The main objective of this study was to survey and collect range plants species capable of growing in severe salt affected lands and under saline irrigation to save fresh groundwater for other beneficial purposes. To achieve this objective, nine plants were collected in the coastal (Arabian Gulf, Red Sea) and inland (Al-Qaseem region) salt affected soils of Saudi Arabia to obtain information for the rehabilitation of degraded lands as sustainable rangelands for range animals. Soil samples were collected from 0-30 and 30-60 cm depth and analyzed for physical and chemical composition. Plant samples were also analyzed for N, P, Na, K, Ca and Mg. Plant species found in abundance were identified as Aeluroapus lagopoides, Avicennia marina, Juncus rigidus, Nitraria retusa, Panicum turgidum, Salsola sp., Suaeda vermiculata, Salicornia europaea and Tamarix amplexicaulis. Statistically evaluation of results using ANOVA and regression techniques showed negative correlation between soil salinity and N, P and K (r = -0.09 to -0.67) and positive (r = 0.11- 0.73) for Ca, Mg and Na. Similarly, the correlation was negative between soil mineral contents (-0.18 to -0.31) and the plant composition for K, Ca, Mg and positive for Na ion (r = 0.54) only. Nutrient value of some plants of forage importance were significantly affected by high soil salinity. Plants such as Juncus rigidus, Nitraria retusa, Panicum turgidum, Suaeda vermiculata, Salicornia europaea and Tamarix amplexicaulis seems to have an excellent potential for the rehabilitation of degraded salt affected lands in Saudi Arabia.
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The Kingdom of Saudi Arabia is a large country with a total land area of around 2.2x106 km2. It is located at 16° N and 32° E. Its climate is characterized by long, hot, dry summer and mild, cool and short winter with a mean annual rainfall of 70 mm. The agricultural lands of Saudi Arabia, which are coarse textured containing salts to varying degrees and mostly irrigated with saline groundwater, are not considered suitable for some of the commonly grown crops. Besides, the soils have low organic matter, high percolation rate, high salinity, low water holding capacity and poor fertility due to arid climate. This situation is further aggravated due to encroachment by wind blown sand over potential agricultural lands, roads, pipe lines and other important infrastructures (Abdulwahid, 1979; Aziz and Abdulwahid, 1977; El-Khatib, 1974; Abolkhair, 1981). Establishment of windbreaks and re-vegetation of sandy desert offers sustainable approach for the rehabilitation of degraded lands (Arnest, 1942; El-Khatib, 1974; Fagotto, 1987). Al-Homaid and Khan (1994) observed in a field study that the production and growth of Prosopis juliflora under moderate watering was similar to that produced by low watering with manure treatment on the upwind slope of a parabolic dune area. The deleterious effects of groundwater salinity were noticed in the form of reduction in survival rates during dry period without irrigation. They also concluded that P. juliflora can be successfully grown with moderate irrigation in an open sandy desert. Many studies have been conducted on the nutrition evaluation (Al-Jaloud et al., 1994), chemical composition (Al-Noaim et al., 1991) of some range plants and their relation to soil properties (Al-Jaloud et al., 2001) in Saudi Arabia. Boer (1996) investigated the soil indicator plants along the Saudi Gulf coast of the Arabian Gulf. He found that the soils of different vegetation types of the Saudi Arabian Gulf were dominated by mangrove, salt marsh and desert plant communities (Avicennia marina, Arthrocnemum macrostachyum, Salicornia europea, Halocnemum strobilaceum. Marcar et al. (2003) studied the survival and growth of the tree species and provenances in response to salinity on a discharge site. They found significance differences between species with E. occidentalis and A. stenophylla showing no growth decline upto ECe of 10 dS m-1, while most other species showed varying rates of decline with increasing salinity. Similarly, Marcar et al. (2000) evaluated tree establishment treatments on saline seeps near Wellington and Young in New South wales. They found that the treatments generally increased basal stem diameter or stem diameter at breast height and crown volume, but the differences were usually no significant. Simpfendorfer and Harden (2000) stated that the addition of calcium as either CaCO3 or CaCl2 to 3 artificial media increased in vitro growth of 15 isolates from 20-135%. Calcium was also shown to increase the severity of root disease caused by 6 isolates of P. clandestine by up to 100% in a glasshouse experiment. Noaman and El-Haddad (2000) studied the response (growth and biomass production) of some halophytes to different levels of salinity. They stated that these halophytes species can be grown productively at a leaching fraction between 0.25 and 0.50 when salinity of irrigation water is less than 20 g L-1. Mensah et al. (2006) evaluated the effect of salinity on germination, growth and yield of five groundnut genotypes. They revealed that salinity significantly delayed germination and also reduced the final percentages at electrical conductivities greater than 2.60 dS m-1. Seedling emergence, radicle elongation, plant height and dry weight also tended to decrease with increasing salinity. Khan et al. (2000) conducted an experiment on the effects of salinity on growth, water relations and ion accumulation of the sub-tropical perennial halophyte, Atriplex griffithii var. stocksii. They concluded that plant total dry weight was significantly inhibited at 360 m M NaCl in sand culture in plant growth chamber. The Na and Cl content in both shoots and roots increased with increases in salinity. Increased treatment levels of NaCl induced decreases in Ca, K and Mg in Plants.
Major factors limiting the sustainable rehabilitation of degraded lands in an arid environment are shortage of fresh water for irrigation, low organic matter, high salinity/sodicity, low fertility, poor drainage and high salinity of groundwater. Besides, there are highly salt affected inland and coastal areas which are defined as sabkhas (land with high watertable and high salt concentration or flat salty marsh). There are few plant communities which grow successfully in these salt affected lands and sandy deserts. Knowledge about the survival of these plants may provide an opportunity for successful rehabilitation of degraded lands as range lands or pastures for the survival of range animals. Information on the ecology and physiology of these plants and their interaction with soil environment is very limited. The main objective of this study is to gather some information about plants of coastal and inland salt affected areas and their relation to the soil environment for the development of sustainable range lands in an arid environment.
|Table 1:||Soil temperature (°C) at 5 cm depth in Jubail area|
MATERIALS AND METHODS
A field survey was carried out during 2005 of inland sabkha (Al-Qaseem region) and salt affected soils of the coastal areas in the Eastern (Qatif. Al-Oquir, Ras Tanura, Safwa) and the Western (Jeddah. Al-Madinah Al-Munawarah) Provinces, Kingdom of Saudi Arabia. Plants were collected, identified and classified according to the nomenclature procedure of Mandaville, (1990). The soil samples were collected from 0-30 and 30-60 cm depth of soil in the vicinity of different plants for soil salinity, mineral contents and textural class to develop relation between plants mineral composition and the soil characteristics.
The climatic data of the various regions was also collected from different meteorological stations of Ministry of Agriculture and Water (MAW, 2004). Mean annual rainfall in the study area ranges between 70-130 mm and is sporadic. Normally, rainy season extends from November to April during winter while during summer the rainfall is nil. The study areas are underlain by hard limestone varying from 0.5 m to more than 3 m deep, soil coarse to medium texture mostly covered with sand and have shallow groundwater table (Depth ranges between 1-10 m in different areas. The maximum mean soil temperature was more than 35°C in July with minimum as 16°C in the month of January. However, the maximum air-temperature in summer exceeds 50°C and reaches close to 70°C on the soil surface. The soil temperature measured at 5 cm depth by Amertech (1984) is presented in Table 1.
RESULTS AND DISCUSSION
Description of plants: The plants collected during investigation belong to the families Poaceae, Avicenniaceae, Juncaceae, Zygophyllaceae, Gramineae, Chenopodiaceae and Tamaricaceae. Description of each plant species in given in Table 2.
|Table 2:||Description of various plants collected from different regions|
|Table 3:||Mean mineral composition of selected plants|
|The plant composition is a mean of three replications|
Chemical composition of plants
Nitrogen: Nitrogen concentration ranged between 0.74-2.33% and varied upto 4-fold in different plants (Table 3). This could be attributed to the arid environment in the region. Chapman (1966) reported the critical limits of nitrogen in the grasses as less than 1.6%, while in some species the deficiency could appear even at the 2.2% level. All the plants showed nitrogen level below the critical limits except Avicennia marina and Nitraria retusa.
Phosphorus: Phosphorus concentration ranged between 0.05-0.19%, showing a variation upto 4-fold among different plants (Table 3). Phosphorus below 0.15% is considered a deficiency level, over 55% of the plants were deficient in phosphorus. Soil phosphorus plays an important role on the plant phosphorus level. The total phosphorus concentration in the soils of Saudi Arabia ranges from 182 to 1088 mg L- 1 and the available phosphorus from 0-90 mg L-1 (Bashour et al., 1985). These concentrations are much lower than those reported by Smeck and Runge (1971). Plant phosphorus variation indicates a fairly uniform phosphorus distribution in the soils of different regions.
Potassium: The Potassium concentration in the plants ranged between 0.51-2.88%, showing a variation up to 6-fold, indicating that there was a significant unbalanced distribution pattern of potassium in plants (Table 3). A potassium level below 1.5% is considered as a deficient level. As a general observation in the NPK group, the potassium concentration was often several fold higher than for the other two nutrients (NP). For example, Singh and Mishra (1987) reported potassium concentration of up to 18-fold from a humid temperate grassland region in the Himalayas compared with nitrogen and phosphorus concentrations of 2 and 8-fold, respectively. It was observed that all the plants fell in the deficient range (66%) except Salsola sp., Suaeda vermiculata and Salicornia europaea which were above deficient level.
Calcium: The calcium concentration ranged between 0.45-1.66% indicating a 4-fold variation in different plants (Table 3). Since 0-35% calcium level is associated with plant deficiency (Haarenen, 1963), so none of the plants were in the deficient range. A suitable ration between calcium and phosphorus is considered a better index for utilization as footage by animals as compare to their absolute concentration (Singh and Mishra, 1987).
|Table 4:||Mean composition of soil samples collected for the selected plants|
|Note: The soil analysis is a mean of three replications|
|Table 5:||Some mean climate parameters of Al-Qaseem region (1995-2003)|
The study showed plant calcium-phosphorus ratio as (2.4-33.2):1 for most of the plants.
Magnesium: The magnesium concentration ranged between 0.26 -2.15% indicating a 7-fold variation in different plants (Table 3). Magnesium concentration of 0.2% in plants is commonly regarded as the minimum dietary concentration for adequate animal health (Kemp, 1960). Only 33% of the investigated plants could be considered deficient in the magnesium dietary requirement.
Sodium: The range of sodium concentration in plants was very high with a minimum and maximum of 0.82 and 10.53%, respectively with overall variation of up to 11-fold (Table 3). The dietary concentration of Na in dry matter required for animals ranges between 0.09-0.21% (Commonwealth Agricultural Bureau, 1980). In the present case, none of the plants was in the deficient range.
Among the various cations, Na is the most toxic ion and plays an important role in the survival of plants under severe soil salinity conditions. The data show that all the plants investigated can survive high soil salinity growing conditions except Juncus rigidus and Panicum turgidum which may grow better under moderate soil and water salinity. The variability in chemical constituents of plants may be attributed to the difference of soil salinity at different places.
Soil analysis: The ranges of different chemical parameters are: SP (18-73%), pH (7.1-7.9), ECe (50.2-161 dS m-1), Na (0.73-3.54%), K (0.012-0.18%), Ca (0.10-0.49%), Mg (0.06-0.22%), Cl (0.13-5.19%), SAR (41.8-200) and the soil texture sandy to silt-loam (Table 4). The analysis reveals that soil salinity is very high in all the places and may be attributed to arid climate conditions associated with low and sporadic rainfall.
Relationship between soil and plant composition: The data in Table 2 and 3 were analyzed statistically using correlation and regression analysis to determine the effect of soil salinity and composition on plant mineral constituents. A negative value of correlation coefficient (r) was observed for N (-0.67), P (-0.35) and K (-0.09) (Table 5). This suggests that the concentration of these elements decreased in plants with increasing soil salinity which may be due to lower concentration of these elements in soil as compared to other nutrient elements. The positive values of (r) for Ca (0.11), Mg (0.73) and Na (0.48) indicate that these elements increased with increasing soil salinity which may be attributed to the high concentration of these elements in soil solution (Table 6). The order of decrease for nutrient elements of forage value was N > P > K while ascending order for other elements was Mg > Na > Ca. The correlation was very poor except N, Mg and Na between soil salinity, soil composition and plant composition. The soil samples were not analyzed for N and P, hence no correlation was calculated between soil and plants.
|Table 6:||Correlation coefficient (r) between plant composition and soil salinity|
The water-extractable concentrations of soil nutrients may not be a good indicator of plant uptake (CSTPA, 1974; Doll and Lucas, 1973). Moreover, there is no available information on the nutrient index especially for the desert plants growing in coastal and inland salt affected lands where rainfall is low and sporadic. The plants mainly depend for their water needs on the groundwater. The results of poor correlation between soil parameters and plant composition agree with those of Al-Homaid et al. (1990a and b) who also reported similarly poor correlation between soil and plant chemical; constituents.
The mean minimum and mean maximum air-temperature ranged between 8.2-24.2°C and 18.8-36.7°C, respectively (Table 4). The mean minimum and mean maximum relative humidity (%) ranged between 14.4-39.3 and 25.6-57.0, respectively. The man potential pan-Evaporation (mm day-1) ranged between 14 and 440. The mean rainfall ranged between 0.0-118.4 mm month-1 during 1995-2003.
The study highlighted some of the potential plant species such as Aeluroapus lagopoides, Avicennia marina, Juncus rigidus, Nitraria retusa, Panicum turgidum, Salsola sp., Suaeda vermiculata, Salicornia europaea and Tamarix amplexicaulis which can grow under severe salt affected lands and saline irrigation for the development and rehabilitation of inland saline lands and for desert greenification to improve the micro-climate under arid environments.
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