Search

The salinity problem is becoming increasingly widespread in arid countries. In semiarid Tunisia about 50% of the irrigated land is considered as highly sensitive to salinization. To avoid the risk of salinization, it is important to control the soil salinity and keep it below plant salinity tolerance thresholds. The objective of the present study was to provide farmers and rural development offices with a tool and methodology for predicting, monitoring of soil salinity for a better agronomical strategy. The experiments were carried out in the highly complex and heterogeneous semiarid Kalâat Landalous irrigated district of Tunisia. The field and laboratory measurements of soil and water properties were conducted in 1989 and 2006 at different observation scales (2900 ha, 1400 ha, 5200 m long transect, and soil profiles). Seventeen years of reclamation of a saline and waterlogged soil led to the reduction of average electrical conductivity of the soil saturated paste extract (ECe), measured at 5 soil depths (from 0 to 2 m) below the plant salt tolerance threshold and the dilution of groundwater salinity from 18.3 to 6.6 dS m−1. The variation in soil salt storage (ΔMss = Mss2006 − Mss1989) in the vadose zone was negative, equal to about −145 × 103 ton (≈−50 ton ha−1). During the same period, the salt balance (Siw–Sdw) estimated from the input dissolved salt brought by irrigation water (Siw) and output salts exported by the drainage network (Sdw) was equal to −685 × 106 kg and the Sdw was 945 × 106 kg. Under irrigation and efficient drainage, the soil salinization could be considered as a reversible process. At the transect scale, the high clay content and the exchangeable sodium percentage was negatively correlated to saturated hydraulic conductivity. The textural stratification, observed at soil profile scale, favors accumulation of salt in the soil. Based on the findings related to the multiscale assessment of soil salinity and groundwater properties, soil salinization factors were identified and a soil salinization risk map (SRU) was elaborated. The shallow groundwater constitutes the main risk of soil salinization. This map can be used by both land planners and farmers to make appropriate decisions related to crop production, and soil and water management. (Less)

In crop modelling the soil, plant and atmosphere system is regarded as a continuum with regard to root water uptake and transpiration. Crop production, often assumed to be linearly related with transpiration, depends on several factors, including water and nutrient availability and salinity. The effect of crop production factors on crop production is frequently incorporated in crop models using empirical reduction functions, which summarize very complex processes. Crop modelling has mainly focused on conventional crops and specific plant types such as halophytes have received limited attention. Crop modelling of halophytes can be approached as a hierarchy of production situations, starting at the situation with most optimal conditions and progressively introducing limiting factors. We analyse crop production situations in terms of water- and salt limited production and in terms of combined stresses. We show that experimental data as such may not be the bottleneck, but that data need to be adequately processed, to provide the basis for a first analysis. Halophytic crops offer a production perspective in saline areas, but in other areas long-term use of low quality irrigation water for halophyte production can result in serious soil quality problems. An overview is given of potential problems concerning the use of (saline) irrigation water, leading to the conclusion that soil quality changes due to poor quality water should be considered in determining the areas selected for halophyte growing.