Effects of different sources of irrigation water and soil types and their interactions on the growth...

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The 3rd International Conference for Development and the Environment in the Arab world, March, 21-23, 2006, Assiut University, Center for Environmental Studies, Assiut, Egypt

Effects of different sources of irrigation water and soil types and their interactions

on the growth of Avicennia marina seedlings

I. M. Aref`1, El-Juhany L. I. 1 and Khamis M. Y. 2 1Plant Production Department, Faculty of Food and Agricultural Sciences, King Saud

University, P. O. Box 2460 Riyadh 11451 2Ministry of Education, Riyadh 11148, Saudi Arabia

Abstract

Effects of different sources of irrigation water, soil types and their interactions on the growth of Avicennia marina seedlings was carried out in Jizan city (1300 Km south of Riyadh) through a pot experiment. Tap water, sea water, non treated sewage water and a mixture of the last two represent the sources of irrigation water used. While the soil types were soil from under mangrove trees, soil from outside mangrove milieu, a mixture of soil from under and outside mangrove trees with sand and a mixture of peat moss and sand. After eight months of treatment, diameter, number of leaves, total leaf area, leaf dry weight and leaf weight ratio of the seedlings that were irrigated with sea water were significantly greater than those of the seedlings that were irrigated with the other sources of irrigation water. Root length of the seedlings that were irrigated with tap water was significantly greater than those of the seedlings that were irrigated with the other sources of irrigation water. Stem, root and total dry weight of the seedlings that were irrigated with sea water and those were irrigated with tap had similar values, however, these were significantly greater than those of the seedlings that were irrigated with either untreated sewage or the mixture of sea water and untreated sewage. Stem weight ratio of the seedlings that were irrigated with sea water and those irrigated with tap water were similar and were significantly lower than those of the seedlings that were irrigated with untreated sewage and those of the seedlings that were irrigated with the mixture of sea water and untreated sewage. The seedlings that were irrigated with tap water had root weight ratio was greater than those of the seedlings that were irrigated with any other source of irrigation water. Stem diameter of the seedlings grown in soil from outside mangrove milieu was significantly greater than those of the seedlings grown in other soil types apart from those grown in the mixture of peat moss and sand. Similar trends were observed for number of leaves and total leaf area. The seedlings grown in the mixture of mangrove soils and sand had a lower number of branches comparing with those grown in the other soil types. Leaf dry weight of the seedlings grown in the soil from outside mangrove milieu was significantly greater than those of the seedlings grown either in mangrove soil or in the mixture of this and soil from outside mangrove milieu in addition to sand. Leaf weight ratio of the seedlings grown in the soil from outside mangrove milieu and those grown in a mixture of peat moss and sand were similar and significantly greater than that of those of the seedlings grown either in mangrove soil or in the mixture of this and soil from outside mangrove milieu in addition to sand. Stem diameter, number of leaves, dry matter production and leaf weight ratio of the seedlings grown in a mixture of peat moss and sand and irrigated with sea water were greatest than those of the seedlings grown in the other combinations. The seedlings grown in a soil from outside mangrove milieu and irrigated with sea water had total leaf area was greater that those of the seedlings grown in the other combinations. These results show that the growth of Avicennia marina seedlings was affected much when irrigated with untreated sewage.

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I. M. Aref; L. I. El-Juhany and M.Y. Khamis

Introduction Mangrove forests once covered 3/4 of the coastlines of tropical and sub-tropical countries. Today, less than 50% remain, and of this remaining forest, over 50% is degraded and not in good form (Quarto, 2005). Mangrove forests are currently among the most threatened habitats in the world and are disappearing at an accelerated rate (Lauri and Gibson 2000). Mangrove forests in Saudi Arabia spread over tidal zones and islands on Red Sea coast and consist mainly of Avicennia marina and Rhizophora mucronata (Abd-Elghani 1996). These forests play a vital role in Saudi Arabia like in other countries posse mangrove forests. However, they are facing humanitarian threat such as expansion of urban areas, the discharge of untreated sewage from municipal areas, deforestation, industrial pollution, and offshore oil drilling. For instance, there is a small mangrove stand is found on Jeddah’s South Corniche has been subject to a high inflow of nutrients from largely untreated sewage effluent for more than 20 years. This affected mangrove stand are dominated by stunted, multi-stemmed trees with branched, twisting and dead pneumatophores. In turn aerial root capacity has affected the respiration rate of the root system, nutrient uptake and plant development leading to retarded growth of the mangroves (Mandura, 1997). Unfortunately, there is no mangrove conservation programmes have created so far in Saudi Arabia. However, some efforts are being done through The National Commission for Wildlife Conservation and Development (NCWCD). Their activities include rehabilitation of degraded mangrove areas via growing seedlings in the nursery, which mostly is located in sea water by the beach. However, seedlings in the nursery are subjected to encroachment by sea water and/or to pollution either from industrial or municipal sources. On other hand, seedlings usually are grown in sand that may lack of essential nutrients needed. Field (1998) stated that intertidal position can be of great importance for the survival of mangrove seedlings, as tide height is a critical factor in determining survival. This is because seedlings are susceptible to physical damage from flotsam and are subject to physiological stress if submerged for too long. Growing mangrove trees away from the sea is possible providing they given their usual requirements. In Eritrea, a project for planting mangrove trees was carried out in the desert away from the sea and several hundred meters from the high tide line in areas where trees had never grown before, the trees were planted in holes one meter deep were dug and filled with sand to provide drainage then, fertilized with did-ammonium phosphate and iron oxide (Tealeaf et al. 2000). Recently, studies were conducted to describe and classify soils that supported maximum mangrove (included Avicennia marina) establishment and growth under the harsh arid coastal conditions of Kuwait. The results of these studies revealed that plant growth appeared to be the better on the typic Aquisalid soil (Aridisols that have a salic horizon) (Bhat and Suleiman, 2004). The present work is designated to examine the effects of different sources of irrigation water, soil types and their interactions on the growth of Avicennia marina seedlings through a pot experiment in Jazan Region, Saudi Arabia.

Material and methods Plant material and site A pot experiment was carried out in Jizan city (1300 Km south of Riyadh). 288 plastic pot of 30 cm rim diameter were filled-up with different soil types and placed in the greenhouse. Four months old and uniform seedlings of Avicennia marina were obtained from a nursery belongs to the Ministry of Agriculture in Jizan City.

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Experimental design and treatments The experiment was carried out using a randomized complete block design with 18 blocks in factorial arrangement included irrigation water with four levels and soil types with four levels. The four irrigation water used were tap water, sea water, non treated sewage water and a 1:1 (v/v) mixture of the last two. While the soil types were soil from under mangrove trees, soil from outside mangrove trees, a 1:1:1 (v/v) mixture of soil from under and outside mangrove trees with sand and a 1:1 (v/v) mixture of sand and peat moss. The seedlings were planted in the pots at a rate of one seedling for each pot. Harvesting and Measurements Eight months after planting date, all the trees were severed at soil surface and separated into leaves, stem and branches. Stem diameter at 10 cm above the soil surface, total stem height, number of leaves, number of branches, total leaf area. Root system of each tree was extracted from the soil by hand and washed. The length of the longest root of each tree was measured. Leaves, stem, branches and roots were dried in an oven at 75ºC for 48 h. Dry weight of each component was determined and total tree dry weight was calculated. Allocation of dry weight into different tree parts was calculated as leaf, stem and root weight ratio. Root to shoot dry weight was also calculated.

Results Effects of irrigation water on the growth of the seedlings Analysis of variance procedure showed that the seedlings that were irrigated with sea water had stem diameter and number of leaves were significantly greater than those of the seedlings that were irrigated with the other sources of irrigation water (P<0.0004) which did not significantly vary between each other in both traits (Table 1). Total leaf area of the seedlings that were irrigated with sea water was also greater than that of the seedlings that were irrigated with any other sources of irrigation water, followed by that of the seedlings that were irrigated with tap water then, that of the seedlings that were irrigated with the mixture of untreated sewage and sea water (P<0.0001) (Table 1). Root length of seedlings that were irrigated with tap water was significantly greater than those of seedlings that were irrigated with the other sources of irrigation water followed by that in sea water then those of seedlings that were irrigated with either untreated sewage or the mixture of sea water and untreated sewage (P<0.0001) (Table 1). Total stem height and the number of branches of the seedlings were not affected. Leaf dry weight of the seedlings that were irrigated with sea water was significantly greater than those of the seedlings that were irrigated with any other source of irrigation water (P<0.0001) (Table 2). Stem, root and total dry weight of the seedlings that were irrigated with sea water and that were irrigated with tap had similar values, however, these were greater that those of significantly irrigated with either untreated sewage or the mixture of sea water and untreated sewage (P<0.0001) (Table 2). These results show that the growth of the seedlings of Avicennia marina was affected much when irrigated with untreated sewage.

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Table (1). Main effects of irrigation with sea water (SW), tap (TW), untreated sewage (US) and a mixture of sea water and untreated sewage (SW+US) on some growth traits of Avicennia marina seedlings after eight months.

Source of irrigation water Trait SW TW US SW + US Stem diameter (mm tree-1) a

10.54* b 9.66 b 9.43 b

9.20 Stem height (cm tree-1) a

48.27 a43.86 a

49.64 a43.96

Number of leaves (leaf tree-1) a 81.60 b 58.63 b 45.00 b 56.50 Total leaf area (cm2 tree-1) a

284.16 b177.58 c 69.21 cb 102.30

Number of branches (branch tree-1) a 6.38 a4.93 a 4.642 a

5.05 Root length (cm tree-1) b 22.85 a

26.93 c 16.04 c 16.48 *Means followed by the same superscript letters were not significantly different according to Duncan's Multiple Test at P<0.05. Table (2). Main effects of irrigation with sea water, tap, untreated sewage and a mixture of sea water and untreated sewage water on dry weight of Avicennia marina seedlings after eight months.

Source of irrigation water Trait SW TW US SW + US Leaf dry weight (g tree-1) a

3.94* b

2.45 c

0.89 cb

1.41 Stem dry weight (g tree-1) a

4.64 ba

3.82 c

1.72 bc

2.90 Root dry weight (g tree-1) a

3.75 a

4.04 b 1.06

b 1.68

Total dry weight (g tree-1) a12.33

a10.31

b 3.66

b 5.98

*Means followed by the same superscript letters were not significantly different according to Duncan's Multiple Test at P<0.05. Allocation of dry weight into the main tree parts was significantly affected by the sources of irrigation water used (P<0.0001) (Table 3). The seedlings that were irrigated with sea water had significantly greater leaf weight ratio comparing with those of the seedlings that were irrigated with any other source of irrigation water, which did not vary significantly from each other (Table 3). The dry weight allocated to the stems of the seedlings that were irrigated with sea water and those irrigated with tap water were similar and were significantly lower than those of the seedlings that were irrigated with untreated sewage and those that were irrigated with the mixture of sea water and untreated sewage (Table 3). Stem weight ratio of the seedlings irrigated with these two sources of water was similar. The seedlings that were irrigated with tap water had root weight ratio was greater than those of the seedlings that were irrigated with any other source, which did not vary from each other (Table 3). Table (3). Main effects of irrigation with sea water, tap, untreated sewage and a mixture of sea water and untreated sewage water on allocation of dry weight of Avicennia marina seedlings after eight months.

Source of irrigation water Trait SW TW US SW + US Leaf weight ratio a

30 b 22

b 23

b24

Stem weight ratio b 39

b 38

a 49

a 48

Root weight ratio b 31

a 40

b 28

b 28

*Means followed by the same superscript letters were not significantly different according to Duncan's Multiple Test at P<0.05.

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The 3rd International Conference for Development and the Environment in the Arab world, March,21-23, 2006, Assiut University, Center for Environmental Studies, Assiut, Egypt

Effects of different soil types on the growth of the seedlings Analysis of variance showed significant effects of soil type on the growth of Avicennia marina seedlings. Stem diameter of the seedlings grown in soil from outside mangrove was significantly greater than those of the seedlings grown in other soil types apart from those grown in the mixture of sand and peat (P<0.039) (Table 4). Similar trends for number of leaves (P<0.0001) and total leaf area (P<0.0001) of the seedlings were observed (Table 4). The seedlings grown in the mixture of mangrove soil, outside mangrove soil and sand had a lower number of branches comparing with those grown in the other soil types. There was no effect of soil type either on stem height or root length (Table 4). Table (4). Main effects of soil type on the growth of Avicennia marina seedlings after eight months of treatments. Soil types are MS (from under mangrove), OMS (from outside mangrove), MS+OMS+S (a mixture of from under mangrove + from outside mangrove + sand) and P+S (a mixture of peat moss + sand).

Soil type P+S MS+OMS+S OMS MS Trait

9.99 ab

9.50b

a

10.30 9.23b

Stem diameter (mm tree-1) a

46.57 a 45.50

a 48.30

a 41.31 Stem height (cm tree-1)

74.70a

46.05b

69.58 a

51.46 b

Number of leaves (leaf tree-1) a

218.21 b 127.08

a235.10

b111.10 Total leaf area (cm2 tree-1)

5.43 ab

3.70 b

a 6.27 5.57

ab Number of branches (branch tree-1)

a21.44

a 22.26

a 24.32

a 21.42 Root length (cm tree-1)

*Means followed by the same superscript letters were not significantly different according to Duncan's Multiple Test at P<0.05.

Leaf dry weight of the seedlings grown in outside mangrove soil was significantly greater than that of those grown either in mangrove soil or in the mixture of both in addition to sand (P<0.007) (Table 5). The values of leaf dry weight of the seedlings grown in the last two soil types were similar. Soil Type had no significant effects on dry matter production of the other components (Table 5). Leaf weight ratio of the seedlings grown in outside mangrove soil and those grown in a mixture of peat moss and sand were similar and significantly greater than those of those grown either in mangrove soil or in the mixture of both in addition to sand (P<0.0001) (Table 6).

Table (5). Main effects of soil type on dry matter production of Avicennia marina seedlings after eight months of treatments. Soil types are MS (from under mangrove), OMS (from outside mangrove), MS+OMS+S (a mixture of from under mangrove + from outside mangrove + sand) and P+S (a mixture of peat moss + sand).

Soil type Trait MS OMS MS + OMS + S P + S Leaf dry weight (g tree-1) b

1.475 a

3.150 b

1.800 a

3.058

Stem dry weight (g tree-1) a 3.115

a4.064

a 3.519

a 3.826

Root dry weight (g tree-1) a2.530

a 3.482

a 2.642

a 3.405

Total dry weight (g tree-1) a 7.122

a 10.698

a7.962

a 10.291

*Means within consecutive horizontal boxes followed by the same superscript letters were not significantly different according to Duncan's Multiple Test at P<0.05.

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Table (6). Main effects of soil type on allocation of dry matter of Avicennia marina seedlings after eight months of treatments. Soil types are MS (from under mangrove), OMS (from outside mangrove), MS+OMS+S (a mixture of from under mangrove + from outside mangrove + sand) and P+S (a mixture of peat moss + sand).

Soil type Trait MS OMS MS + OMS + S P + S Leaf weight ratio b

23 a

27 b

22 a 28

Stem weight ratio a42

a 40

a45

a 39

Root weight ratio a 35

a33

a34

a33

Effects of irrigation water sources × soil types interactions on the growth of seedlings a- seedling growth Analysis of variance procedure showed that there were interactions between irrigation water resources and soil types on the growth of seedlings diameter (P<0.05), number of leaves (P<0.0005) and total leaf area (P<0.0009) (Table 7). Stem diameter and number of leaves of the seedlings grown in a mixture of sand and peat moss and irrigated with sea water had the greatest value among all those of the seedlings grown in the other combinations (Table 7). The seedlings grown in a soil from outside mangrove and irrigated with sea water had total leaf area was greater that those of the seedlings grown in the other combinations (Table 7). b- Survival percentage The seedlings grown in a mixture of peat moss and sand and irrigated with tap water had 100% survival and those grown in peat moss and sand and irrigated with sea water had 94%, while high death percentage was observed for those grown in different soil types and irrigated with sea water or sea water mixed with untreated sewage (Table 8).

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Table (7). Effects of interactions between soil type (soil from outside mangrove trees, OMS; soil from under mangrove trees, MS; a mixture of soil from outside mangrove trees and soil from under mangrove trees plus sand, OMS + MS + S and, a mixture of peat moss and sans, P + S and irrigation water sources (tap water, TW; sea water, SW; untreated sewage, UTSEW and a mixture of sea water and untreated sewage, SW + UTSEW on the growth of Avicennia marina seedlings after eight months of treatment in pots.

Irrigation water SE SW+UTSEW SE UTSEW SE SW SE TW Soil type Trait

1.69 10.30 0.98 09.62 1.48 10.92 0.95 09.74 OMS 0.00 0.00 0.00 0.00 0.96 09.39 1.15 09.05 MS

1.13 9.66 0.00 0.00 0.77 09.80 1.09 08.94 MS+OMS+S 1.43 8.96 1.32 09.28 1.68 11.17 1.41 10.12 P+S

Diameter (mm plant-1)

16.97 51.00 9.18 52.83 10.23 51.47 11.12 39.95 OMS 0.00 0.00 0.00 0.00 16.61 45.36 8.600 36.58 MS 15.78 47.17 0.00 0.00 11.80 45.86 10.44 44.21 MS+OMS+S 9.11 42.37 12.69 47.25 14.11 48.00 12.60 48.59 P+S

Height (cm plant-1)

10.61 39.50 14.84 42.33 39.93 47.00 10.88 45.80 OMS 0.00 0.00 0.00 0.00 11.94 98.44 28.30 60.00 MS

10.21 50.33 0.00 0.00 27.31 44.14 15.42 35.86 MS+OMS+S 20.74 60.00 24.66 47.00 41.25 101.36 42.03 75.06 P+S

No. of leaves (leaf plant-1)

60.1 130.50 83.77 85.00 249.35 370.31 43.84 129.75 OMS 0.00 0.00 0.00 0.00 67.47 95.14 30.53 129.72 MS 76.21 44.00 0.00 0.00 94.39 182.45 35.97 75.67 MS+OMS+S 64.81 110.20 120.8 57.38 154.24 350.62 192.37 264.56 P+S

Leaf area (cm2 plant-1)

0.00 03.00 2.25 05.33 02.63 08.37 01.59 04.10 OMS 0.00 0.00 0.00 0.00 2.630 03.71 04.59 3.66 MS

1.00 04.00 0.00 0.00 2.710 06.18 01.25 5.28 MS+OMS+S 2.83 05.53 2.99 04.13 03.42 05.68 04.83 5.7 P+S

No. of branches (branch plant-1)

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Table (8). Effects of interactions between soil type (soil from outside mangrove trees, OMS; soil from under mangrove trees, MS; a mixture of soil from outside mangrove trees and soil from under mangrove trees plus sand, OMS + MS + S and, a mixture of peat moss and sans, P + S and irrigation water sources (tap water, TW; sea water, SW; untreated sewage, UTSEW and a mixture of sea water and untreated sewage, SW + UTSEW on Survival percentage of Avicennia marina seedlings after eight months of treatment in pots.

Irrigation water sources SW+UTSEW UTSEW SW TW Soil type

11 33 89 56 OMS 0 0 39 33 MS 0 0 61 39 MS+OMS+S 83 44 94 100 P+S

Survival percentage

c- Dry matter production Analysis of variance showed that there were interactions between soil types and irrigation water on leaf (P<0.0009), stem (P<0.07), roots (P<0.03) and total dry weight (P<0.009) of the seedlings (Table 9). The seedlings grown in peat moss and sand and irrigated with sea water have the greatest values for leaf (5.08 g), stem (5.31 g), roots (4.43 g) and total (14.81 g) dry weight among those of the seedlings grown in the other combinations (Table 9).

Table (9). Effects of interactions between soil type (soil from outside mangrove trees, OMS; soil from under mangrove trees, MS; a mixture of soil from outside mangrove trees and soil from under mangrove trees plus sand, OMS + MS + S and, a mixture of peat moss and sans, P + S and irrigation water sources (tap water, TW; sea water, SW; untreated sewage, UTSEW and a mixture of sea water and untreated sewage, SW + UTSEW on dry matter production of Avicennia marina seedlings after eight months of treatment in pots. Values are means of observations and standard error of mean.

Irrigation water sources SE SW+UTSEW SE UTSEW SE SW SE TW

Soil type Trait

0.49 1.25 1.26 1.23 3.44 4.86 0.77 1.94 OMS 0.00 0.00 0.00 0.00 0.97 1.31 0.51 1.66 MS

1.15 0.67 0.00 0.00 1.47 2.61 0.45 1.01 MS+OMS+S 0.97 1.57 1.29 0.63 2.24 5.08 2.56 3.62 P+S

Leaf dry weight (g plant-1)

3.04 5.25 2.29 2.47 2.99 4.59 1.16 3.37 OMS 0.00 0.00 0.00 0.00 2.73 3.11 1.49 3.12 MS

3.00 1.73 0.00 0.00 1.17 04.2 1.5 3.21 MS+OMS+S 1.51 2.81 2.19 1.16 2.27 5.31 2.39 4.58 P+S

Stem dry weight (g plant-1)

1.56 2.60 1.27 1.27 3.14 4.31 1.18 3.67 OMS 0.00 0.00 0.00 0.00 1.69 2.03 1.68 3.12 MS

1.5 0.87 0.00 0.00 0.85 3.05 0.91 2.77 MS+OMS+S 0.99 1.72 1.66 0.90 1.93 4.43 3.12 5.11 P+S

Root dry weight (g plant-1)

5.09 9.1 4.58 4.97 9.23 14.12 2.49 8.98 OMS 0.00 0.00 0.00 0.00 5.26 6.46 3.52 7.90 MS

5.66 3.27 0.00 0.00 3.12 9.85 2.4 7.00 MS+OMS+S 3.29 6.11 5.12 2.69 5.76 14.81 7.47 13.31 P+S

Total dry weight (g plant-1)

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d- Allocation of dry matter 34% of the total dry matter produced by the seedlings grown in the mixture of peat moss and sand and irrigated with sea water was allocated to the leaves (P<0.01) (Table 10). This was greater than the proportions of dry matter allocated to the leaves of the seedlings grown in the other combinations (Table 10). The proportion of dry matter allocated to stem of the seedlings grown in soil from outside mangrove milieu and irrigated with untreated sewage was 57% and was greater than those allocated to the stems of the seedlings grown in the other combinations (Table 10). Table (10). Effects of interactions between soil type (soil from outside mangrove trees, OMS; soil from under mangrove trees, MS; a mixture of soil from outside mangrove trees and soil from under mangrove trees plus sand, OMS + MS + S and, a mixture of peat moss and sans, P + S and irrigation water sources (tap water, TW; sea water, SW; untreated sewage, UTSEW and a mixture of sea water and untreated sewage, SW + UTSEW on allocation of dry matter of Avicennia marina seedlings after eight months of treatment in pots.

Irrigation water sources

SE SW+ UTSEW SE UTSEW SE SW SE TW

Soil type Trait

014.0 14.0 014.0 24.0 06.0 33.0 6.00 22.0 OMS

0.00 0.00 0.00 0.00 05.0 22.0 06.0 23.0 MS

0.00 20.0 0.00 0.00 07.0 25.0 06.0 15.0 MS+OMS+S

05.0 25.0 05.0 20.0 06.0 34.0 10.0 25.0 P+S

LWR

01.0 57.0 01.0 50.0 06.0 36.0 06.0 37.0 OMS

0.00 0.00 0.00 0.00 09.0 46.0 04.0 39.0 MS

0.00 53.0 0.00 0.00 07.0 43.0 07.0 44.0 MS+OMS+S

01.0 46.0 01.0 46.0 07.0 36.0 05.0 35.0 P+S

SWR

05.0 28.00 05.0 24.0 04.0 29.0 09.0 39.0 OMS

0.00 0.00 0.00 0.00 05.00 31.0 04.0 38.0 MS

0.00 26.0 0.00 0.00 04.0 31.0 05.0 40.0 MS+OMS+S

09.0 28.0 09.0 33.0 06.0 30.00 07.0 39.0 P+S

RWR

Discussion

In the present study, irrigating mangrove seedlings with sea water enhanced their growth more than the other sources of irrigation water used. This may attributed to nature of mangrove trees in tolerating salinity as they are highly resistant to salinity comparing with the other plants (Macnae, 1968). In a study on the effects of salinity and nitrogen upon the growth of Avicennia marina seedlings grown in 0.1, 0.3 and 0.5 mg l-1 of sodium chloride for three months in greenhouse, Naidoo (1987) found positive effect of salinity in accumulation of dry matter of branches and roots. However, Lopez and Ezcarra (1989) found that stem height and diameter of Laguncularia racemosa, Avicennia germinans and Rhizophora mangale trees in the reverie pools, which had lower level of salinity, were greater than those of the trees in muddy swamps. On the other hand, irrigation with untreated sewage affected the growth of mangrove seedlings mostly up to death. However, mixing sea water with untreated sewage alleviated the severity effects of the later.

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This may resulted from diluted the strength of most harmful substances present in untreated sewage. Many reports were published regarding the adverse effects of discharging wastewater to the mangrove ecosystem. United Nations Environment Programme (2000) reported that the discharge of untreated sewage effluents produces long-term adverse impacts on the ecology of critical coastal ecosystems in localized areas due to the contribution of nutrients and other pollutants. The potential effects of toxic substances in the marine and coastal environments include the destruction of fish and other wildlife leading to a loss of biodiversity, decrease in productivity of mangrove (CAR/RCU, UNEP, 2000). Moreover, Lauri and Gibson (2000) asserted that over time, environmental stress can kill large numbers of mangrove trees. However, mangroves posse high capacity to retain pollutants which probably attributed to their anaerobic conditions, periodically flooded by tides (which resulted in fluctuation of salinities), and high clay and organic matter content (Tam, 1998). Therefore, discharging wastewater to the mangrove ecosystem may have a beneficial effect on their productivity, particularly in areas where nutrient status is low (Wong, et al. 1995). Bhati and Singh (2003) found increased stem height, diameter and number of leaves of Eucalyptus camaldulensis seedlings after 10 month of irrigation with municipal effluent. Mant et al. (2003) postulated that the hydroponic cultivation of Salex viminalis in a gravel medium, supplied only with the nutrients present in primary settled sewage produced apparently normal, healthy-looking trees, indicating that there were no major mineral deficiencies or toxicities caused by the wastewater. In a paper describes the comparative success of eleven species in establishment and early growth under irrigation with winery wastewater and treated municipal wastewater, Stewart and Flinn (1984) concluded that the additional water supplied by irrigation rather than the nutrients contained in the wastewater was the principal reason for the accelerated growth. Using soil from outside mangrove milieu to grow mangrove seedlings increased their growth over those grown either in soil from under mangrove trees or in the mixture of both the former and the later in addition to sand. However, the growth of the seedlings grown in a mixture of sand and peat moss had growth values were close to those of the seedlings grown in the soil from outside mangrove milieu. Soil from outside mangrove milieu is supposedly to be more salty. As we move even farther inland, the soil becomes too salty for the Black Mangrove (Snedaker, 1997). In Kuwait, Bhat and Suleiman (2004) found that the growth of to Avicennia marina and Avicennia germinans appeared to be better on a soil having a salic horizon. In contrast, Soto and Corrales (1988) who noticed that Avicennia germinans trees that grown in five high salty sites along the Pacific coast in Costa Rica have small modified leaves. Generally, mangrove forests are best developed on low energy muddy shorelines, where there is an extensive suitable inter-tidal zone with an abundant supply of fine grain sediment (Field, 1998). The negative effects upon the growth of the seedlings that resulted from using soil from under mangrove trees may attributed to the changes associated with transferring the soil from the sea shore to the location of the experiment. Taking mangrove soil away from sea shore may upset its structure as it can be subjected to solidification due to clay if dried (Arabia Oil Company, Al Gorm Research Centre, 1983). The most noticed adverse effect on the growth of mangrove seedlings in the present study was that resulted from the presence of untreated sewage either solely or mixed with sea water and when associated either with mangrove soil or the mixture of mangrove soil and outside mangrove soil in addition to sand.

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Conclusion Growing mangrove seedlings at the nursery in different soil types and under different irrigation water showed that untreated soil had adverse effects on the growth of the seedlings even when mixed with sea water, while irrigating the seedlings with sea water enhanced their growth. This was also the case when the seedlings were grown in soil from outside mangrove milue. Therefore, planting mangrove seedlings in soil from outside mangrove milue under irrigation with sea water enhanced their growth markedly.

References

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Effects of different sources of irrigation water and soil types and their interactions on the growth...

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