Effects of Soil Salinity From Long Term Irrigation

SCIENTIA HORTICULTUM

ELSEVIER Scientia Horticulturae 64 (1995) 145-157

Effects of soil salinity from long-term irrigation with saline-sodic water on yield

and quality of winter vegetable crops

S. De Pascale *, G. Barbieri

Department ofAgronomy and Plant Breeding, University of Naples, Via Vniuersitir, 100, 80055, Portici Naples, Italy

Accepted 26 June 1995

Abstract

From 1988 onwards a study was carried out to evaluate the long-term effects of increasing water salinity (O%, 0.125%, 0.25%, 0.5% and 1% of commercial NaCl) on some vegetable crops growing in a clay-loam soil. In 1992 and 1993 the effects of the residual soil salinity on yield and some aspects of yield quality were studied in lettuce, endive and fennel grown during irrigation-free

seasons on a field which had undergone the same irrigation treatment since 1988. Within the range of electrical conductivity of the saturated-soil extract (ECe) between 2.0 dS m-l (treatment 0%) and 6.0 dS m- ’ (treatment 1%) the marketable yield decreased by about 60% in endive and fennel and by about 15% in lettuce which proved more tolerant than the other crops. Gas exchange rates and stomata1 conductance were reduced by salinity in lettuce. Soil salinity affected product quality: lettuce and endive appeared to be more sensitive to tipburn and necrotic symptoms occurring in the crop under saline-sodic conditions; fennel heart length, width, and thickness were also significantly reduced and the heart shape tended to be modified in plants grown on salt-affected plots. The results, obtained by analyzing the salt tolerance model of Maas-Hoffman and its descriptive parameters, place lettuce, endive and fennel in the moderately sensitive category. In terms of ECe, the threshold ranged from 1.8 dS m-r (fennel) to 2.7 dS m-l (lettuce) while the slope varied between 5.8% per dS m-l (lettuce) and 15.7% per dS m-r (endive).

Keywords: Water salinity; Salt tolerance; Lactuca sat&a; Cichorium endiuia; Foeniculum vulgare

* Corresponding author.

0304-4238/95/%09.50 0 1995 Elsevier Science B.V. All rights reserved

SSDI 0304-4238(95)00823-3

146 S. De Pascale, G. Barbieri/Scientia Horticulturae 64 (1995) 145-157

1. Introduction

Vegetable crops are grown widely in regions where irrigation water salinity may have long-term negative effects on soil-water-plant relationships (Barbieri and De Pascale, 1992; Graifenberg et al., 1993). Several experiments have been carried out to determine the relative growth response of many vegetable crops to salinity. Nevertheless, some of the existing salt tolerance data were collected in controlled, simplified experimental conditions (plants grown in containers or in pots, soilless culture, greenhouse or growth chamber environments). Few reports are available on the long-term effects of salinity on

plants tested under natural environmental and edaphic conditions, and the results are often contradictory. Such data are normally obtained from small artificially salinized field plots under accepted growing practices, where steady-state conditions and uniform salt distribution are achieved rapidly. The applicability of such information to field situations and the reproducibility of the results obtained from different sites and years, depend on the various environmental, edaphic, biological and management factors influencing salt tolerance (Maas, 1990). In the field, the distribution of salinity in the soil varies in both space and time.

Seasonal variations in soil salinity in relation to plant responses to salinity should be taken into account. Rainfall generally results in some leaching of the top of the soil

profile and after the rainy season the salinity of the whole profile may be markedly reduced. In semi-arid zones, the winter leaching should remove enough salt to reduce salt content in the root zone below the crop tolerance level. Chemical reactions in the soil affect the amount of salt leached, which may be greater than, equal to, or less than the amount of salt added by irrigation water. In salt-affected fields where sodium and chloride concentrations are high, soil salinity may affect vegetable crop growth even

during cool, rainy periods (Epstein and Rains, 1987). Russo (1983a,b) reported that relatively high soil salinity (ECe = 7.5 dSm- * ) may remain even after leaching with 800 mm water before the growing season due to the relatively high exchangeable Na content of the soil. The addition of saline water to soil alters the chemical characteristics of that soil. High sodium and chloride concentrations may cause disorders in mineral nutrition and toxicity. The high activities of Na+ ions, relative to those of Ca2+ and Mg2+, affect soil structure, permeability and tilth. The harmful interactive effects of excessive exchangeable sodium and high pH in the soil as well as a low electrolyte concentration in the infiltrating water can lower soil permeability and decrease its infiltration capacity through the swelling and dispersion of clays and the slaking of aggregates @uchli and

Epstein, 1990). Lettuce and endive are considered to be moderately sensitive crops (Maas and

Hoffman, 1977; Sonneveld, 1988), while fennel moderately tolerant (Gabriels, 1972). Few data are available on the effects of soil salinity on the quality aspects of crops (Mizrahi and Pasternak, 1985; Sonneveld, 1988). To gain information on salt tolerance of vegetable crops, studies were initiated in 1988 at the experimental farm of the University of Naples using a field salinized by irrigating with saline water (Barbieri et al., 1990, 1994; Caruso and Postiglione, 1993; Ruggiero et al., 1994). After equilibrium levels of soil salinity were reached, the effects of the variably lower salinities in winter

S. De Pascale, G. Barbieri/Scientia Horticuhrae 64 (1995) 145-157 147

on plant growth, yield and market quality of these three economically important vegetable crops under rainfed regime were investigated.

2. Materials and methods

The experiments were conducted over 5 years at the University farm ‘Torre Lama’,

near Salerno in the Sele river plain, on clay-loam soil, whose characteristics at the beginning of the trial were: 42% sand; 27% loam; 31% clay; lime traces; 1.57% organic matter; 0.09% total N; pH 7.1; with field capacity (in situ) and - 1.5 MPa water contents of 27.6% and 13.6% (by weight) and bulk density of 1.25 t rnw3.

During the dry season, the effects of drip irrigation with saline water were studied on yield and market quality of some vegetable crops (tomato, snap bean and eggplant) and on soil water content and soil salinity. The treatments consisted of five levels of salinity (O%, 0.125%, 0.25%, 0.5% and 1%) factorially combined with three irrigation intervals (2, 5 and 10 days). Saline water was obtained by adding commercial sea salt (Na+

23.8%, K+ 14.8%, Ca2+ 0.102%, Mg2+ O.l%, Cl- 51.2%, SOi- 0.28%) to the fresh water (0% treatment). Electrical conductivities at 25°C (ECw) of the five irrigation waters were 0.54, 2.30, 4.43, 8.46 and 15.73 dS m-l. Amounts of water applied at each irrigation were equivalent to Class A Pan evaporation between two waterings. The

experimental design was a randomized split-plot design with three replications, with the salinity treatments as main plots and the irrigation intervals as sub-plots of 36.2 m2. To

investigate the long-term effects of irrigation water salinity, each combination of salt concentration in irrigation water and irrigation interval was assigned every year to the same plot. During the winter season, the residual effects of water salinity were investigated.

In 1992, after a snap bean crop, two cultivars of lettuce (Lactuca saliva L.) ‘Bix’ and ‘Ariane R2’, were tested. Seedlings were transplanted on 13 January in rows 0.4 m apart with an in-row spacing of 0.2 m and harvested from 16 April to 27 April. At harvest, number of plants, total head yield, marketable and non-marketable head weight and number were recorded. The non-marketable yield included heads showing tip or

marginal leaf bums, leaf injuries, or weighing less than the commercial minimum weight of 250 g. Leaf number, leaf area (using a Li-Cor 3000 areameter) and dry matter were determined and- the specific leaf weight (SLW) was calculated from a ten-head sample for each plot. Twice during the growing season, net photosynthetic rate (P,), transpiration rate (T,) and stomata1 conductance (C,) were measured, between 11:00 and 13:00 h with a portable infrared gas analyzer (Li-Cor 6200), the measurements being replicated

on three plants in each plot and on three fully expanded, healthy, sun-exposed leaves per plant. During measurements, on 10 March and 14 April, at midday, air temperature

values were 16°C and 22.7”C, RH values were 34% and 36.3% and the photosynthetic active radiation (PAR) values were 646 pmol mm2 s-l and 1334 pmol rnp2 s-l, respectively.

In 1993, after an eggplant crop, endive (Cichorium endiuiu L.), cultivar ‘Wallonne Despa’, and fennel (Foeniculum uulgure Mill.), cultivar ‘Trevi’, were tested. Seedlings were transplanted in a plot of 18 m2, on 30 October 1992 in rows 0.5 m apart with an


in-row spacing of 0.2 m and harvested from 25 to 30 March 1993. At the endive harvest, number of plants, total head yield, marketable and non-marketable head weight and number were recorded. The non-marketable yield included heads showing tip bum or black heart, marginal leaf necrosis, brown areas extending into the intemeival tissue, or weighing less than the commercial minimum weight of 350 g. Maximum diameter of each head cut in half and dry matter of stover were determined from a ten-head sample for each plot. On fennel, number and height of harvested plants were recorded. The plants were then trimmed by removing the oldest outside leaves. Then the leaves were cut 10 cm above the point of the attachment to the heart, leaving a compact heart of straight leaves. Marketable and non-marketable trimmed heart number and weight were determined. Marketable hearts were whole and sound, of regular shape and weighed more than 200 g. Ten trimmed hearts per plot were sampled to determine average dry weight, length (L), the distance between the base and the top of the edible part of the leaves, width (W) and thickness (T), and the ratio L/(wT>“.5 was calculated to measure the cylinder-shaped hearts.

Every year before planting, fertilizers were applied at the rate of 60 kg ha-’ N, 120 kg ha-’ P,O,, 200 kg ha- ’ K,O. Nitrogen fertilizer was sidedressed at the rate of 80 kg ha-’ N as ammonium nitrate applied 4 and 7 weeks after transplanting. Weeds were controlled throughout the life of the crops by a combination of pre-emergence herbicide (trifluralin) and cultivation. Diseases and insects were regularly controlled with a range of commercial chemicals.

Soil samples in 30-cm depth increments were taken monthly throughout the growing season to a depth of 120 cm in each plot to measure soil water content by gravimetric method and analyzed for the electrical conductivity of the saturation extract at 25°C (ECe) (Kalra and Maynard, 1991).

Yield response to soil salinity was described by the Maas and Hoffman linear model (19771, and the salt tolerance functions of crops were evaluated using the following equation: Y, = 100 - S (ECe - T), where Y, is relative yield expressed as percentage of the yield obtained under non-saline conditions, T is the salinity threshold expressed in dS m-l that corresponds to the maximum value of soil salinity that does not reduce yield, S is the slope expressed in % per dS m -’ that indicates the yield reduction percentage per unit increase in soil salinity above the threshold, and ECe is the time-weighed average electrical conductivity of the saturated-soil extract taken from the root zone.

Data were analyzed by ANOVA and means were compared by Duncan’s Multiple Range Test. The residual effects of the irrigation frequencies were not significant and no interactions were found between any of the factors in these experiments.

3. Results

3. I. Soil salinity

At the end of the irrigation seasons, the ECe values in the top 30 cm varied between 3.7 dS m-l (treatment 0%) and 20 dS m-l (treatment 1%) (September 1991) and

S. De Pascale, G. Barbieri/Scientia Horticulturae 64 (1995) 145-157 149

mm 800

700

6OD

500

400

300

200

100

0 1- 2- 3* l^ 2- 3- 1- 2” 3- 1- 2. 3- l^ 2” 3” 1” 2” 3* 1” 2- 3” 1- 2” 3”

Sep act Nov Dee Jan Feb Mar Apr

i

0”““““““““““” 1” 2- 3” 1” 2- 3- 1’ 2- 3- 1- 2. 3- 1- 2^ 3- 1” 2- 3. 1” 2^ 3- 1- 2” 3”

Sep act Nov Dee Jan Feb Mar Apr

Fig. 1. Cumulative rainfall and mean air temperature during the trial periods and long-term averages (solid

line) (10 day basis) (T, transplanting; H, harvest).

between 2.2 and 13 dS m-l (September 1992). The total irrigation depth was 267 mm and 388 mm, respectively, for snap bean (1991) and eggplant (1992). From September to the transplanting of the winter crops, the cumulative rainfall was 556 mm for lettuce and 199 mm for endive and fennel (Fig. 1). Rainfall resulted in leaching the soil profile: in the top 30 cm soil, salinity was reduced to 2.6 (treatment 0%) and 5.2 dS m-l


Table 1

Mean ECe ( f 2 mean standard error) before transplanting and at harvest at different soil depths as a result of

salinity treatments

Soil depth (cm) Transplanting Harvest

NaCl (%) NaCl (%)

0 0.5 1 0 0.5 1

1992

o- 30

30- 60

60- 90

90-120

1993

o- 30

30- 60

60- 90

90-120

2.6*0.2 3.8 f 0.3 5.2 kO.9 2.9 i0.2 6.6* 1.1 7.0* 1.5

2.5 * 0.3 3.9*0.3 5.7f0.5 3.0*0.3 6.8kO.4 7.6 f 0.6

2.450.2 4.1*0.4 7.1 f 1.3 3.OrtO.2 7.1 f 0.6 tx4*0.5

2.2+0.1 4.3 f 0.4 7.5 f 1.3 2.7kO.3 7.0*0.9 8.4 f 0.6

2.2*0.2 4.7*0.5 7.0f0.8 2.1 f 0.2 3.5 f 0.2 5.2 f 1.2

2.3 fO.l 5.250.4 8.8 f 1.7 2.4kO.2 4.4 f 0.4 7.4*1.3

2.0*0.2 5.5*0.5 9.3 *to.9 2.2f0.2 4.7*0.4 8.2k1.6

2.1*0.1 5.9*0.5 9.3 i 0.8 2.3 f 0.3 5.1*0.3 8.8*1.2

(treatment 1%) in the first year, and to 2.2 dS m-l and 7 dS m-r in the second year (Table 1).

During the growing season, the cumulative rainfall was 198 mm (1992) and 257 mm (1993); nevertheless, in the first year soil salinity was brought to levels of 2.9 dS m-l (treatment 0%) and 7 dS m-l (treatment 1%). At harvest in 1993, the salinity was not as high as in the previous year, varying between 2.1 and 5.2 dS m-l in the no- and high-salt plots, due to different rain amount and distribution during the two production cycles. Soil salinity significantly increased from the 0% to the highest salinity treatment at each soil depth (Table 1).

The mean values of ECe in the O-30 cm soil layer tend to be higher in the 2 day than in the 10 day irrigation interval (Fig. 2), though the differences between the two irrigation frequencies were not statistically significant. The same trend was recorded during the dry season, but with significant differences between the short (26 dS m-‘> and the large (18 dS m-‘) irrigation interval: the same water salinity resulted in higher salt accumulation in the soil under high frequency than low frequency irrigation (large irrigation interval and higher watering volume).

In both years soil water content was significantly higher with greater soil salinity both after a wet and a dry period and water ponding persisted after rain for a long time in high salinity treatment (Fig. 3).

3.2. Lettuce

The net photosynthetic rate (P,), transpiration rate (T,) and stomata1 conductance CC,) were not affected by treatment 57 days after transplanting, whereas there was a significant reduction of these physiological parameters in the high-salinity treatment at harvest (Table 2). The lowest P, was associated with the lowest C, values resulting in the lowest T, values, which are the responsible for the control of water loss in leaves;

S. De Pascale, G. Barbieri/Scientia Horticulturae 64 (1995) 145-157 1.51

ECe dS m-’ 7

6-

+ 2 days

~+~ 5 days

- 10 days

0’ I I 1

0 0.25 0.5 0.75 1

Salt concentration of irrigation water %

Fig. 2. Time-weighted ECe vs. salt concentration of irrigation water by year and irrigation interval (layer O-30 cm).

reduction of T, may be due to reduction in stomata1 conductance, indicating an effective stomata1 control of water loss.

No difference was found between saline and control treatments on the survival of the transplanted seedlings (on average 11.6 plants m-*1. Lettuce plants grown on a clay

0

60

80

100

Soil depth cm

120 ’ I 1 / I 20 22 24 26

Soil water content %

26 30

Fig. 3. Soil water content (% dry weight basis) by soil depth and irrigation water salinity in a wet (January 1992) and dry period (March 1992).


Table 2 Gas exchange rates and stomata1 conductance in lettuce (n.s., non significant; * P < 0.05)

P, T, (mg CO, dm-* h-r) (mg H,O dm-* h-l)

10 March 1992

(‘Ariane R2’)

NaCl (%) 0

1

14 April 1992

NaCl (o/o)

0

1

Cultivar

‘Ariane R2’

‘Bix’

26.7 0.862 2768 25.4 1.111 2847

n.s. n.s. n.s.

17.4

10.3

15.0 0.929 3708 12.8 0.802 3953

n.s. n.s. n.s.

1.172 4086

0.560 3546 l I

P,, net photosynthetic rate; C,, stomatol conductance; T,, transpiration rate.

loam soil which underwent the same saline irrigation treatments from 1988 responded to increasing soil salinity by reducing marketable yield (MY) only at the highest salinity level. The percentage of non-marketable plants (non-MY) was significantly higher in the

1% treatment as compared with the control. A comparison between the two cultivars shows that ‘Bix’ gave the higher yield. Product quality was influenced by soil salinity: the incidence of tip bum increased at the higher soil salinity levels that significantly reduced total head leaf area and increased SLW and dry matter percentage (DM) (Table

3).

Table 3

Yield and head characteristics of lettuce (1992): mean values (different letters indicate significant differences

by Duncan’s multiple range test at P < 0.05)

Non-MY MY Weight Head

(o/o) (t ha-‘) (g) Leaf Leaf area Leaf

No. (dm’) DM (%)

NaCl (%) 0 6.0 b 42.2 ab 396 a 20.4 a 38.4 a 6.0 a

0.125 7.6 b 47.7 a 441a 19.6 a 36.1 b 6.1 a

0.25 7.1 b 41.9 ab 398 a 18.9 a 35.0 bc 6.7 b

0.5 9.2 ab 40.6 ab 384 a 18.9 a 33.3 c 6.6 b

1 13.7 a 38.8 b 389 a 21.3 a 34.9 bc 6.8 b

Cultivar

‘Ariane R2’ 12.7 a 37.0 a 360 a 21.8 a 31.0 a 7.3 a

‘Bix’ 5.2 b 47.4 b 447b 17.8 b 40.1 b 5.6 b

MY, marketable yield; DM, dry matter; SLW, specific leaf weight.

SLW

(mg cm-*)

5.7 a

6.5 bc

6.1 ab 7.0 c

6.9 c

7.6 a

5.3 b

S. De Pascale, G. Barbieri/Scientia Horticulturae 64 (1995) 145-157 153

Table 4 Yield and head characteristics of endive (1993): mean values (different letters indicate significant differences

by Duncan’s multiple range test at P < 0.05)

NaCl Non-MY MY Head

(%I (o/o) (t ha-‘) Weight

(g)

Diameter

(cm) Leaf

DM (%I

0 1.9 a 65.4 a 710 a 33.0 a 5.7 a

0.125 2.3 a 63.7 a 684 a 33.6 a 5.9 a

0.25 1.7 a 61.3 a 648 ab 32.7 ab 6.0 a

0.5 1.8 a 56.4 a 605 b 30.7 b 6.0 a

1 46.2 b 21.4 b 442c 27.2 c 7.1 b

MY, marketable yield; DM, dry matter.

3.3. Endive

Number of harvested plants was not affected by treatments (on average 9.4 plants m-‘1. The percentage of non-marketable heads was less than 50% of the total at the highest salinity level due to the occurrence of leaf injury such as marginal necrosis of the external leaves and burning of the young leaf margins or tips. In addition, other

growth aspects which affect market quality of endive were also adversely affected by previous saline irrigations: head diameter and weight were significantly reduced by the soil salinity levels in 0.5% and 1% treatments (Table 4). These effects were reflected in a significant reduction in marketable yield in the high-salt plots: the yield was only 30% of the mean yield of the other treatments. Leaf dry weight increased significantly when plants were grown under permanent saline-sodic conditions.

3.4. Fennel

Plant density at harvest was not affected by salt accumulation in the soil (on average 9.6 plants m-*1. Plant height was significantly reduced by the soil salinity levels in

0.5% and 1% treatments (Table 5). The percentage of non-marketable yield was higher in the 1% treatment due to a reduction in heart weight and length, as with length, the width and thickness of the harvested hearts decreased significantly (90% and 80%,

respectively, of the average of all the other treatments). The average dry weight of the

Table 5 Yield of fennel (1993): mean values (different letters indicate significant differences by Duncan’s multiple

range test at P < 0.05)

NaCl Non-MY

(%) (%o)

0 4.5 b

0.125 5.1 b

0.25 9.2 b

0.5 11.2 b

1 33.2 a

MY

(t ha-‘)

42.0 a 42.2 a 37.7 ab 31.9 b

18.3 c

Plant height

(cm)

64.3 a

64.9 a

62.4 a

57.7 b

53.5 c

MY, marketable yield.

154 S. De Pascale, G. Barbieri /Scientia Horticulturae 64 (1995) 145-157

Table 6

Characteristics and dimension ratios of fennel hearts (different letters indicate significant differences by

Duncan’s multiple range test at P < 0.05)

NaCl Weight DM Thickness T Width W Length L L/T W/T LmIy

(o/o) (g, (o/o) (cm) km) (cm)

0 466a 6.6 a 8.7 a 9.9 a 10.7 a 1.24 a 1.14 a 1.154 a

0.125 482 a 6.8 a 8.5 a 9.8 ab 10.4 a 1.23 a 1.15 ab 1.147 a

0.25 424 ab 7.0 a 8.4 a 9.8 ab 10.4 a 1.25 a 1.18 bc 1.152 a

0.5 378 b 7.5 b 7.7 b 9.2 b 10.2 a 1.33 ab 1.20 c 1.218 b

1 286 c 8.1 c 6.9 c 8.6 c 9.5 b 1.39 b 1.26 d 1.240 b

hearts was increased by saline treatments. The ratios W/T (flatten shape) and L/(wT>“.5 (cylinder-shape) increased under higher soil salinity levels (Table 61, while the ratio L / W (elongated shape) was 1.09 on the average.

3.5. Salt tolerance functions

The yield data over the growing season were significantly correlated to ECe within the O-30 cm layer (Fig. 4). With the ECe levels attained in these experiment, the

100 Relative yield %

60

J 0 2 4 6 8 10

ECedSm-'

. l=FENNEL y=lOO-13.33(ECe-1.76) r=-0.9782" = P-ENDIVE y=lOO-1557(ECe-2.03) r--0.9609" . 3-LETTUCE y-100.5.77(ECe-2.69) r--0.7687"

Fig. 4. Relative yield response of lettuce, endive and fennel to increasing soil salinity compared with the

Maas-Hoffman categories (S, sensitive crops; MS, moderately sensitive crops; MT, moderately tolerant crops;

T, tolerant crops).

S. De Pascale, G. Barbieri/Scientia Horticulturae 64 (1995) 145-157 1.55

threshold values, as defined by Maas and Hoffman, were 2.7 dS m-l for lettuce, 2.0 dS m-l for endive and 1.8 dS m-l for fennel. Yield was reduced at the rate of 5.8% per unit increase in soil salinity for lettuce: this amounted to 2.9 t ha-’ per dS m-l for cultivar ‘Bix’, considering that the control yield was 49.4 t ha-’ and to 2.0 t ha-’ per dS m-l for cultivar ‘Ariane R2’ for a control yield of 35.3 t ha-‘. Yield was reduced at the rate of 15.7% per unit increase in soil salinity for endive corresponding to 10.3 t ha-’ per dS m-‘. Yield was reduced at the rate of 13.3% per unit increase in soil salinity for fennel: this amounted to 5.6 t ha-’ per dS m-l. The 50% reduction in yield occurred at ECe of 5.2 dS m-l for endive and 5.5 for fennel while ECe should have

attained at least 11.4 dS m-l to halve the yield of lettuce.

4. Discussion and conclusion

The ECe levels attained after irrigation with saline water replicated on the same field over 5 years did not affect plant survival following transplanting during winter months. The same result reported for the three crops investigated seems to confirm that high salinity levels do not reduce plant stand after transplanting (seedling establishment) and transplanting can be used for most crops to establish stand in saline soils. Plants may be most sensitive during germination and early seedling stages of development and become relatively tolerant with age as observed in corn (Maas et al., 1983), sorghum (Maas et

al., 19861, wheat (Maas and Poss, 1989) and asparagus (Francois, 1987). The marketable yield was significantly reduced only in plots irrigated with the

highest value of water salinity starting from 1988. The results showed that soil salinity may have growth limiting effects in vegetable crops during cool, rainy periods in a salt-affected field where concentrations of sodium and chloride are high (Epstein and

Rains, 1987). The reduction in crop yields may be attributed to disorders in mineral nutrition and

toxicity caused by high sodium and chloride concentrations in the soil solution. Crop yields could also be adversely affected by soil physical and chemical characteristics altered by applying saline-sodic irrigation water. The soil structure index decreased from 50% to 12% and the soil water infiltration rate from 10 mm h-’ to less than 1 mm h-’ in 0% and 1% treatments, respectively (Ruggiero et al., 1994), which may be

caused by the sodium dominance on the adsorption complex that would determine deflocculation or puddling of the clay particles and can lower soil permeability and decrease its infiltration capacity (Lauchli and Epstein, 1990). These effects are high- lighted by disaggregation, crusting, poor tilth (coarse, cloddy and compacted topsoil aggregates), by higher water content and poor aeration in the rootzone. The increase in infiltration problems due to long-term irrigation with saline-sodic waters is in line with

the reports of Ayers and Westcot (1985) and Bajwa et al. (1992). Lettuce and endive appeared to be sensitive to tipburn and necrotic symptoms

occurring in plants under saline-sodic conditions; these symptoms may be attributed to low uptake rate of calcium, decreased xylem transport of this element or to a different partitioning of cations in plant tissues at high concentration of sodium ions in the soil solution (Sonneveld, 1988). At the end of the irrigation season, in the soil water extract

156 S. De Pascale, G. Barbieri/Scientia Horticulhuae 64 (1995) 145-157

the content of calcium ions was 0.11 meq per 100 g in the 0% treatment while no calcium was detected in the highest salinity plots; on the contrary the concentration of sodium ions varied between 0.12 meq per 100 g and 5.40 meq per 100 g, respectively.

The exchangeable Cazf decreased from 12.58 (treatment 0%) to 6.13 meq 100 g-’ of

soil (treatment 1%) while the exchangeable Na+ increased from 0.38 to 105.85 meq 100 g-’ of soil (Postiglione et al., 1995).

Product quality was affected by soil salinity. Leaf dry matter was positively related to salinity. SLW also increased with salinity and could be due to salinity-induced increases in leaf thickness as reported on tomato (Hayward and Long, 1941), bean (Meri and

Poljakoff-Mayber, 1967) and eggplant (Shalhevet et al., 1993; Ruggiero et al., 1994) leaves. In fennel hearts a shape modification occurred according to salinity; this phenomenon could be determined by a reduction of cell extension and/or division under saline conditions (Greenway and Munns, 1980).

Long-term exposure of roots to high salt concentrations reduced photosynthesis (- 41% in the 1% treatment as compared with the control) and this decline may be due to reduction in stomata1 conductance (-52%) and increasing stomata1 limitations to CO, uptake.

The salt tolerance functions of the crops were obtained by plotting the yield data against the ECe values within the O-30 cm soil layer where are most of the roots of the

vegetable species as reported on lettuce by Rowse (1974) and by Sutton and Merit (1993) and that should be considered the most critical soil layer in term of response of vegetable crops to salinity (Doorenbos and Pruitt, 1977). The results obtained by analyzing the salt tolerance model of Maas-Hoffman and its descriptive parameters, place lettuce and endive in the moderate sensitive category in terms of ECe. Comparing the threshold and slope values with those given by Maas and Hoffman (1977) and Maas (1986) lettuce appears to be less sensitive to salinity: the way plants respond to soil salinity depends not only on irrigation water quality but also on growth stage, soil properties and growing conditions. On the whole, the lower salt sensitivity found in our investigation may be explained by the fact that the results were derived from an experiment conducted in relatively cool and humid conditions under non-irrigated periods while the results reviewed by Maas and Hoffman were derived under hot, dry

conditions during irrigation time. Quantitative data of fennel place this crop among the moderately sensitive ones in contrast with what was reported by Gabriels (1972), who indicated fennel as a moderately tolerant crop though no quantitative information is available regarding its salt tolerance. There are differences in salt sensitivity among the three different crops: fennel and endive had a threshold value as low as many of the sensitive vegetable crops (cabbage, celery, spinach) while lettuce in our experiment showed a higher threshold value such as cucumber, broccoli and tomato and the rate of yield reduction as salinity increased beyond the threshold is milder for lettuce than for some vegetable crops considered moderately tolerant to salinity (beet and squash).

Acknowledgements

Funding for this research was provided by the Italian Ministry of University and Scientific Research (MURST 60%). The authors contributed to this study in equal measure.

S. De Pascale, G. Barbieri/ Scientia Horticulturae 64 (1995) 145-157 157

References

Ayers, R.S. and Westcot, D.W., 1985. Water quality for agriculture. FAO Irrig. Drain. Pap. 29, Rev. 1, FAO,

Rome, 63 pp.

Bajwa, MS., Choudhaty, O.P. and Josan, A.S., 1992. Effect of continuous irrigation with sodic and

saline-sodic waters on soil properties and crop yields under cotton-wheat rotation in northwestern India.

Agric. Water Manage., 22: 345-356.

Barbieri, G. and De Pascale, S., 1992. Salinita dell’acqua d’irrigazione e colture ortofloricole. Colture Protette,

2: 75-81.

Barbieri, G., Caruso, G. and Postiglione, I., 1990. Response of processing tomato to irrigation with saline

water. Proc. 1st. Congress European Society of Agronomy, Paris 5-7, December.

Barbieri, G., De Pascale, S. and Sifola, MI., 1994. Effetti della frequenza di inigazione sulle funzioni di

risposta produttiva della melanzana (Solanum melongena L.) alla salinih. Riv. Agron., 3: 235-246.

Caruso, G. and Postighone, L., 1993. Effetti dell’irrigazione con acqua a diversa concentrazione salina sul

suolo e su cultivar di pomodoro da industria (Lycopersicon lycopersicum L.). Riv. Agron., 3: 211-219.

Doorenbos, J. and Pruitt, W.O., 1977. Crop water requirement. FAO Irrig. Drain. Pap. 24, Rev. Rome, 144 pp.

Epstein, P. and Rams, D.W., 1987. Advances in salt tolerance. Plant and Soil, 99: 17-29.

Francois, L.E., 1987. Salinity effects on asparagus yield and vegetative growth. J. Am. Sot. Hortic. Sci., 112:

432-436.

Gabriels, R., 1972. Tol&nce aux sels des cultures agricoles et horticoles. Rev. Agric., 1: 53-72.

Graifenberg, A., Lipucci di Paola, M. and Giustiniani, L., 1993. Yield and growth of globe artichoke under

saline-sodic conditions. HortScience, 28: 791-793.

Greenway, H. and Munns, R., 1980. Mechanism of salt tolerance in Nonalophytes. Annu. Rev. Plant Physiol.,

31: 141-190.

Hayward, H.B. and Long E.M., 1941. Anatomical and physiological responses of the tomato to varying

concentrations of sodium chloride, sodium sulphate and nutrient solutions. Bot. Gaz., 102: 437-462.

Kalra Y.P. and Maynard, D.G., 1991. Methods manual for forest soil and plant analysis. For. Can. Northwest

Reg. North. For. Cent. Edmonton, Alberta, Inf. Rep. NOR-X-319.

Lauchli, A. and Epstein, E., 1990. Plant response to salinity and sodic conditions. ASCE Man. Rep. Eng.

Pratt., 71: 113-137.

Maas, E.V., 1986. Salt tolerance of plants. Appl. Agric. Res., 1: 12-26.

Maas, E.V., 1990. Crop salt tolerance. ASCE Man. Rep. Eng. Pratt., 71: 262-305.

Maas, E.V. and Hoffman, G.J., 1977. Crop salt tolerance. ASCE J. Irrig. Drain. Div., 103: 115-134.

Maas, E.V. and Pass, J.A., 1989. Salt sensitivity of wheat at various growth stages. Irrig. Sci., 10: 29-40.

Maas, E.V., Hoffman, G.J., Chaba, G.D., Pass, J.A. and Shannon, M.C., 1983. Salt sensitivity of corn at

various growth stages. Irrig. Sci., 4: 45-57.

Maas, E.V., Pass, J.A. and Hoffman, G.J., 1986. Salinity sensitivity of sorghum at three growth stages. Irrig.

Sci., 7: I-11.

Meri, A. and Poljakoff-Mayber, A., 1967. The effect of chlorine salinity on growth of bean leaves in thickness

and in area. Israel J. Bot., 16: 115-123.

Mizrahi, Y. and Pastern& D., 1985. Effect of salinity on quality of various agricultural crops. Plant Soil, 89:

301-307.

Postiglione, L., Barbieri, G. and Tedeschi, A., 1995. Long-term effects of irrigation with saline water on some

characteristics of a clay loam soil. Riv. Agron., 1: 24-30.

Rowse, H.R., 1974. The effect of irrigation on the length, weight and diameter of lettuce roots. Plant Soil, 40:

381-391.

Ruggiero, C., Barbieri, G. and De Pascale, S., 1994. Effetto della irrigazione con acque a diverso contenuto

salino sullo stato idrico, sull’accrescimento e sulla produtzione della melanzana (Solantun melongena L.).

Riv. Agron., 3: 222-234.

Russo, D., 1983a. Leaching characteristics of a stony desert soil. Soil Sci. Sot. Am. J., 47: 431-438.

Russo, D., 1983b. Crop yield-irrigation relationships in a gypsiferous-sodic soil. Agron. J., 75: 427-434.

Shalhevet, J., Heuer, B. and Meiri, A., 1993. Irrigation interval as a factor in the salt tolerance of eggplant.

Inig. Sci., 4: 83-93.

Sonneveld, C., 1988. The salt tolerance of greenhouse crops. Netherlands J. Agric. Sci., 36: 63-73.

Sutton, B.G. and Merit, N., 1993. Maintenance of lettuce root zone at field capacity gives best yields with drip

irrigation. Sci. Hortic., 56: l-l 1.

Documents

Effects of Soil Salinity From Long Term Irrigation