Evaluation of Some Soils in Najd Plateau J. Saudi Soc. Agric. Sci. (1), 2 pp 21-40 (2002) Evaluation of Some Soils in Najd Plateau A. Sh. Sallam Soil Science Department, College of Agriculture, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia. ABSTRACT Soils of a selected area (3210 Km 2 ) within Najd plateau in the Central region of Saudi Arabia were studied in order to evaluate their suitability for agriculture. Interpretations of Landsat TM image indicated the presence of the following landform units: plateau, mountain, scarp, outwash plain, alluvial fans, plains and wadis. Soil profile descriptions and analytical data revealed that the soils are mostly deep, light or medium texture, massive, very low in organic matter (0.3-7.5 g Kg -1 ), and highly calcareous (305.8 797.8 g Kg - 1 CaCO3). Gypsum content was quite low, except for the outwash plain unit that contains from 0.1 14.5 g Kg -1. Generally, the soils are nonsaline to slightly saline, except the soils of outwash plain and plateau (EC e ranges from 4.02 59.78 ds m -1 ). Results showed marginal level for Fe, deficiency for Zn and Mn and sufficient or deficient for Cu. Soil profiles were classified into Entisols and Aridsols orders. The studied area was differentiated in view of type, number and degree of agricultural limitations. The main limitations are the effective root zone, depth to bedrock, amount of gravels, nutrient availability, relief, workability of land, available water, and calcium carbonate content. Therefore, soils of the studied area could be differentiated on the class level to the followings: moderately suitable (S2 n,s2 ), marginally suitable (S3), and not suitable (N). Soils within marginally suitable class were classified into two subclasses; i.e. S3 s2 and S3 s1, s2. These subclasses have one or more of the following limitations; ability of drainage and aeration (s 1 ) and capacity of water retention ( s2 ). - 21 -
A. Sh. Sallam INTRODUCTION The sedimentary Najd plateau is a huge rectangular shaped physiographic region. It comprises most of the arable land at Saudi Arabia (Ministry of Agriculture and Water, 1995). Elevation ranges between 100 to 800 m a.s.l, characterized the region with gradual slope eastwards. Erosion and deposition by both water and wind actions have sculpted the terrain to a series of degradational and aggregational landforms namely: wadis, fans, basins, plateau, rock outcrop and dissected upland. These landforms acquire soils exhibiting variant features in accordance to the acting soil forming factors (Ministry of Agriculture and Water, 1995). Several studies were carried out to classify soils of the region (Mashhady et. al., 1986, Ministry of Agriculture and Water 1985 and 1995, Al-Malik, 1994 and Al-Sheikh et. al., 1995). The applicability of Landsat Thematic Mapper (TM) for Landform mapping was assessed by Conese et al. (1990), who reported that the transformation using the maximum likelihood process has a great significance under different environmental, and agricultural conditions. Qari el al., (1996) found that satellite imagery could be used successfully to predict soil moisture and to assess droughts in the Arabian Shield. The most widely used approaches for suitability classification for a particular use are discussed using FAO's framework for land evaluation (FAO, 1976; Sys, 1979). These basic data for evaluating land suitability for specific crops and the kind of irrigation and management level using both systems, are topography, soils, water and other features; such as infrastructure, markets and socio-economic conditions. The main objective of the current study was to classify and evaluate the soils of the main landforms of Najd plateau in Central Region of Saudi Arabia. - 22 -
Description of the study area Evaluation of Some Soils in Najd Plateau MATERIALS AND METHODS The study area was located south of Huraymala and Malham and intersected by longitudes of 46 and 46 30' E and latitudes 24 30' and 25 4' N with a total area of about 3210 Km 2 (Fig. 1). The area was occupied by sedimentary rocks belonging to Kimmeridgian, Oxfordian and Callovian epoch. These rocks could be grouped into three formations: Jubaila, Hanifa and Tuwaiq (Moshrif, 1984 and Moshrif and Ghalib, 1984). The limestones, shales and sandstones were the main source of soil parent materials. Several geomorphic units are encountered in the study area: Jabal Tuwayq, which is located in the central part of the study area and rising more than 300 m above surrounding lowlands with steep sides. The plateau unit (al Abakkayn), which is bounded on west direction, flat to undulating and dissected with wadis. Escarpment unit occurs at scattered patches at the north and southwest direction, very steep having slopes exceeding 60 % and its surface is being covered by gullies. Outwash plain occupies the southeast part of the study area having gently sloping surface covered with stones and dissected in some parts with very narrow wadis. Several main wadis and its tributers were present most of them flow toward the east and cut through Jabal Tuwayq. Number of alluvial fans at the foot of the scarps especially Jabal Tuwayq and along other scarps. The surface of the fans are covered with intensive natural vegetation. The alluvial plain usually occurs at low elevation, flat to almost flat. Sand dunes covere scattered areas having several types (Ministry of Agriculture and Water, 1995). The meteorological data (Ministry of Agriculture and Water, 1988) indicated that annual average rainfall, temperature and relative humidity were 83.3 mm/year, 24.7 C and 36 %, respectively. Analysis of climatic data indicated that moisture and temperature regimes are torric and hyperthermic (Soil Survey Staff, 1999). The main source of irrigation water is the underground water from Dhruma - 23 -
A. Sh. Sallam aquifer. Total soluble salts of ground water ranges from 1200 to 1500 mg kg-1 (Ministry of Agriculture and Water, 1984). - 24 -
Evaluation of Some Soils in Najd Plateau Data Collection and Image Processing The digital satellite data from Thematic Mapper (TM) sensor of Landsate-5 (spatial resolution = 30 m) was acquired on 19/5/1999 (path 166, row 43). Six bands (1, 2, 3, 4, 5 and 7) were used as they are spectrally and spatially significant for soil applications (Kolawole, 1993). The data were radiometrically corrected using improved darkobject subtraction technique (Chavez, 1988). Also, the geometric correction was carried out using precision control points. From the whole seen, the study area was cut and the False Colour Composite (FCC) (741in R, G, B) was enhanced by non linear stretch and high pass filter 5 x 5. The visual interpretation and the ground truth were carried out to differentiate between the different landform units within the study area using GPS (Fig. 2). A new local map for the area was produced and revised in accordance with the landform features in the field (Fig. 3). Total area of the landform units within the study area were calculated i.e. mountain (M) (1240 Km 2 ), plateau (Pt) (13 Km 2 ), escarpment (Sc) (975 Km 2 ), outwash plain (Ou) (165 Km 2 ), alluvial plain (Pl) (415 Km 2 ), alluvial fans AF (163 Km 2 ), wadi (W) (48 Km 2 ) and sand dunes (Du) (190 Km 2 ). Field study and laboratory analyses Twenty soil profiles representing the dominant landform units; plateau (two profiles), outwash plain (four profiles), alluvial plain (six profiles), alluvial fans (five profiles) and wadi (three profiles) were studied. Nine soil profiles were then selected to represent the following landforms; plateau (profile 1), outwash plain (profile 2 and 3), alluvial plain (profile 4, 5 and 6), alluvial fans (profile 7 and 8) and wadi (profile 9). Soil profiles were morphologically described following the terminology outlined by Soil Survey Staff (1993). Representative soil samples were collected, air-dried, ground gently and then sieved through a 2 mm sieve, the fractions less than 2 mm were kept for laboratory analyses. The following soil analyses were carried out: particle size distribution (Day, 1965), soil ph (Peech, 1965), EC e (Bower and Wilcox, 1965), Calcium carbonate (Allison and Moodie, 1965), soil gypsum (Richards 1954), and organic matter - 25 -
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A. Sh. Sallam (Broadbent, 1965). The plant available nutrients (Fe, Mn, Zn and Cu) in the soil were extracted using NH4HCO3-DTPA as mentioned by Soltanpour and Schwab (1977), then determined by Atomic Absorption Spectrophotometer. Wilting point, field capacity and available water were determined according to Richards (1954). RESULTS AND DISCUSSION Based on the new local map (Fig. 3), the dominant landform units are plateau, outwash plain, alluvial plain, alluvial fans and wadis. Morphological features of representative profiles for each landform unit are summarized in (Table 1 and 2). It indicated that the studied soil profiles vary widely with regard to profile depth, texture, gravel content, consistency and trend of calcium carbonate distribution. However, soils at the plateau (profile 1) and out wash plain (profile 3) were generally shallow due to the prevailing destructive erosional forces caused by both water and wind. Soils within aggregational landforms (i.e., wadis, alluvial plain, fans and outwash plain) are very deep, sandy to sandy loam textured, highly calcareous and differ widely in gravel content. The variations in texture and gravel content were mainly sedimentary relicts. Alluvial deposits have distinctive amount of limestone fragments, and the texture ranges between sand to loam. However, most of alluvial fans and wadi soils (Profiles 7, 8 and9) were characterized by very gravelly layers occurring at depth ranging from the surface to 150 cm. Soil structure was mostly massive as no definite orderly arrangement of natural lines of weakness was visible. The bulk of soil is broken to weak to moderate medium subangulare blocky, single grain structure was recognized with sandy textured horizons. Colour (moist) is either yellowish brown to dark yellowish brown or strong brown. Dry consistence generally ranges from loose to very hard being harder with depth, extremely hard horizons were less common and occurred at depths ranging between 90 to 125 cm. Lime segregations were obsereved in subsurface horizons of profiles 5, 6 and 8. Accordingly, the studied soils were classified on the order level as Entisols and Aridisols. The following sub- great groups were identified Typic Torripsamment, Lithic Torriorthent, Typic Torriorthent and Typic Haplucalcids. - 28 -
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A. Sh. Sallam Data in tables (2 and 3) show that soils of the plateau (profile 1) have sandy loam texture, high calcium carbonate (731. 2 g Kg -1 ), ECe 44.23 ds m -1, ph values (7.45) and organic matter (2.9 g Kg -1 ). Field capacity, wilting point and available water were 0.08, 0.21 and 0.13 cm 3 water/cm 3 soil, respectively. Soils of outwash plain (profile 2 and 3) are shallow (profile 3) to deep (profile 2), texture is mostly sandy loam with a range of clay content from 8.32 to 17.47 %, ph (7.57 to 7.83) and ECe fluctuated between 4.02 and 59.78 ds m -1. Organic matter at surface layer reaches 7.5 g Kg -1 and decrease with depth to 1.0 g Kg -1. Gypsum and CaCO3 contents range between 0.1 14.5 g Kg -1 and 401.0 to 500.2 g Kg -1, respectively. Values of field capacity, wilting point and available water vary between 0.15-0.20, 0.06-0.11 and 0.09-0.11 cm 3 water/cm 3 soil, respectively. Soils of alluvial plain are sandy to sandy loam texture with clay content fluctuated between 0.95 to 12.54 %. The ph values were in the range of 7.49 to 8.45. Soils are almost free saline (ECe 0.52 4.01 ds m -1 ), organic matter and CaCO 3 content range between 0.3 to 7.1 and 305.8 to 797.8 g Kg -1, respectively. Data show that field capacity, wilting point and available water ranges between (0.08-0.19), (0.02-0.09) and (0.05-0.10) cm 3 water/cm 3 soil, respectively. The soils of alluvial fan have sandy to sandy loam texture, ph ranges between (7.49-8.02), ECe ranges between (0.47-5.02 ds m -1 ), organic matter (1.0 to 2.6 g Kg -1 ) and CaCO 3 (324.5 to 574.5 g Kg -1 ). Field capacity, wilting point and available water ranges between 0.10-0.23, 0.03-0.12 and 0.06-0.10 cm 3 water/cm 3 soil, respectively. Soils of wadis were deep, sandy to sandy loam, mildly to moderately alkaline reaction, very low salinity (ECe values less than 0.71 ds m -1 ), low organic matter (1.0 to 4.1 g Kg -1 ) and CaCO3 ranges from 348.0 and 794.5 g Kg -1. The values of field capacity, wilting point and available water ranges between 0.08-0.19, 0.02-0.11 and 0.05-0.08 cm 3 water/cm 3 soil, respectively. Generally, the obtained results revealed that the main variable soil characteristics in the studied units are salinity, CaCO 3 and gypsum contents. Soils of alluvial fans, plains and wadis indicated low salinity levels, which could be the results of leaching from the runoff water during rainy seasons. The relatively high values in the deep layers of - 30 -
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A. Sh. Sallam Table 3. Field capacity, wilting point and available water capacity of the studied soils. Profile Horizon Wilting point Field capacity Available water No Cm 3 water/cm 3 soil 1 C 0.08 0.21 0.13 R 2 C 0.11 0.17 0.11 C2 0.09 0.18 0.11 C3 0.10 0.20 0.10 3 C 0.09 0.19 0.10 2C 0.06 0.15 0.09 R 4 C 0.07 0.15 0.08 C2 0.09 0.18 0.09 2C 0.09 0.19 0.10 5 Ap 0.05 0.12 0.07 C 0.03 0.09 0.06 Ck2 0.02 0.08 0.05 C3 0.09 0.18 0.09 6 Ap 0.03 0.09 0.06 Ck 0.03 0.08 0.06 C2 0.03 0.09 0.06 C3 0.03 0.09 0.06 7 C 0.03 0.10 0.06 C2 0.03 0.10 0.08 2C 0.09 0.17 0.08 C2 0.08 0.16 0.09 8 Ap 0.08 0.16 0.08 Ck 0.10 0.18 0.10 C2 0.12 0.23 0.08 C3 0.09 0.17 0.08 9 C 0.02 0.08 0.05 2C 0.11 0.19 0.08 C2 0.11 0.19 0.05 3C 0.02 0.08 0.05-32 -
Evaluation of Some Soils in Najd Plateau outwash plain soils may reflect the accumulation of salts moved from the surface layers. The low organic matter content at the surface horizons and the deep layers was mainly due to the Torric and hyperthermic moisture and temperature regimes characterizing the studied area. The highly calcareous nature of the soils was mainly attributed to limestone parent rock forming soil parent material. The irregular CaCO 3 distribution within the soils may be functioned by the initial high lime content of parent material. Interpretation of available Fe, Zn, Mn and Cu extracted by NH 4 HCO 3 -DTPA from the surface horizons (Table 4) was conducted according to the guidelines given by Soltanpour and Schwab (1977). Available Fe ranges from 1.82 to 3.85 mg kg -1 that indicates low and marginal levels. Available Zn was relatively low in all samples (0.11 to 0.36 mg kg -1 ) that represent deficient level. Available Mn content ranges from 0.61 to 1.45 mg kg -1, where all of the samples have deficient levels. The result of available Cu indicated that most of the studied samples have deficient level (i.e., <0.5 mg kg -1 ) and the rest are in sufficient levels. Data revealed that soils of outwash plain and the alluvial plain have adequate levels of available Cu. Fertility status is generally low due to the low organic matter, high CaCO 3, low clay content and hot-dry climatic conditions (FAO, 1972). Table 4. Available micronutrients for the surface layer of the studied profiles. Classificatin Profile Horizon Available micronutrients mg Kg -1 No Fe Mn Cu Zn Lithic Torriorthent 1 C 2.45 1.12 0.46 0.15 Typic Torriorthent 2 C 1.84 1.35 1.13 0.22 Lithic Torriorthent 3 C 3.85 1.45 0.81 0.36 Typic Torriorthent 4 C 2.41 0.61 0.52 0.18 Typic Haplucalcids 5 Ap 1.82 0.90 0.10 0.11 Typic Haplucalcids 6 Ap 2.38 0.88 0.10 0.29 Typic Torripsamment 7 C 1.92 0.71 0.44 0.20 Typic Haplucalcids 8 Ap 2.31 0.88 0.11 0.19 Typic Torriorthent 9 C 2.41 1.31 0.10 0.32-33 -
A. Sh. Sallam Land suitability evaluation was carried out based on the evaluation of land limitation (i.e. Climate condition, topography and slope, effective root zone depth, available moisture capacity, calcium carbonate and drainability of soils) Data in (Table 5) show the following classes according to Sys (1979), Sys et al., (1991), Sys (1993) and FAO (1976); - Moderately suitable for agriculture (S2 n, s2 ) (Suitability index = 61.2): Land within this class located in the outwash plain (profiles 2). Soil characteristics of the unit are deep, loamy texture, flat and well drained. Land limitations other than those of climate are ascribed to the presence of slight to moderate capacity of available water, salinity, and high calcium carbonate content. Crops that are adequated to the present existing environmental conditions are vegetable crops (e.g. potato, tomato, cucumber, cappage, cauliflower, lettuce, eggplants, okra, water mellon), fruit crops (data palm, pomegranate, grap, figs), Field crops (wheat, barely) and forage crops (alfalfa). - Marginally suitable land (S3): Land within this class has more limitations than those of (S2). These limitations will increase the required inputs and management required. Soils within this land class are differentiated to the following subclasses: - Marginally suitable for irrigated agriculture (S3 s2 ) (Suitability index 50.6-46.93) due to severe capacity of available water. Soils within this subclass are represented by profiles 4 (Suitability index 50.6) and 8 (Suitability index 46.93). Most of these soils are deep, flat to slightly undulating well drained and have average calcium carbonate content in the range of 406.9 to 529.8 g Kg -1. Agriculture limitations other than those of S2 class include one or more of the following: low available water capacity (0.08 0.1 Cm 3 water/cm 3 soil), (Table 3), slight effective root zone depth and presence of appreciable amount of gravels within the effective rootzone depth. These soils require higher investments and energy costs than those of S2. To cope with soil limitations of these soils the following land utilization types are suggested: field and forage - 34 -
Evaluation of Some Soils in Najd Plateau crops are to be utilized on deep soils under sprinkler irrigation system. Vegetable and fruit crops are to be utilized on moderately or deep soils under the drip irrigation system. - Marginally suitable for irrigated agriculture (S3 s1,s2 ) (Suitability index 25.9) due to severe capacity of available water and the ability of drainage and aeration. Soils within this subclass are represented by profiles 5. Most of these soils are deep, flat, low available water capacity (0.05 0.09 Cm 3 water/cm 3 soil, Table 3), moderate amount of gravels within the effective root-zone depth, rapid infiltration rate and poor fertility level. To cope with soil - 35 -
A. Sh. Sallam limitations; field and forage crops are to be utilized under sprinkler irrigation system, while vegetables and fruit crops are to be utilized under the drip irrigation system. - Not suitable land (N): This soil includes land having severe limitations that are not economically feasible to be corrected. Limitations are so severe as to preclude successful sustained use of the land in the given manner. Land within this suitability class is represented by profiles 1, 3, 6, 7 and 9. Main limitation of land within this suitability class is the shallow depth to the very gravelly zone. Available water capacity within the effective rootzone depth is very low as it ranges from 0.05-0.13 Cm 3 water/cm 3 soil (Table 3). REFERENCES Allison L. E., and C. D. Moodie. (1965). Carbonate, pp. 1379-1369, in Black, C. A. ed., Methods of Soil Analysis, part 2, Amer. Soc. of Agronomy, Madison, Wisconsin. Al-Malik, A. S. (1994). Survey and Classification of Soils on A Selected Area of Wadi Hanifa Basin, Saudi Arabia. M. Sc. Thesis, Soil Science Department,.College of Agriculture, King Saud University, Saudi Arabia. Al-Sheikh, A. A., H. A. El-Kady, M. H. Al-Awajy, A. Sh. Sallam and A. S. Al-Malik. (1995). Clay minerals of soils at Wadi Hanifa (Najd Plateau, Saudi Arabia). Egypt. J. Appl. Sci., 10(6), pp. 411-426. Bower, C. A., and L. V. Wilcox. (1965). Soluble Salts, pp. 933-951, in Black, C. A. ed., Methods of Soil Analysis, part 2, Amer. Soc. of Agronomy, Madison, Wisconsin. - 36 -
Evaluation of Some Soils in Najd Plateau Broadbent, F. E. (1965). Organic Matter, pp. 1397-1400, in Black, C. A. ed., Methods of Soil Analysis, part 2, Amer. Soc. of Agronomy, Madison, Wisconsin. Chavez, P. S.,Jr. (1988). An Improved Dark-Object Subtraction Technique for Atmospheric Scattering Correction of Multispectral Data. Remote Sensing of Environment, 24:459-479. Conese, C., G. Maracchi, F. Masell, and G. Zipoli. (1990). Landscape units identification by means of TM data. 1:909-913. Day, P. R. (1965). Particle Fractionation and Particle Size Analysis, pp. 545-567, in Black, C. A. ed., Methods of Soil Analysis, part 1, Amer. Soc. of Agronomy, Madison, Wisconsin. FAO. (1972). Trace elements in soils and agriculture. Issued with the support of the Swedish International Development Authority (SIDA). Vol. 17,FAO, Rome, Italy. FAO. (1976). A framework for land evaluation. Soil bull. Vol. 32; F.A.O. Rome, Italy. Kolawole, M. O. (1993). Using remote sensing technique to study soil sedimentation flow. Environmental Management, Springer-Verlag New York Inc. (17)1:73-81. Mashhady, A. S., M. A. Hammad and M. Reda. (1986). Soil Resources and Land Potential for Al-Qasseem Region, Saudi Arabia. Agric. Research Center, Coll. Agric. King Saud Univ.1-95. Ministry of Agriculture and Water. (1984). Water Atlas of Saudi Arabia. Ministry of Agriculture and Water Publication, Riyadh, Saudi Arabia, pp. 1-100. - 37 -
A. Sh. Sallam Ministry of Agriculture and Water. (1985). General Soil Map of the Kingdom of Saudi Arabia. Prepared by Ministry of Agriculture and Water in Co-operation with Saudi Arabia-United States Joint Commission of Economic Co-operation. pp. 1-47. Ministry of Agriculture and Water. (1988). Climate Atlas of Saudi Arabia. Prepared by Ministry of Agriculture and Water in Cooperation with Saudi Arabia-United States Joint Commission of Economic Co-operation. pp. 1-118. Ministry of Agriculture and Water. (1995). The Land Resources. Ministry of Agriculture and Water, Land Management Dept., pp. 1-33. Moshrif, M. A. (1984). Sequental Development of Hanifa Formation (Upper Jurassic) Paleoenvironments and Paleogeography, Central Saudi Arabia. J. Petroleum Geology, 7, 4, pp. 451-460. Moshrif, M. A. and A. A. Ghalib. (1984). Sedimentation and Environmental Interpretation of Hanifa Formation (Upper Jurassic), Central Saudi Arabia. J. Coll. Sci. King Saud Univ.., 15(2):479-505. Peech, M. (1965). Hydrogen-Ion Activity, pp. 914-925, in Black, C. A. ed., Methods of Soil Analysis, part 1, Amer. Soc. of Agronomy, Madison, Wisconsin. Qari, M. Y., A. U. Sorman, A. M. Al-Sari and M. M. Hassani. (1996). Landsat and Spot data interpretations of geo-hydrological aspects in Wadi Tabalah aree, Kingdom of Saudi Arabia. J. KAU: Earth Sci., Vol. 9, pp. 1-16. Richards, L. A. (ed.). (1954). Diagnosis and Improvement of Saline and Alkali Soils. U.S.D.A. Handbook No. 60, Indian Edition, Published by Prinlar for Oxford and IBH publishing Co. 66, Janpath New Delhi, India. - 38 -
Evaluation of Some Soils in Najd Plateau Soil Survey Staff. (1993). Soil Survey Manual. USDA Agric., Handb. 18. U. S. Gov. Print. Office, Washington, DC. Soil Survey Staff.(1999). Soil Taxonomy A Basic System of Soil Classification for Making and Interpreting Soil Surveys (2 ed.), USDA, NRCS, Agric. Handb., No. 436, pp.21-114 and 555-654. Soltanpour, P. N. and A. P. Schwab (1977). A new soil test for simultaneous extraction of macro-and micro-nutrient in alkaline soils. Commu. Soil Sci. Plant Annal. 8:195-207. Sys, C. (1979). Evaluation of the physical environment for irrigation in terms of land characteristics and land qualities. World Soil Resources Reports, No. 50, FAO, Rome. Sys, C., E. Van Ranst,. and J. Debaveye. (1991). Land evaluation, Part II, Method in Land evaluation. Agricultal Publications. No. 7, ITC, Belgium. Sys, C. (1993). Land Evaluation, Part III, Crop requirements. No. 7, General Administration for Development Cooperation Place du champ de Mar. 5 bte 57-1050 Brussels-Belgium. - 39 -
A. Sh. Sallam ( ).. (5 ). 3210 ( ) (TM). ( / 7.5 0.3 ). ( / 797.8-305.8) ( / 14.5 >)... :... (S3 s2 and S3 s1, s2 ) - 40 -