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Amelioration of salt stress by irrigation management in pepper plants grown in coconut coir dust
Agricultural Water Management 97 (2010) 1695–1702
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Amelioration of salt stress by irrigation management in pepper plants grown in coconut coir dust J.S. Rubio ∗ , F. Rubio, V. Martínez, F. García-Sánchez Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura, CSIC, Apdo. 164, Espinardo, Murcia, Spain
a r t i c l e
i n f o
Article history: Received 23 November 2009 Accepted 28 May 2010 Available online 23 June 2010 Keywords: Capsicum annuum L. Irrigation schedule Fruit yield Seasonal fruit quality Drainage solution
a b s t r a c t A long-term greenhouse experiment was conducted to study the effects of irrigation frequency and salinity on pepper fruit yield and quality in crops growing in coconut coir. Two salinity levels (4 mM NaCl, 2.6 dS m−1 and 24 mM NaCl, 4.6 dS m−1 ) were combined with four irrigation treatments (one irrigation event every two days (0.5), one irrigation event per day (1), four irrigation events per day (4), and eight irrigation events per day (8)) in a 2 × 4 factorial combination. The effect on fruit quality was evaluated at the early and late harvest seasons, corresponding with two different periods of fruit production (May and July). We found that above-ground total biomass and marketable fruit yield decreased in the salinized treatments. When salinized (24 mM NaCl) nutrient solution (NS) was applied, increasing the number of irrigation events to eight per day resulted in a decrease in the incidence of blossom-end rot and a corresponding increase in the marketable fruit yield. When control (4 mM NaCl) NS was applied, one irrigation event per day yielded as much marketable fruit as was produced with the highest irrigation frequency, and therefore increased water use efficiency, expressed as marketable fruit weight per L of NS applied. When NS containing 24 mM NaCl was used, there was an increase of Cl− but not Na+ in the leaf tissue, with this increase reaching its maximum in the treatment involving eight irrigation events per day. Salinity decreased the Ca2+ concentration of the fruit only in the early harvest season of production. However, increasing irrigation frequency consistently resulted in higher Ca2+ concentration in the fruit. The effects of salinity on the morphological and organoleptic properties of the fruit were more pronounced in the late harvest season. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The favourable growing conditions of the Mediterranean coastal region in Spain contrast sharply with the scarcity of good quality water, which forces growers to use water with moderate or high saline concentrations. It is well known that salinity severely limits the ability of irrigated land to maintain high levels of productivity (Ghassemi et al., 1995). At the same time, in the last decade, irrigation has become an even greater factor in production, as cultivation in soilless systems has increased as a consequence of the phase-out of methyl bromide as a soil fumigant, the increase in urban areas, and the high prices of arable land. For these reasons, it is important to know the best practices of irrigation management for horticultural crops under a soilless system watered with and without saline water. In examining such practices, little attention has been paid to the effect of using organic substrates like coconut coir dust, which is
∗ Corresponding author. Present address: University of California at Davis, Department of Plant Science, Asmundson Hall, 214 Davis, 95616, CA, United States. Tel.: +1 530 752 7482; fax: +1 530 752 9659. E-mail address: [email protected] (J.S. Rubio). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.05.026
biodegradable and environmentally friendly compared with other inert substrates. Sweet pepper, one of the main horticultural crops in Spain, is salt-sensitive, with salinity affecting yield by decreasing the fruit weight and increasing the number of fruits affected by blossomend rot (Rubio et al., 2009). Long-term salt stress conditions also decrease vegetative growth, specifically shoot growth, in pepper plants (De Pascale et al., 2003). As part of any irrigation strategy, the impact of water salinity must be accounted for in two areas: (a) the frequency of watering and (b) the quantity of nutrient solution applied in each irrigation event (Dorais et al., 2001). In a closedcycle, soilless system, high irrigation frequency can mitigate the deleterious effects of salinity, perhaps because the high drainage fractions delay the rate of salt accumulation in the root zone (Savvas et al., 2007). However, in soil-grown crops, high irrigation frequency does not mitigate the salt effect on fruit yield (Assouline et al., 2006). Given the relative lack of investigation into a substrate of coconut coir dust might influence the effects of salinity on fruit production, this research was undertaken with the aim of studying the effects of irrigation frequency on fruit production in pepper plants grown in coconut coir dust and irrigated using water of dif-
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fering qualities. We developed a novel irrigation strategy in which the amount of nutrient solution (NS) is adjusted to keep the electrical conductivity of the drainage solution (ECDS ) at 120% of the EC of the supplied nutrient solution (ECNS ). In this experiment, we used coconut coir dust as the growth medium because it is an organic substrate of high cation exchange capacity and high available water capacity (Sahin et al., 2002; Alarcon and Murcia, 2000), and is therefore suitable for a range of irrigation schedules. Pepper was chosen as it is characterized by long maturation periods and can be harvested several times during its growth cycle. This characteristic allowed us to examine the effects of the treatments on fruit quality at two different harvest seasons: early (fruits from nodes 2 and 3) and late (fruits from nodes 9 to 11). 2. Materials and methods 2.1. Plant growth conditions The experiment was carried out in a polycarbonate greenhouse (600 m2 ) in Santomera (Murcia, Spain) during the winter–summer season of 2004. Seedlings of pepper (Capsicum annuum L. cv. Somontano) were obtained from a commercial nursery and transplanted (21 January 2004) in 40 L (15 cm × 18 cm × 120 cm) coconut bags (cocopeat, Projar, Valencia, Spain) with an available water capacity of 27.4% (easily available water plus buffering water capacity). Three plants per bag and four bags per row resulting in a total of 12 plants per row were placed in single rows with spacing of 1.2 m between rows and 0.33 m between plants in the row. There were 4 rows per treatment. The plant population density was 2.5 plants m−2 and the plants were pruned to form three main stems. Two extra rows before and after the first and last experimental rows were planted to avoid border effects. The plants were cultivated for a period of 188 days. The greenhouse was equipped with a pad-and-fan and a fogging system for the control of temperature and humidity. Fertigation was carried out by an automatic drip irrigation system with three emitters (3 L h−1 ) placed in each
coconut bag. All climatic data inside the greenhouse were recorded by computer every 4 min. Irradiance was measured by a pyranometer (CM14 Kipp & Zonen, Delft, Holland). The day-time temperature was maintained at levels lower than 30 ◦ C and the night-time temperature was never lower than 10 ◦ C. Variations in relative humidity, air temperature, irradiance, and vapor pressure deficit, both inside and outside the greenhouse, were measured on three representative days: establishment of the crop (10 February 2004), start of fruit picking (30 April 2004), and the final harvest (19 July 2004) (see Fig. 1). The drainage solution (DS) was collected from four substrate bags per treatment (one per row). The DS from these four bags was collected and the volume as well as the EC was measured in real-time with a tipping spoon sensor and a conductivity probe (HI7635, Hanna, Quebec, Canada), respectively. Data from the tipping spoon sensor and conductivity probe were recorded with a PC. Drainage percentage (ratio between volume of DS and volume of NS applied) and water use efficiency (WUE; g of fresh marketable fruit per plant and per L of NS applied) were calculated from these measurements. 2.2. Salinity and irrigation treatments The nutrient solutions were prepared using water from the Tajo-Segura aqueduct (pre-fertilizer water quality: pH, 8.1; EC, 1.22 dS m−1 ; HCO3 , 1.05 mM; SO4 − , 4.73; Ca2+ , 2.4 mM; K+ , 0.04 mM; Cl− , 3.57 mM; Na+ , 4.2 mM) mixed with commercial fertilizers, such as potassium nitrate, calcium nitrate, potassium dihydrogen phosphate, and nitric acid for pH control. The concentration of macronutrients (mM) and micronutrients (mg L−1 ) in the standard nutrient solution (EC 2.6 dS m−1 ) was as follows: (macronutrients) NO3 − , 14; H2 PO4 − , 1.5; SO4 2− , 4.73; Ca2+ , 4.7; K+ , 4.85; Mg2+ , 1.95; Cl− , 3.57; Na+ , 4.2; and (micronutrients, in mg L−1 ) Fe, 1.8; Mn, 0.7; Zn, 0.12; B, 0.15; Cu, 0.07; Mo, 0.05. The coconut bags were saturated with the control NS the day before the seedlings were transplanted and then left without irrigation for one week.
Fig. 1. Diurnal pattern in humidity (H), temperature (T), irradiance (I), and vapor pressure deficit (VPD) inside (in) and outside (out) of the greenhouse during three different days of the culture cycle; establishment of the crop (20 DAT, 10 February 2004), start of fruit picking (100 DAT, 30 April 2004), and final harvest (180 DAT, 19 July 2004). At the foot of each figure appears the average value of each climate parameter for that day. The exterior irradiance was not collected at 20 DAT.
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Twenty-three days after transplanting, the salt treatment was started, by adding 20 mM NaCl to the NS, resulting in an EC of 4.6 dS m−1 (salinity treatments). Using a computer, four irrigation treatments were scheduled; one irrigation event every two days (0.5), applied at 13:00 h; one irrigation event per day (1), applied at 13:00 h; four irrigation events per day (4); and eight irrigation events per day (8). The timetable of the four and eight irrigation events was adjusted depending on duration of daylight. During the first 50 days of the experiment, the amount of NS applied was 0.5 L plant−1 day−1 . After this period, in every salt × irrigation treatment, the amount of NS applied per plant and per day was calculated as a function of the ECDS measured in the irrigation event at 13:00 h the previous day, as follows: When the ECDS registered at the end of this irrigation event was higher than 120% of the ECNS (3.1 and 5.5 dS m−1 for the control and salinized treatments, respectively), the amount of NS applied per plant in the irrigation events of the following day was increased by 0.5 L per plant. This level was achieved by increasing the amount of NS by 500 ml for the 0.5 and 1 irrigation events per day and by 125 and 62.5 ml for the 4 and 8 irrigation events per day, respectively. The added amounts lowered the ECDS below the 120% level for the ECNS . 2.3. Yield parameters and plant growth Fruits were harvested weekly at the red mature stage, starting 114 days after transplanting until the end of the experiment. To calculate total fruit biomass and marketable fruit yield, all the fruits from six plants per row were counted and weighed. They were considered to be marketable fruits only if they did not show symptoms of blossom-end rot and if their fresh weight was higher than 100 g. At the end of the experiment (on 23 July) the vegetative abovegrown biomass (leaves and stem) from six plants per block was measured. 2.4. Mineral analysis in fruit and leaf tissue The Ca2+ concentration of mature green fruits was determined in eight replicate plants, using three fruits from each replicate. Leaf nutrient analysis (using the fifth leaf from the top) from three plants per block and treatment was carried out 149 days after transplanting (DAT), and Na+ , Cl− , Ca2+ , K+ , Mg2+ , Fe, Mn, Zn, and Cu concentrations were determined. The fruit and leaf tissues were washed with distilled water, dried in a ventilated oven at 65 ◦ C to constant weight. The concentrations of the cations and micronutrients were determined after digestion with HNO3 –HClO4 (2:1) by inductively coupled plasma spectrometry (Iris Intrepid II, Thermo Electron Corporation, Franklin, USA). The concentration of Cl− was determined after extraction with distilled water, using a silver ion titration chloridometer (HBI Chloridometer; Haake Buchler, Sandle Brook, NJ, USA).
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sured by titrating the juice of the peppers with 0.1 N NaOH to a pH of 8.1. 2.6. Statistical analysis Data were subjected to analysis of variance using a two-way ANOVA (SPSS statistical package, Chicago, IL, USA) with irrigation treatment and salt treatment as main factors. Treatment means were separated using Tukey’s multiple range test (P < 0.05). 3. Results 3.1. Electrical conductivity and water management The total volume of NS applied into the root zone and drained from the root zone increased significantly when NaCl concentration in the NS and the number of irrigation events per day were increased (Table 1). Thus, the highest values for these parameters were reached when the salinized NS was used with an application of eight irrigation events per day. The drainage percentage increased significantly when the NaCl concentration of the NS was increased, but it was not affected by the irrigation schedule. The WUE was higher for the non-salinized nutrient solutions regardless of the irrigation schedule. In both salinized and non-salinized conditions the highest WUE observed was for the 0.5 irrigation treatment. In the salinity treatments there were no significant differences among the one, four and eight irrigation treatments; however, in the non-salinity treatment, the WUE was significantly higher in the treatment with one irrigation event than in that with eight irrigation events. The highest ECDS registered during the growing cycle was found in plants irrigated every other day in both salt treatments, with averages of 4.68 and 7.23 dS m−1 in the control and salinized treatments, respectively (Fig. 2). In the salinized treatments, the irrigation schedule of 8 events per day produced the lowest ECDS during the whole growing cycle when compared with other irrigation schedules. By contrast, in the non-salinity treatments, there were no differences among the one, four and eight irrigation treatments. The differences in the ECDS between the control and salinity treatments were mainly due to differences in Na+ and Cl− concentrations in the drainage, and not affected by the rest of the nutrients (data not shown).
2.5. Fruit quality parameters. Twenty-four fruits per treatment were harvested at random, at the mature red stage, in the early (fruits from nodes 2 and 3) and late (fruits from nodes 9 to 11) harvest seasons. The fruit firmness was immediately measured at three points on the equatorial line of each fruit, using an 8 mm tip penetrometer (Effegi penetrometer, Italy). The fruits were then cut into two halves, and the pulp thickness was measured at two different points in each half. One half of the fruit was used to obtain the percentage of dry matter and the other half of the edible portion (pericarp) was divided into four lots (six fruits each) for analytical measurements. This portion was homogenized and aliquots were analyzed for soluble solid content (◦ Brix), pH, and titratable acidity (TA). Soluble solids (◦ Brix) were estimated at 20 ◦ C by a refractometer (Atago, Tokyo, Japan) and acidity was mea-
Fig. 2. Course of electrical conductivity (EC) in the drainage solutions in a pepper crop grown in coconut coir dust as influenced by NaCl salinity in the nutrient solution and irrigation frequency. For the 0.5 and 1 irrigation treatments the values show the maximum EC reached during an individual irrigation event. In the irrigation treatments with 4 and 8 events per day, each point shows the average of the maximum EC of all drainage events performed that day.
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Table 1 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on total amount of applied and drainaged nutrient solution per plant during a cropping period of 188 days, drainage percentage (DP), and water use efficiency (WUE; weight of marketable fresh fruit per liter of applied nutrient solution). Applied NS (L plant−1 )
Drainaged NS (L plant−1 )
DP (%)
WUE (g L−1 plant−1 )
Control Salinized
303 367
132 205
43.3 55.6
11.21 6.50
0.5 1 4 8
219d 336c 378b 407a
103c 170b 193ab 209a
46.7 49.5 50.7 51.1
11.92a 8.42c 7.83c 8.05c
196 298 346 371 242 374 409 442
80 122 159 168 126 217 226 250
40.8 40.9 46.0 45.5 52.5 58.1 55.3 56.6
16.20a 11.18b 10.01cb 9.60cd 8.56d 6.27e 6.00e 6.80e
NaCl
***
***
*
**
Irrigation schedule
**
***
ns
*
NaCl × Irrigation schedule
ns
ns
ns
*
Main effects NaCl Irrigation schedule
Interaction NaCl × Irrigation schedule NaCl Irrigation schedule 0.5 Control 1 4 8 0.5 Salinized 1 4 8
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Values are means of four replications (coconut bags with three plants for bag). * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
3.2. Plant growth and marketable yield components At the end of the experimental period (188 DAT), the salinity treatment decreased both the above-ground vegetative and fruit biomasses to about 20% of that obtained in the control treatment,
regardless of the irrigation treatment (Table 2). Vegetative biomass increased significantly, by about 20%, when the number of irrigation events per day was raised from 0.5 to 1. However, no significant differences were observed in the biomass among the one, four and eight irrigation event treatments. Fruit biomass increased sig-
Table 2 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on above-ground vegetative biomass, total fruit biomass and marketable fruit yield components. Marketable fruit yield
Above-ground vegetative biomass (kg plant−1 )
Total fruit biomass (kg plant−1 )
Control Salinized
1.64 1.30
3.60 2.92
3.38 2.42
0.5 1 4 8
1.23b 1.53a 1.54a 1.57a
2.85c 3.23b 3.37b 3.75a
2.62c 2.83b 2.96b 3.28a
196b 204ab 204ab 210a
13.4b 13.9ab 14.5ab 15.7a
1.34 1.73 1.63 1.84 1.12 1.32 1.46 1.32
3.20 3.60 3.80 4.12 2.50 2.86 2.94 3.41
3.17b 3.31ab 3.47a 3.56a 2.07d 2.35cd 2.46c 3.01b
201c 209b 211b 222a 192c 199c 197c 197c
15.9ab 16.0a 16.5a 16.1a 10.9c 11.7c 12.5c 15.3b
NaCl
***
***
***
**
**
Irrigation schedule
**
***
***
*
*
NaCl × Irrigation schedule
ns
ns
*
*
*
Main effects NaCl Irrigation schedule
Interaction salt × Irrigation schedule NaCl Irrigation schedule 0.5 Control 1 4 8 0.5 Salinized 1 4 8
Total yield (kg plant−1 )
Mean fruit weight (g) 211 196
No. of fruits per plant 16.1 12.3
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Values are means of 24 plants. * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
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Table 3 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on leaf mineral concentration at 149 days after transplanting. Na+
Cl−
K+
Ca2+
Mg2+
mg gdw −1 Main effects NaCl
Fe
Zn
Mn
Cu
g gdw −1
Control Salinized
0.68 0.72
12.9 58.0
55.8 54.9
46.5 42.6
11.9 12.0
113 112
61.1 74.5
225 319
13.4 17.2
0.5 1 4 8
0.63b 0.69b 0.54b 0.95a
31.0b 26.8b 30.9b 53.2a
55.6 54.3 54.8 56.6
42.2 44.7 45.2 46.0
12.6 12.5 11.6 11.2
94c 114b 112b 131a
44.1c 65.0b 87.9a 74.4ab
285 245 291 268
13.2 15.8 16.6 15.7
0.64 0.78 0.58 0.73 0.62 0.60 0.49 1.16
11.0 12.6 9.7 18.3 51.5 41.1 52.2 88.9
57.3 54.1 54.5 57.2 53.9 54.5 55.0 56.0
43.9 48.1 47.9 46.2 40.5 41.2 42.5 46
12.8 12.3 11.3 11.0 12.3 12.7 11.8 11.3
99 111 102 140 88 116 121 121
43.3 53.2 77.3 70.7 44.8 76.7 98.4 78.0
241 170 256 234 328 319 325 302
13.5 13.6 12.7 13.8 12.9 18.2 20.4 17.5
NaCl
ns
***
ns
ns
ns
ns
*
**
**
Irrigation schedule
**
***
ns
ns
ns
*
***
ns
ns
NaCl × Irrigation schedule
ns
ns
ns
ns
ns
ns
ns
ns
ns
Irrigation schedule
Interaction NaCl × Irrigation schedule NaCl Irrigation schedule 0.5 Control 1 4 8 0.5 Salinized 1 4 8
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Values are means of 12 samples. * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
nificantly as the number of irrigation events per day increased, although there were no significant differences between treatments of one and four irrigation events. The effect of salinity and irrigation frequency can be seen when examining the differences in mean fruit weight, but not in the number of fruits per plant (data not shown). The effect of the irrigation schedule on the marketable fruit yield and its components depended on the salt level in the NS (Table 2). Using control NS, the treatments of 4 and 8 irrigation events produced higher fruit yields than that of the 0.5 irrigation event. The mean fruit weight increased significantly as the irrigation frequency increased, and no significant differences were found in the number of fruits per plant. Using salinized NS, the marketable fruit yield increased significantly when the number of irrigation events per day was increased; no differences were found in the mean fruit weight; however, the number of fruits per plant increased only when the number of irrigations increased from four to eight irrigation events per day.
3.3. Leaf mineral status Leaf concentrations of Cl− but not of Na+ increased when the NaCl concentration was increased in the NS (Table 3). However, regardless of the NaCl concentration in the NS, leaf concentrations of both Na+ and Cl− were significantly higher in plants treated under the regimen of eight irrigation events per day than in those treated under the other regimens. The micronutrients Zn, Mn, and Cu increased significantly in leaves from plants irrigated with high NaCl concentration relative to plants irrigated with non-salinized nutrient solutions; Fe and Zn levels increased significantly when the number of irrigation events per day was increased. The salt and irrigation treatments did not affect the leaf concentrations of K+ , Ca2+ , and Mg2+ .
3.4. Seasonal effect on marketable yield and fruit quality The pattern of fruit yield was similar in all treatments and was characterized by two harvest seasons, with fruits from nodes 1 to 6 in the early season, and fruits from nodes 7 to 20 in the late season (data not shown). Across all treatments, the yield in the early harvest season was slightly higher than 50% of the total yield. The highest fruit yields per node were observed in the second and third nodes. In the late harvest season the highest fruit yields were reached in nodes 9–12. The presence of NaCl in the NS affected the morphology of the fruits harvested in the late harvest season (nodes 7–20) but not in the early harvest season (nodes 1–6; Fig. 3). In the late season the means in fruit weight, hardness, and pulp thickness decreased, and the percentage of dry matter increased in fruits from salinized plants compared with fruits produced by control plants. The mean fruit weight, in both harvest seasons, tended to increase along with the number of irrigation events per day, although the only significant differences were found between the 0.5 and the 8 irrigation treatments. In the late season hardness was higher in fruits watered 4 times per day while pulp thickness was higher in fruits water 8 times per day. In percentage of dry matter in the early period (nodes 1–6), there was a significant interaction between number of irrigation events and salt concentrations in the NS. Dry matter tended to decrease with an increase in the number of irrigation events, except in the case of the non-salinized NS, where it tended to increase up to the four irrigation event treatment. It is noteworthy that mean fruit weight and percentage of dry matter were lower in the late harvest season than in the early harvest season. In both periods of production, irrigation with salinized NS significantly decreased the fruit juice pH and increased its TA, regardless of the irrigation schedule (Fig. 4). The total soluble solids also increased significantly in the salinity treatment but only in fruits from the early harvest season. Fruits from the early harvest period
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Fig. 4. Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4 and 8) on the fruit organoleptic parameters of fruits harvested in two seasons; nodes 1–6 correspond with the early harvest season and the nodes 7–20 correspond with the late harvest season. *, **, and *** indicate significant differences at P < 0.05, 0.01, and 0.001, respectively; ns indicates non-significant differences. Different upper case letters indicate significant differences (P < 0.05) according to Tukey’s multiple range tests between irrigation treatments, regardless of the salt treatment. Each datum point is a mean of 4 replicates ± SE (each replicate contained 6 fruits).
Fig. 3. Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4 and 8) on the fruit morphological parameters of fruits harvested in two seasons; nodes 1–6 correspond with the early harvest season and the nodes 7–20 correspond with the late harvest season. *, **, and *** indicate significant differences at P < 0.05, 0.01, and 0.001, respectively; ns indicates non-significant differences. Means with different lower case letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Different upper case letters indicate significant differences (P < 0.05) between irrigation treatments, regardless of the salt treatment. Each datum point is a mean of 24 fruits ± SE.
had a higher content of total soluble solids (TSS), pH and TA than those from the late harvest period. 3.5. Blossom-end rot incidence and fruit Ca2+ concentration Throughout both harvest seasons a high NaCl concentration in the NS, regardless of the irrigation treatments, resulted in a higher incidence of fruits with blossom-end rot (BER) (Table 4). In treatments with salinized NS, the irrigation schedule showed no effect on BER incidence in the late harvest period. In the early harvest period, however, the application of eight irrigation events per day significantly decreased the number of fruits with BER relative to the rest of irritation treatments. The incidence of BER increased in the fruits harvested during the late harvest season compared with the fruits harvested during the early harvest season. In the early harvest season but not in the later season, fruit Ca2+ concentration decreased with high NaCl concentration in the NS, regardless of the irrigation schedule. Compared with the other irrigation schedules, the eight irrigation events per day regimen significantly increased the fruit Ca2+ concentration in both seasons without regard to NS salinity level.
4. Discussion The results of this experiment show that high irrigation frequencies combined with the application of an adjusted volume of NS could be a good strategy for managing water usage in growing pepper plants under saline conditions. The optimum volume of NS applied can be calculated based on the amount of water applied in every irrigation event and using the ECDS data in the diurnal period of high evaporative demand. This strategy was arrived at based on data obtained under the regimen of eight irrigation events per day, which produced the highest total fruit biomass and fruit marketable yield (Table 2). In the case of non-salinized conditions, the marketable fruit yield (kg per plant) was similar for the 1, 4 and 8 irrigation treatments. However, because the 1 irrigation event treatment showed the highest WUE under our experimental conditions, the regimen involving 1 irrigation event per day can be considered the best water management practice in the absence of salinity. It is well known that pepper plants are very sensitive to saline water (Maas and Hoffman, 1977; Sonneveld and Vanderburg, 1991). Pepper plants under saline conditions are not able to adjust osmotically to maintain adequate water in their leaves, contributing to reduced yield and growth (Navarro et al., 2002). In addition to the osmotic effect, the increase in Na+ and Cl− in the leaves causes additional damage (Lycoskoufis et al., 2005). In our study, salt treatments reduced the above-ground (shoot and fruit) fresh biomass when compared with non-salt treatments, most likely due to the toxicity produced by Cl− as well as to the osmotic effect. However, in irrigation treatments on the salinized plants, high leaf concentrations of Na+ and Cl− did not correlate with reductions in fruit yield, as the irrigation regimen involving eight events per day had the
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Table 4 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on blossom-end rot (BER) incidence and fruit Ca2+ concentration at early (E) and late (L) harvest season. Early and late harvest season correspond to fruits harvested from nodes 1 to 6 and 7 to 10, respectively. Fruit Ca2+ concentration (mg gdw −1 )a
% BER E (1–6)
L (7–20)
E (1–6)
L (720)
Control Salinized
3.50 9.53
15.0 30.6
1.21 1.13
1.02 1.07
0.5 1 4 8
7.29a 6.55a 8.61a 3.60b
22.2 24.1 24.0 20.9
1.02b 1.10b 1.06b 1.48a
0.87b 1.07b 1.04b 1.20a
Irrigation schedule 0.5 1 4 8 0.5 1 4 8
3.54b 4.17b 3.47b 2.81b 10.97a 8.93a 13.78a 4.40b
13.4 15.3 17.3 14.2 31.1 32.9 30.8 27.6
1.09 1.18 1.05 1.50 0.95 1.02 1.07 1.47
0.90 1.08 0.98 1.13 0.84 1.06 1.10 1.27
NaCl
***
***
**
ns
Irrigation schedule
**
ns
**
**
NaCl × Irrigation schedule
*
ns
ns
ns
Main effects NaCl Irrigations schedule
Interaction NaCl × Irrigation schedule NaCl Control
Salinized
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. a The fruits used for tissue Ca2+ determination were green mature fruits without BER symptoms and were harvested between 40 and 43 days after anthesis. Values are means of 8 replicates, each containing 3 fruits. * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
highest fruit yield as well as the highest leaf Na+ and Cl− concentration. Thus, in this case, the osmotic effect of increased salinity appears to be more important than the toxic effect; additionally, eight irrigation events per day might have reduced the osmotic effect by not allowing excessive salt accumulation in the substrate in the interval between irrigation events, as shown by the lowest EC obtained in the DS. In addition to the osmotic effect, leaf water content and specific leaf area (data not shown) both decreased in plants watered every other day (0.5 event per day). It is possible that drought stress could have occurred in these plants, due to a longer period of time between irrigation events. It has been pointed out that in pepper plants drought stress severely restricts leaf and root water potentials, turgor potentials, osmotic potentials, and leaf gas exchange rates, which may directly inhibit leaf expansion (De Pascale et al., 2003). In addition, the higher leaf Na+ and Cl− concentrations observed in plants undergoing the 8 irrigation event treatments could be due to their higher leaf transpiration (Tester and Davenport, 2003; White and Broadley, 2001). Although we did not measure the leaf transpiration in this experiment, the data from Tables 1 and 2 support this hypothesis. The amount of water used per plant (volume applied minus volume drained) to obtain 1 kg of vegetative biomass was higher in the 8 irrigation event treatments (145 L kg−1 vegetative biomass) than in the 0.5, 1 and 4 irritation event treatments (103, 118 and 125 L kg−1 , respectively). Compared with the non-salinity condition, salinity decreased vegetative biomass and total fruit biomass and also increased the number of fruits with BER, further decreasing marketable yield. Nevertheless, the salt effect on the incidence of BER was mitigated in the treatment with the highest irrigation frequency. This positive effect of high irrigation frequencies could be a consequence of maintaining a low ECDS , which produced higher transpiration rates and therefore improved Ca2+ transport to the shoots. It is well known that BER incidence in pepper fruits occurs because of a reduction during the period of rapid fruit expansion in Ca2+ translo-
cation to the fruit tip, which can be caused by a decrease in water uptake by the roots under conditions of high salinity, drought, or low humidity, among others factors (Rubio et al., 2009; Ho and White, 2005; Marcelis and Ho, 1999). The harvest was characterized by two periods of maximal production. The first one occurred in May and beginning of June, from nodes 2 and 3, and the second in mid-July, from nodes 9 to 11. This is an irregular yield pattern known as flushing, common in greenhouse pepper crops (Heuvelink and Körner, 2001) and is promoted by the cyclic fluctuations in fruit sets (Marcelis and HofmanEijer, 1997). Fruit morphology—including mean fruit weight, hardness, pulp thickness, and dry matter—was affected by salinity during the late harvest season (July). Also, the mean fruit weight was severely reduced in the late harvest season in both the control and salinity treated plants. The effects of salinity in the root medium coupled with the adverse climatic conditions registered during this period (higher VPD) may be the main factors responsible for the observed changes in fruit appearance. It has been pointed out in studies on tomato plants that lowering VPD can mitigate the reduction in fruit volume by increasing xylem influx and decreasing fruit transpiration (Guichard et al., 2005), and subsequently reduce the negative effects on the morphology of the fruit. Given that, the differences observed in our study in fruit size between control and salinity treated plants in the late harvest season also explain the differences we observed in fruit hardness, pulp thickness, and percentage of dry matter. Contrary to expectations, the decrease in fruit size in the late harvest season was not accompanied by an increase in the percentage of dry matter and TSS. If only water transport to the fruit had been lower during this period, the TSS and percentage of dry matter should have increased, due to a “concentration effect”. However, TSS and percentage of the dry matter decreased or remained the same, which suggests that the climatic conditions during this period promoted a decrease in both water and solute transport to
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the fruit. However, the decrease in fruit size in the late season was not independent of the salt content in the NS. While the decrease in fruit size was higher in the salinity treated plants than in the control plants, the decrease in the percentage of dry matter was higher in the control plants than in the salinity treated plants. It is therefore probable that salinity decreased water transport to the fruits during this period. At the highest irrigation frequencies, the decrease in pH and the increase in acidity due to salinity seemed to be related to the accumulation of Cl− and Na+ in the fruit. These results agree with previous research (Reina-Sanchez et al., 2005; Del Amor et al., 2001). 5. Conclusions In sweet pepper crops grown in a soilless system based on coconut coir dust and watered with moderately saline water, a high irrigation frequency combined with regulation of the amount of NS applied, such that the EC of drainage is maintained below 120% of the EC of NS, could prove a good irrigation strategy by mitigating the negative effects of salinity on the total fruit biomass and marketable fruit yield. However, in non-saline conditions, the application of one irrigation event per day offers the best results in terms of water use efficiency. The deleterious effects of salinity in the marketable yield and fruit quality are more perceptible in the late harvest season, as high temperature and dry conditions may act synergistically with high salinity. Acknowledgments J.S. Rubio was a recipient of a FPU fellowship from Ministerio de Educación y Ciencia (Spain). This work was funded by the project AGR/18/FS/02 (Fundacion Séneca, CARM). The authors thank Mark T. Hoyer for the correction of the English in the manuscript. References Alarcon, A.L., Murcia, F., 2000. Cultivo en lana de roca. In: Alarcon, A.L. (Ed.), Tecnologia para cultivos de alto rendimiento. Novedades Agricolas, Murcia, Spain, pp. 245–253 (in Spanish). Assouline, S., Moller, M., Cohen, S., Ben-Hur, M., Grava, A., Narkis, K., Silber, A., 2006. Soil–plant system response to pulsed drip irrigation and salinity: bell pepper case study. Soil Science Society of America Journal 70, 1556–1568.
De Pascale, S., Ruggiero, C., Barbieri, G., Maggio, A., 2003. Physiological responses of pepper to salinity and drought. Journal of the American Society for Horticultural Science 128, 48–54. Del Amor, F.M., Martinez, V., Cerda, A., 2001. Salt tolerance of tomato plants as affected by stage of plant development. HortScience 36, 1260–1263. Dorais, M., Papadopoulos, A.P., Gosselin, A., 2001. Influence of electric conductivity management on greenhouse tomato yield and fruit quality. Agronomie 21, 367–383. Ghassemi, F., Jakeman, A.J., Nix, H.A., 1995. Salinisation of land and water resources: human causes, extent, management and case studies. Wallingford, Oxon, UK. Guichard, S., Gary, C., Leonardi, C., Bertin, N., 2005. Analysis of growth and water relations of tomato fruits in relation to air vapor pressure deficit and plant fruit load. Journal of Plant Growth Regulation 24, 201–213. Heuvelink, E., Körner, O., 2001. Parthenocarpic fruit growth reduces yield fluctuation and blossom-end rot in sweet pepper. Annals of Botany 88, 69–74. Ho, L.C., White, P.J., 2005. A cellular hypothesis for the induction of blossom-end rot in tomato fruit. Annals of Botany 95, 571–581. Lycoskoufis, I.H., Savvas, D., Mavrogianopoulos, G., 2005. Growth, gas exchange, and nutrient status in pepper (Capsicum annuum L.) grown in recirculating nutrient solution as affected by salinity imposed to half of the root system. Scientia Horticulturae 106, 147–161. Maas, E.V., Hoffman, G.J., 1977. Crop salt tolerance. Journal of the Irrigation and Drainage Division 103, 115–134. Marcelis, L.F.M., HofmanEijer, L.R.B., 1997. Effects of seed number on competition and dominance among fruits in Capsicum annuum L. Annals of Botany 79, 687–693. Marcelis, L.F.M., Ho, L.C., 1999. Blossom-end rot in relation to growth rate and calcium content in fruits of sweet pepper (Capsicum annuum L.). Journal of Experimental Botany 50, 357–363. Navarro, J.M., Garrido, C., Carvajal, M., Martinez, V., 2002. Yield and fruit quality of pepper plants under sulphate and chloride salinity. Journal of Horticultural Science and Biotechnology 77, 52–57. Reina-Sanchez, A., Romero-Aranda, R., Cuartero, J., 2005. Plant water uptake and water use efficiency of greenhouse tomato cultivars irrigated with saline water. Agricultural Water Management 78, 54–66. Rubio, J.S., Garcia-Sanchez, F., Rubio, F., Martinez, V., 2009. Yield, blossom-end rot incidence, and fruit qualty in pepper plants under moderate salinity are affected by K+ and Ca2+ fertilization. Scientia Horticulturae 119, 79–87. Sahin, U., Anapali, O., Ercisli, S., 2002. Physico-chemical and physical properties of some substrates used in horticultura. Gartenbauwissenschaft 67 (2), 55–60. Savvas, D., Stamati, E., Tsirogiannis, I.L., Mantzos, N., Barouchas, P.E., Katsoulas, N., Kittas, C., 2007. Interactions between salinity and irrigation frequency in greenhouse pepper grown in closed-cycle hydroponic systems. Agricultural Water Management 91, 102–111. Sonneveld, C., Vanderburg, A.M.M., 1991. Sodium-chloride salinity in fruit vegetable crops in soilless culture. Netherlands Journal of Agricultural Science 39, 115–122. Tester, M., Davenport, R., 2003. Na+ tolerance and Na+ transport in higher plants. Annals of Botany 91, 503–527. White, P.J., Broadley, M.R., 2001. Chloride in soils and its uptake and movement within the plant: A review. Annals of Botany 88, 967–988.
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Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat
Amelioration of salt stress by irrigation management in pepper plants grown in coconut coir dust J.S. Rubio ∗ , F. Rubio, V. Martínez, F. García-Sánchez Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura, CSIC, Apdo. 164, Espinardo, Murcia, Spain
a r t i c l e
i n f o
Article history: Received 23 November 2009 Accepted 28 May 2010 Available online 23 June 2010 Keywords: Capsicum annuum L. Irrigation schedule Fruit yield Seasonal fruit quality Drainage solution
a b s t r a c t A long-term greenhouse experiment was conducted to study the effects of irrigation frequency and salinity on pepper fruit yield and quality in crops growing in coconut coir. Two salinity levels (4 mM NaCl, 2.6 dS m−1 and 24 mM NaCl, 4.6 dS m−1 ) were combined with four irrigation treatments (one irrigation event every two days (0.5), one irrigation event per day (1), four irrigation events per day (4), and eight irrigation events per day (8)) in a 2 × 4 factorial combination. The effect on fruit quality was evaluated at the early and late harvest seasons, corresponding with two different periods of fruit production (May and July). We found that above-ground total biomass and marketable fruit yield decreased in the salinized treatments. When salinized (24 mM NaCl) nutrient solution (NS) was applied, increasing the number of irrigation events to eight per day resulted in a decrease in the incidence of blossom-end rot and a corresponding increase in the marketable fruit yield. When control (4 mM NaCl) NS was applied, one irrigation event per day yielded as much marketable fruit as was produced with the highest irrigation frequency, and therefore increased water use efficiency, expressed as marketable fruit weight per L of NS applied. When NS containing 24 mM NaCl was used, there was an increase of Cl− but not Na+ in the leaf tissue, with this increase reaching its maximum in the treatment involving eight irrigation events per day. Salinity decreased the Ca2+ concentration of the fruit only in the early harvest season of production. However, increasing irrigation frequency consistently resulted in higher Ca2+ concentration in the fruit. The effects of salinity on the morphological and organoleptic properties of the fruit were more pronounced in the late harvest season. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The favourable growing conditions of the Mediterranean coastal region in Spain contrast sharply with the scarcity of good quality water, which forces growers to use water with moderate or high saline concentrations. It is well known that salinity severely limits the ability of irrigated land to maintain high levels of productivity (Ghassemi et al., 1995). At the same time, in the last decade, irrigation has become an even greater factor in production, as cultivation in soilless systems has increased as a consequence of the phase-out of methyl bromide as a soil fumigant, the increase in urban areas, and the high prices of arable land. For these reasons, it is important to know the best practices of irrigation management for horticultural crops under a soilless system watered with and without saline water. In examining such practices, little attention has been paid to the effect of using organic substrates like coconut coir dust, which is
∗ Corresponding author. Present address: University of California at Davis, Department of Plant Science, Asmundson Hall, 214 Davis, 95616, CA, United States. Tel.: +1 530 752 7482; fax: +1 530 752 9659. E-mail address: [email protected] (J.S. Rubio). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.05.026
biodegradable and environmentally friendly compared with other inert substrates. Sweet pepper, one of the main horticultural crops in Spain, is salt-sensitive, with salinity affecting yield by decreasing the fruit weight and increasing the number of fruits affected by blossomend rot (Rubio et al., 2009). Long-term salt stress conditions also decrease vegetative growth, specifically shoot growth, in pepper plants (De Pascale et al., 2003). As part of any irrigation strategy, the impact of water salinity must be accounted for in two areas: (a) the frequency of watering and (b) the quantity of nutrient solution applied in each irrigation event (Dorais et al., 2001). In a closedcycle, soilless system, high irrigation frequency can mitigate the deleterious effects of salinity, perhaps because the high drainage fractions delay the rate of salt accumulation in the root zone (Savvas et al., 2007). However, in soil-grown crops, high irrigation frequency does not mitigate the salt effect on fruit yield (Assouline et al., 2006). Given the relative lack of investigation into a substrate of coconut coir dust might influence the effects of salinity on fruit production, this research was undertaken with the aim of studying the effects of irrigation frequency on fruit production in pepper plants grown in coconut coir dust and irrigated using water of dif-
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fering qualities. We developed a novel irrigation strategy in which the amount of nutrient solution (NS) is adjusted to keep the electrical conductivity of the drainage solution (ECDS ) at 120% of the EC of the supplied nutrient solution (ECNS ). In this experiment, we used coconut coir dust as the growth medium because it is an organic substrate of high cation exchange capacity and high available water capacity (Sahin et al., 2002; Alarcon and Murcia, 2000), and is therefore suitable for a range of irrigation schedules. Pepper was chosen as it is characterized by long maturation periods and can be harvested several times during its growth cycle. This characteristic allowed us to examine the effects of the treatments on fruit quality at two different harvest seasons: early (fruits from nodes 2 and 3) and late (fruits from nodes 9 to 11). 2. Materials and methods 2.1. Plant growth conditions The experiment was carried out in a polycarbonate greenhouse (600 m2 ) in Santomera (Murcia, Spain) during the winter–summer season of 2004. Seedlings of pepper (Capsicum annuum L. cv. Somontano) were obtained from a commercial nursery and transplanted (21 January 2004) in 40 L (15 cm × 18 cm × 120 cm) coconut bags (cocopeat, Projar, Valencia, Spain) with an available water capacity of 27.4% (easily available water plus buffering water capacity). Three plants per bag and four bags per row resulting in a total of 12 plants per row were placed in single rows with spacing of 1.2 m between rows and 0.33 m between plants in the row. There were 4 rows per treatment. The plant population density was 2.5 plants m−2 and the plants were pruned to form three main stems. Two extra rows before and after the first and last experimental rows were planted to avoid border effects. The plants were cultivated for a period of 188 days. The greenhouse was equipped with a pad-and-fan and a fogging system for the control of temperature and humidity. Fertigation was carried out by an automatic drip irrigation system with three emitters (3 L h−1 ) placed in each
coconut bag. All climatic data inside the greenhouse were recorded by computer every 4 min. Irradiance was measured by a pyranometer (CM14 Kipp & Zonen, Delft, Holland). The day-time temperature was maintained at levels lower than 30 ◦ C and the night-time temperature was never lower than 10 ◦ C. Variations in relative humidity, air temperature, irradiance, and vapor pressure deficit, both inside and outside the greenhouse, were measured on three representative days: establishment of the crop (10 February 2004), start of fruit picking (30 April 2004), and the final harvest (19 July 2004) (see Fig. 1). The drainage solution (DS) was collected from four substrate bags per treatment (one per row). The DS from these four bags was collected and the volume as well as the EC was measured in real-time with a tipping spoon sensor and a conductivity probe (HI7635, Hanna, Quebec, Canada), respectively. Data from the tipping spoon sensor and conductivity probe were recorded with a PC. Drainage percentage (ratio between volume of DS and volume of NS applied) and water use efficiency (WUE; g of fresh marketable fruit per plant and per L of NS applied) were calculated from these measurements. 2.2. Salinity and irrigation treatments The nutrient solutions were prepared using water from the Tajo-Segura aqueduct (pre-fertilizer water quality: pH, 8.1; EC, 1.22 dS m−1 ; HCO3 , 1.05 mM; SO4 − , 4.73; Ca2+ , 2.4 mM; K+ , 0.04 mM; Cl− , 3.57 mM; Na+ , 4.2 mM) mixed with commercial fertilizers, such as potassium nitrate, calcium nitrate, potassium dihydrogen phosphate, and nitric acid for pH control. The concentration of macronutrients (mM) and micronutrients (mg L−1 ) in the standard nutrient solution (EC 2.6 dS m−1 ) was as follows: (macronutrients) NO3 − , 14; H2 PO4 − , 1.5; SO4 2− , 4.73; Ca2+ , 4.7; K+ , 4.85; Mg2+ , 1.95; Cl− , 3.57; Na+ , 4.2; and (micronutrients, in mg L−1 ) Fe, 1.8; Mn, 0.7; Zn, 0.12; B, 0.15; Cu, 0.07; Mo, 0.05. The coconut bags were saturated with the control NS the day before the seedlings were transplanted and then left without irrigation for one week.
Fig. 1. Diurnal pattern in humidity (H), temperature (T), irradiance (I), and vapor pressure deficit (VPD) inside (in) and outside (out) of the greenhouse during three different days of the culture cycle; establishment of the crop (20 DAT, 10 February 2004), start of fruit picking (100 DAT, 30 April 2004), and final harvest (180 DAT, 19 July 2004). At the foot of each figure appears the average value of each climate parameter for that day. The exterior irradiance was not collected at 20 DAT.
J.S. Rubio et al. / Agricultural Water Management 97 (2010) 1695–1702
Twenty-three days after transplanting, the salt treatment was started, by adding 20 mM NaCl to the NS, resulting in an EC of 4.6 dS m−1 (salinity treatments). Using a computer, four irrigation treatments were scheduled; one irrigation event every two days (0.5), applied at 13:00 h; one irrigation event per day (1), applied at 13:00 h; four irrigation events per day (4); and eight irrigation events per day (8). The timetable of the four and eight irrigation events was adjusted depending on duration of daylight. During the first 50 days of the experiment, the amount of NS applied was 0.5 L plant−1 day−1 . After this period, in every salt × irrigation treatment, the amount of NS applied per plant and per day was calculated as a function of the ECDS measured in the irrigation event at 13:00 h the previous day, as follows: When the ECDS registered at the end of this irrigation event was higher than 120% of the ECNS (3.1 and 5.5 dS m−1 for the control and salinized treatments, respectively), the amount of NS applied per plant in the irrigation events of the following day was increased by 0.5 L per plant. This level was achieved by increasing the amount of NS by 500 ml for the 0.5 and 1 irrigation events per day and by 125 and 62.5 ml for the 4 and 8 irrigation events per day, respectively. The added amounts lowered the ECDS below the 120% level for the ECNS . 2.3. Yield parameters and plant growth Fruits were harvested weekly at the red mature stage, starting 114 days after transplanting until the end of the experiment. To calculate total fruit biomass and marketable fruit yield, all the fruits from six plants per row were counted and weighed. They were considered to be marketable fruits only if they did not show symptoms of blossom-end rot and if their fresh weight was higher than 100 g. At the end of the experiment (on 23 July) the vegetative abovegrown biomass (leaves and stem) from six plants per block was measured. 2.4. Mineral analysis in fruit and leaf tissue The Ca2+ concentration of mature green fruits was determined in eight replicate plants, using three fruits from each replicate. Leaf nutrient analysis (using the fifth leaf from the top) from three plants per block and treatment was carried out 149 days after transplanting (DAT), and Na+ , Cl− , Ca2+ , K+ , Mg2+ , Fe, Mn, Zn, and Cu concentrations were determined. The fruit and leaf tissues were washed with distilled water, dried in a ventilated oven at 65 ◦ C to constant weight. The concentrations of the cations and micronutrients were determined after digestion with HNO3 –HClO4 (2:1) by inductively coupled plasma spectrometry (Iris Intrepid II, Thermo Electron Corporation, Franklin, USA). The concentration of Cl− was determined after extraction with distilled water, using a silver ion titration chloridometer (HBI Chloridometer; Haake Buchler, Sandle Brook, NJ, USA).
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sured by titrating the juice of the peppers with 0.1 N NaOH to a pH of 8.1. 2.6. Statistical analysis Data were subjected to analysis of variance using a two-way ANOVA (SPSS statistical package, Chicago, IL, USA) with irrigation treatment and salt treatment as main factors. Treatment means were separated using Tukey’s multiple range test (P < 0.05). 3. Results 3.1. Electrical conductivity and water management The total volume of NS applied into the root zone and drained from the root zone increased significantly when NaCl concentration in the NS and the number of irrigation events per day were increased (Table 1). Thus, the highest values for these parameters were reached when the salinized NS was used with an application of eight irrigation events per day. The drainage percentage increased significantly when the NaCl concentration of the NS was increased, but it was not affected by the irrigation schedule. The WUE was higher for the non-salinized nutrient solutions regardless of the irrigation schedule. In both salinized and non-salinized conditions the highest WUE observed was for the 0.5 irrigation treatment. In the salinity treatments there were no significant differences among the one, four and eight irrigation treatments; however, in the non-salinity treatment, the WUE was significantly higher in the treatment with one irrigation event than in that with eight irrigation events. The highest ECDS registered during the growing cycle was found in plants irrigated every other day in both salt treatments, with averages of 4.68 and 7.23 dS m−1 in the control and salinized treatments, respectively (Fig. 2). In the salinized treatments, the irrigation schedule of 8 events per day produced the lowest ECDS during the whole growing cycle when compared with other irrigation schedules. By contrast, in the non-salinity treatments, there were no differences among the one, four and eight irrigation treatments. The differences in the ECDS between the control and salinity treatments were mainly due to differences in Na+ and Cl− concentrations in the drainage, and not affected by the rest of the nutrients (data not shown).
2.5. Fruit quality parameters. Twenty-four fruits per treatment were harvested at random, at the mature red stage, in the early (fruits from nodes 2 and 3) and late (fruits from nodes 9 to 11) harvest seasons. The fruit firmness was immediately measured at three points on the equatorial line of each fruit, using an 8 mm tip penetrometer (Effegi penetrometer, Italy). The fruits were then cut into two halves, and the pulp thickness was measured at two different points in each half. One half of the fruit was used to obtain the percentage of dry matter and the other half of the edible portion (pericarp) was divided into four lots (six fruits each) for analytical measurements. This portion was homogenized and aliquots were analyzed for soluble solid content (◦ Brix), pH, and titratable acidity (TA). Soluble solids (◦ Brix) were estimated at 20 ◦ C by a refractometer (Atago, Tokyo, Japan) and acidity was mea-
Fig. 2. Course of electrical conductivity (EC) in the drainage solutions in a pepper crop grown in coconut coir dust as influenced by NaCl salinity in the nutrient solution and irrigation frequency. For the 0.5 and 1 irrigation treatments the values show the maximum EC reached during an individual irrigation event. In the irrigation treatments with 4 and 8 events per day, each point shows the average of the maximum EC of all drainage events performed that day.
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Table 1 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on total amount of applied and drainaged nutrient solution per plant during a cropping period of 188 days, drainage percentage (DP), and water use efficiency (WUE; weight of marketable fresh fruit per liter of applied nutrient solution). Applied NS (L plant−1 )
Drainaged NS (L plant−1 )
DP (%)
WUE (g L−1 plant−1 )
Control Salinized
303 367
132 205
43.3 55.6
11.21 6.50
0.5 1 4 8
219d 336c 378b 407a
103c 170b 193ab 209a
46.7 49.5 50.7 51.1
11.92a 8.42c 7.83c 8.05c
196 298 346 371 242 374 409 442
80 122 159 168 126 217 226 250
40.8 40.9 46.0 45.5 52.5 58.1 55.3 56.6
16.20a 11.18b 10.01cb 9.60cd 8.56d 6.27e 6.00e 6.80e
NaCl
***
***
*
**
Irrigation schedule
**
***
ns
*
NaCl × Irrigation schedule
ns
ns
ns
*
Main effects NaCl Irrigation schedule
Interaction NaCl × Irrigation schedule NaCl Irrigation schedule 0.5 Control 1 4 8 0.5 Salinized 1 4 8
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Values are means of four replications (coconut bags with three plants for bag). * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
3.2. Plant growth and marketable yield components At the end of the experimental period (188 DAT), the salinity treatment decreased both the above-ground vegetative and fruit biomasses to about 20% of that obtained in the control treatment,
regardless of the irrigation treatment (Table 2). Vegetative biomass increased significantly, by about 20%, when the number of irrigation events per day was raised from 0.5 to 1. However, no significant differences were observed in the biomass among the one, four and eight irrigation event treatments. Fruit biomass increased sig-
Table 2 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on above-ground vegetative biomass, total fruit biomass and marketable fruit yield components. Marketable fruit yield
Above-ground vegetative biomass (kg plant−1 )
Total fruit biomass (kg plant−1 )
Control Salinized
1.64 1.30
3.60 2.92
3.38 2.42
0.5 1 4 8
1.23b 1.53a 1.54a 1.57a
2.85c 3.23b 3.37b 3.75a
2.62c 2.83b 2.96b 3.28a
196b 204ab 204ab 210a
13.4b 13.9ab 14.5ab 15.7a
1.34 1.73 1.63 1.84 1.12 1.32 1.46 1.32
3.20 3.60 3.80 4.12 2.50 2.86 2.94 3.41
3.17b 3.31ab 3.47a 3.56a 2.07d 2.35cd 2.46c 3.01b
201c 209b 211b 222a 192c 199c 197c 197c
15.9ab 16.0a 16.5a 16.1a 10.9c 11.7c 12.5c 15.3b
NaCl
***
***
***
**
**
Irrigation schedule
**
***
***
*
*
NaCl × Irrigation schedule
ns
ns
*
*
*
Main effects NaCl Irrigation schedule
Interaction salt × Irrigation schedule NaCl Irrigation schedule 0.5 Control 1 4 8 0.5 Salinized 1 4 8
Total yield (kg plant−1 )
Mean fruit weight (g) 211 196
No. of fruits per plant 16.1 12.3
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Values are means of 24 plants. * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
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Table 3 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on leaf mineral concentration at 149 days after transplanting. Na+
Cl−
K+
Ca2+
Mg2+
mg gdw −1 Main effects NaCl
Fe
Zn
Mn
Cu
g gdw −1
Control Salinized
0.68 0.72
12.9 58.0
55.8 54.9
46.5 42.6
11.9 12.0
113 112
61.1 74.5
225 319
13.4 17.2
0.5 1 4 8
0.63b 0.69b 0.54b 0.95a
31.0b 26.8b 30.9b 53.2a
55.6 54.3 54.8 56.6
42.2 44.7 45.2 46.0
12.6 12.5 11.6 11.2
94c 114b 112b 131a
44.1c 65.0b 87.9a 74.4ab
285 245 291 268
13.2 15.8 16.6 15.7
0.64 0.78 0.58 0.73 0.62 0.60 0.49 1.16
11.0 12.6 9.7 18.3 51.5 41.1 52.2 88.9
57.3 54.1 54.5 57.2 53.9 54.5 55.0 56.0
43.9 48.1 47.9 46.2 40.5 41.2 42.5 46
12.8 12.3 11.3 11.0 12.3 12.7 11.8 11.3
99 111 102 140 88 116 121 121
43.3 53.2 77.3 70.7 44.8 76.7 98.4 78.0
241 170 256 234 328 319 325 302
13.5 13.6 12.7 13.8 12.9 18.2 20.4 17.5
NaCl
ns
***
ns
ns
ns
ns
*
**
**
Irrigation schedule
**
***
ns
ns
ns
*
***
ns
ns
NaCl × Irrigation schedule
ns
ns
ns
ns
ns
ns
ns
ns
ns
Irrigation schedule
Interaction NaCl × Irrigation schedule NaCl Irrigation schedule 0.5 Control 1 4 8 0.5 Salinized 1 4 8
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Values are means of 12 samples. * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
nificantly as the number of irrigation events per day increased, although there were no significant differences between treatments of one and four irrigation events. The effect of salinity and irrigation frequency can be seen when examining the differences in mean fruit weight, but not in the number of fruits per plant (data not shown). The effect of the irrigation schedule on the marketable fruit yield and its components depended on the salt level in the NS (Table 2). Using control NS, the treatments of 4 and 8 irrigation events produced higher fruit yields than that of the 0.5 irrigation event. The mean fruit weight increased significantly as the irrigation frequency increased, and no significant differences were found in the number of fruits per plant. Using salinized NS, the marketable fruit yield increased significantly when the number of irrigation events per day was increased; no differences were found in the mean fruit weight; however, the number of fruits per plant increased only when the number of irrigations increased from four to eight irrigation events per day.
3.3. Leaf mineral status Leaf concentrations of Cl− but not of Na+ increased when the NaCl concentration was increased in the NS (Table 3). However, regardless of the NaCl concentration in the NS, leaf concentrations of both Na+ and Cl− were significantly higher in plants treated under the regimen of eight irrigation events per day than in those treated under the other regimens. The micronutrients Zn, Mn, and Cu increased significantly in leaves from plants irrigated with high NaCl concentration relative to plants irrigated with non-salinized nutrient solutions; Fe and Zn levels increased significantly when the number of irrigation events per day was increased. The salt and irrigation treatments did not affect the leaf concentrations of K+ , Ca2+ , and Mg2+ .
3.4. Seasonal effect on marketable yield and fruit quality The pattern of fruit yield was similar in all treatments and was characterized by two harvest seasons, with fruits from nodes 1 to 6 in the early season, and fruits from nodes 7 to 20 in the late season (data not shown). Across all treatments, the yield in the early harvest season was slightly higher than 50% of the total yield. The highest fruit yields per node were observed in the second and third nodes. In the late harvest season the highest fruit yields were reached in nodes 9–12. The presence of NaCl in the NS affected the morphology of the fruits harvested in the late harvest season (nodes 7–20) but not in the early harvest season (nodes 1–6; Fig. 3). In the late season the means in fruit weight, hardness, and pulp thickness decreased, and the percentage of dry matter increased in fruits from salinized plants compared with fruits produced by control plants. The mean fruit weight, in both harvest seasons, tended to increase along with the number of irrigation events per day, although the only significant differences were found between the 0.5 and the 8 irrigation treatments. In the late season hardness was higher in fruits watered 4 times per day while pulp thickness was higher in fruits water 8 times per day. In percentage of dry matter in the early period (nodes 1–6), there was a significant interaction between number of irrigation events and salt concentrations in the NS. Dry matter tended to decrease with an increase in the number of irrigation events, except in the case of the non-salinized NS, where it tended to increase up to the four irrigation event treatment. It is noteworthy that mean fruit weight and percentage of dry matter were lower in the late harvest season than in the early harvest season. In both periods of production, irrigation with salinized NS significantly decreased the fruit juice pH and increased its TA, regardless of the irrigation schedule (Fig. 4). The total soluble solids also increased significantly in the salinity treatment but only in fruits from the early harvest season. Fruits from the early harvest period
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Fig. 4. Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4 and 8) on the fruit organoleptic parameters of fruits harvested in two seasons; nodes 1–6 correspond with the early harvest season and the nodes 7–20 correspond with the late harvest season. *, **, and *** indicate significant differences at P < 0.05, 0.01, and 0.001, respectively; ns indicates non-significant differences. Different upper case letters indicate significant differences (P < 0.05) according to Tukey’s multiple range tests between irrigation treatments, regardless of the salt treatment. Each datum point is a mean of 4 replicates ± SE (each replicate contained 6 fruits).
Fig. 3. Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4 and 8) on the fruit morphological parameters of fruits harvested in two seasons; nodes 1–6 correspond with the early harvest season and the nodes 7–20 correspond with the late harvest season. *, **, and *** indicate significant differences at P < 0.05, 0.01, and 0.001, respectively; ns indicates non-significant differences. Means with different lower case letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. Different upper case letters indicate significant differences (P < 0.05) between irrigation treatments, regardless of the salt treatment. Each datum point is a mean of 24 fruits ± SE.
had a higher content of total soluble solids (TSS), pH and TA than those from the late harvest period. 3.5. Blossom-end rot incidence and fruit Ca2+ concentration Throughout both harvest seasons a high NaCl concentration in the NS, regardless of the irrigation treatments, resulted in a higher incidence of fruits with blossom-end rot (BER) (Table 4). In treatments with salinized NS, the irrigation schedule showed no effect on BER incidence in the late harvest period. In the early harvest period, however, the application of eight irrigation events per day significantly decreased the number of fruits with BER relative to the rest of irritation treatments. The incidence of BER increased in the fruits harvested during the late harvest season compared with the fruits harvested during the early harvest season. In the early harvest season but not in the later season, fruit Ca2+ concentration decreased with high NaCl concentration in the NS, regardless of the irrigation schedule. Compared with the other irrigation schedules, the eight irrigation events per day regimen significantly increased the fruit Ca2+ concentration in both seasons without regard to NS salinity level.
4. Discussion The results of this experiment show that high irrigation frequencies combined with the application of an adjusted volume of NS could be a good strategy for managing water usage in growing pepper plants under saline conditions. The optimum volume of NS applied can be calculated based on the amount of water applied in every irrigation event and using the ECDS data in the diurnal period of high evaporative demand. This strategy was arrived at based on data obtained under the regimen of eight irrigation events per day, which produced the highest total fruit biomass and fruit marketable yield (Table 2). In the case of non-salinized conditions, the marketable fruit yield (kg per plant) was similar for the 1, 4 and 8 irrigation treatments. However, because the 1 irrigation event treatment showed the highest WUE under our experimental conditions, the regimen involving 1 irrigation event per day can be considered the best water management practice in the absence of salinity. It is well known that pepper plants are very sensitive to saline water (Maas and Hoffman, 1977; Sonneveld and Vanderburg, 1991). Pepper plants under saline conditions are not able to adjust osmotically to maintain adequate water in their leaves, contributing to reduced yield and growth (Navarro et al., 2002). In addition to the osmotic effect, the increase in Na+ and Cl− in the leaves causes additional damage (Lycoskoufis et al., 2005). In our study, salt treatments reduced the above-ground (shoot and fruit) fresh biomass when compared with non-salt treatments, most likely due to the toxicity produced by Cl− as well as to the osmotic effect. However, in irrigation treatments on the salinized plants, high leaf concentrations of Na+ and Cl− did not correlate with reductions in fruit yield, as the irrigation regimen involving eight events per day had the
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Table 4 Effects of NaCl concentration in the nutrient solution (control, 4 mM NaCl; salinized, 24 mM NaCl) and number of irrigation events per day (0.5, 1, 4, and 8) on blossom-end rot (BER) incidence and fruit Ca2+ concentration at early (E) and late (L) harvest season. Early and late harvest season correspond to fruits harvested from nodes 1 to 6 and 7 to 10, respectively. Fruit Ca2+ concentration (mg gdw −1 )a
% BER E (1–6)
L (7–20)
E (1–6)
L (720)
Control Salinized
3.50 9.53
15.0 30.6
1.21 1.13
1.02 1.07
0.5 1 4 8
7.29a 6.55a 8.61a 3.60b
22.2 24.1 24.0 20.9
1.02b 1.10b 1.06b 1.48a
0.87b 1.07b 1.04b 1.20a
Irrigation schedule 0.5 1 4 8 0.5 1 4 8
3.54b 4.17b 3.47b 2.81b 10.97a 8.93a 13.78a 4.40b
13.4 15.3 17.3 14.2 31.1 32.9 30.8 27.6
1.09 1.18 1.05 1.50 0.95 1.02 1.07 1.47
0.90 1.08 0.98 1.13 0.84 1.06 1.10 1.27
NaCl
***
***
**
ns
Irrigation schedule
**
ns
**
**
NaCl × Irrigation schedule
*
ns
ns
ns
Main effects NaCl Irrigations schedule
Interaction NaCl × Irrigation schedule NaCl Control
Salinized
ns indicates non-significant differences. Means followed by different letters are significantly different (P < 0.05) according to Tukey’s multiple range tests. a The fruits used for tissue Ca2+ determination were green mature fruits without BER symptoms and were harvested between 40 and 43 days after anthesis. Values are means of 8 replicates, each containing 3 fruits. * Significant difference at P < 0.05. ** Significant difference at P < 0.01. *** Significant difference at P < 0.001.
highest fruit yield as well as the highest leaf Na+ and Cl− concentration. Thus, in this case, the osmotic effect of increased salinity appears to be more important than the toxic effect; additionally, eight irrigation events per day might have reduced the osmotic effect by not allowing excessive salt accumulation in the substrate in the interval between irrigation events, as shown by the lowest EC obtained in the DS. In addition to the osmotic effect, leaf water content and specific leaf area (data not shown) both decreased in plants watered every other day (0.5 event per day). It is possible that drought stress could have occurred in these plants, due to a longer period of time between irrigation events. It has been pointed out that in pepper plants drought stress severely restricts leaf and root water potentials, turgor potentials, osmotic potentials, and leaf gas exchange rates, which may directly inhibit leaf expansion (De Pascale et al., 2003). In addition, the higher leaf Na+ and Cl− concentrations observed in plants undergoing the 8 irrigation event treatments could be due to their higher leaf transpiration (Tester and Davenport, 2003; White and Broadley, 2001). Although we did not measure the leaf transpiration in this experiment, the data from Tables 1 and 2 support this hypothesis. The amount of water used per plant (volume applied minus volume drained) to obtain 1 kg of vegetative biomass was higher in the 8 irrigation event treatments (145 L kg−1 vegetative biomass) than in the 0.5, 1 and 4 irritation event treatments (103, 118 and 125 L kg−1 , respectively). Compared with the non-salinity condition, salinity decreased vegetative biomass and total fruit biomass and also increased the number of fruits with BER, further decreasing marketable yield. Nevertheless, the salt effect on the incidence of BER was mitigated in the treatment with the highest irrigation frequency. This positive effect of high irrigation frequencies could be a consequence of maintaining a low ECDS , which produced higher transpiration rates and therefore improved Ca2+ transport to the shoots. It is well known that BER incidence in pepper fruits occurs because of a reduction during the period of rapid fruit expansion in Ca2+ translo-
cation to the fruit tip, which can be caused by a decrease in water uptake by the roots under conditions of high salinity, drought, or low humidity, among others factors (Rubio et al., 2009; Ho and White, 2005; Marcelis and Ho, 1999). The harvest was characterized by two periods of maximal production. The first one occurred in May and beginning of June, from nodes 2 and 3, and the second in mid-July, from nodes 9 to 11. This is an irregular yield pattern known as flushing, common in greenhouse pepper crops (Heuvelink and Körner, 2001) and is promoted by the cyclic fluctuations in fruit sets (Marcelis and HofmanEijer, 1997). Fruit morphology—including mean fruit weight, hardness, pulp thickness, and dry matter—was affected by salinity during the late harvest season (July). Also, the mean fruit weight was severely reduced in the late harvest season in both the control and salinity treated plants. The effects of salinity in the root medium coupled with the adverse climatic conditions registered during this period (higher VPD) may be the main factors responsible for the observed changes in fruit appearance. It has been pointed out in studies on tomato plants that lowering VPD can mitigate the reduction in fruit volume by increasing xylem influx and decreasing fruit transpiration (Guichard et al., 2005), and subsequently reduce the negative effects on the morphology of the fruit. Given that, the differences observed in our study in fruit size between control and salinity treated plants in the late harvest season also explain the differences we observed in fruit hardness, pulp thickness, and percentage of dry matter. Contrary to expectations, the decrease in fruit size in the late harvest season was not accompanied by an increase in the percentage of dry matter and TSS. If only water transport to the fruit had been lower during this period, the TSS and percentage of dry matter should have increased, due to a “concentration effect”. However, TSS and percentage of the dry matter decreased or remained the same, which suggests that the climatic conditions during this period promoted a decrease in both water and solute transport to
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the fruit. However, the decrease in fruit size in the late season was not independent of the salt content in the NS. While the decrease in fruit size was higher in the salinity treated plants than in the control plants, the decrease in the percentage of dry matter was higher in the control plants than in the salinity treated plants. It is therefore probable that salinity decreased water transport to the fruits during this period. At the highest irrigation frequencies, the decrease in pH and the increase in acidity due to salinity seemed to be related to the accumulation of Cl− and Na+ in the fruit. These results agree with previous research (Reina-Sanchez et al., 2005; Del Amor et al., 2001). 5. Conclusions In sweet pepper crops grown in a soilless system based on coconut coir dust and watered with moderately saline water, a high irrigation frequency combined with regulation of the amount of NS applied, such that the EC of drainage is maintained below 120% of the EC of NS, could prove a good irrigation strategy by mitigating the negative effects of salinity on the total fruit biomass and marketable fruit yield. However, in non-saline conditions, the application of one irrigation event per day offers the best results in terms of water use efficiency. The deleterious effects of salinity in the marketable yield and fruit quality are more perceptible in the late harvest season, as high temperature and dry conditions may act synergistically with high salinity. Acknowledgments J.S. Rubio was a recipient of a FPU fellowship from Ministerio de Educación y Ciencia (Spain). This work was funded by the project AGR/18/FS/02 (Fundacion Séneca, CARM). The authors thank Mark T. Hoyer for the correction of the English in the manuscript. References Alarcon, A.L., Murcia, F., 2000. Cultivo en lana de roca. In: Alarcon, A.L. (Ed.), Tecnologia para cultivos de alto rendimiento. Novedades Agricolas, Murcia, Spain, pp. 245–253 (in Spanish). Assouline, S., Moller, M., Cohen, S., Ben-Hur, M., Grava, A., Narkis, K., Silber, A., 2006. Soil–plant system response to pulsed drip irrigation and salinity: bell pepper case study. Soil Science Society of America Journal 70, 1556–1568.
De Pascale, S., Ruggiero, C., Barbieri, G., Maggio, A., 2003. Physiological responses of pepper to salinity and drought. Journal of the American Society for Horticultural Science 128, 48–54. Del Amor, F.M., Martinez, V., Cerda, A., 2001. Salt tolerance of tomato plants as affected by stage of plant development. HortScience 36, 1260–1263. Dorais, M., Papadopoulos, A.P., Gosselin, A., 2001. Influence of electric conductivity management on greenhouse tomato yield and fruit quality. Agronomie 21, 367–383. Ghassemi, F., Jakeman, A.J., Nix, H.A., 1995. Salinisation of land and water resources: human causes, extent, management and case studies. Wallingford, Oxon, UK. Guichard, S., Gary, C., Leonardi, C., Bertin, N., 2005. Analysis of growth and water relations of tomato fruits in relation to air vapor pressure deficit and plant fruit load. Journal of Plant Growth Regulation 24, 201–213. Heuvelink, E., Körner, O., 2001. Parthenocarpic fruit growth reduces yield fluctuation and blossom-end rot in sweet pepper. Annals of Botany 88, 69–74. Ho, L.C., White, P.J., 2005. A cellular hypothesis for the induction of blossom-end rot in tomato fruit. Annals of Botany 95, 571–581. Lycoskoufis, I.H., Savvas, D., Mavrogianopoulos, G., 2005. Growth, gas exchange, and nutrient status in pepper (Capsicum annuum L.) grown in recirculating nutrient solution as affected by salinity imposed to half of the root system. Scientia Horticulturae 106, 147–161. Maas, E.V., Hoffman, G.J., 1977. Crop salt tolerance. Journal of the Irrigation and Drainage Division 103, 115–134. Marcelis, L.F.M., HofmanEijer, L.R.B., 1997. Effects of seed number on competition and dominance among fruits in Capsicum annuum L. Annals of Botany 79, 687–693. Marcelis, L.F.M., Ho, L.C., 1999. Blossom-end rot in relation to growth rate and calcium content in fruits of sweet pepper (Capsicum annuum L.). Journal of Experimental Botany 50, 357–363. Navarro, J.M., Garrido, C., Carvajal, M., Martinez, V., 2002. Yield and fruit quality of pepper plants under sulphate and chloride salinity. Journal of Horticultural Science and Biotechnology 77, 52–57. Reina-Sanchez, A., Romero-Aranda, R., Cuartero, J., 2005. Plant water uptake and water use efficiency of greenhouse tomato cultivars irrigated with saline water. Agricultural Water Management 78, 54–66. Rubio, J.S., Garcia-Sanchez, F., Rubio, F., Martinez, V., 2009. Yield, blossom-end rot incidence, and fruit qualty in pepper plants under moderate salinity are affected by K+ and Ca2+ fertilization. Scientia Horticulturae 119, 79–87. Sahin, U., Anapali, O., Ercisli, S., 2002. Physico-chemical and physical properties of some substrates used in horticultura. Gartenbauwissenschaft 67 (2), 55–60. Savvas, D., Stamati, E., Tsirogiannis, I.L., Mantzos, N., Barouchas, P.E., Katsoulas, N., Kittas, C., 2007. Interactions between salinity and irrigation frequency in greenhouse pepper grown in closed-cycle hydroponic systems. Agricultural Water Management 91, 102–111. Sonneveld, C., Vanderburg, A.M.M., 1991. Sodium-chloride salinity in fruit vegetable crops in soilless culture. Netherlands Journal of Agricultural Science 39, 115–122. Tester, M., Davenport, R., 2003. Na+ tolerance and Na+ transport in higher plants. Annals of Botany 91, 503–527. White, P.J., Broadley, M.R., 2001. Chloride in soils and its uptake and movement within the plant: A review. Annals of Botany 88, 967–988.