Abstract
Water supplies have been decreasing in several semi-arid regions, and it is therefore necessary to adopt irrigation strategies aimed at maximizing water use efficiency. In this paper, the effects of saline and deficit irrigation on water use efficiency and on potato crop response, based on observations of soil and plant water status, were investigated. Experiments were carried out in Central Tunisia, by monitoring potato crop growth during two seasons in four distinct treatments (T1–T4), represented by two different irrigation doses and two water qualities. For irrigation scheduling purposes, thresholds of soil matric potential, soil water content and Crop Water Stress Index (CWSI) were identified with the aim to quantify the effects of water and/or salinity stress on the achievable yield. Experiments allowed verifying that crop yield is strongly affected by the seasonal amount and quality of applied water. Despite differences of crop yield between treatments T2, T3 and T4 not being statistically significant (P < 0.05), crop yield varied between 26.3 t/ha (T3 in 2015) to 16.3 t/ha (T4 in 2015). However, crop yield decline of 17.0 t/ha and 12.0 t/ha per each 100 mm decrease of applied water were observed under the application of water electrical conductivity of 1.6 dS/m and 4.1 dS/m respectively. On the other hand, an increase of 1.0 dS/m in water electrical conductivity caused a yield decline rate of about 10%. The results achieved showed that under the semi-arid climate of Tunisia, potato crop irrigation should be scheduled to avoid water deficit; however, the possibility to reduce water supply can be envisaged when water availability is limited, but with the awareness to accept the shortage of production. Finally, when saline water is the only source available to the farm, it is necessary to avoid the reduction of irrigation doses, to prevent excessive salt accumulation in the root zone with unavoidable effects on crop yield.
Highlights
In arid and semiarid regions, up to 70–80% of the total water resources are used for agriculture [1]
Thresholds of soil matric potential, soil water content and Crop Water Stress Index (CWSI) were identified with the aim to quantify the effects of water and/or salinity stress on the achievable yield
Crop yield decline of 17.0 t/ha and 12.0 t/ha per each 100 mm decrease of applied water were observed under the application of water electrical conductivity of 1.6 dS/m and 4.1 dS/m respectively
Summary
In arid and semiarid regions, up to 70–80% of the total water resources are used for agriculture [1]. In Tunisia, the potato represents the second main crop, with a total surface of about 7% of irrigated lands and a production of 360,000 tons per year [5]. Under the semi-arid climate of Central Tunisia, winter and early spring rainfall usually provide part of the water needed to satisfy crop transpiration requirements. Since the beginning of April, air temperature tends to increase and the amount of rainfall decreases. This is the period when plants achieve their full development stage, have the highest demand for water and are very sensitive to water deficit [7]. When coping with water and saline stress, irrigation scheduling should account for the dependency of crop yield from water quality and quantity, in order to minimize water losses and to optimize irrigation water use efficiency (WUE) as well as to limit the salt build-up in the root zone [11]
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