Saline water irrigation effects on soil salinity distribution and some physiological responses of field grown Chemlali olive

Abstract

The shortage of water resources of good quality is becoming an issue in arid and semi arid regions. Per consequent, the use of water resources of marginal quality is becoming an important consideration, particularly in arid regions in Tunisia, where large quantities of saline water are used for irrigation. Nevertheless, the use of these waters in irrigated lands requires the control of soil salinity and a comprehensive analysis even beyond the area where water is applied. The aim of this study was to investigate the effects of saline water irrigation on soil salinity distribution and some physiological traits of field-grown adult olive trees (Olea europaea L. cv. Chemlali) under contrasting environmental conditions of the arid region in the south of Tunisia. The plants were subjected, over two growing seasons, to two drip irrigated treatments: fresh water (ECe=1.2dSm−1, FW) and saline water (ECe=7.5dSm−1, SW). Saline water irrigation (SW) has led to a significant increase in soil salinity. Furthermore, these results showed that soil salinity and soil moisture variations are not only dependent on water salinity level but are also controlled by a multitude of factors particularly the soil texture, the distance from the irrigation source and climatic conditions (rainfall pattern, temperature average, …). On the other hand, salt treatment reduced leaf midday water potential (LMWP), relative water content and photosynthetic activity and increased the leaf proline content, and this increase was season-dependent. Indeed, LMWP in SW plants decreased to −3.71MPa. Furthermore, the highest level of proline in SW plants was registered during summer period (2.19μmol/mg Fw). The proline accumulation recorded in stressed plants has allowed them to preserve appropriate leaf water status and photosynthetic activity. More to the point, this olive cultivar seems to be more sensible to soil salinity during the intense growth phase. Such tendencies would help to better manage water resources for irrigation, particularly under actual climatic conditions of water scarcity. For example, in the case of the availability of different water qualities, it would be better to preserve those of high quality for olive irrigation during the intense vegetative growth phase, in coincidence with high salt sensitive period, and those of low quality for irrigation during partial growth and plant rest phases. What’s more, the urgent use of saline water for irrigation should not be applied without taking into consideration the different surroundings conditions where it is used, particularly the water salinity level, the soil type, the adopted irrigation system, the degree of the crop salt tolerance, the plant growth phase and the climatic conditions of the experimental site.