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Long term responses of olive trees to salinity
Agricultural Water Management 96 (2009) 1105–1113
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Long term responses of olive trees to salinity J.C. Melgar a,*, Y. Mohamed b, N. Serrano c, P.A. Garcı´a-Galavı´s d, C. Navarro c, M.A. Parra e, M. Benlloch a, R. Ferna´ndez-Escobar a a
Departmento de Agronomı´a, Universidad de Co´rdoba, Edificio ‘Celestino Mutis’, Campus Universitario de Rabanales, Ctra. Madrid-Ca´diz km. 396. 14071 Co´rdoba, Spain Desert Research Center, 1 Mathaf El-Matariya Street, El-Matariya, Cairo, Egypt c Instituto Andaluz de Investigacio´n y Formacio´n Agraria, Pesquera y Alimentaria ‘‘Alameda del Obispo’’, Av. Mene´ndez-Pidal s/n, 14004 Co´rdoba, Spain d Instituto Andaluz de Investigacio´n y Formacio´n Agraria, Pesquera y Alimentaria ‘‘Las Torres-Tomejil’, Ctra. Sevilla-Cazalla de la Sierra, km. 12.2, 41200 Alcala´ del Rı´o, Sevilla, Spain e Departamento de Ciencias y Recursos Agrı´colas y Forestales, Universidad de Co´rdoba, Edificio ‘Celestino Mutis’, Campus Universitario de Rabanales, Ctra. Madrid-Ca´diz km. 396, 14071 Co´rdoba, Spain b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 8 October 2008 Accepted 5 February 2009 Available online 27 March 2009
Water demand for irrigation is increasing in olive orchards due to enhanced yields and profits. Because olive trees are considered moderately tolerant to salinity, irrigation water with salt concentrations that can be harmful for many of fruit tree crops is often used without considering the possible negative effects on olive tree growth and yield. We studied salt effects in mature olive trees in a long term field experiment (1998–2006). Eighteen-year-old olive trees (Olea europaea L.) cv. Picual were cultivated under drip irrigation with saline water composed of a mixture of NaCl and CaCl2. Three irrigation regimes (i. no irrigation; ii. water application considering soil water reserves, short irrigation; iii. water application without considering soil water reserves and adding a 20% more as a leaching fraction, long irrigation) and three salt concentrations (0.5, 5 or 10 dS m 1) were applied. Treatments were the result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Growth parameters, leaf and fruit nutrition, yield, oil content and fruit characteristics were annually studied. Annual leaf nutrient analyses indicate that all nutrients were within the adequate levels. After 8 years of treatment, salinity did not affect any growth measurement and leaf Na+ and Cl concentration were always below the toxicity threshold of 0.2 and 0.5%, respectively. Annual and accumulated yield, fruit size and pulp:stone ratio were also not affected by salts. However, oil content increased linearly with salinity, in most of the years studied. Soil salinity measurements showed that there was no accumulation of salts in the upper 30 cm of the soil (where most of the roots are present) because of leaching by rainfall at the end of the irrigation period. Results suggest that a proper management of saline water, supplying Ca2+ to the irrigation water, using drip irrigation until winter rest and seasonal rainfall typical of the Mediterranean climate leach the salts from the first 0–60 cm depth, and growing a tolerant cultivar, can allow using high saline irrigation water (up to 10 dS m 1) for a long time without affecting growth and yield in olive trees. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Olea europaea Salt tolerance Drip fertigation Calcium supply
1. Introduction Olive trees are mainly grown in semiarid regions with Mediterranean climate, where scarce and irregular rainfall causes low yields. Around the Mediterranean Basin, olive trees have been traditionally cultivated in dry lands. However, the water demand for irrigation is increasing in olive orchards because of enhanced yields and profits (Orgaz and Fereres, 2004), leading to the use of low-quality water resources. Because olive trees are considered
* Corresponding author. Present address: Citrus Research and Education Center, University of Florida/IFAS. 700 Experiment Station Road, 33850 Lake Alfred, FL, USA. Tel.: +34 957 218 498; fax: +34 957 218 569. E-mail address: [email protected] (J.C. Melgar). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.02.009
moderately tolerant to salinity (Maas and Hoffman, 1977; FAO, 1985; Rugini and Fedeli, 1990) and water resources in the Mediterranean basin are scarce, irrigation water with high salt concentration (5–10 dS m 1) causing electrical conductivities of the soil saturation extract (ECe) between 3 and 6 dS m 1 (FAO, 1985) is often used without considering the negative effects of poor water quality on olive tree growth and productivity. Under field conditions, where salinity is non uniformly distributed with depth or time (Shalhevet, 1994; Corwin et al., 2007), and in a fluctuating saline environment at Mediterranean latitudes, early-fall rainfalls allow the accumulated salinity to be annually removed from the root-zone and plants to assimilate CO2 and produce new growth at considerable rates (Tattini et al., 2008). Salinity is generally accepted to reduce shoot growth (Tattini et al., 1992; Klein et al., 1994), pollen viability and germination, number
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of flowers and fruits (Cresti et al., 1994). Salinity effects on yield depend on the concentration (Klein et al., 1992; Wiesman et al., 2004) but even though tolerance is a cultivar-dependent characteristic (Marı´n et al., 1995; Chartzoulakis, 2005) most of the cultivars under semiarid and transient-state salinity conditions may develop well with no significant reduction of yield with a ECe in a range between 3 and 6 dS m 1 (Aragu¨e´s et al., 2005; Bernstein, 1964; FAO, 1985; Maas and Hoffman, 1977). However, little is know about the long term effects of salinization of trees in the field (Gucci and Tattini, 1997). Effects on oil quality are also contradictory due to the scarce number of studies carried out (Zarrouk et al., 1996; Wiesman et al., 2004). Olive tree responses to salinity stress can vary with cultivar (Therios and Misopolinos, 1988; Marı´n et al., 1995), although tolerant genotypes seem to be more able to exclude toxic ions than sensitive ones (Gucci and Tattini, 1997). Salt tolerance is mainly associated to salt-exclusion mechanisms operating in the roots, preventing salt translocation rather than salt absorption (Benlloch et al., 1991; Tattini et al., 1995; Demiral, 2005) by holding Na+ and Cl at the root level and limiting the accumulation of these ions into actively growing shoots. Olive trees are less sensitive to leaf Cl than Na+, especially at high salinities (Aragu¨e´s et al., 2005) and Cl uptake and transport to the shoot in olive trees is lower than Na+ (Tattini et al., 1992). Calcium is also supposed to play an important role in Na+ exclusion and retention mechanisms, which may be an important ability for survival under saline conditions (Melgar et al., 2006; Tattini and Traversi, 2008). Although much research has been devoted to study NaCl concentrations that allow an optimum growth (Bernstein, 1975; Therios and Misopolinos, 1988; Rugini and Fedeli, 1990; Klein et al., 1994) and the physiological mechanisms of salt tolerance in olive trees (Benlloch et al., 1991; Tattini et al., 1994; Gucci and Tattini, 1997; Gucci et al., 1997), long term experiments under field conditions with mature trees are scarce (Wiesman et al., 2004; Aragu¨e´s et al., 2005) and more information is needed. The aim of this work was to evaluate long term effects of saline irrigation on vegetative growth, yield and fruit characteristics of mature olive trees growing under field conditions. 2. Materials and methods 2.1. Field conditions, plant material and irrigation management The experiment was carried out at ‘La Mina’ Experimental Farm, located in Cabra, southern Co´rdoba province, Spain (37.28N, 4.26W) from 1998 to 2006. The climate is Mediterranean with a mean annual precipitation of 702 mm and a marked summer drought (30 mm in the June–September period). The mean annual reference evapotranspiration (ET0), as calculated according to Hargreaves’ method (Hargreaves and Samani, 1985) is 1250 mm, and the mean annual temperature is 16 8C. The slope of the orchard ranges from 2% to 9%. The soil is a clay loam (calcixerollic xerochrept) (Soil Survey Staff, 1994) with an average of 35% clay. A hard limy layer can be found between the 0.4–0.5-m depth in certain zones, which impedes the penetration of both roots and water. The volumetric soil water content (u, m3 m 3) measured in the laboratory was 0.33. Eighteen-year-old ‘Picual’ olive trees spaced at 7 m 7 m were selected for the experiment. Average tree volume, measured every year after harvesting and before pruning, was between 60 and 67 m3. A randomized block design with four blocks and seven treatments was used. Each experimental plot consisted of four trees bordered by a double guard row. Seven treatments were applied, as a result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Salt concentrations in the irrigation water were the following: (i)
control, with good water quality: a pH of 7.6 and an EC of 0.5 dS m 1 (Na+ 0.45 mM, K+ 0.04 mM, Ca2+ 7.64 mM, Mg2+ 2.76 mM and Cl 1.20 mM); (ii) water with EC = 5 dS m 1; (iii) water with EC = 10 dS m 1. The latter two were prepared with good water quality plus salts as described below. Three different irrigation regimes were carried out: (i) no irrigation; (ii) water application considering soil water content (short irrigation); (iii) water application without considering soil water reserves and applying a 20% more as a leaching fraction (long irrigation). Olive trees were drip-irrigated daily during the dry season. Four drip emitters per tree (4 L h 1) connected to a single drip line, two per side of the tree, were used. During the first 3 years (1998– 2000), irrigation doses were established after estimating the soil water content by determining the crop evapotranspiration (ETc) using the FAO method (Doorenbos and Pruitt, 1977) and the effective precipitation (EP) in the wet season. ETc was calculated as: ETc = ET0 Kr Kc, where Kr was the coefficient of ground covered by the crop (Fereres and Castel, 1981) with a value of 0.6 and Kc was determined by Fereres et al. (1981) with values of 0.60 in April and October, 0.55 in May, June and September, and 0.50 in July and August. Kr was estimated by the following formula: Kr = 2 Sc/100 (Fereres et al., 1981), where Sc was the percentage of soil shaded by the canopy. The average value of Sc was 45%, and it was calculated as: Sc = pD2N/400, where D was the average diameter (m) of the tree and N was the tree density (trees ha 1). For the short irrigation treatment, net irrigation requirements were expressed as: NIR = SWD ETc + EP, where NIR was the net irrigation requirements and SWD was the soil water deficit (and was calculated as the difference between the soil water content at the end and at the beginning of each irrigation period, 15 days). For the long irrigation treatment, NIR were simply calculated as NIR = ETc EP. As irrigation doses were overestimated and over-irrigation and runoff problems were observed, six drip emitters per tree were used after 2000 and irrigation doses were re-established by monitoring the soil water content through four permanent humidity probes (Thetaprobe ML2x, Delta-T, Cambridge, United Kingdom) per irrigated treatment installed in control treatments at four different depths (30, 60, 90 and 120 cm) under the drip emitter. Data were hourly collected with a data logger (DL2e, Delta-T, Cambridge, United Kingdom), weekly downloaded and used to determine the irrigation doses for the following week. They were established in order to maintain soil water content at 95% of field capacity (0.46 m3 m 3) at the 60-cm depth for short irrigation and 95% of field capacity (0.45 m3 m 3) at the 90-cm depth for long irrigation (which means water was reaching the deepest layers and the leaching fraction initially established for this treatment was maintained). The number of drip emitters was increased again in 2003 up to eight per tree (2 L h 1) in order to improve water distribution and reduce flooding problems. Saline solutions were prepared weekly in four 3000-L tanks. They were filled with good quality water and a different mixture of NaCl and CaCl2 in order to reach a sodium adsorption ratio (SAR) value of 10 mmol1/2 L 1/2 and an EC of 5 or 10 dS m 1. These solutions were pump-stirred for at least four more hours after they were prepared and also daily, for thirty minutes, before injecting in the irrigation system. NaCl and CaCl2 concentrations in irrigation water were: 30.9 mM NaCl and 9.5 mM CaCl2 for 5 dS m 1 treatment, and 49.9 mM NaCl and 25.0 mM CaCl2 for 10 dS m 1 treatment. Applied water and salts during the whole experimental period are shown in Table 1. 2.2. Soil measurements Soil salinity and sodicity was monitored through three soil samplings per year: at the beginning, middle and end of the
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Table 1 Effective precipitation (estimated as 80% of annual precipitation), annual ETc and irrigation applied (mm) in the dry period during the 9 experimental years. 1998
1999
2000
2001
2002
2003
2004
2005
2006
Effective precipitation ETc
374 493
530 573
551 628
450 627
588 713
453 763
565 742
322 644
489 627
Rain fed Short irrigation Long irrigation
Irrigation applied 0 0 74 320 180 410
0 160 295
0 170 266
0 159 199
0 231 287
0 120 147
0 153 192
0 53 62
Short irrigation 5 dS m 1 Short irrigation 10 dS m 1 Long irrigation 5 dS m 1 Long irrigation 10 dS m 1
NaCl (kg tree 5 8 5 28
21 39 26 47
12 21 22 39
14 23 19 38
11 22 15 27
13 25 18 28
9 16 12 21
11 20 13 25
2 4 3 5
Short irrigation 5 dS m 1 Short irrigation 10 dS m 1 Long irrigation 5 dS m 1 Long irrigation 10 dS m 1
CaCl2 (kg tree 3 8 7 25
12 37 15 45
7 20 13 37
10 26 13 42
8 25 10 30
9 27 12 31
6 18 8 23
8 22 9 28
2 5 2 5
1
)
1
)
irrigation season. Soil samples were taken using an Edelman auger, 4-cm diameter, at 20 cm from the dripper and at three different depths (0–30, 30–60, 60–90 cm) in each experimental plot. Different drippers (first, second or third dripper from the trunk) and different sides of the dripper (either sides or only one side) were selected for each measurement in order to avoid taking samples from the same place. After sampling, soil samples were well mixed and holes were carefully refilled with leftover fine soil in order to avoid water to penetrate through preferential ways. Electrical conductivity in the saturation paste extract was determined using a conductivimeter (Crison Micro CM2200, Crison, Alella, Spain). Sodium, Ca2+, Mg2+ and K+ concentration were measured using an atomic absorption spectrophometer (PerkinElmer 3100, PerkinElmer Inc., Wellesley, MA, USA). Sodium adsorption ratio was calculated as: SAR = CNa+/(CCa2+ + CMg2+)1/2, where C represents concentration (mM). Cationic exchange capacity (CEC) was determined by the ammonium acetate method (Schollenberger and Simon, 1945) and exchangeable Na+ concentration were calculated to determine exchangeable sodium percentage (ESP) as: ESP = 100 [exchangeable Na+]/CEC.
bearing shoots in July, September and December. Four leaves per tree were sampled, introduced in closed test tubes and freshweighed (FW). After being oven-dried at 80 8C for 72 h, dry weight (DW) was measured and leaf water content (%) calculated as LWC = 100 (FW DW)/FW. Eighty leaves were fresh weighed and scanned every year to measure leaf area using an image analysis software (APS Assess, Winnipeg, Canada). Specific leaf area (SLA) was determined as the ratio of leaf area to leaf fresh weight. Vegetative growth was obtained at the end of each growing season by measuring shoot length on 20 random shoots per tree. Yield per tree was measured at harvest, and a representative sample of 2 kg of fruit per plot was taken to determine fruit characteristics. Fruit size was determined as 100 fruit weight. Pulp:stone ratio was calculated after pitting a fruit sample of approximately 140 g. Oil content (% FW) was determined by nuclear magnetic resonance (NMR) (Minispec NMS100, Bruker Optik GmbH, Ettlingen, Germany) as reported in Del Rı´o and Romero (1999).
2.3. Leaf analysis
Pulp and stone were separately put in paper bags and dried at 80 8C for at least 72 h. Subsequently, both were ground and mineral analyses were done following the same methods previously described for leaves.
A hundred fully expanded, mature leaves per plot taken from the middle portion of non-bearing shoots in July were annually sampled for the determination of nutrient concentration. Leaves were washed, dried at 80 8C for 72 h, ground and stored in an oven at 60 8C until analysis. Samples were ashed in a muffle furnace at 600 8C for at least 12 h, and dissolved in 0.1 N HCl. Nitrogen was determined with an EuroVector EA3000 CHN analyzer (EuroVector S.p.A., Milan, Italy) by the Dumas procedure (Dumas, 1831). Total P was determined by colorimetry using the method described by Murphy and Riley (1962). Boron was determined in the extract by colorimetry (Greweling, 1976). Potassium, Ca2+, Mg2+, Zn, Mn, Fe and Cu were measured using an atomic absorption spectrophometer (PerkinElmer 1100B, PerkinElmer Inc., Wellesley, MA, USA). Chloride ions were extracted with 10% (v/v) acetic acid from a similar sample of leaves collected at the same time and concentrations were determined colorimetrically (LKB Biochrom Novaspec 4049 Spectrophotometer, Cambridge, UK) by the mercuric thiocyanate reaction (Florence and Farrar, 1971).
2.5. Fruit analysis
2.6. Statistical analysis Data were subjected to analyses of variance and regression analyses. Yield data were analysed by covariance using the aboveground tree volume as covariate. Vegetative growth, yield, tree nutritional status and fruit mineral contents were subjected to a factorial analysis, studying the interaction between factors when it existed. Non-irrigated treatment was compared with saline treatments running an ANOVA based on a randomized block analysis. Means were separated using Tukey’s test and a 5% rejection level was applied. All statistical analyses were made using Statistix 8.0 statistical package (Analytical Software, Tallahassee, FL, USA). 3. Results
2.4. Vegetative growth, yield and fruit characteristics
3.1. Soil measurements
Leaf water content was determined from samples of fully expanded, mature leaves taken from the middle portion of non-
Winter leaching of salts reduced soil salinity mainly in the superficial layer (0–30 cm); salinity decreased more than 60% after
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Fig. 1. Evolution of the electrical conductivity of saturated soil-paste extract at 3 depth intervals (0–30, 30–60 and 60–90 cm) before, during and after each irrigation season along the 9 years of the experiment.
the rainy season in the 0–30 cm depth layer in 5 of the 8 years studied, and in 4 years for the 30–60 cm depth layer (Fig. 1). Soil Na+ and Ca2+ concentrations linearly increased with EC in the irrigation water for all soil layers (data not shown). When soil salt content was monitored along the year, a salinization period related to irrigation season was clearly observed as a consequence of salinity in the irrigation water, followed by a leaching cycle related to the rain season. Thus, similar cyclical changes were observed each year due to leaching by rainfall which prevented salt accumulation. However, salt concentrations gradually increased in the deepest layers, especially during the irrigation season and in the most saline treatment, although salinization was very slow (0.048 and 0.077 dS m 1 year 1 at the beginning and at the end of the irrigation season, respectively). Sodium absorption relation increased with EC in the irrigation water; highest values were recorded in the 0–30 cm depth layer (2.1, 11.2 and 11.7 in control, 5 and 10 dS m 1, respectively) and decreased in the deepest layers. A cyclical pattern was observed each year, with the lowest values at the beginning of the irrigation
season and the highest values at the middle and at the end of the irrigation season. Exchangeable sodium percentage values were 1.2, 12 and 11.5% in the superficial layer (0–30 cm) and 1.5, 13.5 and 12.7% in the 30–60 cm depth layer for control, 5 and 10 dS m 1, respectively. 3.2. Nutritional status, growth and yield Salinity did not change the tree nutritional status during the 9 years of experiment (data not shown) and Na+, Cl or Ca2+concentrations in the leaves were not affected by salinity (Table 2). It did not affect any of the growth parameters measured: shoot length, leaf area and specific leaf area (Table 3). Differences between saline treatments and rain-fed one were not observed either (data not shown) even in low rainfall years. Likewise, non-significant differences in leaf water content in response to salinity were observed (data not shown). Saline treatments did not change annual yield in any of the 9 years studied or in the accumulated yield (1998–2006) (Table 4).
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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Table 2 Na+, Cl and Ca2+ concentration in leaves sampled in July during the 9 experimental years. Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CVb (%) EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance Short irrigation 0.5 Short irrigation 5 Short irrigation 10 Long irrigation 0.5 Long irrigation 5 Long irrigation 10 CV (%)
1998
1999
Na+ Salinity 0.05 0.02 0.05 0.02 0.05 0.01 N.S. N.S. Irrigation dose 0.04 0.03 0.05 0.02 N.S. N.S. 27.9 33.7 Cl Salinity 0.01 0.03 0.01 0.03 0.01 0.03 N.S. N.S. Irrigation dose 0.01 0.03 0.01 0.03 N.S. N.S. Salinity irrigation dose
45.9
17.5
2000
2001
2002
2003
2004
2005
2006
0.04 0.05 0.05 N.S.
0.03 0.05 0.04 N.S.
0.03 0.03 0.03 N.S.
0.03 0.04 0.04 N.S.
0.04 0.04 0.04 N.S.
0.03 0.03 0.03 N.S.
0.04 0.03 0.03 N.S.
0.04 0.05 N.S. 18.5
0.05 0.03 N.S. 6.0
0.03 0.03 N.S. 11.8
0.04 0.03 N.S. 11.5
0.04 0.03 N.S. 27.3
0.03 0.03 N.S. 29.5
0.03 0.03 N.S. 40.7
0.01 0.01 0.01 N.S.
0.02 0.03 0.03 N.S.
0.02 0.03 0.03 N.S.
0.03 0.03 0.04 N.S.
0.04 0.03 0.03 N.S.
0.04 0.04 0.04 N.S.
0.01 0.01 N.S.
0.02 0.03 N.S.
0.02 0.03 N.S.
0.04 0.03 N.S.
0.03 0.03 N.S.
0.04 0.04 N.S.
33.3
15.3
35.0
17.4
8.9
30.3
0.02 0.02 0.03 0.03 0.04 0.02 18.6
ab ab ab ab a ab
1.79 1.70 1.76 N.S.
1.43 1.41 1.50 N.S.
1.43 1.36 1.38 N.S.
1.64 1.58 1.57 N.S.
1.04 1.01 1.04 N.S.
0.83 0.95 0.86 N.S.
1.78 2.00 1.81 N.S.
1.77 1.72 N.S. 4.9
1.42 1.47 N.S. 4.2
1.42 1.36 N.S. 4.2
1.69 1.51
1.02 1.04 N.S. 3.7
0.90 0.86 N.S. 10.0
1.92 1.80 N.S. 18.3
2+
EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance CV (%) a
Ca Salinity 1.22 1.42 1.38 1.07 1.32 1.22 N.S. N.S. Irrigation dose 1.27 1.31 1.21 1.17 N.S. N.S. 12.2 19.5
*
6.5
*
N.S. and indicate non-significant differences and significant differences at P 0.05, respectively; in the interaction salinity irrigation dose, means followed by a different lower-case letters indicate significant differences at P 0.05 by Tukey’s test (n = 5). b Coefficient of variation.
Differences were not either found when rain-fed and saline treatments were compared (data not shown). 3.3. Fruit characteristics Fruit size was not affected by salinity in the irrigation water in any year (Table 5). Differences were not either found when rain-fed and salinity treatments were compared (data not shown). However, oil content significantly increased linearly with salinity in four of the 9 years studied (Table 6). Salinity did not affect pulp:stone ratio (Table 7). 3.4. Fruit nutrient content Salinity caused very small changes in fruit nutrient content. Interactions between salinity and irrigation doses for N and K+ content in 2 of the 9 years and a slight decrease in Ca2+ content in 2002 were the only changes observed, although these values were not confirmed in the following years (data not shown). A trend of a lower K+ content in fruits of rain-fed trees with respect to saline treatments was observed, although significant differences were only found in 2001. Higher Cl content in saline treatments than in control was found in 2 years, but significant changes were not observed in Na+ content (Table 8).
4. Discussion Salts dynamic in the soil and the evolution of SAR and ECe indicated that SAR levels were always among the levels initially suggested. Under realistic field conditions, uniformity does not normally exist and the best estimation of the effective salinity during transient conditions, when salt is non-uniformly distributed with depth, is the average salinity within the root-zone (Shalhevet, 1994). Winter rainfalls annually leached the accumulated salts in the soil profile during saline irrigation and, as a consequence, ECe at the beginning of each irrigation period had a similar value to the control treatments, as Shalhevet (1994) suggested for Mediterranean type climates with seasonal rainfall. Sodium adsorption ratio values showed a cyclical year pattern related to the irrigation: with the lowest values at the beginning of the irrigation season and the highest values at the middle of the end. The reduction in SAR values during the rainy season is mainly due to the ion leaching (Na+, Ca2+ and Mg2+) and also to the replacement of exchangeable Na+ by Ca2+ resulting from the solubilization of CaCO3 caused by the rains. These results agree with Metochis (1999) and Keller and Bliesner (1990), who reported that soil salt contents under saline drip irrigation remained stable after 9 years with rainfall about 400 mm year 1 although there is a high risk of soil salinization if rainfall is lower than 250 mm. On the
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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Table 3 Shoot length (cm), leaf area (cm2) and specific leaf area (g cm2) measured during the 9 experimental years. Irrigation treatment
1998 Shoot length Salinity 7.2 6.0 5.9 N.S. Irrigation dose 6.1 6.7 N.S. 29.2
EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CVb (%)
1999
2000
2001
2002
2003
2004
2005
2006
3.7 3.3 3.4 L**Q*
4.8 4.5 4.5 N.S.
5.8 5.5 5.7 N.S.
6.2 5.8 5.8 N.S.
4.2 4.0 4.1 N.S.
7.0 7.5 7.1 N.S.
4.8 4.9 4.5 N.S.
4.9 5.0 4.7 N.S.
3.4 3.5 N.S. 5.4
4.6 4.6 N.S. 9.6
5.5 5.8 N.S. 9.6
5.7 6.2 7.9
4.2 4.0 N.S. 12.1
7.0 7.3 N.S. 8.8
4.7 4.7 N.S. 10.8
4.9 4.9 N.S. 11.6
3.7 3.7 3.8 N.S.
4.0 3.8 3.9 N.S.
3.4 3.3 3.4 N.S.
3.5 3.4 3.5 N.S.
3.0 3.2 3.0 Q*
3.4 3.4 3.4 N.S.
3.2 3.3 3.3 N.S.
3.8 3.6 N.S. 6.4
3.9 3.9 N.S. 5.2
3.4 3.3 N.S. 4.7
3.5 3.4 N.S. 3.3
3.0 3.1 N.S. 4.4
3.4 3.5 N.S. 4.6
3.2 3.4 N.S. 6.3
40.0 39.6 39.8 N.S.
38.3 39.9 37.9 N.S.
38.8 39.1 39.6 N.S.
38.0 38.0 39.0 N.S.
41.4 40.8 42.2 N.S.
44.3 45.2 44.8 N.S.
42.4 39.7 38.7 N.S.
39.6 42.1 N.S. 2.5
38.7 38.7 N.S. 5.5
39.3 39.1 N.S. 3.9
38.6 38.0 N.S. 4.2
41.3 41.7 N.S. 6.7
45.6 43.9 N.S. 8.5
41.9 38.7 N.S. 11.8
Leaf area Salinity 4.6 4.8 4.7 4.7 4.6 4.7 N.S. N.S. Irrigation dose 4.3 4.7 4.5 4.7 N.S. N.S. 11.5 9.9
EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance CV (%)
Specific leaf area Salinity 38.2 39.1 38.4 N.S. Irrigation dose 37.4 39.0 N.S. 3.0
EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance CV (%)
*
a N.S., * and ** indicate non-significant differences, significant differences at P 0.05 and significant differences at P 0.01, respectively; L and Q indicate linear and quadratic response, respectively. Each factor was studied separately as no interaction was observed between both factors. b Coefficient of variation.
Table 4 Effect of salinity and irrigation dose on annual yield and accumulated yield (kg tree 1998
1999
2000
2001
1
) (1998–2006).
2002
2003
2004
2005
2006
Yield EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CV (%)b a b
Salinity 9.5 56.9 12.3 49.6 12.1 51.6 N.S. N.S. Irrigation dose 9.8 52.3 12.4 53.1 N.S. N.S. 74.5 18.5
1998–2006 Accum. yield
62.3 63.4 60.4 N.S.
59.8 52.2 56.2 N.S.
47.0 41.1 40.0 N.S.
48.6 43.8 47.2 N.S.
44.1 44.5 42.4 N.S.
40.4 43.9 40.4 N.S.
50.4 49.4 47.2 N.S.
419.0 400.2 397.5 N.S.
61.6 62.4 N.S. 12.7
53.3 58.9 N.S. 15.9
46.4 39.0 N.S. 23.2
45.8 47.2 N.S. 21.4
45.4 42.0 N.S. 15.8
39.4 43.8 N.S. 17.8
48.7 49.3 N.S. 13.8
402.7 408.1 N.S. 5.2
N.S. indicates non-significant differences. Each factor was studied separately as no interaction was observed between both factors. Coefficient of variation.
other side, ESP highest values were lower than 15%, which cannot be considered harmful for the trees (Freeman et al., 1994). This confirms the results reported by Weissbein et al. (2008), who suggested that an efficient cultivation of mature olive trees irrigated with moderate saline water (4.2 dS m 1) is closely related to proper soil leaching management and maintaining ECe in the root zone below 6 dS m 1. Leaf concentrations of Na+ and Cl were always under toxicity levels (0.2 and 0.5%, respectively, Bernstein, 1975; Klein et al., 1994), regardless of EC in irrigation water and effects of saline irrigation on leaf Na+ or Cl concentration were not observed. Gucci and Tattini (1997) reported that tolerant genotypes are more able to exclude toxic ions than sensitive ones and, consequently,
toxic ion concentration in the leaves is lower in tolerant than in sensitive ones. ‘Picual’, the cultivar used in this experiment, is considered as one of the most tolerant cultivars (Marı´n et al., 1995), and can partially explain the regulation in the toxic ion concentration observed. Calcium can also play an important role regulating leaf Na+ concentration and protecting the structure of the cell wall and plasmatic membrane. Likewise, its function in regulating the selectivity of the ionic absorption probably had a relevant importance. An increase in the availability of Ca2+ at the root zone has been shown to ameliorate the detrimental effects of salinity stress in most species (Lynch and La¨uchli, 1985; Cramer, 2002). Based on recent works in olive trees (Melgar et al., 2006; Tattini and Traversi, 2008), Ca2+ in the irrigation water is thought
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
1111
Table 5 Effect of salinity and irrigation dose on fruit size (g). Irrigation treatment EC (dS m 1) 0.5 5 10 Significanceb Short irrigation Long irrigation Significance CVc (%) a b c
1998
1999
Fruit size Salinity 5.47 2.91 5.74 3.19 5.19 2.90 N.S. N.S. Irrigation dose 5.53 3.04 5.39 2.96 N.S. N.S. 15.5 22.4
2000
2001
2002
2003
2004
2.84 2.83 2.68 N.S.
3.13 3.30 2.96 N.S.
4.44 4.53 4.25 N.S.
3.06 3.07 3.10 N.S.
3.80 3.83 3.66 N.S.
2.66 2.93 N.S. 19.5
3.22 3.04 N.S. 18.5
4.20 4.61 N.S. 12.7
3.17 2.98 N.S. 9.5
3.70 3.83 N.S. 9.8
2005a
2006
No available data for years 2005–2006. N.S. indicates non-significant differences. Each factor was studied separately as no interaction was observed between both factors. Coefficient of variation.
Table 6 Effect of salinity and irrigation dose on oil yield (% FW). Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CV (%)b
1998
1999
Oil yield Salinity 18.5 27.3 19.0 27.7 19.9 27.6 N.S. N.S. Irrigation dose 19.2 27.3 19.0 27.8 N.S. N.S. 6.3 5.0
2000
2001
2002
2003
2004
2005
2006
29.1 30.0 30.3 N.S.
26.7 27.3 28.7 L**
24.0 24.7 26.9 L***
28.8 29.5 31.0 L**
22.6 24.1 25.0 L**
23.4 24.7 24.5 N.S.
17.2 17.4 18.5 N.S.
29.5 30.1 N.S. 2.8
27.4 27.7 N.S. 2.0
25.0 25.4 N.S. 1.8
29.8 29.7 N.S. 2.3
23.7 24.1 N.S. 6.6
24.3 24.1 N.S 7.5
18.0 17.4 N.S. 6.9
a N.S., ** and *** indicate non-significant differences, significant differences at P 0.01 and significant differences at P 0.001, respectively; L indicates linear response. Each factor was studied separately as no interaction was observed between both factors. b Coefficient of variation.
to decrease Na+ uptake and transport to the shoot. Leaf Cl concentration did not reach toxic levels in any of the treatments either. In olive, Cl uptake and transport to the shoot is lower than Na+ (Bongi and Loreto, 1989; Bartolini et al., 1991; Tattini et al., 1992) and does not cause decrease in photosynthesis or growth if Cl concentration in water tissues is lower than 80 mM (Bongi and Loreto, 1989). Nutrient imbalances are frequently observed in plants under saline stress. The excessive concentration of an element can cause a
decrease in foliar concentration of another one, even reaching deficient levels, such as the induced K+ deficiency by Na+ excess, or the decrease of NO3 uptake as a consequence of a Cl excessive content (Lea-Cox and Syvertsen, 1993). Although low leaf K+ and N contents were observed in some years, they were not a consequence of saline ions because their concentration did not change between saline and control treatments. Leaf water content did not change as a consequence of salinity or the amount of water applied. Olive tree is a drought tolerant
Table 7 Effect of salinity and irrigation dose on pulp:stone ratio. Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance 0.5 Short irrigation 0.5 Long irrigation 5 Short irrigation 5 Long irrigation 10 Short irrigation 10 Long irrigation CV (%)b a
*
1998
1999
Pulp:stone Salinity 4.6 4.0 5.0 4.4 4.4 4.2 N.S. N.S. Irrigation dose 4.8 4.2 4.5 4.2 N.S. N.S. Salinity irrigation dose
11.5
15.3
2000
2001
2002
2003
3.5 3.6 3.3 N.S.
4.7 4.9 4.5 N.S.
6.0 6.1 6.2 N.S.
3.4 3.6 N.S.
4.7 4.6 N.S.
5.8 6.4
19.1
16.7
*
10.4
2005
2006
4.7 4.9 4.7 N.S.
5.0 4.7 4.8 N.S.
3.9 3.8 4.1 N.S.
4.6 4.7 N.S.
4.9 4.8 N.S.
3.8 4.1 N.S.
7.6
9.9
7.4
2004
5.1 5.8 5.2 5.5 5.5 5.0 5.9
ab a ab ab ab b
N.S. and indicate non-significant differences and significant differences at P 0.05, respectively; in the interaction salinity irrigation dose, means followed by a different lower-case letters indicate significant differences at P 0.05 by Tukey’s test (n = 5). b Coefficient of variation.
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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Table 8 Na+ and Cl content in fruit during 8 experimental years (1999–2006). Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea
1998
1999
2000
2001
2002
2003
2004
2005
2006
0.18 0.19 0.13 N.S.
0.22 0.28 0.30 N.S.
0.19 0.20 0.23 N.S.
0.14 0.15 0.12 N.S.
0.18 0.17 0.22 N.S.
0.27 0.25 0.18 N.S.
0.43 0.44 0.57 N.S.
0.29 0.28 0.31 N.S.
0.17 0.17 N.S. 16.9
0.27 0.27 N.S. 31.3
0.24 0.18 N.S. 18.2
0.13 0.15 N.S. 16.7
0.18 0.18 N.S. 7.1
0.25 0.22 N.S. 26.6
0.43 0.53 N.S. 30.0
0.30 0.28 N.S. 10.1
0.28 0.33 0.35 N.S.
0.53 0.66 0.75 N.S.
0.45 0.57 0.58 N.S.
0.50 0.53 0.53 N.S.
0.25 0.30 0.27 Q**
0.37 0.43 0.46 L*
0.10 0.11 0.11 N.S.
0.21 0.21 0.23 N.S.
0.31 0.33 N.S. 10.1
0.58 0.71 N.S. 21.2
0.56 0.51 N.S. 15.4
0.47 0.57 N.S. 12.2
0.26 0.29
0.41 0.43 N.S. 3.2
0.11 0.11 N.S. 15.7
0.21 0.23 N.S. 14.2
Na+ Salinity
Irrigation dose Short irrigation Long irrigation Significance CV (%)b EC (dS m 1) 0.5 5 10 Significance
Cl Salinity
Irrigation dose Short irrigation Long irrigation Significance CV (%)
*
5.8
a N.S., * and ** indicate non-significant differences, significant differences at P 0.05 and significant differences at P 0.01, respectively; L and Q indicate linear and quadratic response, respectively. Each factor was studied separately as no interaction was observed between both factors. b Coefficient of variation.
species and its leaves can reach extremely low values of water content before loosing turgency (Larsen et al., 1989). A higher salt concentration in the external solution causes a decrease in leaf water content and higher water contents are associated with higher salt tolerance. Differences between months or year are thought to be due to differences in seasonal rainfall. It has been generally reported that a significant yield reduction occurs in olives cultivated under high saline conditions (values of EC in the irrigation water higher than 7.5 dS m 1, Klein et al., 1992; Gucci and Tattini, 1997; Wiesman et al., 2004) in comparison with control conditions. However, existing data with lower values are contradictory (Bouaziz, 1990; Klein et al., 1992; Chartzoulakis, 2005). Results obtained in this study showed no differences in annual or accumulated yield among treatments, as it was also reported by Bouaziz (1990) and Weissbein et al. (2008), both experiments were carried out under field conditions. The lack of alternate bearing between 1999 and 2006 is also remarkable. Low yield was recorded only in the first year (1998) and it was a consequence of an infection of Spilocaea oleagina. This absence of fluctuations is not due to continuous low yields and/or lack of high yields as a consequence of salt stress, because there were no differences in yield between saline and control treatments in any of the years studied. Saline irrigation did not cause changes in any of the growth parameters measured: shoot length, leaf area or specific leaf area. Olive tree is an alternate-bearing species that usually shows low shoot growth in ‘‘on’’ years, which limits, at the same time, the number of nodes and potential flower buds. The results from this experiment show that, at the same time there were no changes in yield, differences in shoot length have not been detected between different years. However, shoot growth was lower than expected for an adult and irrigated olive grove. This could be partially attributed to the north-oriented slope of the grove and the shady conditions, which could cause a shorter shoot growth than expected, limiting high yield in ‘‘on’’ years. Salinity did not affect fruit characteristics like fruit size or pulp:stone ratio. Although some authors reported no clear patterns of oil accumulation in response to irrigation with saline water (Weissbein et al., 2008, EC in the irrigation water of 4.2 dS m 1), oil
yield was affected by salts in some years of our experiment. A slight trend of increase of oil yield with the highest EC in the irrigation water was observed during the first 3 years, confirming a linear response and statistical differences during the rest of the years. However, there were no differences when fruits from the rain-fed trees were compared with saline irrigated ones. Probably, the absence of differences during the first 3 years is due to the higher water doses applied, more than the lack of effect of saline irrigation, because it was since the fourth year when the irrigation doses began to be controlled by the humidity probes and the amount of applied water was reduced. Water stress has been documented to have the largest effect on fruit development and oil content (Lavee et al., 1990; Tombesi, 1994) but references are contradictory on the effect of salinity and more research on this topic is needed. Fruit extraction content of any nutrient was not affected by salinity, but Cl content between 1998 and 2002 showed a trend of accumulation in fruits of saline treatments. Differences appeared in 2 years of the experiment, with higher contents for the higher EC in the irrigation water. Fruit from rain-fed trees showed lower Cl contents than saline treatments and even than control treatments in some of the years. It was probably because Cl uptake and high mobility are closely linked to uptake fluxes and water movement inside the plant (White and Broadley, 2001). Considering the previous results, the absence of effects in the trees after 9 years of experiment is thought to be a consequence of the following factors: - Plant material: we used mature trees of cv. Picual, considered as a salt tolerant (Marı´n et al., 1995). As it has been previously said, tolerant genotypes have a higher capacity of excluding the toxic ions than sensitive ones (Gucci and Tattini, 1997) and it reduces Na+ concentration in the leaves. - Calcium: Ca2+ supply in the irrigation water probably had a positive effect protecting the cell wall and the plasmatic membrane and regulating the selectivity of ionic uptake (Melgar et al., 2006; Tattini and Traversi, 2008). This explains, at least in part, a reduction in uptake and transport of Na+ to the shoot.
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- Irrigation management: Drip irrigation allowed applying water with a high frequency and maintaining a high humidity in the soil, avoiding a harmful salt concentration for the trees. Furthermore, irrigation was maintained until typical season rainfalls leached salts in the soil profile and trees started winter dormancy. As a conclusion, results from this work indicate that saline irrigation in olive groves with similar characteristics to those previously cited can produce profitable agronomic results like those from trees irrigated with good quality water. Likewise, it is noticeable that there were no differences between saline and rain-fed treatments, although climate conditions (700 mm is a relatively high amount of rainfalls) are thought to have played an important role in this. Acknowledgements This research was supported by the Comisio´n Interministerial de Ciencia y Tecnologı´a, Spain, projects no. AGF96-1116, AGL20012447, AGL2004-02387, and AGL2005-3273. Grateful acknowledgement is made to IFAPA for the use of the experimental farm ‘La Mina’ and their technical assistance. References Aragu¨e´s, R., Puy, J., Royo, A., Espada, J.L., 2005. Three-year field response of young olive trees (Olea europaea L., cv. Arbequina) to soil salinity: trunk growth and leaf ion accumulation. Plant Soil 271, 265–273. Bartolini, G., Mazuelos, C., Troncoso, A., 1991. Influence of Na2SO4 and NaCl salts on survival, growth and mineral composition of young olive plants in inert sand culture. Adv. Hort. Sci. 5, 73–76. Benlloch, M., Arboleda, F., Barranco, D., Ferna´ndez-Escobar, R., 1991. Response of young olive trees to sodium and boron excess in irrigation water. HortScience 26, 867–870. Bernstein, L., 1964. Effects of salinity on mineral composition and growth of plants. In: Proc. 4th Int. Coll. Plant Anal. Fert. Prob. 4, Bruxelles, Belgium, pp. 25–45. Bernstein, L., 1975. Effect of salinity and sodicity on plant growth. Ann. Rev. Phytopathol. 13, 295–312. Bongi, G., Loreto, F., 1989. Gas-exchange properties of salt-stressed olive (Olea europaea L.) leaves. Plant Physiol. 90, 1408–1416. Bouaziz, A., 1990. Behaviour of some olive varieties irrigated with brackish water and grown intensively in the central part of Tunisia. Acta Hortic. 286, 247–250. Chartzoulakis, K.S., 2005. Salinity and olive: growth, salt tolerance, photosynthesis and yield. Agric. Water Manage. 78, 108–121. Corwin, D.L., Rhoades, J.D., Sˇimu˚nek, J., 2007. Leaching requirement for soil salinity control: steady-state versus transient models. Agric. Water Manage. 90, 165– 180. Cramer, G.R., 2002. Sodium–calcium interactions under salinity stress. In: La¨uchli, A., Lu¨ttge, U. (Eds.), Salinity. Environment-Plants-Molecules. Kluwer Academic Publishers, Dordrecht. Cresti, M., Ciampolini, F., Tattini, M., Cimato, A., 1994. Effect of salinity on productivity and oil quality of olive (Olea europaea L.) plants. Adv. Hortic. Sci. 8, 211–214. Del Rı´o, C., Romero, A.M., 1999. Whole, unmilled olives can be used to determine their oil content by nuclear magnetic resonance. HortTechnology 9, 675–680. Demiral, M.A., 2005. Comparative response of two olive (Olea europaea L.) cultivars to salinity. Turk. J. Agric. For. 29, 267–274. Doorenbos, J., Pruitt, W.O., 1977. Guidelines for predicting crop water requirements. FAO irrigation and drainage paper no. 24. Food and Agriculture Organization of the United Nations, Rome, pp. 15–29, 112–115. Dumas, J.B.A., 1831. Procedes de l’analyse organic. Ann. Chim. Phys. 247, 198–213. FAO (Food and Agriculture Organization), 1985. Water quality for agriculture. FAO Irrigation and Drainage Paper 29, Rome, Italy. Fereres, E., Castel, J.R., 1981. Drip irrigation management. In: Fereres, E. (Ed.), Drip irrigation management. Division of Agricultural Sciences, University of California, Leaflet no. 21259. Fereres, E., Pruitt, W.O., Beutel, J.A., Henderson, D.W., Holzapfel, E., Shulbach, H., Uriu, K., 1981. ET and drip irrigation scheduling. In: Fereres, E. (Ed.), Drip
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Long term responses of olive trees to salinity J.C. Melgar a,*, Y. Mohamed b, N. Serrano c, P.A. Garcı´a-Galavı´s d, C. Navarro c, M.A. Parra e, M. Benlloch a, R. Ferna´ndez-Escobar a a
Departmento de Agronomı´a, Universidad de Co´rdoba, Edificio ‘Celestino Mutis’, Campus Universitario de Rabanales, Ctra. Madrid-Ca´diz km. 396. 14071 Co´rdoba, Spain Desert Research Center, 1 Mathaf El-Matariya Street, El-Matariya, Cairo, Egypt c Instituto Andaluz de Investigacio´n y Formacio´n Agraria, Pesquera y Alimentaria ‘‘Alameda del Obispo’’, Av. Mene´ndez-Pidal s/n, 14004 Co´rdoba, Spain d Instituto Andaluz de Investigacio´n y Formacio´n Agraria, Pesquera y Alimentaria ‘‘Las Torres-Tomejil’, Ctra. Sevilla-Cazalla de la Sierra, km. 12.2, 41200 Alcala´ del Rı´o, Sevilla, Spain e Departamento de Ciencias y Recursos Agrı´colas y Forestales, Universidad de Co´rdoba, Edificio ‘Celestino Mutis’, Campus Universitario de Rabanales, Ctra. Madrid-Ca´diz km. 396, 14071 Co´rdoba, Spain b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 8 October 2008 Accepted 5 February 2009 Available online 27 March 2009
Water demand for irrigation is increasing in olive orchards due to enhanced yields and profits. Because olive trees are considered moderately tolerant to salinity, irrigation water with salt concentrations that can be harmful for many of fruit tree crops is often used without considering the possible negative effects on olive tree growth and yield. We studied salt effects in mature olive trees in a long term field experiment (1998–2006). Eighteen-year-old olive trees (Olea europaea L.) cv. Picual were cultivated under drip irrigation with saline water composed of a mixture of NaCl and CaCl2. Three irrigation regimes (i. no irrigation; ii. water application considering soil water reserves, short irrigation; iii. water application without considering soil water reserves and adding a 20% more as a leaching fraction, long irrigation) and three salt concentrations (0.5, 5 or 10 dS m 1) were applied. Treatments were the result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Growth parameters, leaf and fruit nutrition, yield, oil content and fruit characteristics were annually studied. Annual leaf nutrient analyses indicate that all nutrients were within the adequate levels. After 8 years of treatment, salinity did not affect any growth measurement and leaf Na+ and Cl concentration were always below the toxicity threshold of 0.2 and 0.5%, respectively. Annual and accumulated yield, fruit size and pulp:stone ratio were also not affected by salts. However, oil content increased linearly with salinity, in most of the years studied. Soil salinity measurements showed that there was no accumulation of salts in the upper 30 cm of the soil (where most of the roots are present) because of leaching by rainfall at the end of the irrigation period. Results suggest that a proper management of saline water, supplying Ca2+ to the irrigation water, using drip irrigation until winter rest and seasonal rainfall typical of the Mediterranean climate leach the salts from the first 0–60 cm depth, and growing a tolerant cultivar, can allow using high saline irrigation water (up to 10 dS m 1) for a long time without affecting growth and yield in olive trees. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Olea europaea Salt tolerance Drip fertigation Calcium supply
1. Introduction Olive trees are mainly grown in semiarid regions with Mediterranean climate, where scarce and irregular rainfall causes low yields. Around the Mediterranean Basin, olive trees have been traditionally cultivated in dry lands. However, the water demand for irrigation is increasing in olive orchards because of enhanced yields and profits (Orgaz and Fereres, 2004), leading to the use of low-quality water resources. Because olive trees are considered
* Corresponding author. Present address: Citrus Research and Education Center, University of Florida/IFAS. 700 Experiment Station Road, 33850 Lake Alfred, FL, USA. Tel.: +34 957 218 498; fax: +34 957 218 569. E-mail address: [email protected] (J.C. Melgar). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.02.009
moderately tolerant to salinity (Maas and Hoffman, 1977; FAO, 1985; Rugini and Fedeli, 1990) and water resources in the Mediterranean basin are scarce, irrigation water with high salt concentration (5–10 dS m 1) causing electrical conductivities of the soil saturation extract (ECe) between 3 and 6 dS m 1 (FAO, 1985) is often used without considering the negative effects of poor water quality on olive tree growth and productivity. Under field conditions, where salinity is non uniformly distributed with depth or time (Shalhevet, 1994; Corwin et al., 2007), and in a fluctuating saline environment at Mediterranean latitudes, early-fall rainfalls allow the accumulated salinity to be annually removed from the root-zone and plants to assimilate CO2 and produce new growth at considerable rates (Tattini et al., 2008). Salinity is generally accepted to reduce shoot growth (Tattini et al., 1992; Klein et al., 1994), pollen viability and germination, number
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J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
of flowers and fruits (Cresti et al., 1994). Salinity effects on yield depend on the concentration (Klein et al., 1992; Wiesman et al., 2004) but even though tolerance is a cultivar-dependent characteristic (Marı´n et al., 1995; Chartzoulakis, 2005) most of the cultivars under semiarid and transient-state salinity conditions may develop well with no significant reduction of yield with a ECe in a range between 3 and 6 dS m 1 (Aragu¨e´s et al., 2005; Bernstein, 1964; FAO, 1985; Maas and Hoffman, 1977). However, little is know about the long term effects of salinization of trees in the field (Gucci and Tattini, 1997). Effects on oil quality are also contradictory due to the scarce number of studies carried out (Zarrouk et al., 1996; Wiesman et al., 2004). Olive tree responses to salinity stress can vary with cultivar (Therios and Misopolinos, 1988; Marı´n et al., 1995), although tolerant genotypes seem to be more able to exclude toxic ions than sensitive ones (Gucci and Tattini, 1997). Salt tolerance is mainly associated to salt-exclusion mechanisms operating in the roots, preventing salt translocation rather than salt absorption (Benlloch et al., 1991; Tattini et al., 1995; Demiral, 2005) by holding Na+ and Cl at the root level and limiting the accumulation of these ions into actively growing shoots. Olive trees are less sensitive to leaf Cl than Na+, especially at high salinities (Aragu¨e´s et al., 2005) and Cl uptake and transport to the shoot in olive trees is lower than Na+ (Tattini et al., 1992). Calcium is also supposed to play an important role in Na+ exclusion and retention mechanisms, which may be an important ability for survival under saline conditions (Melgar et al., 2006; Tattini and Traversi, 2008). Although much research has been devoted to study NaCl concentrations that allow an optimum growth (Bernstein, 1975; Therios and Misopolinos, 1988; Rugini and Fedeli, 1990; Klein et al., 1994) and the physiological mechanisms of salt tolerance in olive trees (Benlloch et al., 1991; Tattini et al., 1994; Gucci and Tattini, 1997; Gucci et al., 1997), long term experiments under field conditions with mature trees are scarce (Wiesman et al., 2004; Aragu¨e´s et al., 2005) and more information is needed. The aim of this work was to evaluate long term effects of saline irrigation on vegetative growth, yield and fruit characteristics of mature olive trees growing under field conditions. 2. Materials and methods 2.1. Field conditions, plant material and irrigation management The experiment was carried out at ‘La Mina’ Experimental Farm, located in Cabra, southern Co´rdoba province, Spain (37.28N, 4.26W) from 1998 to 2006. The climate is Mediterranean with a mean annual precipitation of 702 mm and a marked summer drought (30 mm in the June–September period). The mean annual reference evapotranspiration (ET0), as calculated according to Hargreaves’ method (Hargreaves and Samani, 1985) is 1250 mm, and the mean annual temperature is 16 8C. The slope of the orchard ranges from 2% to 9%. The soil is a clay loam (calcixerollic xerochrept) (Soil Survey Staff, 1994) with an average of 35% clay. A hard limy layer can be found between the 0.4–0.5-m depth in certain zones, which impedes the penetration of both roots and water. The volumetric soil water content (u, m3 m 3) measured in the laboratory was 0.33. Eighteen-year-old ‘Picual’ olive trees spaced at 7 m 7 m were selected for the experiment. Average tree volume, measured every year after harvesting and before pruning, was between 60 and 67 m3. A randomized block design with four blocks and seven treatments was used. Each experimental plot consisted of four trees bordered by a double guard row. Seven treatments were applied, as a result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Salt concentrations in the irrigation water were the following: (i)
control, with good water quality: a pH of 7.6 and an EC of 0.5 dS m 1 (Na+ 0.45 mM, K+ 0.04 mM, Ca2+ 7.64 mM, Mg2+ 2.76 mM and Cl 1.20 mM); (ii) water with EC = 5 dS m 1; (iii) water with EC = 10 dS m 1. The latter two were prepared with good water quality plus salts as described below. Three different irrigation regimes were carried out: (i) no irrigation; (ii) water application considering soil water content (short irrigation); (iii) water application without considering soil water reserves and applying a 20% more as a leaching fraction (long irrigation). Olive trees were drip-irrigated daily during the dry season. Four drip emitters per tree (4 L h 1) connected to a single drip line, two per side of the tree, were used. During the first 3 years (1998– 2000), irrigation doses were established after estimating the soil water content by determining the crop evapotranspiration (ETc) using the FAO method (Doorenbos and Pruitt, 1977) and the effective precipitation (EP) in the wet season. ETc was calculated as: ETc = ET0 Kr Kc, where Kr was the coefficient of ground covered by the crop (Fereres and Castel, 1981) with a value of 0.6 and Kc was determined by Fereres et al. (1981) with values of 0.60 in April and October, 0.55 in May, June and September, and 0.50 in July and August. Kr was estimated by the following formula: Kr = 2 Sc/100 (Fereres et al., 1981), where Sc was the percentage of soil shaded by the canopy. The average value of Sc was 45%, and it was calculated as: Sc = pD2N/400, where D was the average diameter (m) of the tree and N was the tree density (trees ha 1). For the short irrigation treatment, net irrigation requirements were expressed as: NIR = SWD ETc + EP, where NIR was the net irrigation requirements and SWD was the soil water deficit (and was calculated as the difference between the soil water content at the end and at the beginning of each irrigation period, 15 days). For the long irrigation treatment, NIR were simply calculated as NIR = ETc EP. As irrigation doses were overestimated and over-irrigation and runoff problems were observed, six drip emitters per tree were used after 2000 and irrigation doses were re-established by monitoring the soil water content through four permanent humidity probes (Thetaprobe ML2x, Delta-T, Cambridge, United Kingdom) per irrigated treatment installed in control treatments at four different depths (30, 60, 90 and 120 cm) under the drip emitter. Data were hourly collected with a data logger (DL2e, Delta-T, Cambridge, United Kingdom), weekly downloaded and used to determine the irrigation doses for the following week. They were established in order to maintain soil water content at 95% of field capacity (0.46 m3 m 3) at the 60-cm depth for short irrigation and 95% of field capacity (0.45 m3 m 3) at the 90-cm depth for long irrigation (which means water was reaching the deepest layers and the leaching fraction initially established for this treatment was maintained). The number of drip emitters was increased again in 2003 up to eight per tree (2 L h 1) in order to improve water distribution and reduce flooding problems. Saline solutions were prepared weekly in four 3000-L tanks. They were filled with good quality water and a different mixture of NaCl and CaCl2 in order to reach a sodium adsorption ratio (SAR) value of 10 mmol1/2 L 1/2 and an EC of 5 or 10 dS m 1. These solutions were pump-stirred for at least four more hours after they were prepared and also daily, for thirty minutes, before injecting in the irrigation system. NaCl and CaCl2 concentrations in irrigation water were: 30.9 mM NaCl and 9.5 mM CaCl2 for 5 dS m 1 treatment, and 49.9 mM NaCl and 25.0 mM CaCl2 for 10 dS m 1 treatment. Applied water and salts during the whole experimental period are shown in Table 1. 2.2. Soil measurements Soil salinity and sodicity was monitored through three soil samplings per year: at the beginning, middle and end of the
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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Table 1 Effective precipitation (estimated as 80% of annual precipitation), annual ETc and irrigation applied (mm) in the dry period during the 9 experimental years. 1998
1999
2000
2001
2002
2003
2004
2005
2006
Effective precipitation ETc
374 493
530 573
551 628
450 627
588 713
453 763
565 742
322 644
489 627
Rain fed Short irrigation Long irrigation
Irrigation applied 0 0 74 320 180 410
0 160 295
0 170 266
0 159 199
0 231 287
0 120 147
0 153 192
0 53 62
Short irrigation 5 dS m 1 Short irrigation 10 dS m 1 Long irrigation 5 dS m 1 Long irrigation 10 dS m 1
NaCl (kg tree 5 8 5 28
21 39 26 47
12 21 22 39
14 23 19 38
11 22 15 27
13 25 18 28
9 16 12 21
11 20 13 25
2 4 3 5
Short irrigation 5 dS m 1 Short irrigation 10 dS m 1 Long irrigation 5 dS m 1 Long irrigation 10 dS m 1
CaCl2 (kg tree 3 8 7 25
12 37 15 45
7 20 13 37
10 26 13 42
8 25 10 30
9 27 12 31
6 18 8 23
8 22 9 28
2 5 2 5
1
)
1
)
irrigation season. Soil samples were taken using an Edelman auger, 4-cm diameter, at 20 cm from the dripper and at three different depths (0–30, 30–60, 60–90 cm) in each experimental plot. Different drippers (first, second or third dripper from the trunk) and different sides of the dripper (either sides or only one side) were selected for each measurement in order to avoid taking samples from the same place. After sampling, soil samples were well mixed and holes were carefully refilled with leftover fine soil in order to avoid water to penetrate through preferential ways. Electrical conductivity in the saturation paste extract was determined using a conductivimeter (Crison Micro CM2200, Crison, Alella, Spain). Sodium, Ca2+, Mg2+ and K+ concentration were measured using an atomic absorption spectrophometer (PerkinElmer 3100, PerkinElmer Inc., Wellesley, MA, USA). Sodium adsorption ratio was calculated as: SAR = CNa+/(CCa2+ + CMg2+)1/2, where C represents concentration (mM). Cationic exchange capacity (CEC) was determined by the ammonium acetate method (Schollenberger and Simon, 1945) and exchangeable Na+ concentration were calculated to determine exchangeable sodium percentage (ESP) as: ESP = 100 [exchangeable Na+]/CEC.
bearing shoots in July, September and December. Four leaves per tree were sampled, introduced in closed test tubes and freshweighed (FW). After being oven-dried at 80 8C for 72 h, dry weight (DW) was measured and leaf water content (%) calculated as LWC = 100 (FW DW)/FW. Eighty leaves were fresh weighed and scanned every year to measure leaf area using an image analysis software (APS Assess, Winnipeg, Canada). Specific leaf area (SLA) was determined as the ratio of leaf area to leaf fresh weight. Vegetative growth was obtained at the end of each growing season by measuring shoot length on 20 random shoots per tree. Yield per tree was measured at harvest, and a representative sample of 2 kg of fruit per plot was taken to determine fruit characteristics. Fruit size was determined as 100 fruit weight. Pulp:stone ratio was calculated after pitting a fruit sample of approximately 140 g. Oil content (% FW) was determined by nuclear magnetic resonance (NMR) (Minispec NMS100, Bruker Optik GmbH, Ettlingen, Germany) as reported in Del Rı´o and Romero (1999).
2.3. Leaf analysis
Pulp and stone were separately put in paper bags and dried at 80 8C for at least 72 h. Subsequently, both were ground and mineral analyses were done following the same methods previously described for leaves.
A hundred fully expanded, mature leaves per plot taken from the middle portion of non-bearing shoots in July were annually sampled for the determination of nutrient concentration. Leaves were washed, dried at 80 8C for 72 h, ground and stored in an oven at 60 8C until analysis. Samples were ashed in a muffle furnace at 600 8C for at least 12 h, and dissolved in 0.1 N HCl. Nitrogen was determined with an EuroVector EA3000 CHN analyzer (EuroVector S.p.A., Milan, Italy) by the Dumas procedure (Dumas, 1831). Total P was determined by colorimetry using the method described by Murphy and Riley (1962). Boron was determined in the extract by colorimetry (Greweling, 1976). Potassium, Ca2+, Mg2+, Zn, Mn, Fe and Cu were measured using an atomic absorption spectrophometer (PerkinElmer 1100B, PerkinElmer Inc., Wellesley, MA, USA). Chloride ions were extracted with 10% (v/v) acetic acid from a similar sample of leaves collected at the same time and concentrations were determined colorimetrically (LKB Biochrom Novaspec 4049 Spectrophotometer, Cambridge, UK) by the mercuric thiocyanate reaction (Florence and Farrar, 1971).
2.5. Fruit analysis
2.6. Statistical analysis Data were subjected to analyses of variance and regression analyses. Yield data were analysed by covariance using the aboveground tree volume as covariate. Vegetative growth, yield, tree nutritional status and fruit mineral contents were subjected to a factorial analysis, studying the interaction between factors when it existed. Non-irrigated treatment was compared with saline treatments running an ANOVA based on a randomized block analysis. Means were separated using Tukey’s test and a 5% rejection level was applied. All statistical analyses were made using Statistix 8.0 statistical package (Analytical Software, Tallahassee, FL, USA). 3. Results
2.4. Vegetative growth, yield and fruit characteristics
3.1. Soil measurements
Leaf water content was determined from samples of fully expanded, mature leaves taken from the middle portion of non-
Winter leaching of salts reduced soil salinity mainly in the superficial layer (0–30 cm); salinity decreased more than 60% after
1108
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
Fig. 1. Evolution of the electrical conductivity of saturated soil-paste extract at 3 depth intervals (0–30, 30–60 and 60–90 cm) before, during and after each irrigation season along the 9 years of the experiment.
the rainy season in the 0–30 cm depth layer in 5 of the 8 years studied, and in 4 years for the 30–60 cm depth layer (Fig. 1). Soil Na+ and Ca2+ concentrations linearly increased with EC in the irrigation water for all soil layers (data not shown). When soil salt content was monitored along the year, a salinization period related to irrigation season was clearly observed as a consequence of salinity in the irrigation water, followed by a leaching cycle related to the rain season. Thus, similar cyclical changes were observed each year due to leaching by rainfall which prevented salt accumulation. However, salt concentrations gradually increased in the deepest layers, especially during the irrigation season and in the most saline treatment, although salinization was very slow (0.048 and 0.077 dS m 1 year 1 at the beginning and at the end of the irrigation season, respectively). Sodium absorption relation increased with EC in the irrigation water; highest values were recorded in the 0–30 cm depth layer (2.1, 11.2 and 11.7 in control, 5 and 10 dS m 1, respectively) and decreased in the deepest layers. A cyclical pattern was observed each year, with the lowest values at the beginning of the irrigation
season and the highest values at the middle and at the end of the irrigation season. Exchangeable sodium percentage values were 1.2, 12 and 11.5% in the superficial layer (0–30 cm) and 1.5, 13.5 and 12.7% in the 30–60 cm depth layer for control, 5 and 10 dS m 1, respectively. 3.2. Nutritional status, growth and yield Salinity did not change the tree nutritional status during the 9 years of experiment (data not shown) and Na+, Cl or Ca2+concentrations in the leaves were not affected by salinity (Table 2). It did not affect any of the growth parameters measured: shoot length, leaf area and specific leaf area (Table 3). Differences between saline treatments and rain-fed one were not observed either (data not shown) even in low rainfall years. Likewise, non-significant differences in leaf water content in response to salinity were observed (data not shown). Saline treatments did not change annual yield in any of the 9 years studied or in the accumulated yield (1998–2006) (Table 4).
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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Table 2 Na+, Cl and Ca2+ concentration in leaves sampled in July during the 9 experimental years. Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CVb (%) EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance Short irrigation 0.5 Short irrigation 5 Short irrigation 10 Long irrigation 0.5 Long irrigation 5 Long irrigation 10 CV (%)
1998
1999
Na+ Salinity 0.05 0.02 0.05 0.02 0.05 0.01 N.S. N.S. Irrigation dose 0.04 0.03 0.05 0.02 N.S. N.S. 27.9 33.7 Cl Salinity 0.01 0.03 0.01 0.03 0.01 0.03 N.S. N.S. Irrigation dose 0.01 0.03 0.01 0.03 N.S. N.S. Salinity irrigation dose
45.9
17.5
2000
2001
2002
2003
2004
2005
2006
0.04 0.05 0.05 N.S.
0.03 0.05 0.04 N.S.
0.03 0.03 0.03 N.S.
0.03 0.04 0.04 N.S.
0.04 0.04 0.04 N.S.
0.03 0.03 0.03 N.S.
0.04 0.03 0.03 N.S.
0.04 0.05 N.S. 18.5
0.05 0.03 N.S. 6.0
0.03 0.03 N.S. 11.8
0.04 0.03 N.S. 11.5
0.04 0.03 N.S. 27.3
0.03 0.03 N.S. 29.5
0.03 0.03 N.S. 40.7
0.01 0.01 0.01 N.S.
0.02 0.03 0.03 N.S.
0.02 0.03 0.03 N.S.
0.03 0.03 0.04 N.S.
0.04 0.03 0.03 N.S.
0.04 0.04 0.04 N.S.
0.01 0.01 N.S.
0.02 0.03 N.S.
0.02 0.03 N.S.
0.04 0.03 N.S.
0.03 0.03 N.S.
0.04 0.04 N.S.
33.3
15.3
35.0
17.4
8.9
30.3
0.02 0.02 0.03 0.03 0.04 0.02 18.6
ab ab ab ab a ab
1.79 1.70 1.76 N.S.
1.43 1.41 1.50 N.S.
1.43 1.36 1.38 N.S.
1.64 1.58 1.57 N.S.
1.04 1.01 1.04 N.S.
0.83 0.95 0.86 N.S.
1.78 2.00 1.81 N.S.
1.77 1.72 N.S. 4.9
1.42 1.47 N.S. 4.2
1.42 1.36 N.S. 4.2
1.69 1.51
1.02 1.04 N.S. 3.7
0.90 0.86 N.S. 10.0
1.92 1.80 N.S. 18.3
2+
EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance CV (%) a
Ca Salinity 1.22 1.42 1.38 1.07 1.32 1.22 N.S. N.S. Irrigation dose 1.27 1.31 1.21 1.17 N.S. N.S. 12.2 19.5
*
6.5
*
N.S. and indicate non-significant differences and significant differences at P 0.05, respectively; in the interaction salinity irrigation dose, means followed by a different lower-case letters indicate significant differences at P 0.05 by Tukey’s test (n = 5). b Coefficient of variation.
Differences were not either found when rain-fed and saline treatments were compared (data not shown). 3.3. Fruit characteristics Fruit size was not affected by salinity in the irrigation water in any year (Table 5). Differences were not either found when rain-fed and salinity treatments were compared (data not shown). However, oil content significantly increased linearly with salinity in four of the 9 years studied (Table 6). Salinity did not affect pulp:stone ratio (Table 7). 3.4. Fruit nutrient content Salinity caused very small changes in fruit nutrient content. Interactions between salinity and irrigation doses for N and K+ content in 2 of the 9 years and a slight decrease in Ca2+ content in 2002 were the only changes observed, although these values were not confirmed in the following years (data not shown). A trend of a lower K+ content in fruits of rain-fed trees with respect to saline treatments was observed, although significant differences were only found in 2001. Higher Cl content in saline treatments than in control was found in 2 years, but significant changes were not observed in Na+ content (Table 8).
4. Discussion Salts dynamic in the soil and the evolution of SAR and ECe indicated that SAR levels were always among the levels initially suggested. Under realistic field conditions, uniformity does not normally exist and the best estimation of the effective salinity during transient conditions, when salt is non-uniformly distributed with depth, is the average salinity within the root-zone (Shalhevet, 1994). Winter rainfalls annually leached the accumulated salts in the soil profile during saline irrigation and, as a consequence, ECe at the beginning of each irrigation period had a similar value to the control treatments, as Shalhevet (1994) suggested for Mediterranean type climates with seasonal rainfall. Sodium adsorption ratio values showed a cyclical year pattern related to the irrigation: with the lowest values at the beginning of the irrigation season and the highest values at the middle of the end. The reduction in SAR values during the rainy season is mainly due to the ion leaching (Na+, Ca2+ and Mg2+) and also to the replacement of exchangeable Na+ by Ca2+ resulting from the solubilization of CaCO3 caused by the rains. These results agree with Metochis (1999) and Keller and Bliesner (1990), who reported that soil salt contents under saline drip irrigation remained stable after 9 years with rainfall about 400 mm year 1 although there is a high risk of soil salinization if rainfall is lower than 250 mm. On the
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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Table 3 Shoot length (cm), leaf area (cm2) and specific leaf area (g cm2) measured during the 9 experimental years. Irrigation treatment
1998 Shoot length Salinity 7.2 6.0 5.9 N.S. Irrigation dose 6.1 6.7 N.S. 29.2
EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CVb (%)
1999
2000
2001
2002
2003
2004
2005
2006
3.7 3.3 3.4 L**Q*
4.8 4.5 4.5 N.S.
5.8 5.5 5.7 N.S.
6.2 5.8 5.8 N.S.
4.2 4.0 4.1 N.S.
7.0 7.5 7.1 N.S.
4.8 4.9 4.5 N.S.
4.9 5.0 4.7 N.S.
3.4 3.5 N.S. 5.4
4.6 4.6 N.S. 9.6
5.5 5.8 N.S. 9.6
5.7 6.2 7.9
4.2 4.0 N.S. 12.1
7.0 7.3 N.S. 8.8
4.7 4.7 N.S. 10.8
4.9 4.9 N.S. 11.6
3.7 3.7 3.8 N.S.
4.0 3.8 3.9 N.S.
3.4 3.3 3.4 N.S.
3.5 3.4 3.5 N.S.
3.0 3.2 3.0 Q*
3.4 3.4 3.4 N.S.
3.2 3.3 3.3 N.S.
3.8 3.6 N.S. 6.4
3.9 3.9 N.S. 5.2
3.4 3.3 N.S. 4.7
3.5 3.4 N.S. 3.3
3.0 3.1 N.S. 4.4
3.4 3.5 N.S. 4.6
3.2 3.4 N.S. 6.3
40.0 39.6 39.8 N.S.
38.3 39.9 37.9 N.S.
38.8 39.1 39.6 N.S.
38.0 38.0 39.0 N.S.
41.4 40.8 42.2 N.S.
44.3 45.2 44.8 N.S.
42.4 39.7 38.7 N.S.
39.6 42.1 N.S. 2.5
38.7 38.7 N.S. 5.5
39.3 39.1 N.S. 3.9
38.6 38.0 N.S. 4.2
41.3 41.7 N.S. 6.7
45.6 43.9 N.S. 8.5
41.9 38.7 N.S. 11.8
Leaf area Salinity 4.6 4.8 4.7 4.7 4.6 4.7 N.S. N.S. Irrigation dose 4.3 4.7 4.5 4.7 N.S. N.S. 11.5 9.9
EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance CV (%)
Specific leaf area Salinity 38.2 39.1 38.4 N.S. Irrigation dose 37.4 39.0 N.S. 3.0
EC (dS m 1) 0.5 5 10 Significance Short irrigation Long irrigation Significance CV (%)
*
a N.S., * and ** indicate non-significant differences, significant differences at P 0.05 and significant differences at P 0.01, respectively; L and Q indicate linear and quadratic response, respectively. Each factor was studied separately as no interaction was observed between both factors. b Coefficient of variation.
Table 4 Effect of salinity and irrigation dose on annual yield and accumulated yield (kg tree 1998
1999
2000
2001
1
) (1998–2006).
2002
2003
2004
2005
2006
Yield EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CV (%)b a b
Salinity 9.5 56.9 12.3 49.6 12.1 51.6 N.S. N.S. Irrigation dose 9.8 52.3 12.4 53.1 N.S. N.S. 74.5 18.5
1998–2006 Accum. yield
62.3 63.4 60.4 N.S.
59.8 52.2 56.2 N.S.
47.0 41.1 40.0 N.S.
48.6 43.8 47.2 N.S.
44.1 44.5 42.4 N.S.
40.4 43.9 40.4 N.S.
50.4 49.4 47.2 N.S.
419.0 400.2 397.5 N.S.
61.6 62.4 N.S. 12.7
53.3 58.9 N.S. 15.9
46.4 39.0 N.S. 23.2
45.8 47.2 N.S. 21.4
45.4 42.0 N.S. 15.8
39.4 43.8 N.S. 17.8
48.7 49.3 N.S. 13.8
402.7 408.1 N.S. 5.2
N.S. indicates non-significant differences. Each factor was studied separately as no interaction was observed between both factors. Coefficient of variation.
other side, ESP highest values were lower than 15%, which cannot be considered harmful for the trees (Freeman et al., 1994). This confirms the results reported by Weissbein et al. (2008), who suggested that an efficient cultivation of mature olive trees irrigated with moderate saline water (4.2 dS m 1) is closely related to proper soil leaching management and maintaining ECe in the root zone below 6 dS m 1. Leaf concentrations of Na+ and Cl were always under toxicity levels (0.2 and 0.5%, respectively, Bernstein, 1975; Klein et al., 1994), regardless of EC in irrigation water and effects of saline irrigation on leaf Na+ or Cl concentration were not observed. Gucci and Tattini (1997) reported that tolerant genotypes are more able to exclude toxic ions than sensitive ones and, consequently,
toxic ion concentration in the leaves is lower in tolerant than in sensitive ones. ‘Picual’, the cultivar used in this experiment, is considered as one of the most tolerant cultivars (Marı´n et al., 1995), and can partially explain the regulation in the toxic ion concentration observed. Calcium can also play an important role regulating leaf Na+ concentration and protecting the structure of the cell wall and plasmatic membrane. Likewise, its function in regulating the selectivity of the ionic absorption probably had a relevant importance. An increase in the availability of Ca2+ at the root zone has been shown to ameliorate the detrimental effects of salinity stress in most species (Lynch and La¨uchli, 1985; Cramer, 2002). Based on recent works in olive trees (Melgar et al., 2006; Tattini and Traversi, 2008), Ca2+ in the irrigation water is thought
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Table 5 Effect of salinity and irrigation dose on fruit size (g). Irrigation treatment EC (dS m 1) 0.5 5 10 Significanceb Short irrigation Long irrigation Significance CVc (%) a b c
1998
1999
Fruit size Salinity 5.47 2.91 5.74 3.19 5.19 2.90 N.S. N.S. Irrigation dose 5.53 3.04 5.39 2.96 N.S. N.S. 15.5 22.4
2000
2001
2002
2003
2004
2.84 2.83 2.68 N.S.
3.13 3.30 2.96 N.S.
4.44 4.53 4.25 N.S.
3.06 3.07 3.10 N.S.
3.80 3.83 3.66 N.S.
2.66 2.93 N.S. 19.5
3.22 3.04 N.S. 18.5
4.20 4.61 N.S. 12.7
3.17 2.98 N.S. 9.5
3.70 3.83 N.S. 9.8
2005a
2006
No available data for years 2005–2006. N.S. indicates non-significant differences. Each factor was studied separately as no interaction was observed between both factors. Coefficient of variation.
Table 6 Effect of salinity and irrigation dose on oil yield (% FW). Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance CV (%)b
1998
1999
Oil yield Salinity 18.5 27.3 19.0 27.7 19.9 27.6 N.S. N.S. Irrigation dose 19.2 27.3 19.0 27.8 N.S. N.S. 6.3 5.0
2000
2001
2002
2003
2004
2005
2006
29.1 30.0 30.3 N.S.
26.7 27.3 28.7 L**
24.0 24.7 26.9 L***
28.8 29.5 31.0 L**
22.6 24.1 25.0 L**
23.4 24.7 24.5 N.S.
17.2 17.4 18.5 N.S.
29.5 30.1 N.S. 2.8
27.4 27.7 N.S. 2.0
25.0 25.4 N.S. 1.8
29.8 29.7 N.S. 2.3
23.7 24.1 N.S. 6.6
24.3 24.1 N.S 7.5
18.0 17.4 N.S. 6.9
a N.S., ** and *** indicate non-significant differences, significant differences at P 0.01 and significant differences at P 0.001, respectively; L indicates linear response. Each factor was studied separately as no interaction was observed between both factors. b Coefficient of variation.
to decrease Na+ uptake and transport to the shoot. Leaf Cl concentration did not reach toxic levels in any of the treatments either. In olive, Cl uptake and transport to the shoot is lower than Na+ (Bongi and Loreto, 1989; Bartolini et al., 1991; Tattini et al., 1992) and does not cause decrease in photosynthesis or growth if Cl concentration in water tissues is lower than 80 mM (Bongi and Loreto, 1989). Nutrient imbalances are frequently observed in plants under saline stress. The excessive concentration of an element can cause a
decrease in foliar concentration of another one, even reaching deficient levels, such as the induced K+ deficiency by Na+ excess, or the decrease of NO3 uptake as a consequence of a Cl excessive content (Lea-Cox and Syvertsen, 1993). Although low leaf K+ and N contents were observed in some years, they were not a consequence of saline ions because their concentration did not change between saline and control treatments. Leaf water content did not change as a consequence of salinity or the amount of water applied. Olive tree is a drought tolerant
Table 7 Effect of salinity and irrigation dose on pulp:stone ratio. Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea Short irrigation Long irrigation Significance 0.5 Short irrigation 0.5 Long irrigation 5 Short irrigation 5 Long irrigation 10 Short irrigation 10 Long irrigation CV (%)b a
*
1998
1999
Pulp:stone Salinity 4.6 4.0 5.0 4.4 4.4 4.2 N.S. N.S. Irrigation dose 4.8 4.2 4.5 4.2 N.S. N.S. Salinity irrigation dose
11.5
15.3
2000
2001
2002
2003
3.5 3.6 3.3 N.S.
4.7 4.9 4.5 N.S.
6.0 6.1 6.2 N.S.
3.4 3.6 N.S.
4.7 4.6 N.S.
5.8 6.4
19.1
16.7
*
10.4
2005
2006
4.7 4.9 4.7 N.S.
5.0 4.7 4.8 N.S.
3.9 3.8 4.1 N.S.
4.6 4.7 N.S.
4.9 4.8 N.S.
3.8 4.1 N.S.
7.6
9.9
7.4
2004
5.1 5.8 5.2 5.5 5.5 5.0 5.9
ab a ab ab ab b
N.S. and indicate non-significant differences and significant differences at P 0.05, respectively; in the interaction salinity irrigation dose, means followed by a different lower-case letters indicate significant differences at P 0.05 by Tukey’s test (n = 5). b Coefficient of variation.
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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Table 8 Na+ and Cl content in fruit during 8 experimental years (1999–2006). Irrigation treatment EC (dS m 1) 0.5 5 10 Significancea
1998
1999
2000
2001
2002
2003
2004
2005
2006
0.18 0.19 0.13 N.S.
0.22 0.28 0.30 N.S.
0.19 0.20 0.23 N.S.
0.14 0.15 0.12 N.S.
0.18 0.17 0.22 N.S.
0.27 0.25 0.18 N.S.
0.43 0.44 0.57 N.S.
0.29 0.28 0.31 N.S.
0.17 0.17 N.S. 16.9
0.27 0.27 N.S. 31.3
0.24 0.18 N.S. 18.2
0.13 0.15 N.S. 16.7
0.18 0.18 N.S. 7.1
0.25 0.22 N.S. 26.6
0.43 0.53 N.S. 30.0
0.30 0.28 N.S. 10.1
0.28 0.33 0.35 N.S.
0.53 0.66 0.75 N.S.
0.45 0.57 0.58 N.S.
0.50 0.53 0.53 N.S.
0.25 0.30 0.27 Q**
0.37 0.43 0.46 L*
0.10 0.11 0.11 N.S.
0.21 0.21 0.23 N.S.
0.31 0.33 N.S. 10.1
0.58 0.71 N.S. 21.2
0.56 0.51 N.S. 15.4
0.47 0.57 N.S. 12.2
0.26 0.29
0.41 0.43 N.S. 3.2
0.11 0.11 N.S. 15.7
0.21 0.23 N.S. 14.2
Na+ Salinity
Irrigation dose Short irrigation Long irrigation Significance CV (%)b EC (dS m 1) 0.5 5 10 Significance
Cl Salinity
Irrigation dose Short irrigation Long irrigation Significance CV (%)
*
5.8
a N.S., * and ** indicate non-significant differences, significant differences at P 0.05 and significant differences at P 0.01, respectively; L and Q indicate linear and quadratic response, respectively. Each factor was studied separately as no interaction was observed between both factors. b Coefficient of variation.
species and its leaves can reach extremely low values of water content before loosing turgency (Larsen et al., 1989). A higher salt concentration in the external solution causes a decrease in leaf water content and higher water contents are associated with higher salt tolerance. Differences between months or year are thought to be due to differences in seasonal rainfall. It has been generally reported that a significant yield reduction occurs in olives cultivated under high saline conditions (values of EC in the irrigation water higher than 7.5 dS m 1, Klein et al., 1992; Gucci and Tattini, 1997; Wiesman et al., 2004) in comparison with control conditions. However, existing data with lower values are contradictory (Bouaziz, 1990; Klein et al., 1992; Chartzoulakis, 2005). Results obtained in this study showed no differences in annual or accumulated yield among treatments, as it was also reported by Bouaziz (1990) and Weissbein et al. (2008), both experiments were carried out under field conditions. The lack of alternate bearing between 1999 and 2006 is also remarkable. Low yield was recorded only in the first year (1998) and it was a consequence of an infection of Spilocaea oleagina. This absence of fluctuations is not due to continuous low yields and/or lack of high yields as a consequence of salt stress, because there were no differences in yield between saline and control treatments in any of the years studied. Saline irrigation did not cause changes in any of the growth parameters measured: shoot length, leaf area or specific leaf area. Olive tree is an alternate-bearing species that usually shows low shoot growth in ‘‘on’’ years, which limits, at the same time, the number of nodes and potential flower buds. The results from this experiment show that, at the same time there were no changes in yield, differences in shoot length have not been detected between different years. However, shoot growth was lower than expected for an adult and irrigated olive grove. This could be partially attributed to the north-oriented slope of the grove and the shady conditions, which could cause a shorter shoot growth than expected, limiting high yield in ‘‘on’’ years. Salinity did not affect fruit characteristics like fruit size or pulp:stone ratio. Although some authors reported no clear patterns of oil accumulation in response to irrigation with saline water (Weissbein et al., 2008, EC in the irrigation water of 4.2 dS m 1), oil
yield was affected by salts in some years of our experiment. A slight trend of increase of oil yield with the highest EC in the irrigation water was observed during the first 3 years, confirming a linear response and statistical differences during the rest of the years. However, there were no differences when fruits from the rain-fed trees were compared with saline irrigated ones. Probably, the absence of differences during the first 3 years is due to the higher water doses applied, more than the lack of effect of saline irrigation, because it was since the fourth year when the irrigation doses began to be controlled by the humidity probes and the amount of applied water was reduced. Water stress has been documented to have the largest effect on fruit development and oil content (Lavee et al., 1990; Tombesi, 1994) but references are contradictory on the effect of salinity and more research on this topic is needed. Fruit extraction content of any nutrient was not affected by salinity, but Cl content between 1998 and 2002 showed a trend of accumulation in fruits of saline treatments. Differences appeared in 2 years of the experiment, with higher contents for the higher EC in the irrigation water. Fruit from rain-fed trees showed lower Cl contents than saline treatments and even than control treatments in some of the years. It was probably because Cl uptake and high mobility are closely linked to uptake fluxes and water movement inside the plant (White and Broadley, 2001). Considering the previous results, the absence of effects in the trees after 9 years of experiment is thought to be a consequence of the following factors: - Plant material: we used mature trees of cv. Picual, considered as a salt tolerant (Marı´n et al., 1995). As it has been previously said, tolerant genotypes have a higher capacity of excluding the toxic ions than sensitive ones (Gucci and Tattini, 1997) and it reduces Na+ concentration in the leaves. - Calcium: Ca2+ supply in the irrigation water probably had a positive effect protecting the cell wall and the plasmatic membrane and regulating the selectivity of ionic uptake (Melgar et al., 2006; Tattini and Traversi, 2008). This explains, at least in part, a reduction in uptake and transport of Na+ to the shoot.
J.C. Melgar et al. / Agricultural Water Management 96 (2009) 1105–1113
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