crop salt tolerance is still far from being complete.

The paper analyses the present concept for rating the salt tolerance of irrigated crops following the 4-layer-profile after FAO and USDA, where the vertical movement of solutes is considered. This concept does not reflect the effects of the lateral salt movement, which dominate between water applications to cover the plant water supply. Field experiments with onions under irrigation with brackish waters of increasing salinity and under strongly arid climate (Saudi Arabia) have shown a continuous increase of soil salinization in the rhizospheric soil (soil adhering the roots) as compared to the bulk soil (soil far from roots). The presented model calculation demonstrates the effect of roothair length and rhizospheric soil volume on salt concentrations in the rhizospheric soil solution. The effects of root morphology in conjunction with soil properties are considered as an important link to complete our understanding on crop salt tolerance with respect to optimize irrigation technique and breeding of more tolerant crops.