Introduction

Wheat (Triticum aestivum L.) is one of the most widely grown crops through many parts of the world. In terms of both hectares cultivated and quantity of product consumed by mankind wheat represents 30% of the world edible dry matter (DM) and up to 60% of the daily calory intake in several developing countries (FAOSTAT 2017). Therefore, increasing wheat production is essential national target to fill the gap between production and consumption, especially in developing countries (Hafez and Kobata 2012). The consumption of wheat in Egypt annually is about 18.9 Mt, although the Egyptian production is about 9.0 Mt (Malr 2014). Grain yield in wheat is a polygenic trait and is also influenced by a number of environmental factors including cruel drought (Campuzano et al. 2012). Therefore, it is now very necessary to develop new techniques to cope with this upcoming problem of food security with less usage of water.

As an important signaling molecule, salicylic acid plays multifaceted role in plants during stresses like increasing the stress tolerance (Li et al. 2014), involve its roles as an antioxidant, enzyme cofactor, and electron transport (Alonso et al. 2009) to minimize the damages due to oxidative stress (Hayat et al. 2010). Salicylic acid stabilizes the protein and membrane structure and capable scavenges the reactive oxygen species (ROS) by acting as cofactors in the enzymatic reactions (Asadi et al. 2013). SA improves the antioxidative system (Arfan et al. 2007), alleviates lipid peroxidation (Alonso et al. 2009) and regulates many physiological processes like the senescence, photosynthesis (Li et al. 2014), the cell growth and development, and stomata functioning (Hayat et al. 2010). Salicylic acid has been documented to play an intriguing role in reducing the damage action of water loss in leaves (Hayat et al. 2010), decreasing the ion leakage (Asadi et al. 2013) and osmotic regulation (Li et al. 2014) triggered by stress experienced by plants.

Soil salinity is one of the environmental conditions that severely limit plant growth and productivity across the globe (Pirasteh-Anosheh et al. 2015; Waqas et al. 2017). Salt stress is thought to substantially cause degradation of plant growth regulators (PGRs) (Pirasteh-Anosheh et al. 2012; El-Hendawy et al. 2017). In saline affected soil, exogenous application of plant growth regulators has been considered as an alternative strategy to reduce the adverse effect relative to salinity (Pirasteh-Anosheh et al. 2014; Hafez 2016). Salicylic acid (SA) as one of the plant growth regulators is believed to improvement in defence mechanisms under salinity stress conditions (Pirasteh-Anosheh et al. 2017). Munns (2005), De Leon et al. (2015) have reported that negative impacts of salt stress on plants could be ameliorated by exogenous application of SA.

World crop production is also negatively affected by drought stress (Pask and Reynolds 2013), and quick climate change scenario has further exacerbated this status (Zhang et al. 2013), which may threaten the food security. About 40–60% of agricultural land is being affected by drought worldwide (Varga et al. 2015). Drought stress is becoming common in the wheat-growing regions including Egypt. In wheat, drought stress affects the pollination which results in the poor grain yield (Varga et al. 2017). Drought stress also decreases the water and solute potential of grains, thus affecting the grain-filling metabolism (Hafez and Seleiman 2017). Most of abiotic stresses, including drought, cause imbalance between the production and quenching of reactive oxygen species (ROS) (Hafez and Gharib 2016). These ROS are very deleterious for the biological membranes and nucleic acid (Passioura 2012). Yields have developed various mechanisms, which support them to avoid drought stress. Some of those mechanisms contain activation of antioxidants system, and accumulation of osmolytes/compatible solutes, which assist them to avoid stress by maintaining the subcellular membranes from the ROS damage (Tuberosa 2012). Water stress stimulates accumulation of compatible solutes for example glycerol, sugars, betaines and proline. Proline is one of the most osmolytes accumulating in plants when exposing to environmental stresses (Pirasteh-Anosheh et al. 2012). Accumulation of proline encourages water retention in plants thereby ameliorating harnful impacts of water stress (Varga et al. 2015). Thus, proline is considered as a metabolic measure of drought tolerance (Zhang et al. 2013). Although exogenous application of salicylic acid to crops cultivated under water stress in saline soil has been investigated considerably, there is little information on the amelioration of crops from drought and salinity deteriorate using SA (Pirasteh-Anosheh et al. 2014; Varga et al. 2017). Such researches could be significant for wheat, as it is the first most important crop in the globe, and its growth and productivity are adversely affected by drought and salinity stress (Pirasteh-Anosheh et al. 2017; Hafez and Seleiman 2017). Thus, the key objective of the current study was to investigate whether SA could mitigate the negative and harmful impact of drought and salinity on wheat plants. In this research we assessed the impact of exogenous application with SA on wheat growth, yield related-traits, productivity and water use efficiency under water stress in saline soil.

Materials and Methods

Experimental Site and Growth Conditions

A field experiment was conducted to test the effect of water deficit on grain yield and water use efficiency in wheat (Sakha 93 cultivar) which is salt-tolerant. The experiment was conducted in 2015/2016, from 27 December to 8 May and repeated in 2016/2017, from 29 December to 10 May at Water Requirements Research Station (El-Karada), Water Management Research Institute, National Water Research Centre, Kafrelsheikh Governorate (North Delta, Latitude: 31°6′N/Longitude: 30°56′E), Egypt. During the growing cycles of wheat from December to May, The meteorological data were obtained from the agro-meteorological station adjacent to the experimental location and are presented in Table 1. The texture of the experimental soil was characterized as clayey (58.4% clay, 21.4% silt, and 20.2% sand) with 1.30% organic matter in the 0–60-cm surface layer, soil bulk density of 1.18 g cm−3, field capacity of 40.92%, wilting point of 22.24% and available soil moisture 18.68%. Before seedbed preparation, the Soil was ploughed twice and randomized three soil samples (0–60 cm depth) were taken for analysis. Physical and chemical properties of the soil are shown in Table 2.

Table 1 Meteorological data for El-Karada Station during 2015/2016 and 2016/2017 growing seasons
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Table 2 Chemical properties of soil used in 2015/2016 and 2016/2017 growing seasons
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Experimental Design and Agronomic Practices

The field experimental design consisted of water stress by irrigation at 50, 70 and 90% depletion of the available soil moisture from the depth 0–60 cm and two levels of salicylic acid foliar spraying replicated four times in a randomized complete block split-plot design, keeping irrigation treatments (50, 70 and 90% depletion of the available soil moisture) as the main plots and salicylic acid levels (0 and 200 ppm) as the subplots. Salicylic acid was foliar applied twice at a rate of 200 ppm (192 g ha−1) at 40 and 60 days after sowing. The sub-plot size was 15 m2 (3 × 5). The rows were 5 m long and spaced 0.15 m apart. To avoid the impact of lateral movement of irrigation water, the main plots were isolated by levees 1.5 wide. Seeds were planted at a seeding rate of 142.8 kg ha−1. Phosphorus fertilizer was applied during the soil preparation at the rate of 35 kg P2O5 ha−1 in the form of super phosphate 15% P2O5. Potassium fertilizer was applied as one dose directly before the first irrigation at the rate of 57 kg K2O ha−1 in the form of potassium sulphate 48% K2O. Nitrogen fertilizer was applied at two equal doses directly before the first and second irrigations at a rate of 180 kg N ha−1 in the form of urea 46.5% N. Other agronomic practices such as protecting wheat plants from weeds and diseases were completed in a timely manner.

Observations and Measurements Data Analysis

Free proline content in the leaves was determined following the method of (Bates et al. 1973). Leaf samples (0.5 g) were homogenized in 5 ml of sulphosalycylic acid (3%) using mortar and pestle. About 2 ml of extract was taken in test tube and to it 2 ml of glacial acetic acid and 2 ml of ninhydrin reagent were added. The reaction mixture was boiled in water bath at 100 °C for 30 min. After cooling the reaction mixture, 6 ml of toluene was added and then transferred to a separating funnel. After thorough mixing, the chromophore containing toluene was separated and absorbance read at 520 nm in spectrophotometer against toluene blank. Proline concentration was determined using a calibration curve and expressed as μ mol proline g−1 FW.

Leaf relative water content: at heading stage, leaves detached from the stem were weighted to determine fresh weight (FW). Turgid weight (TW) was estimated after the leaves were kept floating in distilled water into a closed petri dish at 10 °C in the dark for 24 h and weighted again. Dry weight (DW) was determined for leaves samples after oven-drying for 72 h at 80 °C. RWC was calculated using the following equation:

$${\text{LRWC }}\left( \% \right) = \left[ {\left( {{\text{FW}} - {\text{DW}}} \right)/\left( {{\text{TW}} - {\text{DW}}} \right)} \right] \times 100\;\;(\text{Chelah et al.} 2011).$$

Stomatal conductance (gs) was measured on fully expanded flag leaves from the abaxial surface as mmol H2O m−2 s−1 from three plants in each plot with a dynamic diffusion porometer (Delta-T AP4, Delta-T Devices Ltd, Cambridge, UK) at fine days. Two measurements from both adaxial and abaxial surfaces of the leaf were taken. It measured in the fine days (following weather) every 4 or 7 days from booting till harvest with a porometer (Izanloo et al. 2008). Measurement in the top leave and front (ra) and back side (rb) of the center of the leaf.

$${\text{Total leaf conductance }}\left( {{\text{r}}_{\text{l}} } \right){\text{ is 1}}/{\text{r}}_{\text{l}} = 1/{\text{r}}_{\text{a}} + 1/{\text{r}}_{\text{b}} .$$

At maturity, 10 samples from each experimental plot were randomly selected for counting 1000-grain weight, number of grains per spike and number of spikes per m2. In addition, at physiological maturity, 6 m2 area of each plot were manually harvested from the middle. The whole harvested plants of the 6 m2 were weighted to calculate the biological yield. Then, grains of the harvested plants were threshed with a thresher machine, dried in oven at + 85 °C for 24 h and then the weight of grain yield was measured. Straw yield was measured by subtracting the weight of grain yield from the weight of biological yield. Eventually, harvest index was counted as the ratio of grain yield to biological yield, and then the value was multiplied with 100 to be expressed as percent.

Uptake of N, P, K and Na were measured from multiplying a percentage of the specified element (nitrogen, phosphorus, potassium and sodium) by grain and straw yield as a dry matter to calculate total nitrogen uptake (kg ha−1), total phosphorus uptake (kg ha−1), total potassium uptake (kg ha−1) and total sodium uptake (kg ha−1). Nitrogen element was determined by macro-kjldahle technique according to AOAC (1975). Phosphorus, potassium and sodium elements were determined according to the flame photometer according to Jackson (1958).

Water consumptive use is the sum of the volumes of water used by vegetative growth of a given area in transpiration and building of plant tissues plus that evaporated from adjacent soil (Israelsen and Hansen 1962). Consumptive use of wheat plant was computed as the difference in soil moisture content in the soil samples taken before and after irrigation. Water consumptive use was obtained using the following equation (Israelsen and Hansen 1962).

$${\text{C}}.{\text{U}}\; = \;{\text{D}}\; \times \;{\text{Bd}}\; \times \;\left( {\varTheta_{ 2} {-}\varTheta_{ 1} } \right)/ 100,$$

D, soil depth in cm; Bd, soil bulk density, g cm−3; Ɵ2, soil moisture % after next irrigation, Ɵ1, soil moisture % before next irrigation. Water consumptive use was computed for all irrigation from sowing up to harvest.

The water use efficiency (WUE; kg m−3) was calculated by dividing the grain yield (kg ha−1) by the water used during the vegetation period (WU; m3 ha−1) (Doorenbos and Pruitt 1977).

Data analysis

Data obtained were subjected to an analysis of variance (ANOVA) procedures according to Gomez and Gomez (1984) using the MSTAT-C Statistical Software package. Means were compared using Tukey’s multiple range test, when the ANOVA showed significant differences (P < 0.05). Standard error of mean was obtained from the analysis for each parameter. Standard error of means (SEM) was obtained from the analysis of variance using Predictive Analytics Software (PASW).

Results

Results illustrated in Table 3 showed that irrigation at 50% depletion of the available soil moisture decreased soil salinity as reflected on the EC of soil extract compared with the other irrigation treatments. The EC values before sowing varied from 3.94 ds m−2 in 2015/2016 season to 3.35 ds m−2 in 2016/2017 season. Under the condition of 50% depletion of the available soil moisture treatment compared with initial soil samples, the values of EC decreased and the values varied from 2.57 ds m−2 in 2015/2016 season to 2.34 ds m−2 in 2016/2017 season after harvesting. In addition, the condition of treatment 70% depletion of soil moisture, the EC values varied from 2.95 ds m−2 in 2015/2016 season to 2.65 ds m−2 in 2016/2017 season after harvesting. Furthermore, the condition of treatment 90% depletion of soil moisture, the EC values varied from 3.28 ds m−2 in 2015/2016 season to 3.08 ds m−2 in 2016/2017 season after harvesting. The magnitude of reduction in EC values for 50% depletion treatment had augmented 70 and 90% depletion treatments respectively, to be 13% and 22% in 2015/2016 season, and to be 12% and 25% in 2016/2017 season (Table 3).

Table 3 Soil chemical analysis before and after growing seasons 2015/2016 and 2016/2017
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Effect of Irrigation Treatments and Salicylic Acid Application on Cations and Anions

As shown in Table 3, it was found that under the condition of 50% depletion of the available soil moisture treatment, the concentration of soluble sodium was lower after harvesting in the successive seasons as compared with initial soil samples which was higher. Regarding, the average Na+ concentration under irrigation treatments. Na+ concentration increased from 13.45 to 11.94 meq L−1 under treatment of 50% depletion in the successive seasons respectively, to 19.25 and 16.47 meq L−1 under treatment of 70% depletion in the successive seasons respectively and to 20.87 and 19.85 meq L−1 under treatment of 90% depletion in the successive seasons respectively. In general, increasing available soil moisture from 10 to 30 and 50% decreased the concentration of soluble sodium, relatively in both seasons.

The other soluble cations such K+ and Ca++, under treatment 50% depletion of the available soil moisture increased soluble cations and its downward movement compared to 70% depletion treatment followed by 90% depletion treatment, in both seasons, respectively (Table 3).

Soluble Cl– in the soil decreased with the increasing the available soil moisture from 10 to 50%. The accumulation of Na+ would predictably insure the accumulation of Cl− (Table 3). After irrigation at 50% depletion, the Cl− concentration values varied from 10.55 meq L−1 in 2015/2016 season to 9.66 meq L−1 in 2016/2017 season compared with initial soil samples which was higher (23.56 and 19.21 meq L−1 in both seasons, respectively). Also, after irrigation at 70% depletion, the Cl− concentration values varied from 15.67 meq L−1 in 2015/2016 season to 15.22 meq L−1 in 2016/2017 season. Moreover, after irrigation at 90% depletion, the Cl− concentration values varied from 19.74 meq L−1 in 2015/2016 season to 18.45 meq L−1 in 2016/2017 season.

Effect of Irrigation Treatments and Salicylic Acid Application on Sodium Absorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP)

Data presented in Table 3 showed that increasing available soil moisture from 10 to 30 and 50% decreased both SAR and ESP in both seasons 2015/2016 and 2016/2017. Under 50% depletion of the available soil moisture, SAR varied from 4.72 in 2015/2016 season to 5.68 in 2016/2017 season compared with initial soil samples which was higher (9.57 and 7.65 in both seasons, respectively). At 70% depletion, SAR increased gradually up to 7.59 in 2015/2016 season and 7.95 in 2016/2017 season. While under 90% depletion, SAR increased more than under 50% and 70% depletion of the available soil moisture to reach 9.75 in 2015/2016 season and 10.82 in 2016/2017 season.

Meanwhile, under 50% depletion of the available soil moisture, ESP varied from 6.85 in 2015/2016 season to 6.87 in 2016/2017 season compared with initial soil samples which was higher (11.09 and 11.33 in both seasons, respectively). At 70% depletion, ESP increased gradually up to 9.57 in 2015/2016 season and 10.25 in 2016/2017 season. While under 90% depletion, ESP increased more than under 50% and 70% depletion of the available soil moisture to reach 10.98 in 2015/2016 season and 10.75 in 2016/2017 season.

Effect of Irrigation Treatments and Salicylic Acid Application on Proline Content

Based on the data presented in Fig. 1, showed that irrigation at 50% depletion of the available soil moisture decreased proline content in both years of study. Figure 1 showed a significant relationship between proline content and irrigation treatments. The proline content significantly increased under treatment 90% depletion of soil moisture but was declined under treatment 70% depletion of soil moisture and was the lowest under treatment 50% depletion of soil moisture in both seasons. It was apparent from Fig. 1 that salicylic acid application increased proline content under all irrigation treatments in both years of study.

Fig. 1
figure 1

Effect of salicylic acid application on proline content (μmol proline g−1 FW) under different irrigation treatments in 2015/2016 and 2016/2017 seasons. The data are the mean ± SE of three replicates. Significant differences of the means according to Duncan’s multiple range test (P ≤ 0.05) are indicated with different letters

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Effect of Irrigation Treatments and Salicylic Acid Application on Stomatal Conductance

As shown in Fig. 2, among irrigation treatments, 50% depletion of the available soil moisture remained superior with higher stomatal conductance compared with 70% and followed by 90% depletion in both seasons. As can be observed in Fig. 2, the stomatal conductance significantly decreased when salicylic acid applied under all irrigation treatments in both seasons.

Fig. 2
figure 2

Effect of salicylic acid application on stomatal conductance (gs) (mmol m−2 s−1) under different irrigation treatments in 2015/2016 and 2016/2017 seasons. The data are the mean ± SE of three replicates. Significant differences of the means according to Duncan’s multiple range test (P ≤ 0.05) are indicated with different letters

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Effect of Irrigation Treatments and Salicylic Acid Application on Relative Water Content

The effect of irrigation treatments and salicylic acid are shown in Fig. 3, treatment 50% depletion of the available soil moisture recorded maximum relative water content while 70% and 90% depletion of the available soil moisture remained less in this regard with low relative water content during both years of study. Likewise, salicylic acid application led to markedly increase in relative water content under all irrigation treatments during both years of study. The relative water content tended to increase under treatment 50% depletion of the available soil moisture with salicylic acid application in both seasons, and was superior than other irrigation treatments.

Fig. 3
figure 3

Effect of salicylic acid application on leaf relative water content (RWC) (%) under different irrigation treatments in 2015/2016 and 2016/2017 seasons. The data are the mean ± SE of three replicates. Significant differences of the means according to Duncan’s multiple range test (P ≤ 0.05) are indicated with different letters

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Nutrient Uptake

Total Nitrogen Uptake

Figure 4 showed that total nitrogen uptake was high significantly influenced by irrigation treatments and salicylic acid application in wheat cultivar in two growing seasons. There was an interaction effect between irrigation treatments and foliar spraying by salicylic acid on total N uptake in both seasons of study. The total N uptake was highly significant increased with all irrigation treatments exposed to foliar spraying by salicylic acid in both seasons compared with unsprayed treatments. The application of salicylic acid led to increase of total N uptake by 20 and 25% under treatment 50% depletion of the available soil moisture in both seasons, respectively. Meanwhile, total N uptake increased by 22 and 28% under treatment 70% depletion of the available soil moisture in both seasons, respectively. Moreover, total N uptake increased by 12 and 10% under treatment 90% depletion of the available soil moisture in both seasons, respectively. Salicylic acid application increased total N uptake by 7 and 5% under 50% depletion compared to 70% depletion and by 28 and 31% compared to 90% depletion in both seasons, respectively. The highest total N uptake was associated with application of salicylic acid under 50% and 70% depletion of the available soil moisture in both seasons.

Fig. 4
figure 4

Effect of salicylic acid application on total N, P, K, Na (kg ha−1) under different irrigation treatments in 2015/2016 and 2016/2017 seasons. The data are the mean ± SE of three replicates. Significant differences of the means according to Duncan’s multiple range test (P ≤ 0.05) are indicated with different letters

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Total Phosphorus Uptake

Referring to Fig. 4, it is obvious that the irrigation treatments and salicylic acid interaction was significant in both growing seasons which showed that maximum of total P uptake was achieved at application of salicylic acid under 50% depletion of the available soil moisture to give 35 and 33 kg ha−1 in both seasons, respectively. While, treatment 90% depletion of the available soil moisture gave a minimum of total P uptake to reach 18 and 17 kg ha−1 in both seasons, respectively. Application of salicylic acid led to increase total P uptake by 30 and 28% under 50% depletion of the available soil moisture compared to control treatment in both seasons, respectively.

Total Potassium Uptake

Data presented in Fig. 4, indicated that K uptake was significant affected by irrigation treatments and salicylic acid application. The treatment in which available soil moisture was 50% depletion absorbed higher K with salicylic acid application compared to 70% and 90% depletion of the available soil moisture which absorbed lower K uptake in the growing seasons. The overall mean values were 175 and 170 kg ha−1 when irrigation at 50% depletion, 150 and 146 kg ha−1 when irrigation at 70% depletion, 140 and 130 kg ha−1 when irrigation at 90% depletion in both seasons, respectively. Application of salicylic acid led to increase total K uptake by 16 and 18% under 50% depletion of the available soil moisture compared to control treatment in both seasons, respectively.

Total Sodium Uptake

Data in Fig. 4, revealed that Na+ uptake was significant affected by irrigation treatments and salicylic acid application. The highest total sodium uptake values were (32 and 30 kg ha−1) under 50% depletion of the available soil moisture. Whereas the lowest total sodium uptake (20 and 21 kg ha−1) was resulted from 70% followed by (7 and 9 kg ha−1) 90% depletion of the available soil moisture in both seasons, respectively. Application of salicylic acid led to reduction in total Na+ uptake under all irrigation treatments in both seasons. The magnitude of reduction was greater under treatment 50% depletion of the available soil moisture more than 70% and 90% depletion in both seasons.

Effect of Irrigation Treatments and Salicylic Acid on Yield Related-Traits

1000-Grain Weight

It is obvious in Table 4 that the 1000-grain weight was influenced significantly by irrigation treatments. 1000-grain weight of 50% depletion gave significantly highest weight than 70% and 90% depletion of available soil moisture in 2015/2016 and 2016/2017 seasons. 1000-grain weight values were 52.76 and 51.68 g at 50% soil moisture depletion, 51.34 and 50.37 g at 70% soil moisture depletion and 49.27 and 48.07 g at 90% soil moisture depletion in 2015/2016 and 2016/2017 seasons, respectively. Furthermore, it is shown in Table 4 that the 1000-grain weight was highly significantly affected by salicylic acid application. Salicylic acid application gave significant higher 1000-grain weight than control plants. The overall mean values were 53.25 and 52.35 g at application of 200 ppm of SA, meanwhile 47.15 and 46.18 g at control treatment in 2015/2016 and 2016/2017 seasons, respectively. No significant interaction was found between irrigation treatments and salicylic acid in both seasons.

Table 4 Effect of irrigation treatments and salicylic acid on (1000-grain weight, number of grains spike−1 and number of spikes m−2, respectively) in 2015/2016 and 2016/2017 seasons
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Number of Grains Spike−1

Regarding irrigation treatments, the data in Table 4 revealed that irrigation treatments resulted in significantly larger number of grains spike−1. The highest number of grains spike−1 was obtained from treatment 50% depletion of available soil moisture. Whereas the lowest number of grains spike−1 resulted from 90% depletion of available soil moisture in both seasons of study. The overall mean values of number of grains spike−1 were higher (48.12 and 46.24) at 50% depletion of available soil moisture followed by 70% depletion (45.25 and 43.43), but at 90% depletion, number of grains spike−1 were low (41.58 and 40.25) in 2015/2016 and 2016/2017 respectively. Data in Table 4 indicated that number of grains spike−1 was significantly influenced by salicylic acid application compared with untreated plants in 2015/2016 and 2016/2017 growing seasons. The overall mean values were higher (47.38 and 46.44) when applied 200 ppm of salicylic acid, and lower number of grains spike−1 (42.85 and 40.55) with control treatment in both seasons, respectively. The interaction was no significant difference between irrigation treatments and salicylic acid in both seasons.

Number of Spikes m−2

Concerning the effect of irrigation treatments on number of spikes m−2 as shown in Table 4, it was observed that the largest number of spikes m−2 was obtained from treatment 50% depletion of available soil moisture followed by 70% depletion then 90% depletion of available soil moisture in both seasons. The overall mean values were (294.81 and 278.25) for 50% depletion, (285.42 and 271.34) for 70% depletion and (219.54 and 207.53) for 90% depletion in both seasons (2015/2016 and 2016/2017), respectively. In addition, data presented in Table 4 revealed that number of spikes m−2 was highly significant affected by salicylic acid application in both seasons compared to untreated plants. Application of 200 ppm of salicylic acid was significantly superior to control treatment. The overall mean values were higher (284.74 and 280.84) when applied 200 ppm of salicylic acid, and lower number of grains spike−1 (275.85 and 271.78) with control treatment in both seasons, respectively. The interaction was no significant difference between irrigation treatments and salicylic acid in both seasons..

Effect of Irrigation Treatments and Salicylic Acid on Yield Productivity

Grain Yield (t ha−1)

The results allocated in Table 5 showed that grain yield was significantly higher with irrigation at 50% depletion of available soil moisture than 70% and 90% depletion of available soil moisture. Averages of grain yield were 6.18, 5.85 and 4.95 t ha−1 in 2015/2016 and 5.98, 5.67 and 4.65 t ha−1 in 2016/2017 seasons, respectively. The analysis of variance in Table 5 showed that the differences were highly significant between salicylic acid treatments in both years of study. Application of 200 ppm of salicylic acid (6.08 and 5.45 t ha−1) surpassed untreated plants (5.15 and 4.85 t ha−1) in grain yield in both seasons. The interaction was no significant difference between irrigation treatments and salicylic acid in both seasons.

Table 5 Effect of irrigation treatments and salicylic acid on grain yield (t ha−1), straw yield (t ha−1) and harvest index (%), respectively) in 2015/2016 and 2016/2017 seasons
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Straw Yield (t ha−1)

Data allocated in Table 5 showed that irrigation treatment was highly significant influenced the straw yield in which 50% depletion of available soil moisture treatment resulted in significantly higher straw yield more than 70% and 90% depletion of available soil moisture treatments. Averages of grain yield were 9.75, 9.45 and 9.02 t ha−1 in 2015/2016 and 10.22, 9.88 and 8.44 t ha−1 in 2016/2017 seasons, respectively. The analysis of variance in Table 5 showed that the differences were highly significant between salicylic acid treatments in both years of study. Application of 200 ppm of salicylic acid (10.78 and 10.12 t ha−1) surpassed untreated plants (10.04 and 9.57 t ha−1) in straw yield in both seasons. The interaction was no significant difference between irrigation treatments and salicylic acid in both seasons.

Harvest Index (%)

Regarding the influence of irrigation treatments on harvest index, it is observed that irrigation at 50% depletion of available soil moisture treatment increased significantly harvest index as compared to irrigation at 70% and 90% depletion of available soil moisture treatments in both seasons as shown in Table 5. It was clear from the results that treatment 50% DAM gave the highest harvest index (38.82 and 37.94%), while treatment 70% DAM produced harvest index values (36.24 and 36.02) and 90% DAM produced (35.44 and 35.55%) in both seasons, respectively. Also, harvest index was significantly different between salicylic acid treatments in both seasons as shown in Table 5. The respective overall mean values for application of 200 ppm of salicylic acid were (36.75 and 35.82%). Meanwhile, untreated plants were 33.95 and 33.64% in both seasons, respectively.

Effect of irrigation treatments and salicylic acid on water consumptive use and water use efficiency

Water Consumptive Use

As shown in Fig. 5, the maximum water consumptive use during 2015/2016 and 2016/2017 was achieved by the wheat plants to which treatment 50% depletion of available soil moisture and it was followed by treatment 70% depletion. Whilst, significantly the lowest CU during both seasons was noted from wheat plants subjected to treatment 90% depletion of available soil moisture. Application of 200 ppm of salicylic acid augmented with exhibited significantly the highest value for CU whilst the lowest CU was recorded from wheat plants subjected to control treatment regardless irrigation treatments during 2015/2016 and 2016/2017 seasons. Salicylic acid application decreased water consumptive use by 7 and 8% at 50% depletion. While, decreased water consumptive use by 8% and 12% at 70% depletion and by 6% and 7% at 90% depletion during 2015/2016 and 2016/2017 seasons, respectively (Fig. 5). Data stated in Fig. 5 indicated that salicylic acid has useful effect on wheat grain yield not only under higher depletion of the available soil moisture treatment but also under all irrigation treatments. In this connection, 50% depletion of the available soil moisture treatment produced more grain yield if salicylic acid was applied than without exogenously applied SA. CU amount 6770.3 m3 ha−1 in 2015/2016 season and 6546.1 m3 ha−1 in 2016/2017 season, for 50% depletion without SA treatment, however CU amount was 6330.2 3 m3 ha−1 in 2015/2016 season and 6063.9 m3 ha−1 in 2016/2017 season) for 50% depletion with SA treatment. In this case water saving was 440.1 m3 ha−1 in 2015/2016 season and 482.2 m3 ha−1 in 2016/2017 season when applied SA.

Fig. 5
figure 5

Effect of salicylic acid application on water consumptive use (m3 ha−1) under different irrigation treatments in 2015/2016 and 2016/2017 seasons. The data are the mean ± SE of three replicates. Significant differences of the means according to Duncan’s multiple range test (P ≤ 0.05) are indicated with different letters

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Water Use Efficiency

Water use efficiency reached the maximal values in both seasons under irrigation at 70% depletion of the available soil moisture but, however, without marked differences in comparing to those recorded 50% depletion of the available soil moisture. Whilst, water use efficiency reached the minimal values in both seasons under irrigation at 90% depletion of the available soil moisture in 2015/2016 and 2016/2017 seasons (Fig. 6). Application of 200 ppm of SA augmented with exhibited significantly the highest value for WUE whilst the lowest WUE was recorded from wheat plants subjected to control treatment regardless irrigation treatments during 2015/2016 and 2016/2017 seasons. Water use efficiency values were 0.99, 1.00 and 0.93 kg m−3 at 50, 70 and 90% depletion with application of 200 ppm SA. Whilst, Water use efficiency values were 0.90, 0.91 and 0.82 kg m−3 at 50, 70 and 90% depletion without application of SA, respectively in 2015/2016 season. A similar trend was noted during 2016/2017 growth season. Application of SA led to increase of WUE by 10% and 11% compared to control treatment at 50% depletion. Meanwhile, 10% and 16% compared to control treatment at 70% depletion. However, 12% and 13% compared to control treatment at 70% depletion in both seasons, respectively.

Fig. 6
figure 6

Effect of salicylic acid application on water use efficiency (kg ha−1) under different irrigation treatments in 2015/2016 and 2016/2017 seasons. The data are the mean ± SE of three replicates. Significant differences of the means according to Duncan’s multiple range test (P ≤ 0.05) are indicated with different letters

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Discussion

Soil Chemical Properties

This study sought to elucidate the protective role of salicylic acid in ameliorating the water stress through enhancing the physiological traits and productivity of wheat plants as well as water use efficiency under 50, 70 and 90% depletion of the available soil moisture with and without salicylic acid in saline soil condition. Given that SA plays key roles in the regulation of plant growth, development, the interaction with other organisms, and the responses to environmental stresses. This corresponds with the finding of Li et al. (2014).

Saline soil condition significantly perturbed EC, Na, K, Ca, Cl, ESP and SAR, while irrigation treatments and salicylic acid enhanced the soil chemical properties in wheat plants showing its potential to alleviate the detrimental effects of salinity. This depicts that to tackle salinity from root zone helps the plants to strengthen the leaf physiological and molecular mechanisms. This was also confirmed by Hafez (2016).

In general increasing available soil moisture from 10 to 30 and 50% decreased EC and Na values, consequently. The rate of reduction in values increased as the effect of irrigation on dissolved salt and the role of optimal irrigation to prevent the accumulation of salts, then the salinity is easily removed down. Additionally, all cations are easily dissolved and translocated from the upper to the lower layers (Waqas et al. 2017).

Proline content, stomatal conductance and relative water content

The results of the present study showed the association between water stress and both reduction leaf RWC and stomatal conductance whilst increasing proline content of wheat leaves (Figs. 1, 2, 3). Such findings are in accordance with those found by Razmi et al. (2017) who reported that increasing proline content in leaves is recognized as important osmoprotectants in wheat under abiotic stresses like drought and salinity and help to regulate metabolic status, and is often considered to be involved in maintaining the water content while reduced the activity of proline oxidase. The improved proline content in SA-treated plants could be attributed to a decrement in dissolved proteins (Pirasteh-Anosheh et al. 2014). Concerning leaf RWC, stomatal conductance of wheat leaves, there was a substantial adverse impact of water deficit resulting in reduction RWC and stomatal conductance (Khalilzadeh et al. 2016). Wheat plants exposed to water stress reduced RWC and stomatal conductance compared to those grown under well–watered condition. Stomatal conductance is one of the earliest responses to water stress (Waqas et al. 2017), compared to the well-watered whereas the decrease in the photosynthetic rate was associated with the closure of stomata under water stress. SA alleviated the negative effects of water stress on leaf photosynthesis by increasing RWC and stomatal conductance (El-Bially et al. 2018). Consequently, the enhancement of the effects of SA on the RWC, stomatal conductance and proline content was attributable to its stimulatory effects on Rubisco enzyme activity and upregulating the related photosynthetic enzyme activities at the chloroplast level (Rahneshan et al. 2018). This proved that SA, as a growth regulator, has a pivotal impact in protecting plants under abiotic stresses (Pirasteh-Anosheh et al. 2017).

Nutrient Uptake

Ion uptake was highly significant influenced by irrigation treatments. The results could be attributed to the decrease of the nutrient in wheat plants as soil moisture decreased which may be due to reducing the solubility of minerals in the soil where the films are thin and the path length of movement increases; hence, movement of cations and anions to root is reduced. Moreover, high tension exerts a physiological effect on root, elongation, turgidity and number of root hairs decrease with increasing tension (Gunes et al. 2007). Water and salt stress significantly reduced ion nutrient uptake in terms of N, P, K and Na. confirming findings from earlier studies that nutrient status is sensitive to the previous stresses. Increasing the depletion of available soil moisture from 50 to 90% did not enhance nutrient uptake of wheat plants. The relationships between water availability and ion uptake responses showed that nutrient uptake like N, P, K and Na will decrease without sufficient water being available to the plant. It may be attributed to a decreased transpiration rate to transport nutrients from roots to leaves (Jini and Joseph 2017). In addition soil water availability which supplies the required nutrients to the leaves by quick absorption. Treatment of 50% depletion has been recommended to more effectively improve nutrient absorption. When wheat plants suffer from a water shortage, the efficacy of exogenous foliar spraying by salicylic acid is higher than that without salicylic acid. The higher nutrient uptake N, P, K in the leaves of wheat plants treated by SA in all irrigation treatments in saline soil might be attributed to the physiological mechanisms involved in osmoregulation. Whilst, Na uptake in leaves is far below the level of Na toxicity (Hu et al. 2008). SA stimulated N, P, K uptake in wheat leaves and succeeded in decreasing Na uptake. These results are in agreement with the findings of Jini and Joseph (2017) who reported that SA regulates ion uptake due to antioxidant activity and the protective role of SA on membranes. From the results, it was proved that the SA application could be responsible for improvement ion balance in wheat plants (Razmi et al. 2017).

Yield related-traits

Higher depletion of the available soil moisture impeded photosynthesis-related parameters such as number of spikes m−2, numbers of grains spike−1 and 1000-grain weight and possibly by an ion imbalance, this is in consistent with the reports of (Farooq et al. 2015). The influence of exogenously applied SA was associated with an increase in number of spikes m−2, numbers of grains spike−1, 1000-grain weight (Table 4). Similar findings for exogenously applied SA have been reported for wheat by (Hafez and Gharib 2016). It was cleared that exogenously applied alleviated the adverse effects of water stress in terms of yield related-traits in wheat plants (Campuzano et al. 2012). This may be attributed to increment of nitrogen uptake, metabolic managed and consequently increase dry matter accumulation when SA was exogenously applied (Li et al. 2014). In addition, it has been demonstrated that exogenously applied SA has vital role in growing canopy photosynthesis and metabolic transport of photosynthetic assimilates to wheat grains through the impact on phloem loading (Hayat et al. 2010). From mentioned above, it was stated that the highest number of spikes m−2, numbers of grains spike−1 and 1000-grain weight were obtained when the combination of 50% depletion and SA was applied (Table 4). Exogenously applied SA could increase grain yield, straw yield and harvest index regardless of irrigation treatments. Exogenously applied SA could ameliorate the oxidative stress of wheat through transcriptional regulation of multiple defense pathways. Exogenously applied SA can enhance the impacts caused by water stress through improving reactive species biosynthesis (Akc and Samsunlu 2012). These finding stated that SA application could increment antioxidant content to resist ROS damage induced by water stress, which in accordance with aforementioned suggestions that salicylic acid application might significantly contribute to water-stress tolerance by protection against oxidative damage of membranes (Alonso et al. 2009). This research provides necessary information for physiological mechanisms including salicylic acid and plant tolerance to stress. Moreover, this experiment provides evidence for the use of SA application in arid and semiarid regions to increase grain yield, straw yield and harvest index. Hafez and Seleiman (2017) pointed out that SA application was recommended for wheat yield and supplied with ample water. Implication of salicylic acid tends to minimize the decline in grain yield (Razmi et al. 2017).

Water Relations

The findings in Fig. 6 reported that WUE was improved by application of SA in 70% DAM in both years of study. Figure 6 also showed that water use efficiency attained the maximal values under 50% DAM plus 200 ppm SA, which was on par with 70% DAM plus 200 ppm SA compared to the untreated ones. These results could reveal the positive and benefit impact of salicylic acid in reducing the adverse effect of water stress in wheat plants (Akc and Samsunlu 2012). These findings could be pointed out in the viewpoint of grain yield produced under such conditions more than under other ones, due to higher WUE values. It can be illustrated that at low water use efficiency, photosynthetic carbon assimilation is declined due to decreasing flow of CO2 into mesophyll tissue and the stomata closure (Khataar et al. 2018), as there was a strong correlation between WUE and grain yield (Li et al. 2014). This elucidates that high leaf relative water content is an indication of an increment in swelling pressure in plant cells, leading to improve in growth (Alonso et al. 2009). This improvement was probably associated with the actual rate of photosynthetic CO2 assimilation, stomatal conductance and CO2 supply (El-Bially et al. 2018). After watering stress, stomata close gradually with a parallel decrease in photosynthetic CO2 assimilation and water use efficiency (Razmi et al. 2017). Our results explained that the efficacy of exogenously applied SA able to relatively convert water consumptive use into production of grains under 70% depletion of the available soil moisture as well 50% depletion of the available soil moisture, whereas, 70% depletion was on par with 50% depletion for WUE. Therefore, irrigating SA–treated wheat plants with 70% depletion of the available soil moisture probably preserve an adequate condition of stomata closure resulting in enhancing leaf relative water content and cell turgidity (Razmi et al. 2017).

Conclusion

In arid and semi-arid areas, farmers often have to use less water than required to irrigate their fields, leading to a significant reduction in crop productivity. Therefore,

in our study, we recommend that farmers rely on exogenously application of salicylic acid in wheat crop to alleviate the adverse effects resulting in water stress under salt affected soil conditions. Herein, foliar application of salicylic acid during the vegetative growth stage is considered beneficial and crucial. Even if irrigation water is available, it is recommended to use the treatment of 70% depletion of the available soil moisture (DAM) plus salicylic acid which can save irrigation water to irrigate more fields. Subsequently, the treatment of 70% depletion of the available soil moisture plus salicylic acid (SA) could be a promising practice in water-deficient regions under saline soil condition for enhancing wheat productivity and water use efficiency.