Effect of deficit irrigation and growing seasons on plant water status, fruit yield and water use efficiency of squash under saline soil

Scientia Horticulturae 186 (2015) 89–100

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Effect of deficit irrigation and growing seasons on plant water status, fruit yield and water use efficiency of squash under saline soil Taia A. Abd El-Mageed a,∗ , Wael M. Semida b a b

Soil and Water Department, Faculty of Agriculture, Fayoum University, Fayoum 63514, Egypt Horticulture Department, Faculty of Agriculture, Fayoum University, Fayoum 63514, Egypt

a r t i c l e

i n f o

Article history: Received 30 October 2014 Received in revised form 8 February 2015 Accepted 11 February 2015 Keywords: Squash yield Plant water status Water use efficiency Growing season and deficit drip irrigation

a b s t r a c t A successive summer and fall experiments were conducted to study the effect of deficit irrigation growing seasons on the squash water status, total fruit yield and water use efficiency (WUE) in saline soil (ECe 12.6 dS m−1 ). Three treatment levels of actual evapotranspiration (ETc ) were tested in each season. The irrigations treatments were: (1) control, (100%) where irrigation was applied in order to avoid any considerable soil water deficit. (2) DI85% , where deficit irrigation (85% of control irrigation regime) was applied and (3) DI70% , where 70% of the control regime was applied. In well-watered conditions seasonal water use by squash was 479 over 86 days in summer and 306 mm over 91 days in fall season, respectively. Interaction between season and deficit irrigation treatment significantly affected plant water status as evaluated by relative water content, canopy temperature, photosynthesis efficiency. Leaf area index (LAI), total soluble solid (TSS), harvest index (HI), water-use efficiency, fruit weight, and fruit length have also been affected. After two seasons (i.e., fall and summer), soil salinity (ECe ), and both of Cl− and Na+ concentrations declined significantly in 0–60 cm depth and more reduction were achieved in 0–20 cm soil depth than in 20–40 and 40–60 cm depths. Squash yield the fall growing season was higher by 19.54% comparison with the yield in summer season the highest water use efficiency (WUE) was obtained at I85% IWA. In two seasons the highest squash yield was recorded under well irrigated treatment, control (100% ETc ) but non-significant differences between I100% and I85% were recorded. Therefore, under limited irrigation water, it is recommended to irrigate squash plants at I85% to produce not only the same yields, approximately, but also to save more of water as compared to I100% treatment. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Squash (Cucurbita pepo L.) belongs to Cucarbitaceae family; it is one of the most important cash crops, especially, in newly reclaimed areas of Egypt. Squash is rich in carbohydrates and amino acids as well as they contain many minerals beneficial to humans. The total area cultivated to this crop was estimated at 40,000 ha in 2007 with annual yield production of 1 million t (Egyptian Ministry of Agriculture, 2007). Squash is an important commercial crop that has gained popularity for both open-field and greenhouse in the Mediterranean region (Amer, 2011; Rouphael and Colla, 2005). In recent years the available amount of water to agriculture is declining worldwide because the rapid population growth and the greater

∗ Corresponding author. Tel.: +20 1067536208; fax: +20 84 6334964. E-mail address: [email protected] (T.A.A. El-Mageed). http://dx.doi.org/10.1016/j.scienta.2015.02.013 0304-4238/© 2015 Elsevier B.V. All rights reserved.

incidence of drought caused by climate change and different human activities (World Bank, 2006). Salinity is considered as one of the major limiting factors to plant growth and crop productivity in many areas, particularly in arid and semi-arid regions. Deleteriously affecting over than 800 million hectares of land worldwide (Munns, 2005). Plant morphological and physiological processes are negatively affects by salt stress through osmotic and ionic stress, and different biochemical responses in plants (Khan, 2003). Growth of squash plants was shown to be moderately sensitive to moderately tolerant to salt stress depending on cultivar or growth stage (Francois, 1985). Successful management of the limited amount of water available for agricultural uses depends on better agricultural practices and enhanced understandings of water productivity (Howell, 2001; Jones, 2004). Deficit irrigation (i.e., irrigation below the optimum crop water requirements) is a strategy for water-saving by which crops are subjected to a certain level of water stress either during a particular period or throughout the whole growing season (Pereira et al., 2002). The main goal of using DI is to increase WUE by

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reducing the amount of water applied with watering or by reducing the number of irrigation events (Kirda, 2002). Deficit irrigation effects on growth and productivity of many vegetables and field crops have been widely investigated (Karam et al., 2006; Ertek et al., 2004; Fereres and Soriano, 2007; Igbadun et al., 2008; Amer, 2011). Research evidences has shown that DI is successful in increasing water productivity for different crops without causing severe yield reduction (Geerts and Raes, 2009). El-Dewiny (2011) reported that summer squash yield decreased by increasing water deficits. Rouphael and Colla (2005) observed that, the total and marketable yield and fruit weight and number were significantly affected by the growing season and the irrigation system and not by their interaction. The lower yield recorded during the summer-fall growing season was related to a reduction in both fruit mean weight and fruit number. Ertek et al. (2004) showed that, the highest summer squash yield was obtained from an irrigation treatment with a plant-pan coefficient of 0.85 in Van, Turkey. Similarly, the fruit yield of squash was significantly affected by increasing irrigation quantities Al-Omran et al. (2005). Also, WUE values were generally increased with irrigation quantity, but decreased at the highest irrigation level. Also, he found that water use efficiency linearly increased as irrigation water applied increased for deficit irrigation level and decreased for excessive irrigation level. However, the effects of DI are crop-specific. Therefore, it is necessary to evaluate the impact of DI strategies with multi-years open field experiments, before generalizing the most appropriate irrigation scheduling method to be adapted in a specific location for a given crop (Scholberg et al., 2000; Igbadun et al., 2008). The present study reveals the effect of deficit irrigation with saline water on leaf water status, growth, yield, and WUE of squash in summer and fall season and investigate the temporal changes in the electrical conductivity (ECe ), Cl− and Na+ within squash plant root zone (i.e., 0–60 cm). 2. Materials and methods

Staff, 1999). The soil of the site where the experiments were carried out for the two seasons had the top soil (0–100 cm depth) as saline sandy loam in texture, with a bulk density of 1.57 kg m−3 . The total available water was about 12.88%/60 cm depth. Tables 3 and 4 show some physical and chemical properties of the soil of the experimental site. According to Ayers and Wesctcot (1985) scale the used irrigation water lies within the second categories for salinity and sodicity levels (C2 S1 , ECiw = 0.75–3.00 dS m−1 and SAR < 6.0). Table 2 shows some ionic composition for irrigation water. 2.3. Irrigation water application (IWA) The squash plants were irrigated 2 days intervals by different amounts of water, AIW were determined as a percentage of the crop evapotranspiration (ETc ) representing one of the following three treatments: I100 = 100%, DI85% = 85% and DI70% = 70% of ETc . The daily ETo was computed according to the following equation (Allen et al., 1998) as follows:



ETo =



0.408 (Rn − G) +  900/ (Tmean + 273) u2 (es − ea )  +  (1 + 0.34u2 )

(1)

where ETo is the reference evapotranspiration (mm day−1 ),  the slope of the saturation vapor pressure curve at air temperature (kPa ◦ C−1 ), Rn the net radiation at the crop surface (MJ m−2 d−1 ), G Soil heat flux density (MJ m−2 d−1 ),  psychometric constant = (0.665 × 10−3 × P), kPa ◦ C−1 (Allen et al., 1998), P is the atmospheric pressure (kPa), U2 wind speed at 2 m height (m s−1 ), es is the saturation vapor pressure (kPa), ea actual vapor pressure (kPa) (es − ea ) is the saturation vapor pressure deficit (kPa), and Tmean mean daily air temperature at 2 m height (◦ C). The average of daily ETo in El-Fayoum was 10.16, 10.74, 10.66, 9.9, 8.64, 6.61, 4.63 and 3.49 mm day−1 in May, June, July, August, September, October, November and December, respectively. The crop water requirements (ETc ) were estimated using the crop coefficient according to the following equation:

2.1. Experimental site

ETc = ETo × Kc

This study was conducted in a farmer’s field located in El Fayoum province which occupies a depression west of the Nile at 90 km southwest of Cairo, Egypt between latitudes 29◦ 02 and 29◦ 35 N and longitudes 30◦ 23 and 31◦ 05 E. Table 1 indicates the climatic data of El Fayoum during the months of the study. According to the aridity index (Ponce et al., 2000) the area is located under hyper arid climatic condition.

where ETc is the crop water requirement (mm day−1 ) and Kc is the crop coefficient. The duration of the different crop growth stages were 25, 35, 25, and 15 days for initial, crop development, mid-season and late season stages, respectively, and the crop coefficients (Kc ) of initial, mid and end stages were 0.6, 1 and 0.75, respectively, according to Allen et al. (1998). The amount of irrigation water applied to each treatment during the irrigation regime was determined by using the following equation:

2.2. Soil of the experimental site

IWA =

The soils of the studied area could be classified at the family level as Typic Torripsamments, siliceous, hyperthermic, moderately deep. In addition, the suitability of the studied soil could be ranged between not suitable and marginally suitable (Soil Survey

(2)

A × ETc × Ii × Kr Ea × 1000 × (1 − LR)

(3)

where IWA is the irrigation water applied (m3 ), A is the (m2 ), ETc is the crop water requirements (mm day−1 ), Ii is the irrigation intervals (day), Ea is the application efficiency (%) (Ea = 85), Kr covering

Table 1 Monthly weather data at Fayoum, Egypt during 2013 summer and fall growing seasons. Tmin (◦ C)

Month

a

May June July August September October November December

20.8 22.6 24.6 25.2 23.6 19.54 17.47 10.3

Tmax (◦ C)

Tavg (◦ C)

RHavg (%)

U2 m s−1

Rs MJ m−2 d−1

ETo mm d−1

Ep mm d−1

38.5 39.0 37.1 38.1 36.6 30.79 29.13 24.1

29.65 30.8 30.9 31.6 30.1 25.11 23.32 17.2

42.0 43.0 46.0 49.5 43.7 43.03 40.53 53.05

1.90 1.50 2.0 1.60 2.1 2.0 2.2 2.3

14.36 15.35 14.26 12.65 11.38 8.61 7.81 6.8

10.16 10.74 10.66 9.90 8.64 6.61 4.63 3.49

7.8 8.3 7.5 6.8 5.8 4.18 2.54 2.0

a Tavg , Tmax , and Tmin are average, maximum, and minimum temperatures, respectively, RHavg is average relative humidity, U2 is average wind speed, Rs is average solar radiation, ETo is average potential evapotranspiration (Allen et al., 1998), and Ep is average of measured pan evaporation class A.

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Table 2 Ionic composition for irrigation water. Ionic concentration (Meq L−1 )

ECa (dS m−1)

pH

SARb

1.32

2.77

7.46

5.38

Bulk density (g cm−3 )

Ksat (cm h−1 )

F.C. (%)

W.P. (%)

A.W. (%)

1.60 1.55

2.22 1.55

25.33 22.19

9.73 12.13

15.60 10.06

CO3 2−

HCO3 −

Cl−

SO4 2−

Ca2+

Mg2+

Na+

K+

0.00

4.35

16.73

6.82

7.34

6.84

12.4

a b

EC means the average electrical conductivity. SAR means sodium adsorption ratio.

Table 3 Some initial physical properties of the studied soils. Layer (cm)

0–30 30–60

Particle size distribution Sand (%)

Silt (%)

Clay (%)

Texture class

79.25 77.23

10.00 10.10

10.75 10.67

LS LS

F.C. = field capacity, W.P. = wilting point, A.W. = available water, LS = loamy and sat = hydraulic conductivity.

factor and to calculate (Kr ), Decroix and Cecroix method was used (Vermeirem and Jobling, 1980): Kr = (0.10 + GC ) ≤ 1,

(4)

where GC is the ground cover. Also, LR is the leaching requirements (m3 ). LR =

ECw 2Max ECe

(5)

where ECw is the electrical conductivity of the irrigation water, dS m−1 and Max ECe is the maximum electrical conductivity of the soil saturation extract for a given crop (see the table shown in according Doorenbos and Pruitt (1984) and Keller and Bliesner (1990)). 2.4. Plant management and physiological measurements Squash hybrid Hi Tech® seeds were sown 0.5 m apart in each bed about 0.05 m away from the drip line at a depth of 0.04 m, drip irrigated with a one line and one dripper per plant giving 4.0 L h−1 . Seeds were planted on 9 May and 13 September, and terminated on 4 August and 7 December in the 2013 summer and fall growing seasons, respectively. All treatments were separated as surrounded by 1 m non-irrigated area. Plants were adequately watered in first irrigation. Irrigation treatments were initiated one week after full germination. Chemical fertilization was practiced at the recommended rate for squash production in this area, 150 kg ha−1 N, 60 kg ha−1 P and 70 kg ha−1 K. The cultural, disease and pest management practices were the same as local commercial crop production. Canopy temperature (Tc ) was measured with a hand-held infrared thermometer (Fluk 574, Everett WA, USA) at an emissivity of 0.98 and a spectral response range of 8–14 ␮m. At the end of every season five individual plants were randomly chosen from each experimental plot and evaluated for plant height and leaf area measurements. Leaf area per plant was measured using digital planometer (Planix 7). Leaf area index (LAI) was determined by dividing plant leaf area per its used area.

On two different sunny days, chlorophyll fluorescence was measured using a portable fluorometer (Handy PEA, Hansatech Instruments Ltd, Kings Lynn, UK). One leaf (at the same age) was chosen per plant to conduct the fluorescence measurements. Maximum quantum yield of PS II Fv /Fm was calculated using the formulae; Fv /Fm = (Fm − F0 )/Fm (Maxwell and Johnson, 2000). Fv /F0 reflects the efficiency of electron donation to the PSII RCs and the rate of photosynthetic quantum conversion at PSII RCs. Fv /F0 was calculated using the formulae; Fv /F0 = (Fm − F0 )/F0 (Spoustová et al., 2013). Performance index of photosynthesis based on the equal absorption (PIABS ) was calculated as reported by Clark et al. (2000). The relative water content (RWC) of fully expanded third leaf from top per replicate was determined in fresh leaf discs of 2 cm2 diameter, excluding midrib discs were weighed quickly and immediately floated on double distilled water (DDW) in Petri dishes to saturate them with water for the next 6 h, in dark. The adhering water of the discs was blotted and turgor mass was noted. Dry mass of the discs was recorded after dehydrating them at 70 ◦ C for 48 h. RWC was calculated by placing the values in the following formula (Hayat et al., 2007):

RWC (%) =





(FM − DM) × 100 (TM − DM)

(6)

Total soluble sugars concentration was assessed according to Irigoyen et al., 1992, using a UV-160A UV Visible Recording Spectrometer, Shimadzu, Japan. Cumulative Fruits were quantified by harvesting every 5 days and weighting the fruits on six randomly selected plants from each plot. At each harvest, number of fruits plant−1 , fresh fruit weight plant−1 , were recorded for each replicate. The first and last harvest dates were the 7th Jun and 4st August for SS and 9th October and 7th December for FS, respectively. Harvest index (HI) was determined as a ratio of fruit yield to total biomass production on a dry mass basis.

Table 4 Basic soil salinity of the initial soil profile in 2013. Depth (cm)

0–30 30–60 40–60 a b

Composition of soil paste extract (Meq L−1 )

ECa (dS m−1 )

CO3 2−

HCO3 −

Cl−

SO4 2−

Ca2+

Mg2+

Na+

K+

0.00 0.00 0.00

6.35 7.38 6.98

65.32 68.65 63.21

49.43 56.07 55.81

35.32 36.21 32.51

24.14 25.74 27.52

60.32 68.35 64.3

1.32 1.8 1.67

EC means the average electrical conductivity. SAR means sodium adsorption ratio.

12.11 13.21 12.6

pH

SARb

7.86 7.88 7.76

11.07 12.27 1173

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during summer season to the different treatments were 479, 407, 335 and 307, 255, 209 mm for fall season for control, DI 85% , and DI70% , respectively. The decrease in water application was different in both DI regimes. In comparisons with control plants, 15 and 30% less irrigation water was applied in the DI85% , and DI70% , irrigation treatments.

3.2. Effect of growing season and deficit irrigation on water status of squash plants

Fig. 1. Mean air temperatures recorded during the summer and fall seasons.

2.5. Water use efficiency (WUE) Water use efficiency (WUE) values as kg fruit m−3 of applied water were calculated for different treatments after harvest according to the following equation (Jensen, 1983): WUE =

Fruit yield (kg ha−1 ) water applied (m3 ha−1 )

(7)

2.6. Soil salt accumulation At the end of fall season, soil salinity was determined by taking two samples per replicate in the control and in, DI85% , DI70% treatments. Soil samples were taken at three depths (0–20, 20–40 and 40–60 cm) and from two positions, under, between drippers. All soil samples were air-dried and sieved through a 2-mm sieve. For each sample, approximately 300 g of soil for ECe measurement was dried, ground, passed through a 10-mesh screen, and saturated with distilled water for 24 h. Several milliliters of solution were extracted through a no. 1 Whitman paper filter in Buchner funnels with a vacuum system. Electrical conductivity (EC 25 ◦ C) of the soil-paste extracts using a calibrated, temperature-compensating, digital readout conductivity instrument (model 3200, YSI, Inc., Yellow Springs, Ohio), Cl− content (in Meq L−1 ) was determined by titration (Page et al., 1982). Sodium ion (Na+ ) content (in Meq L−1 ) were assessed using a Perkin-Elmer Model 52-A Flame Photometer (Page et al., 1982). 2.7. Statistical analysis The statistical analysis of the experimental data was carried out using ANOVA procedures in Genstat statistical package (version 11) (VSN International Ltd, Oxford, UK). Difference between means was compared using least significant difference test (LSD) at 5% level (p ≤ 0.05). 3. Results and discussion 3.1. Climatic conditions and volume water applied Considering average data for the three experimental seasons, average maximum daily temperature during summer and fall seasons were ≈34.39 and 24.82 ◦ C and the minimum air relative humidity was usually ≈45%. Fig. 1 shows the variations of maximum daily temperatures during summer and fall season. As a consequence, the amount of water applied via irrigation was higher in summer than in the fall season in accordance with the high temperature conditions. The total amount of irrigation volumes applied

3.2.1. Canopy temperature Seasonal average of canopy temperature readings were taken in the second and third days from the starting flowering stage every season. The canopy temperature was lower than air temperature, Turner et al. (1986) and the irrigation treatment significantly influenced the canopy temperature. The lower water application, the higher the canopy temperature, (Table 5). For most of the observation in days every season, the differences among the treatments were significant, indicating canopy air temperature difference (CATD) as a useful and reliable indicator in monitoring water status in plants. Canopy air temperature difference on a particular day was positively related to the biophysical parameters, a significant correlation was obtained, for fruit yield and cumulative stress degree day (CSDDs) calculated over the entire growth period (linear with R2 = 0.78 in summer season and 0.82 in fall season Fig. 2). The squash canopy temperature might increase 5–6 ◦ C under severe drought stress, and the squash canopy temperature at flowering stage was significantly and negatively correlated with fruit yield similar to what has been reported for other crops (Chauham et al., 1999; Carrity and O’Toole, 1995; Zhang et al., 2007) in rice crops. Good correlation between canopy temperature depression and yield in wheat was also reported elsewhere (Reynolds et al., 2001). According to the data from Table 5, it could be noted that lower soil water would cause larger canopy-air temperature difference at the flowering stage and lead to lower grain yield. Therefore, the crop canopy temperature closely correlated to the water deficit stress could be used to monitor crop water status, and would be regarded as one of the determinants for reasonable irrigation and drought analysis.

3.2.2. Relative water content (RWC) Responses of relative water content (RWC %) of squash plants grown under the effect of DI and different growing seasons (summer and fall) are presented in Tables 6 and 7. Statistical analysis carried out on relative water content (RWC %) revealed highly significant difference (p < 0.05) between season and deficit irrigation treatments. The effect of growing season on relative water content was not significant. In this regard, Sinclair and Ludlow (1986) reported that RWC considers a measure of plant water status, reflecting the metabolic activity in plant tissues and used as a most meaningful index to identify the legumes with contrasting differences in dehydration tolerance. It has been concluded that there is a relationship between the RWC and the biomass (fresh and dry weight) in squash under the interaction effect of DI stress and growing season indicating that the water status in squash leaves is basically dependent on the respective shoot biomass. This also suggests that squash plants having the greater biomass can maintain the higher water content in leaf, and thus can be more tolerant to drought. This parameter (RWC vs. plant biomass or growth) could be used as a convenient evidence to distinguish the specific and non-specific traits for drought tolerance in squash plants, similar to what has been reported for other crops in semi-arid environment and drip irrigation (Debashis et al., 2008).

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Table 5 Diurnal variation in (Tc − Ta ) of control and stressed treatments during the experimental seasons. Items

Season Summer

Fall

O’clock 14:00

15:00

14:00

15:00

−10.63B −6.4A −6.7A

−9.30C −7.67B −5.00A

−1.00B 1.83A 2.5A

−1.33C 1.47B 3.12A

9

9 Summer Fall

Tc-Ta (oC)

6

6

R² = 0.82 (P=0.05 )

3

3

0

0

-3

-3

-6

R² = 0.78 (P=0

-9

Tc-Ta (oC)

Control100% DI85% DI70%

-6 .05 )

-9 -12

-12 -15

-15 0

3

6

9

12

15

18

21

Yield (Mg ha-1) Fig. 2. Relationship between canopy–air–temperature differential (Tc − Ta ) at flowering stage and total fruit yield of summer and fall squash seasons. Table 6 Means and standard errors for chlorophyll fluorescence (Fv /Fm ), performance index (PI), water relative content (WRC) and total soluble sugars (TSS). Mean ± SE

Items

Season Summer Fall Crop evapotranspiration (ETc ) Control100% DI85% DI70% 

Fv /Fm

Fv /F0

PI

TSS mg g−1 DW

WRC (%)

0.772 ± 0.02A  0.745 ± 0.02A

4.79 ± 0.19A 2.87 ± 0.32B

5.43 ± 1.08A 3.69 ± 0.81B

1.94 ± 0.21A 1.62 ± 0.09B

71.4 ± 2.51A 75.5 ± 1.27A

0.804 ± 0.01A 0.778 ± 0.01A 0.692 ± 0.02B

5.54 ± 0.27A 3.87 ± 0.46B 2.95 ± 0.48C

6.93 ± 1.07A 5.24 ± 0.53A 1.51 ± 0.52B

2.01 ± 0.17A 1.97 ± 0.23A 1.36 ± 0.06B

77.6 ± 0.24A 74.4 ± 3.1AB 68.3 ± 1.7B

Treatment means with the same letter are not significant at the p ≤ 0.05 level.

3.2.3. Chlorophyll efficiency Tables 6 and 7 show negative effects of DI on chlorophyll fluorescence Fv /Fm , Fv /F0 and performance index (PI). These attributes were significantly or insignificantly reduced gradually with the

gradual increase in DI for both summer and fall seasons. The highest chlorophyll fluorescence values were achieved when adequate water was applied (1.0 ETc ). While the low values of chlorophyll fluorescence was in the more severe treatment, DI70% (Table 6).

Table 7 Mean square, F value, and probability for chlorophyll fluorescence (Fv /Fm ), performance index (PI), water relative content (WRC), total soluble sugar (TSS) and water use efficiency %. Items

Season (S) ETc S × ETc Exp. error

d.f.

1 2 2 10

Mean square

F value and probability

Fv /Fm

Fv /F0

PI

TSS mg g−1 DW

WRC (%)

Fv /Fm

Fv /F0

PI

TSS mg g−1 DW

WRC (%)

0.003 0.021 0.001 0.001

30.1 6.43 0.64 0.69

13.52 46.29 0.299 2.56

0.457 0.784 0.559 0.068

72.36 133.49 17.03 26.23

5.19ns 32.82* 0.91*

43.21* 9.24* 0.92*

5.29* 18.11* 0.12*

6.71* 11.52* 8.21*

2.76ns 5.09* 0.65*

ns = nonsignificant. * Significant at the p ≤ 0.05 level.

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Fig. 3. (a) The spatial distribution of ECe (electrical conductivity of the saturated paste extract) along the vertical transects perpendicular drip line at the end of the experiment for control100% (A), DI85% (B) and DI70% (C) irrigation treatments, respectively. (b) The spatial distribution of Cl− concentration along the vertical transect perpendicular drip line at the end of the experiment for control100% (D), DI85% (E) and DI70% (F) irrigation treatments, respectively. (c) The spatial distribution of Na+ concentration along the vertical transect perpendicular drip line at the end of the experiment for control100% (G), DI85% (H) and DI70% (I) irrigation treatments, respectively.

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Higher chlorophyll fluorescence produced higher fruit yields and is thought to also increase sugar content in certain crops. Many reports suggested that using the analysis of chlorophyll ‘a’ fluorescence as a reliable method to determine the changes in the function of PSII under stress conditions (Broetto et al., 2007; Habibi, 2012). Lower photosynthetic activity could be a result in low photochemical efficiency of PSII, as revealed by its lower quantum yield (Pieters and Souki, 2005). Our results reported reductions in Fv /Fm , Fv /F0 and performance index (PI) under DI stress conditions, which were possibly due to the reduction in leaf photosynthetic pigments and RWC (Tables 5 and 6) needed for photosynthesis. These results are in parallel line with those of Gunes et al. (2007), Boughalleb and Hajlaoui (2011) and Habibi (2012) concluding that decreasing Fv /Fm values implies that photochemical conversion efficiency could indicate the possibility of photo-inhibition. The reduction in chlorophyll concentrations due to osmotic stress has been ascribed to the strong damage and loss of chloroplast membranes (Kaiser et al., 1981). The decrease in photosynthetic performance under water stress has also been observed by Ben Ahmed et al. (2009) and Habibi (2012). These reports concluded a significant correlation between Fv /Fm and gs that confirmed the idea that stomatal closure that limits CO2 availability for dark reactions may be one of the mechanisms for photo-inhibition in DI-stressed leaves. Water stress may also reduce photosynthesis rate through direct influence on the metabolic and photochemical processes in the leaf, or indirect influence on stomatal closure and cessation of leaf growth which results in decreased leaf surface area (Dejong, 1996). 3.3. Effect of growing season and deficit irrigation on growth parameters and harvest index (HI) Number of leaves per plant, plant height, and total dry weights per plant and leaf area index (LAI) differences were significant/or insignificant between the two growing seasons since there was less solar radiation in fall season compared with summer season Table 9. Increasing the DI from 15% (I85 treatment) to 30% (I70 treatment) further decreased significantly or insignificantly all growth traits in both growing seasons. The highest number of leaves per plant, plant height, and total dry weights per plant and leaf area index (LAI) were obtained when water was adequately applied (1.0 ETc treatment). High numbers for LAI appear to produce the best yields, and early signs of good leaf growth can predict yield. These results are in agreement with those of Amer (2010) working on corn and Amer (2011) on squash, also this finding was noted earlier in some crop plants (Degu et al., 2008; Gao et al., 2011; Habibi, 2012). HI recorded under FS (0.54) was higher than under SS (0.42) by 28.6% (Table 8) the same trend was obtained by Amer (2011) on squash and Wajid (1990) on corn. Total soluble sugars TSS showed significant differences between spring and fall growing seasons (Tables 6 and 7) due to decreasing weather elements at the end of the fall growing season. They was higher in spring growing season in comparison to the fall growing season was due to higher temperature conditions and solar radiation. Moreover, they were significantly affected by irrigation quantity (ETc ). Results were in accordance with those obtained by Malash et al. (2005) and Amer (2011). 3.4. Soil salinity The experimental soil is classified as a high saline soil (ECe = 12.64 dS m−1 Table 4) and according to scale of Ayers and Wesctcot (1985), the used irrigation water lies within the second category for salinity and sodicity levels (Table 2). After two seasons (fall and summer) from planting, soil salinity (ECe ), and both of Cl− and Na+ concentrations declined significantly in 0–60 cm depth and more reduction were achieved in 0–20 cm soil depth than in 20–40 and 40–60 cm depths. Moreover, the reductions of Cl− and Na+ were

Fig. 4. The regression analysis between irrigation water applied and squash yield and WUE under summer and fall season.

smaller than those of ECe . Additionally, the amount of salt removed from the 0 to 60 cm depth decreased with decreasing IWA threshold Fig. 3a–c). This may happened due to that, drip irrigation with its characteristic of applying water at low discharge rate and high frequency over a long period of time can maintain constant and high soil water contents in the root zone, reduce salinity levels in the soil water by leaching, particularly near the drip emitters, and reduce deep percolation, These results are in conformity with those of (Goldberg et al., 1976; Elfving, 1982; Keller and Bliesner, 1990; Hou et al., 2009). Additionally, during irrigation salts in the soil tend to move with the water to the fringes of the wetted area. The result is low salinities in close proximity to the dripper providing a zone of decreased osmotic potential which reduces the osmotic stress on plant growth, this are line with (Kang, 1998; Chen et al., 2009). Recently, some studies have investigated favorable effects of drip irrigation on salt leaching and cotton yield (Rajak et al., 2006; Hou et al., 2009; Chen et al., 2010). Studies have focused on the effects of different levels of SMP on salt distribution in the soil and on crop growth (Jiao et al., 2006; Tan et al., 2008; Dou et al., 2011; Wang et al., 2011; Wan et al., 2012). They have found that after 2–3 years cultivation the very strongly saline soil gradually changed to a moderately saline soil. 3.5. Water use efficiency WUE was significantly affected by growing seasons, irrigation treatment and their interaction Table 11. WUE recorded under FS (5.46 kg m−3 ) was higher than the corresponding WUE yielded under SS (2.96 kg m−3 ) by 46% Table 10. This result may be due to two reasons; first, the IWA of squash in SS (4072 m3 ha−1 ) was higher by 56.03% in comparison with that applied in FS (2609 m3 ha−1 ), due to increasing air temperature during SS as shown in (Fig. 4). This result is in line with those recorded by Rouphael and Colla (2005), who observed that the transpiration rates of hydroponically grown squash were positively correlated with solar radiation and temperature. Second reason, the squash

96

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Table 8 Means and standard errors for leaf no, plant height, total DW, harvest index (HI) and leaf area index (LAI). Mean ± SE

Items

Season Summer Fall Crop evapotranspiration (ETc ) Control100% DI85% DI70% 

Leaf no.

Plant height (cm)

Total DW (g plant−1 )

LAI

HI (%)

26.51 ± 1.08A  21.33 ± ± 1.12B

66.56 ± 1.18A 65.78 ± 2.26A

169.2 ± 7.92A 110.2 ± 9.57B

4.93 ± 0.25A 2.52 ± 0.21B

0.42 ± 0.02B 0.54 ± 0.03A

29.17 ± 1.76A 22.83 ± 1.4B 19.77 ± 0.75C

70.17 ± 3.33A 65.83 ± 2.1AB 62.50 ± 0.96B

165.7 ± 17.62A 135.3 ± 9.84B 118.0 ± 15.87B

4.54 ± 0.63A 3.35 ± 0.53B 3.30 ± 0.5B

0.53 ± 0.03A 0.48 ± 0.02 AB 0.44 ± 03B

Treatment means with the same letter are not significant at the p ≤ 0.05 level.

Table 9 Mean square, F value, and probability for leaf no, plant height, total DW, harvest index (HI) and leaf area index (LAI). Items

d.f.

Mean square Leaf no.

Season (S) ETc S × ETc Exp. error

1 2 2 10

120.64 137.88 8.68 2.56

F value and probability Total DW (g plant−1 )

LAI 26.09 2.94 0.15 0.12

15655.1 3493.1 527.5 221.6

Plant height (cm)

HI (%)

Leaf no. *

2.72 88.67 46.22 14.19

1603.91 47.21 135.63 53.95* 27.79 3.39* 54.52

Total DW (g plant−1 )

LAI *

218.42 24.60* 1.29*

*

70.65 15.77* 2.38*

Plant height (cm)

HI (%)

0.18ns 5.95* 3.10*

29.42* 2.49* 0.51*

ns = nonsignificant. * Significant at the p ≤ 0.05 level.

yield gained under FS (14 Mg ha−1 ) was higher than the corresponding squash yield gained under SS (11.72 Mg ha−1 ) by 11.45%. Concerning the effect of IWA, the averages of WUE were 3.93, 4.58 and 4.12 kg m−3 for I100% , I85% and I70% , respectively; indicating that, the average value of WUE of I85% treatment was higher than those of the I70% and I100% treatments by 11.16 and 14.19%, respectively, Table 10. However, there was no statistical difference between irrigation treatments. These results are in agreement with those of Yaseen et al. (2014) and Al-Mefleh et al. (2012) who mentioned that increasing irrigation levels did not increase the WUE in melon. Fig. 4 show the relationship between WUE under SS and FS was curvilinear (polynomial of 2nd order). This relationship could be expressed as follows: WUE = 2E − 07 × IWA2 − 0.0022 × IWA + 7.9211





R2 = 1 for SS

WUE = −6E − 071 × IWA2 + 0.0024 × IWA + 3.9767





R2 = 1 for FS

where WUE is water use efficiency (kg m−3 ), and IWA is irrigation water applied (m3 ha−1 ). Generally, according to the results of different studies, lower water treatments provided higher IWUE values. Ertek et al. (2004) obtained the highest IWUE values for summer squash under the lowest irrigation conditions (45% of Class A pan evaporation). El-Gindy et al. (2009) determined that the IWUE of drip-irrigated summer squash with lower water amounts

(60% of ETc crop) was higher than for those irrigated with higher water amounts (80% of ETc crop). 3.6. Effects of growing season and deficit irrigation on squash yield Fruit weight (g), fruit length, (cm), fruit diameter, (cm), no. of fruits plant−1 and yield (Mg ha−1 ) were significantly/or insignificantly affected by the growing season and deficit irrigation treatments and their interaction Table 11. The same trend was obtained by Amer (2011) working on squash and Wajid (1990) working on corn. The maximum yield values were obtained when the squash were planted in fall season (FS) as presented in Table 10. Squash yield under FS was 16.29% higher than that under SS (Table 10). The reduction of yield occurred in SS may be due to higher temperature conditions during SS than FS. Similar results were obtained by Wan et al. (2010) working on cucumber and Amer (2011) working on squash who reported that the low yield was due to non-favorable weather. In this concern, the difference between the two growing seasons in mean air temperature (Tmean ) was demonstrated (Fig. 1). During the SS, the daily Tmean ranged from 28.2 and 32.2 ◦ C, while for the FS, Tmean ranged from 18.7 to 31.7 ◦ C. Furthermore, Tmean in the FS was slightly higher in the first 10 days after planting than in the SS (31.7 ◦ C vs. 28.2 ◦ C). The higher yield recorded during the FS was due to an increasing in fruit weight (82.4 g), No. of fruit plant−1 (10.89) and fruit length (15.61 cm) than those obtained from SS which recorded 66.9 g, 9.72

Table 10 Means and standard errors for fruit weight, fruit length, diameter, number of fruits plant−1 , fresh yield and water use efficiency. Items

Season Summer Fall Crop evapotranspiration (ETc ) Control100% DI85% DI70% 

Mean ± SE Fruit weight (g)

Fruit length (cm)

Fruit diameter (cm)

No. of fruits (plant−1 )

Yield (Mg ha−1 )

Water use efficiency

66.9 ± 3.19B  82.4 ± 3.33A

13.74 ± 0.37B 15.61 ± 0.72A

2.69 ± 0.09A 2.61 ± 0.13A

9.72 ± 0.74A 10.89 ± 0.87A

11.72 ± 0.72B 14.00 ± 1.04A

2.96 ± 0.19B 5.46 ± 0.4A

81.3 ± 4.02A 81.6 ± 4.07A 60.9 ± 2.71B

14.84 ± 0.39A 15.37 ± 1.01A 13.82 ± 0.73A

2.98 ± 0.12A 2.58 ± 0.12B 2.39 ± 0.08B

10.67 ± 1.02A 10.75 ± 0.69A 9.50 ± 1.23A

14.31 ± 0.93A 13.99 ± 0.75A 10.27 ± 1.31B

3.93 ± 0.46B 4.58 ± 0.75A 4.12 ± 1.3AB

Treatment means with the same letter are not significant at the p ≤ 0.05 level.

32.61* 0.78* 0.08* 4.27* 5.58* 0.42* 2.07ns 0.99ns 1.88* 0.33ns 7.50* 3.56* 1.10* 4.64 ns 1.18* 21.24* 16.56* 0.49*

Length (cm) Fruit weight (g)

and 13.74 cm for fruit weight, no. of fruit plant−1 , and fruit length, respectively, Table 10. These results are in line with those recorded by Adams (2002). As data in Table 10, the squash yield was significant/or in significant affected by irrigation treatments. Non-significant differences between I100% and I85% were recorded. This result is in agreement with those of Amer (2011) and Wajid (1990) who reported that yield was significantly affected by IWA. As average, the maximum value of yield (14.31 Mg ha−1 ) was obtained when the plants were irrigated with the highest IWA (I100% ), while the minimum value of yield (10.27 Mg ha−1 ) was recorded for the lowest IWA (I70% ), (Table 10). Similar trend of results were obtained by Bekele and Tilahum (2007) in Ethiopia and Igbadun et al. (2012) in Nigeria. Also, this is in agreement with (Ertek et al., 2006; Wang et al., 2009; He-xi et al., 2011) who reported that the cucumber fruit yields increased with the increase of IWA. This result may be due to the sufficient available water in the soil under this level which led to an increase in both water and nutrients’ absorption and consequently an increase in the metabolic mechanisms in the plants leading to an increase in fruit weight, fruit length and no. of fruit plant−1 . Moreover, the reduction in irrigation water by 15 and 30% from IWA for I85% and I70% treatments reduced squash yield by 2.21 and 28.32% lower than the I100% treatment, respectively, Table 10. This result is logic because the shortage of soil water greatly affects various biological processes in plant such as photosynthesis, assimilates translocation, biomass, dry weight as well as the contents of carbohydrate, sugar, starch, amino acids and protein etc. Drought stress also affects the cell membrane stability and gas exchange characteristics in plants (Hamed, 1988) which may be change selectivity of water and nutrients owing to change in osmotic potential in stressed plants compared with those grown under normal irrigation treatments. Fig. 4 show the relationship between IWA and squash yield under SS and FS was curvilinear (polynomial of 2nd order). The same trend was obtained by Igbadun et al. (2012). This relationship could be expressed as follows:

56.564 1.350 0.142 1.735

WUE (kg m

−3

F value and probability

97



R2 = 1

for summer season

46.52 60.69 4.52 10.88



Y = −4E − 06 × IWA2 + 0.02561 × IWA

0.048 1.09 0.519 0.146

12.25 5.86 11.08 5.91

− 25.53

ns = nonsignificant. * Significant at the p ≤ 0.05 level.

31.26 7.41 7.91 6.73 2158.8 1682.9 49.8 101.6 1 2 2 24 Season (S) ETc S × ETc Exp. error

Fruit weight (g)

− 31.89

d.f.

Mean square

Length (cm)

Fruit diameter (cm)

No. of Fruits (plant−1 )

Yield (Mg ha−1 )

Y = −2E − 06 × IWA2 + 0.0185 × IWA

Items

Table 11 Mean square, F value, and probability for fruit weight, fruit length, diameter, number of fruits plant−1 , water use efficiency (WUE) and fresh yield.

Fruit diameter (cm)

No. of fruits (plant−1 )

Yield (Mg ha−1 )

WUE kg m−3

T.A.A. El-Mageed, W.M. Semida / Scientia Horticulturae 186 (2015) 89–100

(R2 = 1) for fall season

where Y is squash yield (Mg ha−1 ), and IWA is irrigation water applied (m3 ha−1 ). The amount of irrigation water applied for SS under I100% , I85% and I70% were 4790, 4072 and 3353 m3 ha−1 , respectively, and the corresponding values for FS were 3070, 2609 and 2149 m3 ha−1 , respectively. In the two seasons, the rates of water saving under SS and FS were 15 and 30%, for I85% and I70% , respectively. Therefore, under limited irrigation water, it’s recommended to irrigate squash plants at I85% to produce not only the same yields, approximately, but also to save more of water as compared to I100% treatment. Rouphael and Colla (2005) found that yield, marketable yield, and fruit weight and number of squash were significantly higher in spring–summer growing season compared with summer-fall growing season due to higher solar radiation and temperature. Cumulative yield was significant by growing season and IWA on except harvesting from no. (1) to no. (6) in SS while from no. (1) to no. (7) in FS (Fig. 5). Differences among treatments for cumulative yield were due to shortage of water, under two seasons, I100% treatment gave the maximum cumulative yield which was followed by I85 % and I75% . Fig. 5 illustrated that the no. of harvesting under FS (12) was greater than that obtained under SS (10) by 20%, and the

T.A.A. El-Mageed, W.M. Semida / Scientia Horticulturae 186 (2015) 89–100

20

20

18

18

14

a

a

12

ns

10 8

-1

12 10

b

b

ns

b

b

8

ns 6

6

ns 4

ns ns

2

2

A

C o n tro l D I 85 %

0 20

0 20

a

D I 70%

18

18

a a

-1

a

14

a

12

ns

10

ns

a

a

14

b

a

12

b b

ns

8

16

a

-1

16

a

10

b

b

ns

8

ns

6

ns

4

Cumulative yield (Mg ha )

4

Cumulative yield (Mg ha )

14

a

a

a

a

16

a

a

-1

Cumulative yield (Mg ha )

16

Cumulative yield (Mg ha )

98

6

ns 4

2

2

B

0

0 0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

H a rv e s tin g N o Fig. 5. Seasonal variations of cumulative yield for the different irrigation treatments for two consecutive seasons’ summer (A) and fall (B) (2013). Data reported are averages of 18 determinations per treatment. Errors bars are the standard error. Below each daily determination (ns) indicate that differences among treatments are not statistically significant at p < 0.05; whereas values followed by different letters indicate significant differences at p < 0.05.

fruit weight and no. of fruit plant−1 at each harvesting under FS was higher than that obtained under SS.

4. Conclusions Squash grown in 2013 summer and fall growing seasons was evaluated by applying deficit drip irrigation (70, 85 and 100% ETc ) under saline soil. Results showed that in well-watered conditions, seasonal water use by squash was 479 over 86 days in summer and 306 mm over 91 days in fall season, respectively. Water use of squash in the fall growing season was lower by 36% in comparison with those grown in the summer season. Squash yield the fall growing season was higher by 19.54% comparison with the yield in summer season. Summing up the results of the study, it is possible to conclude that after two season experiment, there were larger reductions

in ECe , Cl− and Na+ in 0–20 cm depth than those in 20–40 and 40–60 cm depths. By evaluating the soil salt changes above 20 cm soil layer among the three irrigation treatments, I100% treatment had a greater effect on the soil salinity of deep soil layer (0–60 cm) than those of other treatments. Further work is needed to establish the water management practices that will assure the lands will remain no saline if water and crop management is done properly. The higher yield recorded during the FS was due to an increasing in fruit weight, no. of fruit plant−1 and fruit length, than those obtained from SS In the two seasons, the rates of water saving under SS and FS were 15 and 30%, for I85% and I70% , respectively. In two seasons the highest squash yield was recorded under well irrigated treatment, control (100% ETc ) but non-significant differences between I100% and I85% were recorded. The total squash fruit yield varied from a growing season to another season. The irrigation water levels should be restricted when there is no difference in the crop yield. The highest water use efficiency (WUE) was obtained at

T.A.A. El-Mageed, W.M. Semida / Scientia Horticulturae 186 (2015) 89–100

I85% IWA. Based on the WUE, the most preferable irrigation level is I85% IWA. However, making decision to select either the I70% or I85% IWA depends on the availability and cost water, total fruit yield, and fruit price. Therefore, under limited irrigation water, it’s recommended to irrigate squash plants at I85% to produce not only the same yields, approximately, but also to save more of water as compared to I100% treatment. References Adams, P., 2002. Nutritional control in hydroponics. In: Savvas, D., Passam, H.C. (Eds.), Hydroponic Production of Vegetables and Ornamentals. Embryo Publications, Athens, Greece, pp. 211–261. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration Guidelines for Computing Crop Water Requirements. Irrigation and Drainage Paper 56, FAO, Rome, pp. 300. Al-Mefleh, N.K., Samarah, N., Zaitoun, S., Al-Ghzawi, A., 2012. 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