Directory UMM :Data Elmu:jurnal:S:Scientia Horticulturae:Vol84.Issue1-2.Apr2000:
Scientia Horticulturae 84 (2000) 37±47
Effects of NaCl or nutrient-induced salinity on
growth, yield, and composition of eggplants
grown in rockwool
D. Savvas*, F. Lenz
Institut fuÈr Obst-und GemuÈsebau der UniversitaÈt Bonn, Auf dem HuÈgel 6, 53121 Bonn, Germany
Accepted 3 September 1999
Abstract
The effects of increasing the salt concentration of a basic nutrient solution from 2.1 up to
4.7 dS mÿ1 by providing either additional amounts of nutrients or 25 mmol lÿ1 NaCl on growth,
yield, fruit quality and mineral composition of eggplants were investigated. The extra nutrients used
to raise the electrical conductivity were added either at the same ionic concentration ratio as in the
basic nutrient solution or at an increased ratio of K to total cation concentration.
The vegetative growth and the number of ¯owers per plant were not in¯uenced by any of the
salinity treatments. In contrast, the fresh fruit yield of eggplant was signi®cantly reduced to the
same extent in all salinity treatments. The yield depression was a result of a decline in mean fruit
weight, whereas the number of fruits per plant was not affected. However, recalculation of the data
on dry weight basis revealed no signi®cant differences between the treatments. The percentage of
eggplant fruits graded Class 1 was signi®cantly reduced at 4.7 dS mÿ1, whilst the kind of salts used
to induce salinity had no signi®cant effect on fruit quality. The increase of electrical conductivity up
to 4.7 dS mÿ1 by the addition of extra nutrients did not result in a higher nutrient uptake, with the
exception of P in roots, and P and organic N in the petioles of older leaves. In contrast, the
concentrations of Mg and NO3±N were reduced in some plant parts when salinity was increased by
the addition of extra nutrients, regardless of the proportions of cations in the nutrient solution. All
salinity treatments reduced the concentration of Mg in the leaves to the same degree, thus indicating
that this salt effect is not ion speci®c. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Eggplant; Growth responses; Hydroponics; Mineral composition; Nutrient solution;
Salinity
*
Corresponding author. Current address: Faculty of Agricultural Technology, T.E.I. of Epirus,
PO Box 110, 47100 Arta, Greece. Tel.: 30-681-77-468; fax: 30-681-77-468.
E-mail address: [email protected] (D. Savvas).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 9 9 ) 0 0 1 1 7 - X
38
D. Savvas, F. Lenz / Scientia Horticulturae 84 (2000) 37±47
1. Introduction
The soilless cultivation of eggplants has expanded considerably over the last
two decades. Whereas, initially, open hydroponic systems were mostly involved,
recent environmental regulations against groundwater pollution and the requirement to minimize water and fertilizer consumption have led to the recycling of
nutrient solutions. However, if the tap water used to prepare the nutrient solution
has a high salt concentration (usually NaCl but also Ca and Mg bicarbonates and
sulphates) the reuse of the drain water may result in salt accumulation in the
nutrient solution, accompanied by depletion of other nutrients such as K
(Sonneveld, 1981; Savvas and Manos, 1999). If modern automatic equipment is
used to control the recycling of the drain solution, this process might be retarded
by progressively increasing the target electrical conductivity (EC) of the nutrient
solution which is given as a preset value to the control system (Savvas and
Manos, 1999). However, this would expose the plants gradually to a salt stress.
Moreover, if tap water with a high salt content is used, the total salt concentration
of the nutrient solution supplied to the plants will essentially be higher than the
recommended target value of EC for the crop. Hence, the question is raised, as to
how the eggplants respond to a moderate increase of EC in the nutrient solution.
The responses of hydroponically grown eggplants to increasing EC in the
nutrient solution due only to the presence of NaCl have been well documented
(Savvas and Lenz, 1994b, 1996). However, the detrimental effects of salinity on
plants may be either indiscriminate (osmotic), if the total salt concentration
determines the extent of growth restriction, or ion speci®c, if the kind of salts
being in excess in the nutrient solution is crucial for the plant response (Bernstein,
1975; Shannon and Grieve, 1999). Therefore, when studying the in¯uence of
increasing salinity on growth and development of eggplant in soilless culture
systems, it is important to compare nutrient solutions having equal electrical
conductivities but different ionic composition.
This paper reports some results concerning the responses of eggplants grown
on rockwool to a moderate increase in the EC of the supplied nutrient solution,
induced either by NaCl or by providing additional amounts of nutrients at two
different cation proportions.
2. Materials and methods
Seedlings of eggplant (Solanum melongena L.) cv. `Leanda' raised on rockwool
cubes (0.7 l) were transferred to 32 uncovered rockwool slabs (90 cm
15 cm 7.5 cm) in a heated glasshouse as soon as they had formed ®ve true
leaves. The slabs were placed in eight plastic channels (four slabs per channel).
Immediately after planting, the channels were covered with a black-white
39
D. Savvas, F. Lenz / Scientia Horticulturae 84 (2000) 37±47
polyethylene ®lm. In each channel, ®ve plants were placed. The eight channels
were arranged in four rows spaced 120 cm apart. Additional plant rows were
placed on the four sides around the experimental installation to prevent margin
effects. All plants were trained with three stems. The minimum day/night
temperatures were set at 21/198C prior to the beginning of ¯owering and 21/168C
thereafter. No measures were taken to improve fruit set.
In each channel (experimental unit) an individual tank was provided to supply
the plants with nutrient solution via a drip irrigation system. The nutrient solution
was automatically supplied to the plants at a rate of 20 l/h per channel using a
pump and a special timer for irrigation scheduling. In each channel, the nutrient
solution was continuously recirculating during the day to maintain a constant
nutrient and water status in the root zone, whereas at the night no solution was
supplied to the plants.
Four different nutrient solution treatments were applied to the eight
experimental units, so that each treatment was duplicated. In particular, there
was a basic nutrient solution (BNS) suitable for eggplants (Voogt, 1986) having
an EC of 2.1 dS mÿ1 and three saline nutrient solutions having the same EC
(4.7 dS mÿ1). The EC was raised up to 4.7 dS mÿ1 by adding to the basic solution
either nutrients at the same ionic concentration ratio as in the BNS, or nutrients at
an increased K/(K Ca Mg) ratio, or 25 mmol lÿ1 NaCl. The increased K/
(K Ca Mg) ratio (meq/meq) was 0.473 whilst the standard value was 0.40.
The compositions of the four nutrient solutions are given in Table 1.
Table 1
Composition of the four nutrient solutions used as experimental treatmentsa
Nutrient
Basic nutrient
solution (BNS)
K/(K Ca Mg)
0.40
K/(K Ca Mg)
0.47
BNS 25 mM
NaCl
NOÿ
3
H2 POÿ
4
2ÿ
SO4
NH
4
K
Ca2
Mg2
NaCl
Fe
Mn
Zn
B
Cu
Mo
15.50
1.50
1.50
0.75
7.75
3.75
2.00
±
15.00
10.00
5.00
25.00
0.75
0.50
34.10
3.30
3.30
1.65
17.05
8.25
4.40
±
33.00
22.00
11.00
55.00
1.65
1.10
34.10
3.30
3.30
1.65
20.05
7.35
3.80
±
33.00
22.00
11.00
55.00
1.65
1.10
15.50
1.50
1.50
0.75
7.75
3.75
2.00
25.00
15.00
10.00
5.00
25.00
0.75
0.50
a
The concentrations of macronutrients, NaCl, and micronutrients are given in mM, mM and
mM, respectively.
40
D. Savvas, F. Lenz / Scientia Horticulturae 84 (2000) 37±47
All nutrient solutions were prepared using rain water. The amount of nutrient
solution consumed by the plants was replenished regularly during each day. Every
10 days the concentration of N, P, K, Ca, and Mg was determined and adjusted in
all nutrient solutions. Moreover, at fortnightly intervals the nutrient solutions
were renewed completely in all tanks. In each experimental unit, 14 l of nutrient
solution per plant were in recirculation during the day. This ratio proved to be
suf®cient to prevent considerable changes in the nutrient ratios in short periods of
less than 10 days. However, in the NaCl-salinity treatment, the Na concentration
in the nutrient solution was measured and adjusted by adding NaCl twice weekly.
The eggplant seedlings were planted on 15 March and the exposure to salinity
began 10 days later. The ®rst harvest took place on 2 May and the experiment was
terminated on 2 October. During the whole growing period, the opening ¯owers
per plant in each treatment were counted weekly and marked to avoid a double
registration. Ripening fruits were harvested twice weekly, weighed, and graded to
determine the percentage of yield graded Class 1. Grading was performed in
accordance with the European Community standards, whilst a fruit weight of
175 g was the lowest size accepted for Class 1. Since at each ¯ower level of
eggplant, besides one basal ¯ower, some additional ¯owers may also be produced
(Nothmann et al., 1979; Passam and Khah, 1992), the ¯owers and the harvested
fruits were recorded either as basal or as additional ones. Moreover, the
proportion of small fruit yield (
Effects of NaCl or nutrient-induced salinity on
growth, yield, and composition of eggplants
grown in rockwool
D. Savvas*, F. Lenz
Institut fuÈr Obst-und GemuÈsebau der UniversitaÈt Bonn, Auf dem HuÈgel 6, 53121 Bonn, Germany
Accepted 3 September 1999
Abstract
The effects of increasing the salt concentration of a basic nutrient solution from 2.1 up to
4.7 dS mÿ1 by providing either additional amounts of nutrients or 25 mmol lÿ1 NaCl on growth,
yield, fruit quality and mineral composition of eggplants were investigated. The extra nutrients used
to raise the electrical conductivity were added either at the same ionic concentration ratio as in the
basic nutrient solution or at an increased ratio of K to total cation concentration.
The vegetative growth and the number of ¯owers per plant were not in¯uenced by any of the
salinity treatments. In contrast, the fresh fruit yield of eggplant was signi®cantly reduced to the
same extent in all salinity treatments. The yield depression was a result of a decline in mean fruit
weight, whereas the number of fruits per plant was not affected. However, recalculation of the data
on dry weight basis revealed no signi®cant differences between the treatments. The percentage of
eggplant fruits graded Class 1 was signi®cantly reduced at 4.7 dS mÿ1, whilst the kind of salts used
to induce salinity had no signi®cant effect on fruit quality. The increase of electrical conductivity up
to 4.7 dS mÿ1 by the addition of extra nutrients did not result in a higher nutrient uptake, with the
exception of P in roots, and P and organic N in the petioles of older leaves. In contrast, the
concentrations of Mg and NO3±N were reduced in some plant parts when salinity was increased by
the addition of extra nutrients, regardless of the proportions of cations in the nutrient solution. All
salinity treatments reduced the concentration of Mg in the leaves to the same degree, thus indicating
that this salt effect is not ion speci®c. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Eggplant; Growth responses; Hydroponics; Mineral composition; Nutrient solution;
Salinity
*
Corresponding author. Current address: Faculty of Agricultural Technology, T.E.I. of Epirus,
PO Box 110, 47100 Arta, Greece. Tel.: 30-681-77-468; fax: 30-681-77-468.
E-mail address: [email protected] (D. Savvas).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 9 9 ) 0 0 1 1 7 - X
38
D. Savvas, F. Lenz / Scientia Horticulturae 84 (2000) 37±47
1. Introduction
The soilless cultivation of eggplants has expanded considerably over the last
two decades. Whereas, initially, open hydroponic systems were mostly involved,
recent environmental regulations against groundwater pollution and the requirement to minimize water and fertilizer consumption have led to the recycling of
nutrient solutions. However, if the tap water used to prepare the nutrient solution
has a high salt concentration (usually NaCl but also Ca and Mg bicarbonates and
sulphates) the reuse of the drain water may result in salt accumulation in the
nutrient solution, accompanied by depletion of other nutrients such as K
(Sonneveld, 1981; Savvas and Manos, 1999). If modern automatic equipment is
used to control the recycling of the drain solution, this process might be retarded
by progressively increasing the target electrical conductivity (EC) of the nutrient
solution which is given as a preset value to the control system (Savvas and
Manos, 1999). However, this would expose the plants gradually to a salt stress.
Moreover, if tap water with a high salt content is used, the total salt concentration
of the nutrient solution supplied to the plants will essentially be higher than the
recommended target value of EC for the crop. Hence, the question is raised, as to
how the eggplants respond to a moderate increase of EC in the nutrient solution.
The responses of hydroponically grown eggplants to increasing EC in the
nutrient solution due only to the presence of NaCl have been well documented
(Savvas and Lenz, 1994b, 1996). However, the detrimental effects of salinity on
plants may be either indiscriminate (osmotic), if the total salt concentration
determines the extent of growth restriction, or ion speci®c, if the kind of salts
being in excess in the nutrient solution is crucial for the plant response (Bernstein,
1975; Shannon and Grieve, 1999). Therefore, when studying the in¯uence of
increasing salinity on growth and development of eggplant in soilless culture
systems, it is important to compare nutrient solutions having equal electrical
conductivities but different ionic composition.
This paper reports some results concerning the responses of eggplants grown
on rockwool to a moderate increase in the EC of the supplied nutrient solution,
induced either by NaCl or by providing additional amounts of nutrients at two
different cation proportions.
2. Materials and methods
Seedlings of eggplant (Solanum melongena L.) cv. `Leanda' raised on rockwool
cubes (0.7 l) were transferred to 32 uncovered rockwool slabs (90 cm
15 cm 7.5 cm) in a heated glasshouse as soon as they had formed ®ve true
leaves. The slabs were placed in eight plastic channels (four slabs per channel).
Immediately after planting, the channels were covered with a black-white
39
D. Savvas, F. Lenz / Scientia Horticulturae 84 (2000) 37±47
polyethylene ®lm. In each channel, ®ve plants were placed. The eight channels
were arranged in four rows spaced 120 cm apart. Additional plant rows were
placed on the four sides around the experimental installation to prevent margin
effects. All plants were trained with three stems. The minimum day/night
temperatures were set at 21/198C prior to the beginning of ¯owering and 21/168C
thereafter. No measures were taken to improve fruit set.
In each channel (experimental unit) an individual tank was provided to supply
the plants with nutrient solution via a drip irrigation system. The nutrient solution
was automatically supplied to the plants at a rate of 20 l/h per channel using a
pump and a special timer for irrigation scheduling. In each channel, the nutrient
solution was continuously recirculating during the day to maintain a constant
nutrient and water status in the root zone, whereas at the night no solution was
supplied to the plants.
Four different nutrient solution treatments were applied to the eight
experimental units, so that each treatment was duplicated. In particular, there
was a basic nutrient solution (BNS) suitable for eggplants (Voogt, 1986) having
an EC of 2.1 dS mÿ1 and three saline nutrient solutions having the same EC
(4.7 dS mÿ1). The EC was raised up to 4.7 dS mÿ1 by adding to the basic solution
either nutrients at the same ionic concentration ratio as in the BNS, or nutrients at
an increased K/(K Ca Mg) ratio, or 25 mmol lÿ1 NaCl. The increased K/
(K Ca Mg) ratio (meq/meq) was 0.473 whilst the standard value was 0.40.
The compositions of the four nutrient solutions are given in Table 1.
Table 1
Composition of the four nutrient solutions used as experimental treatmentsa
Nutrient
Basic nutrient
solution (BNS)
K/(K Ca Mg)
0.40
K/(K Ca Mg)
0.47
BNS 25 mM
NaCl
NOÿ
3
H2 POÿ
4
2ÿ
SO4
NH
4
K
Ca2
Mg2
NaCl
Fe
Mn
Zn
B
Cu
Mo
15.50
1.50
1.50
0.75
7.75
3.75
2.00
±
15.00
10.00
5.00
25.00
0.75
0.50
34.10
3.30
3.30
1.65
17.05
8.25
4.40
±
33.00
22.00
11.00
55.00
1.65
1.10
34.10
3.30
3.30
1.65
20.05
7.35
3.80
±
33.00
22.00
11.00
55.00
1.65
1.10
15.50
1.50
1.50
0.75
7.75
3.75
2.00
25.00
15.00
10.00
5.00
25.00
0.75
0.50
a
The concentrations of macronutrients, NaCl, and micronutrients are given in mM, mM and
mM, respectively.
40
D. Savvas, F. Lenz / Scientia Horticulturae 84 (2000) 37±47
All nutrient solutions were prepared using rain water. The amount of nutrient
solution consumed by the plants was replenished regularly during each day. Every
10 days the concentration of N, P, K, Ca, and Mg was determined and adjusted in
all nutrient solutions. Moreover, at fortnightly intervals the nutrient solutions
were renewed completely in all tanks. In each experimental unit, 14 l of nutrient
solution per plant were in recirculation during the day. This ratio proved to be
suf®cient to prevent considerable changes in the nutrient ratios in short periods of
less than 10 days. However, in the NaCl-salinity treatment, the Na concentration
in the nutrient solution was measured and adjusted by adding NaCl twice weekly.
The eggplant seedlings were planted on 15 March and the exposure to salinity
began 10 days later. The ®rst harvest took place on 2 May and the experiment was
terminated on 2 October. During the whole growing period, the opening ¯owers
per plant in each treatment were counted weekly and marked to avoid a double
registration. Ripening fruits were harvested twice weekly, weighed, and graded to
determine the percentage of yield graded Class 1. Grading was performed in
accordance with the European Community standards, whilst a fruit weight of
175 g was the lowest size accepted for Class 1. Since at each ¯ower level of
eggplant, besides one basal ¯ower, some additional ¯owers may also be produced
(Nothmann et al., 1979; Passam and Khah, 1992), the ¯owers and the harvested
fruits were recorded either as basal or as additional ones. Moreover, the
proportion of small fruit yield (