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Response to soil salinity of two chickpea varieties differing in drought tolerance
Agricultural Water Management 50 (2001) 83–96
Response to soil salinity of two chickpea varieties differing in drought tolerance N. Katerjia, J.W. van Hoornb,*,1, A. Hamdyc, M. Mastrorillid, T. Oweise, R.S. Malhotrae a
INRA, Unite´ de Recherche, Environnement et Grandes Cultures, 78850 Thivernal-Grignon, France b Sub-Department Water Resources, Wageningen University, The Netherlands c Istituto Agronomico Mediterraneo, 70010 Valenzano, Bari, Italy d Istituto Sperimentale Agronomico, 70125 Bari, Italy e ICARDA, P.B. 5466, Aleppo, Syria Accepted 21 March 2001
Abstract Two chickpea varieties, differing in drought tolerance, were grown in lysimeters filled with clay, and were irrigated with waters of three different salinity levels. Under non-saline conditions, both varieties, slightly differing in pre-dawn leaf water potential during the growth period, gave almost the same yield. Salinity had a slight effect on the leaf water potential and the osmotic adjustment. Both were slightly higher for the drought tolerant variety, but much lower in comparison with sugar beet, tomato and lentil. The drought tolerant variety showed an earlier senescence in leaf and dry matter development and flowering which were accelerated by salinity. The drought sensitive variety, however, showed under slightly saline conditions (ECe ¼ 2:5 dS/m) from 135 days after sowing onwards a different behaviour by the growth of new leaves and flowers, a delay in senescence, leading to the same yield as under non-saline conditions. Under saline conditions (ECe ¼ 3:8 dS/m) the drought sensitive variety showed the same yield reduction of about 70% as the drought tolerant variety. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Crop water stress; Crop water use efficiency; Leaf water potential; Osmotic adjustment; Salt tolerance; Drought tolerance; Chickpea
* 1
Corresponding author. Tel.: þ31-26-3335570; fax: þ31-317-484885. Retired.
0378-3774/01/$ – see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 1 ) 0 0 1 0 7 - X
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1. Introduction Chickpea (Cicer arietinum L.) is the third most widely grown grain legume in the world after bean and soybean (D’amore et al., 1996). The mediterranean origin of the crop imparts special significance to chickpea in the agriculture of this area, where it has multiple functions in the traditional farming systems. Besides being an important source of human and animal food, the crop also plays an important role in the maintenance of soil fertility, particularly in the dry, rainfed area (Saxena, 1990). In regions with a mediterranean climate, chickpea is sown in autumn or spring and grows during the cool, wet months of winter and spring. In both environments it is exposed to drought (Leport et al., 1999) during pod formation and seed filling (terminal drought). References are nowadays available for the classification of varieties according to drought tolerance (ICARDA, 2000). In chickpea, the ability of a crop to complete its life cycle before serious soil water deficit develops (drought escape), a deep root system, osmotic adjustment, high leaf water potential, early flowering and maturity, high biomass, and apparent redistribution of stem and leaf dry matter during pod filling are associated with drought tolerance (Morgan et al., 1991; Siddique et al., 1993; Silim and Saxena, 1993a,b; Subbarao et al., 1995; Thomson et al., 1997; Leport et al., 1998, 1999). The cool season food legumes are relatively more salt sensitive as compared to other crops and exhibit very little genetic diversity for salt tolerance (Malhotra, 1997). Few publications are available about the salt tolerance of chickpea. Franc¸ois and Maas (1994) classify chickpea as moderately salt sensitive, but without mentioning values for the threshold and the slope of the relationship between yield and soil salinity. Saxena (1987) mentions a yield reduction of 50% at an ECe of 3 dS/m, but Saxena et al. (1993) indicate that the critical value is much influenced by growth factors such as soil water status, relative humidity, temperature and nutrition. Very little experimental work under field conditions has been done with respect to salt tolerance of chickpea varieties (Malhotra, 1997). Greenhouse experiments with nutrient solutions cannot be generalized to field conditions as was shown in a previous paper on lentils (Katerji et al., 2001). Slightly saline soil and water of marginal quality for complementary irrigation during dry years are used more and more in the mediterranean area (Hamdy et al., 1993), a practice asking for a better knowledge of the salt tolerance of different varieties. This paper describes an experiment in which two chickpea varieties differing in tolerance to terminal drought were irrigated with waters of increasing salinity. Both varieties were compared during the entire life cycle with respect to the following parameters:
emergence; water stress and osmotic adjustment; leaf area biomass, flowering, senescence and yield; evapotranspiration and water use efficiency.
This comparison allows one to check whether tolerance to terminal drought corresponds with salt tolerance.
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2. Experimental procedure 2.1. Set-up The experiment was carried out at the Mediterranean Agronomic Institute (IAM), Bari, southern Italy between December 1999 and June 2000. The set-up consisted of 30 lysimeters of reinforced fibre glass with a diameter of 1.20 m and a depth of 1.20 m. A layer of coarse sand and gravel, 0.10 m thick, was overlain by a repacked soil profile of 1 m. At the bottom of the lysimeter, a pipe serving as a drainage outlet connected the lysimeter to a drainage reservoir. The set-up was covered at a height of 4 m by a sheet of transparent plastic to protect the assembly against precipitation. The lysimeter was filled with clay, the properties of which are presented in Table 1. The lysimeters were irrigated with water of three different qualities: the control treatment with fresh water containing 3.7 meq Cl/l and an electrical conductivity (EC) of 0.9 dS/m, and two saline treatments containing 15 and 30 meq Cl/l and an EC of 2.3 and 3.6 dS/m, obtained by adding equivalent amounts of NaCl and CaCl2 to fresh water. For each water quality, five tanks were available. Table 2 presents the chemical composition. The three salinity treatments will be identified by the abbreviations S1, S2, and S3. Just before sowing 6 l fresh water was applied on all treatments to obtain a sufficient emergence. Afterwards, surplus water was added at each irrigation to provide a leaching fraction of about 0.2. Water was applied when the evaporation of the class A pan had attained about 80 mm. The evapotranspiration of the irrigation interval was calculated as the difference between the amounts of irrigation and drainage water. For determining soil salinity, the average chloride concentration of soil water was calculated from the balance of irrigation and drainage water and converted into EC of soil water by the equation ln EC ¼ 0:824 ln Cl 1:42, established for this type of irrigation water and soil (van Hoorn et al., 1993). Moreover, soil water samplers were installed in Table 1 Soil properties Particle size in % of mineral parts <2 mm
2–50 mm
>50 mm
49
22
29
% CaCO3
11.4
% Organic matter 1.1
% Water (v/v) pF 2.0
pF 4.2
38.5
21.9
Bulk density (kg/dm3) 1.41
Table 2 Chemical composition of irrigation water (meq/l) Treatment
Ca2þ
Mg2þ
Naþ
Kþ
Cl
HCO3
SO42
EC (dS/m)
Fresh 15 meq Cl/l 30 meq Cl/l
6.3 10.8 15.8
2.9 2.8 3.1
2.3 8.6 16.6
0.4 0.4 0.4
3.7 15.0 29.5
7.3 6.7 6.4
0.7 0.9 0.8
1.1 2.3 3.6
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every lysimeter at four successive depths (17.5, 42.5, 67.5 and 92.5 cm) for determining the EC and the chemical composition of soil water. Since 30 lysimeters were available for testing two varieties at three salinity levels, five lysimeters were available for each of the six combinations. 2.2. Crops Two chickpea varieties were supplied by ICARDA. Variety ILC 3279, described by Singh et al. (1992), presents the following characteristics: late maturing, high shoot biomass, sensitive to terminal hydric stress (ICARDA, 2000), 100 seed weight of 28.9. This variety is indicated in this experiment as variety A. Variety Filip 87-59C, described by Singh et al. (1996), presents the following characteristics: early growth and flowering, tolerant to terminal drought, 100 seed weight of 33 g. This variety is indicated as variety B. The two varieties were sown on 23 December 1999 (day t) at a density of 80 grains per lysimeter. After emergence, the number of plants were reduced to 54 to obtain the same number for all treatments. Fertilising was done at a rate of 40 kg N/ha, 135 kg P/ha and 170 kg K/ha by adding NH4NO3 and KH2PO4 dissolved in water, during the early seedling stage and about 80 days after sowing. 2.3. Phenological observations The emergence and the survival of the seedlings was determined by daily counting of the number of plants during the first month after sowing till the survival percentage became stable at t þ 44. Chickpea makes a dense cover, especially under non-saline conditions. To determine the phenological dates and the development of the number of green and yellow leafs and the number of flowers, two plants per lysimeter were marked. Thus, the number of leafs and flowers is the average of 10 observations. When 50% of the plants had attained a phenological stage, this date was noted. 2.4. Water stress of the plant The pre-dawn leaf water potential was measured on one plant branch in each lysimeter. Due to the early senescence of some treatments, the branches were taken from the top of the green vegetation. During some typical days, the leaf water potential was measured every 2 h, also on five branches per treatment. 2.5. Pressure–volume curve for determining osmotic and turgor potential The pressure–volume curves that show the relationship between the leaf water potential and the relative water content of the leaf, were established from two replicates for all six treatments, following the procedure described in a previous paper (Katerji et al., 1997).
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2.6. Growth and yield The leaf area and the dry matter of leaf and stem were determined at the successive phenological stages on one plant in each lysimeter, first the leaf area and afterwards, the dry matter. At harvest the yield of grain and straw and the yield components (number of pods per plant, number of grains per 100 pods, weight of 1000 grains) were measured from all plants present on the lysimeters. 2.7. Statistical analysis The statistical analysis was made by the Student–Neumann–Keuls test at the 5% level to distinguish the variety effect by comparing the control treatments irrigated with fresh water and the salinity effect by comparing the saline treatments S2 and S3 with the control S1.
3. Results 3.1. Soil salinity Table 3 presents the average salinity of the soil profile, obtained from the salt balance, and shows almost the same values for the corresponding treatments of both varieties with a slight increase during the growing season. According to the observations of the soil water samplers, the salinity slightly increased with depth, as may be expected on long term in view of the regularly applied surplus water. 3.2. Emergence The emergence (Table 4) at 12 days after sowing already shows a difference between both varieties and a delay due to salinity. The emergence percentage for the corresponding treatments was always higher for variety B that for variety A and the delay due to salinity less pronounced. Treatment differences were only significant (P > 0:05) during the first 22 days after sowing, except for the most saline treatment of variety A, which remained about 20% lower than the control. Table 3 Average soil salinity (ECe, dS/m) of the soil profile during the growing season Variety A
Start End Average
Variety B
S1
S2
S3
S1
S2
S3
0.8 0.9 0.8
2.1 2.9 2.5
3.4 4.2 3.8
0.7 0.9 0.8
2.1 2.7 2.4
3.5 4.1 3.8
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Table 4 Emergence percentage of two chickpea varieties at three salinity levels Treatment
Days after sowing 12
14
17
22
28
44
S1 S2 S3
12 2 2
37 14 10
84 72 42
91 89 69
93 92 73
93 93 75
S1 S2 S3
26 24 2
78 65 22
99 92 67
100 95 91
100 96 95
100 96 96
A
B
3.3. Phenological stage Table 5 presents the principal phenological stages. Variety B shows a shorter life cycle (earlier ramification, flowering, etc.) than variety A, which is in agreement with the description of Singh et al. (1992, 1996). The saline treatments could be harvested at an earlier date than the control. 3.4. Water stress and osmotic adjustment The pre-dawn leaf water potential (Fig. 1) showed the usual trend of an increase after irrigation and a decrease during the irrigation interval. The value of the control AS1 varied between about 0.23 and 0.47 MPa during most of the growing season. Salinity had a significant effect. The picture for variety B was the same, the values being only slightly higher than those of the corresponding treatments of variety A, an average difference of 0.04 MPa at the S1 and S2 level, and 0.06 MPa at the S3 level. Fig. 2 shows the leaf water potential in variety A during the day 134 after sowing near the end of an irrigation cycle, 2 days before irrigation. The leaf water potential decreased regularly after dawn and attained its minimum around 13 h. The maximum difference between the most saline treatment and the control is small, 0.15 MPa, compared Table 5 Successive phenological stages in days after sowing on 24 December 1999 Variety A
Emergence Start of ramification Start of flowering Start of pod formation End of fruit formation Harvest
Variety B
S1
S2
S3
S1
S2
S3
14 46 122 130 140 190
16 52 114 127 134 183
18 56 122 130 137 183
12 42 97 110 130 190
13 43 97 110 128 174
16 50 97 110 128 174
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Fig. 1. Pre-dawn leaf water potential vs. days after sowing, variety A.
with the differences observed on maize, sunflower and sugar beet (Katerji et al., 1996, 1997). Variety B showed the same evolution, but always at a higher level than variety A. Table 6 presents the maximum osmotic potential (relative water content: 1), measured on 2 days at the end of an irrigation cycle. The statistical analysis showed the followings. The maximum osmotic potential decreases with time. This means an osmotic adjustment to the phenological stage, already observed in chickpea by Leport et al. (1999). The maximum osmotic potential decreases with increasing salinity, which means an osmotic adjustment to salinity, but this adjustment did not increase with time as contrasted with sugar beet (Katerji et al., 1997), tomato (Katerji et al., 1998) and lentil
Fig. 2. Leaf water potential during the 134th day after sowing, variety A.
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Table 6 Maximum osmotic potential at two growth stages (MPa) Days after sowing
119 133
Variety A
Variety B
S1
S2
S3
S1
S2
S3
0.728 0.877
0.744 0.886
0.782 0.913
0.647 0.771
0.683 0.794
0.728 0.900
(Katerji et al., 2001). The osmotic adjustment to salinity is also lower for chickpea than for sugar beet, tomato and lentil. The maximum osmotic potential of variety B is slightly higher than that of variety A, in agreement with the observations of the pre-dawn leaf water potential and confirming the observations of Silim and Saxena (1993a) who observed that drought tolerant varieties show a higher leaf water potential than sensitive varieties. The low osmotic adjustment of chickpea in this experiment corresponds with the results of Leport et al. (1999), who studied the osmotic adjustment of six irrigated and rainfed chickpea varieties differing in drought tolerance. They observed that when the difference between the midday leaf water potentials ranged between 0.1 and 0.3 MPa, values also observed in this experiment, the osmotic potentials were almost the same. When, however, the difference attained 2 MPa, there was a considerable genetic variation from 0 to 1.3 MPa in osmotic adjustment between the six chickpea genotypes. 3.5. Growth, flowering and evapotranspiration Figs. 3 and 4 present respectively the leaf area and the dry matter and Table 7 the number of flowers. The control treatments AS1 and BS1 did not show a difference in dry matter development. The leaf area values were the same till 158 days after sowing, but afterwards, the leaf area of variety B decreased more, due to earlier senescence. Flowering of variety B also started earlier, but the number of flowers was lower. The most saline treatments AS3 and BS3 also showed no significant differences in dry matter and leaf area, excepted at 169 days after sowing, when the leaf area of variety B was significantly lower, due to earlier senescence. Flowering of variety B also started earlier, but the maximum number of flowers was the same. The saline treatments AS2 and BS2 showed the same development of leaf area and dry matter till 135 days after sowing. Flowering of variety B started earlier, but at 135 days after sowing the number of flowers was the same for both varieties. Afterwards, the leaf area and the dry matter of variety A increased more and the difference with the control treatment became less than for variety B. Flowering of the saline treatment AS2 still continued and the number of flowers at 168 after sowing was even higher than that of the control treatment. The later senescence was caused by the growth of new leaves. At 158 days after sowing the number of green leaves (Table 8) of the control treatment was about 50% higher than that of the saline treatment AS2, but afterwards, the difference decreased and at 174 days after sowing the numbers were equal. Table 9, presenting the percentage
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Fig. 3. Leaf area vs. days after sowing.
of yellow leaves, also shows the later senescence of the saline treatment AS2. The percentage increased between 136 and 174 days after sowing from 16 to 70 for the control treatment and from 17 to 53 for the saline treatment. The evapotranspiration (Table 10) was affected by salinity from 66 days after sowing onwards. Variety did not affect the evapotranspiration till 137 days after sowing. Afterwards, the evapotranspiration of variety B was lower due the earlier senescence, in agreement with Tables 8 and 9. After the last irrigation before harvest, the values of the
Fig. 4. Dry matter vs. days after sowing.
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Table 7 Number of flowers per plant Days after sowing
97 118 136 158 168
Variety A
Variety B
S1
S2
S3
S1
S2
S3
0 0 34.6 26.4 5.2
0 2.8 20.4 20.4 10.0
0 1.0 19.4 11.4 6.2
4.3 21.4 27.0 14.4 5.8
3.2 16.4 20.0 11.2 1.4
4.5 11.0 18.6 12.8 1.0
Table 8 Number of green leaves per plant Days after sowing
97 118 136 158 168 174 183
Variety A
Variety B
S1
S2
S3
S1
S2
S3
29 64 135 196 131 80 31
30 41 94 127 101 78 Harvest
15 25 74 57 36 20 Harvest
29 77 121 128 88 41 21
21 58 91 113 56 Harvest
21 36 76 11 Harvest
control treatment and the saline treatment AS2 were about the same, owing to the late appearance of new leaves on the latter. 3.6. Yield and water use efficiency The control treatments of both varieties did not differ significantly with respect to total dry biomass, grain yield and yield components (Table 11). The ratio between grain yield and total dry biomass ranged around 0.33, also at the higher salinity levels. Table 9 Percentage of yellow leaves Days after sowing
97 118 136 158 168 174 183
Variety A
Variety B
S1
S2
S3
S1
S2
S3
3 18 16 27 51 70 89
23 32 17 23 40 53 Harvest
22 49 24 47 67 94 Harvest
21 17 29 24 48 76 88
39 31 21 32 67 Harvest
42 34 29 46 93 Harvest
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Table 10 Evapotranspiration in mm/day Days after sowing
Variety A
0–66 66–93 93–119 119–137 137–160 160–Harvest
Variety B
S1
S2
S3
S1
S2
S3
0.7 1.1 3.1 6.4 10.1 5.3
0.5 0.7 2.6 5.4 6.9 5.5
0.6 0.5 1.6 3.1 3.9 3.1
0.6 0.9 3.1 6.4 9.0 3.1
0.5 0.7 2.6 4.3 4.7 2.9
0.5 0.7 1.7 3.3 3.1 1.4
The most saline treatments also did no differ, except with respect to the number of grains per pod, being slightly higher for variety A, and the weight of 1000 grains, being slightly higher for variety B. The reduction in grain yield, about 70% at an ECe of 3.8 dS/ m, is caused by three factors, the number of pods per plant, the number of grains per 100 pods and the weight of 1000 grains, which means that salinity affects flowering, fecundation and grain filling. At the intermediate salinity, an ECe of 2.5 dS/m, variety A presented a yield of total dry biomass and grain almost equal to that of the control treatment. The yield components, however, show a significant difference in the number of pods per plant, which was higher, and the weight of 1000 grains, which was lower for the saline treatment. These differences were caused by the late flowering and the not yet completed grain filling at harvest time. Variety B showed a significant yield reduction compared with the control treatment. The yield reduction is due to a lower number of grains per 100 pods and a lower weight of 1000 grains, caused by the salinity affect on fecundation and grain filling. Owing to the experimental set-up of lysimeters, equipped with soil water samplers at successive depth, the measurement of root development was limited to a depth of 25 cm. Salinity as well as variety had a clear effect on root development. The water use efficiency of variety A (Table 12) increased at the intermediate salinity level, since its yield was almost the same and the evapotranspiration much lower than for the control treatment. The water use efficiency of variety B decreased with increasing Table 11 Yield of chickpea Variety A
2
Total dry biomass (g/m ) Grain (g/m2) Plants per m2 Pods per plant Grain per pod Weight of 1000 grains (g) Weight of roots in 0.0156 m3 (g)
Variety B
S1
S2
S3
S1
S2
S3
1308 474 44 40 102 26.6 8.8
1255 460 44 55 96 19.8 5.6
444 134 45 20 90 16.8 2.4
1308 420 43 36 107 25.4 3.5
680 240 43 32 81 21.5 3.4
413 130 42 20 76 20.6 1.0
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Table 12 Evapotranspiration, grain yield and water use efficiency (kg grains per m3 water) Variety A
Evapotranspiration (m) Grain yield (kg/m2) Water use efficiency (kg/m3)
Variety B
S1
S2
S3
S1
S2
S3
0.61 0.47 0.77
0.47 0.46 0.98
0.29 0.13 0.46
0.52 0.42 0.81
0.33 0.24 0.73
0.24 0.13 0.54
salinity. The control and the most saline treatment of variety B showed somewhat higher values than those of variety A, since the evapotranspiration was lower due to the earlier senescence.
4. Discussion and conclusion This study clearly shows that a difference in terminal drought tolerance does not correspond with a similar difference in salt tolerance, but leads to a different behaviour of the varieties when irrigated with waters of increasing salinity. When chickpea is irrigated with fresh water, both varieties A and B, differing in terminal drought tolerance, show almost the same reaction with respect to hydric stress, expressed by the pre-dawn leaf water potential, growth of leaf area and dry matter, and finally yield. The slight difference in water use efficiency is caused by lower evapotranspiration, owing to earlier senescence of variety B. Under slightly saline conditions, at an ECe of 2.5 dS/m, both varieties show the same development till 135 days after sowing. Afterwards, variety A shows an adaptation to soil salinity and catches up with the fresh water treatment by the growth of new leaves and flowers and a delay in senescence, leading to the same yield and even to a higher water use efficiency. Variety B, however, adapts a behaviour of drought escape by accelerating its growth and by reducing its leaf area, dry matter and flowering. Since the yield reduction of about 50% was stronger than the reduction in evapotranspiration of about 30%, the water use efficiency was almost 25% lower. Under almost saline conditions, at an ECe of 3.8 dS/m, both varieties adapt the same behaviour of drought escape as variety B already showed at a lower salinity, causing a yield reduction of about 70%. Since the growth acceleration of variety B is stronger, its water use efficiency is higher that that of variety A. The difference in emergence, about 20% lower for variety A at the highest salinity level, has been eliminated artificially in our experiment after the emergence percentage became stable. Without this elimination, the difference in water use efficiency could even have been larger. Silim and Saxena (1993a) concluded that ‘‘short duration cultivars, in general, give low yields in seasons with higher rainfall, as compared to medium to late maturing cultivars. This is due to the fact that these cultivars cannot make full use of available water and might leave a large component of potentially transpirable water as unused in the soil’’. Our experiment also indicates that a late variety profits from saline water as long as
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salinity does not exceed an ECe of 2.5 dS/m. The early variety, however, does not adapt in the same way. The observations of this study point towards three factors that enable the late variety A to optimize water under slightly saline conditions. A stronger root development, allowing a better use of soil water. Although the measurements were limited to a depth of 25 cm, Swelam (2000) generalizes our observations by showing that also for the total depth of the root system the mass of roots of variety A is two times that of variety B, under non-saline and slightly saline conditions. The ability to create a large biomass by catching up in growth of leaves, dry matter and flowering. According to our yield observations, a strong relationship, a ratio of about 0.33, exists between the total dry biomass and the grain yield. Thomson and Siddique (1997) and Thomson et al. (1997) observed the same. Siddique et al. (1993) suggest that the ability of forming a large biomass be considered as a selection criterion for drought tolerance of chickpea. The ability for maintaining a high nitrogen fixation under slightly saline conditions. The nitrogen balances of both varieties (van Hoorn et al., 2002) indicate that variety A maintained its nitrogen fixation under slightly saline conditions at the same level as under non-saline conditions, and two times higher than variety B. These three factors merit to be considered for improving the salt tolerance of chickpea.
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Morgan, J.M., Rodriquez-Maribona, B., Knights, E.J., 1991. Adaptation to water-deficit in chickpea breeding lines by osmoregulation: relationship to grain yields in the field. Field Crops Res. 27, 61–70. Saxena, N.P., 1987. Problems and prospects to screen and breed for tolerance to soil salinity: a case study with chickpea. In: Adaptation of Chickpea and Pigeonpea to Abiotic Stresses. Proceedings of the Consultants’ Workshop. ICRISAT, Patancheru, India, 19–21 December 1984, pp. 11–120. Saxena, N.P., 1990. Status of chickpea in the Mediterranean basin. In: Present Status and Future Prospects of Chickpea Crop Production and Improvement in the Mediterranean Countries. Seminar Zaragoza (Spain). Options Me´ diterraneennes (CIHEAM) Se´ rie A, Vol. 9, 11–13 July 1988, pp. 17–24. Saxena, N.P., Johanson, C., Saxena, M.C., Silim, S.N., 1993. Selection for drought and salinity resistance in cool season food legumes. In: Singh, K.B., Saxena, M.C. (Eds.), Breeding for Stress Resistance in Cool Season Food Legumes. Wiley, New York, pp. 245–270. Siddique, K.H.M., Walton, G.H., Seymour, M., 1993. A comparison of seed yields of winter grain legumes in Western Australia. Aust. J. Exp. Agric. 33, 915–922. Silim, S.N., Saxena, M.C., 1993a. Adaptation of spring-sown chickpea to the Mediterranean basin. II. Response to moisture supply. Field Crops Res. 34, 121–136. Silim, S.N., Saxena, M.C., 1993b. Adaptation of spring-sown chickpea to the Mediterranean basin. II. Factors influencing yield under drought. Field Crops Res. 34, 137–146. Singh, K.B., Malhotra, R.S., Saxena, M.C., 1992. Registration of ILC 3279 chickpea. Crop Sci. 32, 826–827. Singh, K.B., Omar, M., Saxena, M.C., Johanson, C., 1996. Registration of FLIP 87-59C, a drought tolerance chickpea germplasm line. Crop Sci. 36, 472. Subbarao, G.B., Johanson, C., Slinkard, A.E., Rao, R.C.N., Saxena, N.P., Chauhan, Y.S., 1995. Strategies for improving drought resistance in grain legumes. Crit. Rev. Plant Sci. 14, 469–523. Thomson, B.D., Siddique, K.H.M., 1997. Grain legumes species in low rainfall Mediterranean-type environments. II. Canopy development, radiation interception and dry matter production. Field Crops Res. 54, 189–199. Thomson, B.D., Siddique, K.H.M., Barr, M.D., Wilson, J.M., 1997. Grain legume species in low rainfall Mediterranean-type environments. I. Phenology and seed yield. Field Crops Res. 54, 173–187. Swelam, A., 2000. Saline irrigation management and salt tolerance of chickpea varieties. M.Sc. Thesis no. 207, Mediterranean Agronomic Institute (IAM), Bari, 166 pp. van Hoorn, J.W., Katerji, N., Hamdy, A., Mastrorilli, M., 1993. Effect of saline water on soil salinity and on water stress, growth and yield of wheat and potatoes. Agric. Water Manage. 23, 247–265. van Hoorn, J.W., Katerji, N., Hamdy, A., Masterorilli, M., 2002. Effect of salinity on yield and nitrogen uptake of four grain legumes and on biological nitrogen contribution from the soil. Agric. Water Manage., in press.
Response to soil salinity of two chickpea varieties differing in drought tolerance N. Katerjia, J.W. van Hoornb,*,1, A. Hamdyc, M. Mastrorillid, T. Oweise, R.S. Malhotrae a
INRA, Unite´ de Recherche, Environnement et Grandes Cultures, 78850 Thivernal-Grignon, France b Sub-Department Water Resources, Wageningen University, The Netherlands c Istituto Agronomico Mediterraneo, 70010 Valenzano, Bari, Italy d Istituto Sperimentale Agronomico, 70125 Bari, Italy e ICARDA, P.B. 5466, Aleppo, Syria Accepted 21 March 2001
Abstract Two chickpea varieties, differing in drought tolerance, were grown in lysimeters filled with clay, and were irrigated with waters of three different salinity levels. Under non-saline conditions, both varieties, slightly differing in pre-dawn leaf water potential during the growth period, gave almost the same yield. Salinity had a slight effect on the leaf water potential and the osmotic adjustment. Both were slightly higher for the drought tolerant variety, but much lower in comparison with sugar beet, tomato and lentil. The drought tolerant variety showed an earlier senescence in leaf and dry matter development and flowering which were accelerated by salinity. The drought sensitive variety, however, showed under slightly saline conditions (ECe ¼ 2:5 dS/m) from 135 days after sowing onwards a different behaviour by the growth of new leaves and flowers, a delay in senescence, leading to the same yield as under non-saline conditions. Under saline conditions (ECe ¼ 3:8 dS/m) the drought sensitive variety showed the same yield reduction of about 70% as the drought tolerant variety. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Crop water stress; Crop water use efficiency; Leaf water potential; Osmotic adjustment; Salt tolerance; Drought tolerance; Chickpea
* 1
Corresponding author. Tel.: þ31-26-3335570; fax: þ31-317-484885. Retired.
0378-3774/01/$ – see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 1 ) 0 0 1 0 7 - X
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1. Introduction Chickpea (Cicer arietinum L.) is the third most widely grown grain legume in the world after bean and soybean (D’amore et al., 1996). The mediterranean origin of the crop imparts special significance to chickpea in the agriculture of this area, where it has multiple functions in the traditional farming systems. Besides being an important source of human and animal food, the crop also plays an important role in the maintenance of soil fertility, particularly in the dry, rainfed area (Saxena, 1990). In regions with a mediterranean climate, chickpea is sown in autumn or spring and grows during the cool, wet months of winter and spring. In both environments it is exposed to drought (Leport et al., 1999) during pod formation and seed filling (terminal drought). References are nowadays available for the classification of varieties according to drought tolerance (ICARDA, 2000). In chickpea, the ability of a crop to complete its life cycle before serious soil water deficit develops (drought escape), a deep root system, osmotic adjustment, high leaf water potential, early flowering and maturity, high biomass, and apparent redistribution of stem and leaf dry matter during pod filling are associated with drought tolerance (Morgan et al., 1991; Siddique et al., 1993; Silim and Saxena, 1993a,b; Subbarao et al., 1995; Thomson et al., 1997; Leport et al., 1998, 1999). The cool season food legumes are relatively more salt sensitive as compared to other crops and exhibit very little genetic diversity for salt tolerance (Malhotra, 1997). Few publications are available about the salt tolerance of chickpea. Franc¸ois and Maas (1994) classify chickpea as moderately salt sensitive, but without mentioning values for the threshold and the slope of the relationship between yield and soil salinity. Saxena (1987) mentions a yield reduction of 50% at an ECe of 3 dS/m, but Saxena et al. (1993) indicate that the critical value is much influenced by growth factors such as soil water status, relative humidity, temperature and nutrition. Very little experimental work under field conditions has been done with respect to salt tolerance of chickpea varieties (Malhotra, 1997). Greenhouse experiments with nutrient solutions cannot be generalized to field conditions as was shown in a previous paper on lentils (Katerji et al., 2001). Slightly saline soil and water of marginal quality for complementary irrigation during dry years are used more and more in the mediterranean area (Hamdy et al., 1993), a practice asking for a better knowledge of the salt tolerance of different varieties. This paper describes an experiment in which two chickpea varieties differing in tolerance to terminal drought were irrigated with waters of increasing salinity. Both varieties were compared during the entire life cycle with respect to the following parameters:
emergence; water stress and osmotic adjustment; leaf area biomass, flowering, senescence and yield; evapotranspiration and water use efficiency.
This comparison allows one to check whether tolerance to terminal drought corresponds with salt tolerance.
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2. Experimental procedure 2.1. Set-up The experiment was carried out at the Mediterranean Agronomic Institute (IAM), Bari, southern Italy between December 1999 and June 2000. The set-up consisted of 30 lysimeters of reinforced fibre glass with a diameter of 1.20 m and a depth of 1.20 m. A layer of coarse sand and gravel, 0.10 m thick, was overlain by a repacked soil profile of 1 m. At the bottom of the lysimeter, a pipe serving as a drainage outlet connected the lysimeter to a drainage reservoir. The set-up was covered at a height of 4 m by a sheet of transparent plastic to protect the assembly against precipitation. The lysimeter was filled with clay, the properties of which are presented in Table 1. The lysimeters were irrigated with water of three different qualities: the control treatment with fresh water containing 3.7 meq Cl/l and an electrical conductivity (EC) of 0.9 dS/m, and two saline treatments containing 15 and 30 meq Cl/l and an EC of 2.3 and 3.6 dS/m, obtained by adding equivalent amounts of NaCl and CaCl2 to fresh water. For each water quality, five tanks were available. Table 2 presents the chemical composition. The three salinity treatments will be identified by the abbreviations S1, S2, and S3. Just before sowing 6 l fresh water was applied on all treatments to obtain a sufficient emergence. Afterwards, surplus water was added at each irrigation to provide a leaching fraction of about 0.2. Water was applied when the evaporation of the class A pan had attained about 80 mm. The evapotranspiration of the irrigation interval was calculated as the difference between the amounts of irrigation and drainage water. For determining soil salinity, the average chloride concentration of soil water was calculated from the balance of irrigation and drainage water and converted into EC of soil water by the equation ln EC ¼ 0:824 ln Cl 1:42, established for this type of irrigation water and soil (van Hoorn et al., 1993). Moreover, soil water samplers were installed in Table 1 Soil properties Particle size in % of mineral parts <2 mm
2–50 mm
>50 mm
49
22
29
% CaCO3
11.4
% Organic matter 1.1
% Water (v/v) pF 2.0
pF 4.2
38.5
21.9
Bulk density (kg/dm3) 1.41
Table 2 Chemical composition of irrigation water (meq/l) Treatment
Ca2þ
Mg2þ
Naþ
Kþ
Cl
HCO3
SO42
EC (dS/m)
Fresh 15 meq Cl/l 30 meq Cl/l
6.3 10.8 15.8
2.9 2.8 3.1
2.3 8.6 16.6
0.4 0.4 0.4
3.7 15.0 29.5
7.3 6.7 6.4
0.7 0.9 0.8
1.1 2.3 3.6
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every lysimeter at four successive depths (17.5, 42.5, 67.5 and 92.5 cm) for determining the EC and the chemical composition of soil water. Since 30 lysimeters were available for testing two varieties at three salinity levels, five lysimeters were available for each of the six combinations. 2.2. Crops Two chickpea varieties were supplied by ICARDA. Variety ILC 3279, described by Singh et al. (1992), presents the following characteristics: late maturing, high shoot biomass, sensitive to terminal hydric stress (ICARDA, 2000), 100 seed weight of 28.9. This variety is indicated in this experiment as variety A. Variety Filip 87-59C, described by Singh et al. (1996), presents the following characteristics: early growth and flowering, tolerant to terminal drought, 100 seed weight of 33 g. This variety is indicated as variety B. The two varieties were sown on 23 December 1999 (day t) at a density of 80 grains per lysimeter. After emergence, the number of plants were reduced to 54 to obtain the same number for all treatments. Fertilising was done at a rate of 40 kg N/ha, 135 kg P/ha and 170 kg K/ha by adding NH4NO3 and KH2PO4 dissolved in water, during the early seedling stage and about 80 days after sowing. 2.3. Phenological observations The emergence and the survival of the seedlings was determined by daily counting of the number of plants during the first month after sowing till the survival percentage became stable at t þ 44. Chickpea makes a dense cover, especially under non-saline conditions. To determine the phenological dates and the development of the number of green and yellow leafs and the number of flowers, two plants per lysimeter were marked. Thus, the number of leafs and flowers is the average of 10 observations. When 50% of the plants had attained a phenological stage, this date was noted. 2.4. Water stress of the plant The pre-dawn leaf water potential was measured on one plant branch in each lysimeter. Due to the early senescence of some treatments, the branches were taken from the top of the green vegetation. During some typical days, the leaf water potential was measured every 2 h, also on five branches per treatment. 2.5. Pressure–volume curve for determining osmotic and turgor potential The pressure–volume curves that show the relationship between the leaf water potential and the relative water content of the leaf, were established from two replicates for all six treatments, following the procedure described in a previous paper (Katerji et al., 1997).
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2.6. Growth and yield The leaf area and the dry matter of leaf and stem were determined at the successive phenological stages on one plant in each lysimeter, first the leaf area and afterwards, the dry matter. At harvest the yield of grain and straw and the yield components (number of pods per plant, number of grains per 100 pods, weight of 1000 grains) were measured from all plants present on the lysimeters. 2.7. Statistical analysis The statistical analysis was made by the Student–Neumann–Keuls test at the 5% level to distinguish the variety effect by comparing the control treatments irrigated with fresh water and the salinity effect by comparing the saline treatments S2 and S3 with the control S1.
3. Results 3.1. Soil salinity Table 3 presents the average salinity of the soil profile, obtained from the salt balance, and shows almost the same values for the corresponding treatments of both varieties with a slight increase during the growing season. According to the observations of the soil water samplers, the salinity slightly increased with depth, as may be expected on long term in view of the regularly applied surplus water. 3.2. Emergence The emergence (Table 4) at 12 days after sowing already shows a difference between both varieties and a delay due to salinity. The emergence percentage for the corresponding treatments was always higher for variety B that for variety A and the delay due to salinity less pronounced. Treatment differences were only significant (P > 0:05) during the first 22 days after sowing, except for the most saline treatment of variety A, which remained about 20% lower than the control. Table 3 Average soil salinity (ECe, dS/m) of the soil profile during the growing season Variety A
Start End Average
Variety B
S1
S2
S3
S1
S2
S3
0.8 0.9 0.8
2.1 2.9 2.5
3.4 4.2 3.8
0.7 0.9 0.8
2.1 2.7 2.4
3.5 4.1 3.8
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Table 4 Emergence percentage of two chickpea varieties at three salinity levels Treatment
Days after sowing 12
14
17
22
28
44
S1 S2 S3
12 2 2
37 14 10
84 72 42
91 89 69
93 92 73
93 93 75
S1 S2 S3
26 24 2
78 65 22
99 92 67
100 95 91
100 96 95
100 96 96
A
B
3.3. Phenological stage Table 5 presents the principal phenological stages. Variety B shows a shorter life cycle (earlier ramification, flowering, etc.) than variety A, which is in agreement with the description of Singh et al. (1992, 1996). The saline treatments could be harvested at an earlier date than the control. 3.4. Water stress and osmotic adjustment The pre-dawn leaf water potential (Fig. 1) showed the usual trend of an increase after irrigation and a decrease during the irrigation interval. The value of the control AS1 varied between about 0.23 and 0.47 MPa during most of the growing season. Salinity had a significant effect. The picture for variety B was the same, the values being only slightly higher than those of the corresponding treatments of variety A, an average difference of 0.04 MPa at the S1 and S2 level, and 0.06 MPa at the S3 level. Fig. 2 shows the leaf water potential in variety A during the day 134 after sowing near the end of an irrigation cycle, 2 days before irrigation. The leaf water potential decreased regularly after dawn and attained its minimum around 13 h. The maximum difference between the most saline treatment and the control is small, 0.15 MPa, compared Table 5 Successive phenological stages in days after sowing on 24 December 1999 Variety A
Emergence Start of ramification Start of flowering Start of pod formation End of fruit formation Harvest
Variety B
S1
S2
S3
S1
S2
S3
14 46 122 130 140 190
16 52 114 127 134 183
18 56 122 130 137 183
12 42 97 110 130 190
13 43 97 110 128 174
16 50 97 110 128 174
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Fig. 1. Pre-dawn leaf water potential vs. days after sowing, variety A.
with the differences observed on maize, sunflower and sugar beet (Katerji et al., 1996, 1997). Variety B showed the same evolution, but always at a higher level than variety A. Table 6 presents the maximum osmotic potential (relative water content: 1), measured on 2 days at the end of an irrigation cycle. The statistical analysis showed the followings. The maximum osmotic potential decreases with time. This means an osmotic adjustment to the phenological stage, already observed in chickpea by Leport et al. (1999). The maximum osmotic potential decreases with increasing salinity, which means an osmotic adjustment to salinity, but this adjustment did not increase with time as contrasted with sugar beet (Katerji et al., 1997), tomato (Katerji et al., 1998) and lentil
Fig. 2. Leaf water potential during the 134th day after sowing, variety A.
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Table 6 Maximum osmotic potential at two growth stages (MPa) Days after sowing
119 133
Variety A
Variety B
S1
S2
S3
S1
S2
S3
0.728 0.877
0.744 0.886
0.782 0.913
0.647 0.771
0.683 0.794
0.728 0.900
(Katerji et al., 2001). The osmotic adjustment to salinity is also lower for chickpea than for sugar beet, tomato and lentil. The maximum osmotic potential of variety B is slightly higher than that of variety A, in agreement with the observations of the pre-dawn leaf water potential and confirming the observations of Silim and Saxena (1993a) who observed that drought tolerant varieties show a higher leaf water potential than sensitive varieties. The low osmotic adjustment of chickpea in this experiment corresponds with the results of Leport et al. (1999), who studied the osmotic adjustment of six irrigated and rainfed chickpea varieties differing in drought tolerance. They observed that when the difference between the midday leaf water potentials ranged between 0.1 and 0.3 MPa, values also observed in this experiment, the osmotic potentials were almost the same. When, however, the difference attained 2 MPa, there was a considerable genetic variation from 0 to 1.3 MPa in osmotic adjustment between the six chickpea genotypes. 3.5. Growth, flowering and evapotranspiration Figs. 3 and 4 present respectively the leaf area and the dry matter and Table 7 the number of flowers. The control treatments AS1 and BS1 did not show a difference in dry matter development. The leaf area values were the same till 158 days after sowing, but afterwards, the leaf area of variety B decreased more, due to earlier senescence. Flowering of variety B also started earlier, but the number of flowers was lower. The most saline treatments AS3 and BS3 also showed no significant differences in dry matter and leaf area, excepted at 169 days after sowing, when the leaf area of variety B was significantly lower, due to earlier senescence. Flowering of variety B also started earlier, but the maximum number of flowers was the same. The saline treatments AS2 and BS2 showed the same development of leaf area and dry matter till 135 days after sowing. Flowering of variety B started earlier, but at 135 days after sowing the number of flowers was the same for both varieties. Afterwards, the leaf area and the dry matter of variety A increased more and the difference with the control treatment became less than for variety B. Flowering of the saline treatment AS2 still continued and the number of flowers at 168 after sowing was even higher than that of the control treatment. The later senescence was caused by the growth of new leaves. At 158 days after sowing the number of green leaves (Table 8) of the control treatment was about 50% higher than that of the saline treatment AS2, but afterwards, the difference decreased and at 174 days after sowing the numbers were equal. Table 9, presenting the percentage
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Fig. 3. Leaf area vs. days after sowing.
of yellow leaves, also shows the later senescence of the saline treatment AS2. The percentage increased between 136 and 174 days after sowing from 16 to 70 for the control treatment and from 17 to 53 for the saline treatment. The evapotranspiration (Table 10) was affected by salinity from 66 days after sowing onwards. Variety did not affect the evapotranspiration till 137 days after sowing. Afterwards, the evapotranspiration of variety B was lower due the earlier senescence, in agreement with Tables 8 and 9. After the last irrigation before harvest, the values of the
Fig. 4. Dry matter vs. days after sowing.
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Table 7 Number of flowers per plant Days after sowing
97 118 136 158 168
Variety A
Variety B
S1
S2
S3
S1
S2
S3
0 0 34.6 26.4 5.2
0 2.8 20.4 20.4 10.0
0 1.0 19.4 11.4 6.2
4.3 21.4 27.0 14.4 5.8
3.2 16.4 20.0 11.2 1.4
4.5 11.0 18.6 12.8 1.0
Table 8 Number of green leaves per plant Days after sowing
97 118 136 158 168 174 183
Variety A
Variety B
S1
S2
S3
S1
S2
S3
29 64 135 196 131 80 31
30 41 94 127 101 78 Harvest
15 25 74 57 36 20 Harvest
29 77 121 128 88 41 21
21 58 91 113 56 Harvest
21 36 76 11 Harvest
control treatment and the saline treatment AS2 were about the same, owing to the late appearance of new leaves on the latter. 3.6. Yield and water use efficiency The control treatments of both varieties did not differ significantly with respect to total dry biomass, grain yield and yield components (Table 11). The ratio between grain yield and total dry biomass ranged around 0.33, also at the higher salinity levels. Table 9 Percentage of yellow leaves Days after sowing
97 118 136 158 168 174 183
Variety A
Variety B
S1
S2
S3
S1
S2
S3
3 18 16 27 51 70 89
23 32 17 23 40 53 Harvest
22 49 24 47 67 94 Harvest
21 17 29 24 48 76 88
39 31 21 32 67 Harvest
42 34 29 46 93 Harvest
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Table 10 Evapotranspiration in mm/day Days after sowing
Variety A
0–66 66–93 93–119 119–137 137–160 160–Harvest
Variety B
S1
S2
S3
S1
S2
S3
0.7 1.1 3.1 6.4 10.1 5.3
0.5 0.7 2.6 5.4 6.9 5.5
0.6 0.5 1.6 3.1 3.9 3.1
0.6 0.9 3.1 6.4 9.0 3.1
0.5 0.7 2.6 4.3 4.7 2.9
0.5 0.7 1.7 3.3 3.1 1.4
The most saline treatments also did no differ, except with respect to the number of grains per pod, being slightly higher for variety A, and the weight of 1000 grains, being slightly higher for variety B. The reduction in grain yield, about 70% at an ECe of 3.8 dS/ m, is caused by three factors, the number of pods per plant, the number of grains per 100 pods and the weight of 1000 grains, which means that salinity affects flowering, fecundation and grain filling. At the intermediate salinity, an ECe of 2.5 dS/m, variety A presented a yield of total dry biomass and grain almost equal to that of the control treatment. The yield components, however, show a significant difference in the number of pods per plant, which was higher, and the weight of 1000 grains, which was lower for the saline treatment. These differences were caused by the late flowering and the not yet completed grain filling at harvest time. Variety B showed a significant yield reduction compared with the control treatment. The yield reduction is due to a lower number of grains per 100 pods and a lower weight of 1000 grains, caused by the salinity affect on fecundation and grain filling. Owing to the experimental set-up of lysimeters, equipped with soil water samplers at successive depth, the measurement of root development was limited to a depth of 25 cm. Salinity as well as variety had a clear effect on root development. The water use efficiency of variety A (Table 12) increased at the intermediate salinity level, since its yield was almost the same and the evapotranspiration much lower than for the control treatment. The water use efficiency of variety B decreased with increasing Table 11 Yield of chickpea Variety A
2
Total dry biomass (g/m ) Grain (g/m2) Plants per m2 Pods per plant Grain per pod Weight of 1000 grains (g) Weight of roots in 0.0156 m3 (g)
Variety B
S1
S2
S3
S1
S2
S3
1308 474 44 40 102 26.6 8.8
1255 460 44 55 96 19.8 5.6
444 134 45 20 90 16.8 2.4
1308 420 43 36 107 25.4 3.5
680 240 43 32 81 21.5 3.4
413 130 42 20 76 20.6 1.0
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Table 12 Evapotranspiration, grain yield and water use efficiency (kg grains per m3 water) Variety A
Evapotranspiration (m) Grain yield (kg/m2) Water use efficiency (kg/m3)
Variety B
S1
S2
S3
S1
S2
S3
0.61 0.47 0.77
0.47 0.46 0.98
0.29 0.13 0.46
0.52 0.42 0.81
0.33 0.24 0.73
0.24 0.13 0.54
salinity. The control and the most saline treatment of variety B showed somewhat higher values than those of variety A, since the evapotranspiration was lower due to the earlier senescence.
4. Discussion and conclusion This study clearly shows that a difference in terminal drought tolerance does not correspond with a similar difference in salt tolerance, but leads to a different behaviour of the varieties when irrigated with waters of increasing salinity. When chickpea is irrigated with fresh water, both varieties A and B, differing in terminal drought tolerance, show almost the same reaction with respect to hydric stress, expressed by the pre-dawn leaf water potential, growth of leaf area and dry matter, and finally yield. The slight difference in water use efficiency is caused by lower evapotranspiration, owing to earlier senescence of variety B. Under slightly saline conditions, at an ECe of 2.5 dS/m, both varieties show the same development till 135 days after sowing. Afterwards, variety A shows an adaptation to soil salinity and catches up with the fresh water treatment by the growth of new leaves and flowers and a delay in senescence, leading to the same yield and even to a higher water use efficiency. Variety B, however, adapts a behaviour of drought escape by accelerating its growth and by reducing its leaf area, dry matter and flowering. Since the yield reduction of about 50% was stronger than the reduction in evapotranspiration of about 30%, the water use efficiency was almost 25% lower. Under almost saline conditions, at an ECe of 3.8 dS/m, both varieties adapt the same behaviour of drought escape as variety B already showed at a lower salinity, causing a yield reduction of about 70%. Since the growth acceleration of variety B is stronger, its water use efficiency is higher that that of variety A. The difference in emergence, about 20% lower for variety A at the highest salinity level, has been eliminated artificially in our experiment after the emergence percentage became stable. Without this elimination, the difference in water use efficiency could even have been larger. Silim and Saxena (1993a) concluded that ‘‘short duration cultivars, in general, give low yields in seasons with higher rainfall, as compared to medium to late maturing cultivars. This is due to the fact that these cultivars cannot make full use of available water and might leave a large component of potentially transpirable water as unused in the soil’’. Our experiment also indicates that a late variety profits from saline water as long as
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salinity does not exceed an ECe of 2.5 dS/m. The early variety, however, does not adapt in the same way. The observations of this study point towards three factors that enable the late variety A to optimize water under slightly saline conditions. A stronger root development, allowing a better use of soil water. Although the measurements were limited to a depth of 25 cm, Swelam (2000) generalizes our observations by showing that also for the total depth of the root system the mass of roots of variety A is two times that of variety B, under non-saline and slightly saline conditions. The ability to create a large biomass by catching up in growth of leaves, dry matter and flowering. According to our yield observations, a strong relationship, a ratio of about 0.33, exists between the total dry biomass and the grain yield. Thomson and Siddique (1997) and Thomson et al. (1997) observed the same. Siddique et al. (1993) suggest that the ability of forming a large biomass be considered as a selection criterion for drought tolerance of chickpea. The ability for maintaining a high nitrogen fixation under slightly saline conditions. The nitrogen balances of both varieties (van Hoorn et al., 2002) indicate that variety A maintained its nitrogen fixation under slightly saline conditions at the same level as under non-saline conditions, and two times higher than variety B. These three factors merit to be considered for improving the salt tolerance of chickpea.
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