Salt transfer under irrigation with treated wastewater in semi-arid Tunisia

Abstract: A continuously growing population in the world has resulted in more agricultural activity in arid- and semi-arid areas where it once was harder to cultivate crops. Due to the high evaporation and the lack of rainfall in these areas it is necessary to irrigate the fields. In some areas it has become more and more common to use treated wastewater as an alternative irrigation source. When the soil is irrigated with saline treated wastewater, some of the salt will be concentrated in the soil. Excessive soil salinity can e.g. limit the plant water uptake, thus decreases the crop production, and it could lead to sever soil degradation. However, it is possible to use moderately saline water for irrigation without a significant risk for severe soil salinization if certain rules for water and soil management are established, implemented and followed. Therefore the main objective of this thesis is to do an assessment of the soil salinity in agricultural soil as a result of irrigation with treated wastewater. This master thesis will also try to estimate the effects on the soil salinity after a major rainfall event. This will be done with a field study that was conducted outside the city of Nabeul in the north-east of semi-arid Tunisia during 2 months. The soil salinity assessment done in this thesis can only be considered a qualitative one and the result can only be seen as an indication of an increase or decrease in the soil salinity over this particular field. However, the indications can be a help when deciding the objectives and limitations on future studies in this area. It has been concluded that a general increase in the soil salinity after two irrigation events cannot be seen. However, it was concluded that a small decrease in soil salinity could be seen already after 57.5 mm of rain. This indicating that the Tunisian winter rains can leach the soil from the salts added during irrigation, and that there is no significant risk of soil salinization in this field.