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We irrigated field-grown celery (Apium graveolens L. var. dulce [Mill.] Pers. 'Tall Utah') with four concentrations of saline water, NSC (nonstressed control), SW1, SW2, and SW3, corresponding to EC of 0.5, 4.4, 8.5, and 15.7 dS·m^-1, respectively, plus a nonirrigated control (NIC) and investigated the effects of the treatments on water relations, yield and ion content. In addition, we compared simultaneously plant response to both salt and drought stress by using a modified version of the threshold-slope model. Increasing salinity of the irrigation water reduced fresh and dry weights of the shoots, but increased the dry matter percentage in shoots. The marketable yield was moderately affected by salinity (25% reduction at EC 8.5 dS·m^-1). In contrast, a severe water stress dramatically decreased the marketable yield from 23 t·ha^-1 (average of the irrigated treatments) to <7 t·ha^-1 (nonirrigated control). Na⁺ and Cl^- concentrations increased in salinized plants whereas nitrogen content, K⁺, Ca²⁺, and Mg²⁺ concentrations decreased upon salinization. Midday leaf water potentials (Ψ_t) decreased from -1.48 MPa (0.5 dS·m^-1) to -2.05 MPa (15.7 dS·m^-1) and - 2.17 MPa (nonirrigated control), though the reduction in leaf cellular turgor was less severe. The maintenance of high leaf cellular turgor was positively correlated to a decrease in osmotic potential and to an increased bulk modulus of elasticity. These results indicate that it is possible to irrigate celery with saline water (up to 8.5 dS·m^-1) with acceptable losses in marketable yield and confirmed that in the field, this species has the ability to efficiently regulate water and ion homeostasis. In the absence of irrigation, celery plants were unable to cope with the drought stress experienced, although this was comparable, in terms of soil water potential, to the one caused by saline irrigation.

Production of vegetable crops can be limited by saline irrigation water. The variability of crop salt tolerance under different environmental conditions requires species-specific and environment-specific field evaluations of salt tolerance. Data on field performances of vegetable crops grown on soils that have been irrigated with saline water for many years are lacking. In this study we analyzed the long-term effect of irrigation with saline water on soil properties and on responses of field-grown pepper (Capsicum annuum L.) plants in these soils. Yield, gas exchanges, water relations, and solute accumulation were measured in plants grown under three different irrigation treatments: a nonsalinized control (EC_w = 0.5 dS·m^-1) and two concentrations of commercial sea salt, corresponding to EC_w of 4.4 and 8.5 dS·m^-1, respectively. In addition, a nonwatered drought stress treatment was included. Irrigation water with an EC of 4.4 dS·m^-1 resulted in 46% reduction in plant dry weight (leaves plus stem) and 25% reduction in marketable yield. Increasing the electrical conductivity of the irrigation water to 8.5 dS·m^-1 caused a 34% reduction in plant dry weight and a 58% reduction in marketable yield. Leaf and root cellular turgor and net CO₂ assimilation rates of leaves in salt-stressed plants decreased along with a reduction in leaf area and dry matter accumulation. High concentrations of Na⁺ and Cl^- in the irrigation water did not significantly alter the level of K⁺ in leaves and fruit. In contrast, drought stressed plants had higher concentrations of leaf K⁺ compared to well watered control plants. These results indicate that Na⁺ and K⁺ may play similar roles in maintaining cellular turgor under salinity and drought stress, respectively. The regulation of ion loading to the shoots was most likely functionally associated with physiological modifications of the root/shoot ratio that was substantially smaller in salinized vs. drought stressed plants. From an agronomic perspective, irrigation with moderately saline water (4.4 dS·m^-1) it is recommendable, compared to no irrigation, to obtain an acceptable marketable yield in the specific environment considered.

Irrigation is a vital component of the world agriculture. It is practiced worldwide on ≈270 million hectares and it consents to produce 40% of our total food. Agricultural water consumption accounts for 70% of total freshwater use. The competition for this precious resource is increasing tremendously. Therefore, it is becoming critically important to optimize agricultural water use efficiency (WUE) defined as the ratio of crop yield over the applied water. This requires a shift from maximizing productivity per unit of land area to maximizing productivity per unit of water consumed. To maximize WUE it is necessary to conserve water and to promote maximal crop growth. The former requires minimizing losses through runoff, seepage, evaporation, and transpiration by weeds. The latter objective may be accomplished by planting high-yielding crops/cultivars well adapted to local soil and climatic conditions. Optimizing growing conditions by proper timing of planting and harvesting, tillage, fertilization, and pest control also contribute to improve crop growth. Most of these techniques refer to proven technology, whose implementation and/or fine-tuning in current farming systems may tremendously improve water management efficiency. In this paper, after discussing the importance of irrigation in agriculture, we will introduce basic concepts that define crop WUE and will finally review the means to improve irrigation efficiency in field vegetable crop production.