MATERIALS AND METHODS

A greenhouse experiment was conducted to study salt stress and ozonated water effects on cucumber yield and yield components. Some chemical and physical properties of experimental field soil listed in Table 1. Cucumber seeds (storm) were sown in a box of coco-peat substrate and young plants at four leaf stages were transferred in 10 L pots filled with soil (80%) and leca+perlite (20%). One cucumber plant was cultivated per pot. Modified Hoagland solution was used for irrigation of the pots. The treatments were defined by a two-factorial design of three irrigation water salinity levels (2, 4 and 6 dS m^–1) and three ozone concentrations (0, 0.5 and 1 ppm). The nine treatment combinations were replicated five times and arranged in a randomized complete block design. The salt solution was prepared by nutrient solution and NaCl and the electrical conductivity of different salinity levels was adjusted by a direct reading conductivity meter. Ozonated water was generated with an electrolytically ozonated water generator. The plants were exposed to ozone concentrations via irrigation with nutrient solution. For preparation of 0.5 and 1 ppm O₃, ozone was added to nutrient solution for 5 and 10 sec, respectively.

Soil analysis: Soil pH was measured in the soil saturation paste and Electrical Conductivity (EC) in saturated extracts. Soil organic carbon (Walkley and Black method), nitrogen (Kejldahl method), available K (with ammonium acetate) available P (Olsen’s method) and Cation Exchange Capacity (CEC) with NH₄OAc method were determined via procedures described in Baruah and Barthakur (1997). Soil texture was performed using the hydrometer method (Gee and Bauder, 1986). Soil bulk density extracted by volumetric cylinder (Lestariningsih et al., 2013).

Plant analysis: Some plant properties including fruit yield (kg m^–2), plant height, stem diameter and total soluble solids were determined at the end of growth period. The fruit weight (for determination of fruit yield) was determined by weighting theses in the air on a precision digital balance with an accuracy of 0.001 g. Plant density was 2.5 plant in m². The plant height and stem diameter was measured with a Meter and digital vernier caliper, respectively. The Total Soluble Solids (TSS) were measured with a digital refractometer (Erma, Tokyo, calibrated using distilled water). The concentrations of some elements in plant, such as P, K, Ca, Mg and Na were determined by drying samples at 100°C and then ashed at 550°C under a gradual increase in temperature (Caballero et al., 2009). The concentrations of P (colorimetrically method), Na and K (flame photometry method) were measured. Also, the concentrations of Ca and Mg were measured either by atomic absorption spectrophotometry. The concentration of NH₄ and NO₃ was determined by Kjeldhal method.

Table 1:	Some chemical and physical properties of experimental field soil
EC: Electrical conductivity, OC: Organic matter, CEC: Cation exchange capacity, ρb: Bulk density

Statistical analysis: Two-way analysis of variance (ANOVA) was applied to estimate the effects of ozonated water and water salinity on studied properties of plant. Means were compared by Least Significant Difference (LSD) test (p<0.05). Statistical procedures were carried out using the software package SAS 9.1.

RESULTS

Fruit yield: Results showed that fruit yield were increased at high ozonated water levels. A decrease in fruit yield was noted as the salinity of irrigation water increased (Fig. 1). There was a significant ozonated water × salts stress interaction on the fruit number contents indicating that the highest fruit yield was obtained at the third level of ozonated water (1 ppm) and 2 dS m^–1 of salinity level (Fig. 1).

Stem diameter: The results also indicated that salinity and ozonated water reduced stem diameter of cucumber, although there were not significant differences (Fig. 2).

Plant height: As shown Fig. 3, a significant increase in plant height was noted as the ozonated water levels increased. Results showed that with higher levels of water salinity the plant height was significantly decreased (Fig. 3). The highest plant height was obtained at the third level of ozonated water (1 ppm) and 2 dS m^–1 of salinity level (Fig. 3).

Total soluble solids: There was a not significant ozonated water×salts stress interaction on total soluble solids. There were not significant differences between 0, 0.5 and 1 ppm ozonated water in total soluble solids. However, statistical testing showed significant increase in total soluble solids with increasing water salinity (Fig. 4).

Concentrations of P, K, Ca, Mg, Na, NH₄ and NO₃ in plant: Statistical testing indicated significant increase in concentration of P and Na with increasing water salinity. Also, application of ozonated water caused increases in concentration of P (across three salinity levels), Na (only 6 dS m^–1 of salinity level) and Mg (in 2 and 6 dS m^–1 of salinity level) (Table 2).

Fig. 1:	Fruit yield in three ozone concentrations at the different salinity levels. The values followed by at least one common character are not statistically different at 5% probability level, according to LSD test

Fig. 2:	Stem diameter in three ozone concentrations at the different salinity levels. The values followed by at least one common character are not statistically different at 5% probability level, according to LSD test

Fig. 3:	Plant height in three ozone concentrations at the different salinity levels. The values followed by at least one common character are not statistically different at 5% probability level, according to LSD test

The highest concentration of P and Na were obtained at the third level of ozonated water (1 ppm) and 6 dS m^–1 of salinity level. The concentration of Ca in 4 dS m^–1 of salinity level was significantly higher than that other salinity levels (Table 2).

Fig. 4:	Total soluble solids in three ozone concentrations at the different salinity levels. The values followed by at least one common character are not statistically different at 5% probability level, according to LSD test

Table 2:	Some concentration elements in three ozone concentrations at the different salinity levels
In each column, the means followed by at least one common character are not statistically different at 5% probability level, according to LSD test

Results indicated that, application of ozonated water decreased the concentrations of in the leaf tissues of tomato than control. Increasing water salinity levels resulted in a significant reduction in NH₄ and these reductions reached the highest values at 6 dS m^–1 water levels compared with control plants. The highest concentration of NH₄ was obtained at the water without O₃ and 2 dS m^–1 of salinity level (Table 2). However, the highest concentration of NO₃ was observed at 1 ppm O₃ and 4 dS m^–1 of salinity level (Table 2).

DISCUSSION

It can be concluded that the application of ozone concentration (especially 1 ppm) increased, the fruit yield and plant height of cucumber. These findings are in alliance with the observations of Ohashi-Kaneko et al. (2009) and Chan et al. (2007), who found that growing properties of plant were greater in plants, treated with ozonated water than for control. The root respiration by ozonated water might be related to increased biomass productivity of cucumber plants. On the other hand, the exposure of roots with high level of oxygen is probably associated with the promotion of biomass productivity. Abdel Nasser (2002) reported that exposure to high ozone concentration (100 ppb) decreased the number and weight of root nodules, water content and leaf area. According to the study on the tomato reported by Ohashi-Kaneko et al. (2009), ozonated water did not harm plants (tomato) but did promote their growth. Sterilization by ozonated water might have decreased root rot, consequently increase water and mineral uptake by plant root (Ohashi-Kaneko et al., 2009). However, Graham et al. (2011) found that the applications of ozone had no significant impact on plant properties. Electrical conductivity of 1.8 dS m^–1 may be generally armful to vegetable crops due to salt stress (De Pascale and Barbieri, 1995). Many studies reported that the yields components of vegetables decreased with increase in water salinity (Malash et al., 2002; Rameeh et al., 2004; Huang et al., 2009). Al-Busaidi et al. (2009) found that under saline condition all plant parameters of different varieties (except for the number of fruits) were reduced compared to the control. The findings of present study indicated that with higher levels of water salinity the studied properties of cucumber were significantly decreased. These results are concurred with the results of Huang et al. (2009) who found that water salinity significantly reduced fruit yield of cucumber owing to a decrease both in mean fruit weight and fruit number. Also, salinity caused a reduction in the number of fruits (Trajkova et al., 2006).

CONCLUSION

In this study, we found that ozonated water can be to use for irrigation of cucumber plant. Overall, the use of ozonated water could provide a useful tool to improve fruit yield of cucumber under salinity stress.