A. M. Al-Moshileh
Department of Plant Production and Protection, College of Agriculture and Veterinary
Medicine, Qassim University, Saudi Arabia.
E mail: amoshileh@hotmail.com
ABSTRACT
The application of chelated calcium (10% calcium) at the rates of 0, 250 and 500 mg Ca +2 /kg soil on potato plants irrigated with saline water (1000,
3000, 6000 and 9000 ppm NaCl) was studied in a pot experiment. Also, an application of calcium chelate (10% calcium) at the rates of 0, 500 and 1000 mg
Ca +2 /kg soil on potato plants irrigated with saline ground water (538, 945, 1652 and 2044 ppm), was studied in some farms within Al-Qassim area. The results indicated that the vegetative growth characters such as plant height, leaf area and number of leaves per plant, and tuber yield were significantly decreased as the salinity level of irrigated water increased. Plants given 500 mg Ca +2 /kg soil had a higher yield than plants without applying calcium or with 250 mg Ca +2 /kg soil in the pot experiment, whereas plants given 500 mg Ca +2 /plant under water salinity level of 945 ppm in the farms experiment had a higher yield than plants without calcium application. Therefore, calcium application might improve potato yield and mitigate the effects of salt stress during plant growth and development . The potato yield increased about 33% and 10% by increasing calcium application from 500 to 1000 mg/plant at the highest salinity levels
1652 and 2044 ppm, respectively.
Key words : ( Solanum tuberosum L.), calcium application, salt stress, water salinity.
1

1. INTRODUCTION
Potato ( Solanum tuberosum L.) is one of the main vegetable crops grown in the Kingdom of Saudi Arabia. The total production of potato in Saudi Arabia was 407,939 tons in 2008 (Ministry of Agriculture, 2007). It is well known that salinity is a limiting factor for crop productivity because it restricts the availability of water and nutrients to plants by lowering the total water potential in the soil. Usually, crop yield is dependent on salt concentration, when salinity below some threshold level. Yield gradually decreases as the salt concentration increases. In arid regions, fresh water is very limited for agriculture, due to low precipitation and high evaporation rate. In central region of Saudi Arabia, low quality water is commonly used for agriculture expansion because of the limited water supply (Mostafa et al.
, 1992 and El-Fakhrani, 1999).
Many environmental and hormonal factors such as wind, gravity, light, cold, salt, auxin, and abscisic acid induce changes in cytosolic calcium levels that precede the physiological responses. Thus, cytosolic calcium can mediate the impact of abiotic and biotic stresses on plants. For example, recent evidence suggests such a role of calcium in cold acclimation (Dhindsa and Monroy,
1994). In addition, environmental stresses, such as heat, freezing temperatures and salinity are known to cause perturbation in plasma membranes, cell wall or both. Therefore, calcium could be expected to play an important role in plant responses to environmental stresses (Palta, 1996). The objective of the present work was to investigate the influence of soil calcium application on the growth and tuber yield of potato grown in sandy soils of the Central Region of Saudi
Arabia under different saline levels of irrigation water.
2. MATERIALS AND METHODS
2.1. Pot experiment
This experiment was conducted under the natural conditions at the College of
Agriculture and Veterinary Medicine, Qassim University, during fall seasons
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of 2000/2001 and 2001/2002, to evaluate the influence of soil calcium application on potato growth and production under different saline levels of irrigation water.
Calcium element as calcium chelate (10% Ca) was incorporated in the pot soils at the rates of C
0
= 0, C1= 250 and C2= 500 mg Ca +2 /kg soil. The salinity levels of irrigation water were W1= 1.56, W2= 4.69, W3= 9.38, and W4= 14.06 dS/m NaCl, equivalent to 1000, 3000, 6000 and 9000ppm, respectively.
Irrigation water salinity levels in the second season were reduced into three levels since the high salinity concentration was very harmful to the plants.
The calcium and salinity treatments were arranged in a completely randomized block design with three replications.
Potato cultivar c.v. Spunta was grown in polyethylene pots containing 14 kg of sandy soil. Soil characteristics were determined according to Page et al.
(1982), (Table 1). Three potato tubers were placed at depth of 5 cm in each pot.
Pots were irrigated with W1-water for two weeks then seedlings were thinned out to one per pot. The total dose of 200 kg K
2
O/ ha as potassium sulfate (40%),
300 kg P/ha as superphosphate (20%), and a dose of 300 kg N/hectare as urea were applied. At this point, irrigation with different concentration of saline water was initiated and was applied as necessary according to soil field capacity.
Soil EC was measured and tap water was applied to wash the accumulated salts beyond the root zone and bring the EC to the desirable level. Plants in all treatments were harvested 110 days after planting date.
3

Table 1: Initial characteristics of the different soil textures used
.
Characteristics
Particle size distribution)%(
Cropping seasons
2000/01 2001/02
Sand
Silt
Clay
Soluble cations (meq1 -1 )
89.70
1.60
8.60
91.00
7.60
1.40
Ca ++
Mg + +
Na +
Soluble anions(meq1 -1 )
3.50
0.60
7.40
3.80
0.50
4.40
Cl –
HCO 3
–
SO = 4 pH (paste)
Organic carbon
2.2. Field experiment
3.80
6.00
5.30
8.10
Trace
4.10
7.70
2.40
7.80
Trace
The field experiment was carried out at the fall season of 2002/2003, in four different locations as shown on table 2. The common total soliable salts in irrigation water are Nacl, Cacl
2
and Kcl. Three experimental units of 20.25m
2 area were chosen randomly in every farm. Calcium element as calcium chelate
(10% Ca) was applied to the soil at the root zone one week after planting date at the rate of 0, 500 and 1000 mg Ca +2 /plant.
4

Table 2. Salinity of irrigation water, soil texture and planting and harvesting dates of the four different locations of chosen farms
Location Soil texture
ٍ
Farm No
Salinity level (ppm)
Planting date
Harvesting time
Sand Silt Clay
1
538 14/9/2002 19/1/2003 91.1
4.6
4.3
2 945 15/9/2002 21/1/2003 96.3
1.8
1.9
3 1652 18/9/2002 22/1/2003 94.4
2.7
2.9
4 2044 19/9/2002 24/1/2003 92.2
4.1
3.7
1.Vegetative growth parameters
Plant height (cm), number of leaves per plant and total leaf area per plant, by measuring the fifth upper leaf at the fully expanded mature stage (cm 2 ) using
(leaf area meter, model L1-1300) were determined for the pot experiment, while percentage of soil coverage by plant foliage leaves was measured to give an indication of leaf area in terms of the field experiment.
2. Potato tuber yield
The number of tubers and total weight per plant were recorded.
Statistical analysis:
The data were statistically tested by the analysis of variance by using
Statistical Analysis System (SAS Institute Inc. Cary, NC. 27511-8000).
Comparison of treatment means was done using Duncan’s multiple range test at
P = 0.05 level of significance.
5

RESULTS AND DISCUSSION
Pot experiment
1.
Vegetative growth parameters
The results presented in Table (3) indicated that increasing calcium application rate from 0.0 to 250mg Ca +2 /kg soil caused a significant decrease in plant height
(8.75 to 7.50cm, respectively) during the first season. Number of leaves per plant followed an opposite trend to that of plant height in response in the second season. At the highest rate of calcium, the plant gave their highest number of leaves per plant (7.67). Similar results were obtained by Tawfik et al . (1996) who found that plants given 550 mg Ca +2 /kg soil and nitrogen during heat stress had higher leaf: stem ratio than nitrogen before stress plants. On the other hand, the calcium application had no significant effect on leaf area.
With respect to the main effect of irrigation water salinity, the results obtained (Table 3) showed that a significant decrease in plant height (18 and 55
%) was associated with salinity level 6000 ppm during the first and second seasons, respectively. Application of the saline water 3000 ppm decreased number of leaves per plant by 15 and 27 % in the first and second seasons, respectively. Under the high salinity water (6000 ppm), number of leaves per plant reduced by 30 and 35 % in 2000/2001 and 2001/2002 seasons, respectively. Moreover, leaf area of potato was decreased by 25 and 20 % in the high salinity water (6000 ppm) during the first and second seasons, respectively.
The reduction of the above mentioned parameters with increasing salinity may be attributed to the deleterious effect of salinity on growth, physiological processes and metabolic activities of growing plants or due to the harmful effect of salinity on soil moisture stress and nutrient balance disorder in the root medium (Dahdoh and Hassan, 1997). These findings are in an agreement with those obtained by Mangal et al ., (1993); Heuer and Nadler (1995) and Karam et al., (1998).
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Table (3): Effect of calcium application and salinity of irrigation water on vegetative growth parameters of potato plants during 2000/01 and 2001/02 seasons.
Treatments Plant height (cm) No. of leaves/plant Leaf area (cm 2 )
2000/01 2001/02 2000/01 2001/02 2000/01 2001/02
Calcium rates
(mg Ca
+2
/kg soil)
0.0 C
0
250 C
1
500 C
2
Water salinity levels
(ppm)
8.75 a*
7.50 b
7.03 b
8.33 a
8.17 a
10.13 a
7.5 a
7.5 a
6.9 a
5.92 b
7.33 ab
7.67 a
77.5 a
78.3 a
77.82 a
65.68 a
67.85 a
66.96 a
1000 W
1
3000 W
2
6000 W
3
9000 W
4
8.75 a
8.75 a
7.17 b
6.38 b
12.7 a
8.25 b
5.67 b
--
9.08 a
7.67 b
6.33 c
6.25 c
8.83 a
6.42 a
5.67 b
--
88.49 a
88.46 a
65.58 b
65.01 b
68.18 a
68.22 a
54.09 b
--
*Means followed by the same letters are not significantly different (P = 0.05) according to
Duncan’s multiple range test..
Table (4): The interaction effect of calcium application and salinity of irrigation water on potato yield during 2000/01and 2001/02 seasons
Treatments No. of tubers/plant
2000/01
Tuber weight
(g/plant)
2001/02 2000/01 2001/02
C
1
C
0
C
2
W
1
6.00 b*
W
2
4.00 c
W
3
W
4
2.75 cd
2.00 d
W
1
8.25 a
W
2
3.00 cd
W
3
W
4
2.75 cd
0.75 e
W
1
5.00 bc
W
2
3.75 c
W
3
W
4
2.75 cd
1.25 ed
5.00 b
1.25 c
1.00 c
--
8.50 a
1.25 c
1.00 c
--
11.25 a
2.50 bc
1.00 c
--
148.4 b
80.10 c
35.3 d
38.4 d
227.8 a
82.20 c
19.30 e
3.60 f
164.4b
124.4b
40.2 d
14.7 e
78.10 b
38.6 c
34.95c
--
114.8 a
37.6 c
32.6 c
--
142.2 a
56.5 bc
34.9 c
--
*Means followed by the same letters are not significantly different (P = 0.05) according to Duncan’s multiple range test.
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Table (5): The main effect of calcium application and salinity of irrigation water on potato yield during 2000/01 and 2001/02 seasons
Treatments No. of tubers/plant Tuber weight
(g/plant)
2000/01 2001/02 2000/01 2001/02
Calcium rates
(mg Ca
+2
/kg soil)
0 C
0
250 C
1
500 C
2
Water salinity levels
(ppm)
3.19 a*
3.69 a
3.69 a
1.87 b
4.00 ab
7.67 a
75.5 a
78.8 a
85.7 a
50.6 b
62.8 ab
77.9 a
1000 W
1
3000 W
2
6000 W
3
9000 W
4
6.42 a
3.58 b
2.75 b
1.33 c
9.03 a
4.50 b
1.0
-- c
180.2 a
94.6 b
31.6 c
18.9 c
111.7 a
44.2 b
34.9 b
--
*Means followed by the same letters are not significantly different (P = 0.05) according to
Duncan’s multiple range test.
2.
Potato tuber yield:
The results presented in Table 6 show the main effect of calcium application and salinity of irrigation water on potato tuber yield. The obtained results indicated that calcium application had a significant effect on number of tubers and tuber weight per plant in the second season. Plants grown under 500 mg Ca +2 /kg soil produced the highest number of tuber per plant and tuber weigh per plant (7.67 and 77.9 g/plant).
With respect to the main effect of irrigation water salinity, results in Table 4 indicated a significant decrease in number of tubers and tuber weight per plant with increasing salinity level of irrigation water beyond 1000 ppm. Under intermediate salinity level (3000 ppm), number of tubers per plant was decreased by 44 and 50% in the first and second seasons compared to plants given 1000 ppm , respectively. In addition, 47.5 and 60.4% decreased the tuber yield per plant in the intermediate salinity during the first and second seasons, respectively. In the high salinity level (6000 ppm), tuber weight was reduced by
82.5 and 68.7% in the first and second seasons, respectively. Similar results
8

were obtained by Levy (1992) and Barakat (1996) who found that when irrigation with saline water was started soon after planting, tuber yield were decreased by 0-17% and 21-79% in the intermediate and the high salinities, respectively.
Concerning the interaction effect between calcium application and salinity of irrigation water on potato yield, the obtained results in Table 5 indicate that the highest tuber weight per plant (227.8 g/plant) was produced by plants grown under 250 mg Ca +2 /kg soil and 1000 ppm salinity level. Increasing calcium application rate from 250 to 500 mg Ca +2 /kg soil caused a significant decrease in potato yield at the lowest salinity level in the first season. Possible explanation for this result could be that the antagonism between ions occurs in the soil, at the plasma lemma of root hairs, or inside roots (Pasternak, 1987), and the higher calcium concentrations in plants are probably greater than the metabolic requirement (Wild, 1988). At the intermediate salinity level (3000 ppm), the plants given 500 mg Ca +2 /kg soil had higher tuber weight per plant (124.4 g/plant) than other treatments of calcium application, in the first season. It may be also observed that there is a positive response in tuber weight per plant to calcium application at each salinity level of irrigation water. However, this response decreased as the salinity level increased. This result would be relevant in avoiding stress effects via enhanced transpirational water loss. Similar results were obtained by Tawfik et al.
, 1996. Therefore, it may be concluded that application of calcium at 500 mg/kg soil can successfully used for improving the salt tolerance of potato plants.
B- Field experiment
Effect of salinity on green coverage and yield
It is clear from table 6 that as water salinity level increased, the plant foliage leaf coverage decreased. The soil coverage by plant gave a very good indication about the plant leaf area. The first treatment (538 ppm) gave the
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highest leaf area and consequently the highest yield. The yield is significantly influenced by irrigation water salinity level.
Table (6): Effect of salinity on green coverage and yield of potato yield during fall season of 2002/2003 .
Green coverage % Yield (T/ha) Salinity of irrigation water
(ppm)
538
945
1652
2044
89.7 a
86.1 b
77.5 c
76.0 c
29.31 a*
27.11 b
22.21 c
20.17 d
*Means followed by the same letters are not significantly different (P = 0.05) according to Duncan’s multiple range test.
Effect of calcium concentration on green coverage and yield
Regardless the effect of salinity level in irrigation water, this study result clarifies the positive influence of calcium element on potato plant leaf area and consequently the total production thereafter. As the calcium application increased, the plant development and production increased. The application of
1000 mg/plant gave the highest plant production at any salinity level (Table 7).
It is evident from tables 6 and 7 that as the water salinity decreased and the calcium rate increased to a certain level, the plant vegetative growth as well as plant production increased. It is clear that potato production came as a result of plant vegetative growth development. This can emphasize the importance role of photosynthesis in carbohydrates manufacturing and translocation down to tubers. This finding is similar to that reported by Al-Moshileh and Motawei
(2001).
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Table (7) Effect of calcium concentration on green coverage and yield of potato yield during fall season of 2002/2003 .
Green coverage %
Calcium concentration
Yield (T/ha)
0
500
1000
76.5 b
84.8 a
85.7 a
22.22 c
25.15 b
26.73 a
*Means followed by the same letters are not significantly different (P = 0.05) according to Duncan’s multiple range test.
Interaction of calcium concentration and water salinity level on green coverage and yield
The highest green foliage coverage percentage as well as highest plant production were observed when applying 500 mg/plant at the salinity level of
945 ppm (Table 8). As the water salinity level increased, the plant requirements for calcium application increased. At the highest water salinity level (2044 ppm), the percentage of green foliage coverage increased when 1000 mg calcium per plant was added. This phenomenon could be ascribed to the increment of plant resistance to salinity. The potato yield increased about 33% and 10% by increasing calcium application from 500 to 1000 mg/plant at the highest salinity levels 1652 and 2044 ppm, respectively. Therefore, calcium application can improve potato yield and mitigate the effects of salt stress during plant growth and development. These results due to the calcium importance referred to the plant cell wall improvement under ecological stress environments
(Palta, 1996).
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Table (8) Interaction between calcium and water salinity concentration on green coverage and yield.
Calcium
concentration
0
Green coverage
500
%
1000 0
Yield (T/ha)
500 1000
Salinity of irrigation water (ppm)
538
945
1652
2044
L.S.D (5%)
86.6
74.3
74.0
71.0
90.6
96.2
77.0
75.3
3.65
92.0
87.6
81.6
81.6
28.21
20.57
20.61
19.49
28.50
32.82
19.72
19.51
5.99
31.22
27.93
26.32
21.45
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