Soil and Land Suitability Assessment

Um Bayada Project – Soil and Land Suitability Assessment

Soils Bulletin No. 7

‫ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﻴﻢ‬

Um Bayada Project North Darfur

Soil and Land Suitability Assessment for Agricultural development and Land Resources Management Dr. El-Abbas Doka M. Ali Soil and Water Sciences Division (SWSD), CAS, SUST

March 2007

Sudan University of Science and Technology (SUST)

College for Agricultural studies – Shambat (CAS)



CONTENTS INTRODUCTION CHAPTER 1 THE STUDY AREA 1.1 1.2

1.3 1.4

Location and general features The environment 1.2.1 Geology and geomorphology 1.2.2 Climate 1.2.3 Vegetation 1.2.4 Water resources Major land use types Infrastructure

CHAPTER 2 SOIL CHARACTERISTICS AND CLASSIFICATION 2.2

Soil characteristics 2.2.1 2.2.2 a. b. c. d. e. f. 2.2.3 a. b. c.

2.3

Previous work Morphological and Physical Characteristics Morphological and Physical Characteristics Parent materials and genesis Stratifications and texture Soil color Structure and porosity Soil- water relationship Chemical characteristics Total Carbonates Cation Exchange Capacity Fertility status

Soil classification 2.3.1

Classification system

2.3.2

Soil classes identified i. ii. iii. iv. v.

2.4

Um Bayada series Mogran series Fouda series Argud series Al Faki series

Mapping Units 2.4.1 2.4.2

Main Concepts Description of Map Units 1

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CHAPTER 3 LAND SUITABILITY CLASSIFICATION 4.1

Land Classification 4.1.1 4.1.2

Land suitability system Land suitability units

CHAPTER4 CONCLUSIONS AND RECOMMONDATIONS REFERENCES

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INTRODUCTION The local geomorphology is largely affected by El Meidoub mountains volcanism and subsequent depositional processes which have led to the creation of Wadis system and the associated alluvium deposits. This as well followed by regional intensive deposition of aeolian sands, which have created the Qozland and the sandy plains. Generally, the lower alluvium deposits are used for irrigated agriculture while rainfed agriculture and grazing are practiced on relatively higher sandy plains. In such unique natural conditions and related different land uses, it is highly required to characterize the associated environmental factors and develop proper methods for soil and water resource utilization and management. The soil study of Um Bayada project area was undertaken as part of an integrated natural resources assessment to provide basic information to enable designing of water harvesting system to enable agricultural development. It is thought that the development project could utilize the abundant surface waters carried seasonally by eight wadis and their tributaries for arable farming and other relevant uses. These wadis are Mogran, Angro, Seyal, Bado, Forgan, Shaw, Owr and Kabish. Although the soil study is mainly confined to the flood plain areas where surface water would be used for irrigated agriculture, but some surrounding relatively higher rainfed agriculture lands (Qoz and Gurdud) are also included as grazing lands to ensure an integrated development program. In this regard, the present major land use types, which are rainfed and grazing, will be considered besides introducing irrigated agriculture. Recently the area has witnessed considerable ecological and environmental hazards due to annual rainfall fluctuation because of adverse cyclic climatic changes. Soil erosion and degradation, drop of water table, deforestation, over grazing are some of disasters to be mentioned in this regard. This situation has led to rather complete land degradation in some areas and desertification in others. Consequently, land system has gone into many complications and as well critical conflicts have started between the different users. The formerly functioning rotational system of grazing and cultivation that permit restoration of resources had inevitably deteriorated and collapsed. However, in such semi-arid environment that is characterized by unreliable climate and vulnerable ecosystem, resources have to be assessed and as well, the defined limitations are to be observed and monitored.

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CHAPTER 1 THE STUDY AREA 1.1 Location and general features The study area is located in North Darfur State, north east of Al-Fasher the state capital and lies within Malha Locality. The main road which connects Al-Fasher to Hamrat Al-Sheikh in North Kordofan runs across Um Bayada area. The presence of Al-Meidoub dome and associated subsequent uplifts, have influenced local and regional sequence of land formation and degradation. The existing Wadis were rejuvenated and / or new ones were developed dissecting the southern forelands. This includes the Jebel Meidoub volcanics, the underlying Basement Complex plateau and other overlying sedimentary formations. This initiated severe erosion in upper parts and extensive deposition in the lower plains. The Southern foreland of Jebel Meidoub dome is drained mainly by Wadi Mogran, Angro, Seyal, Bado, Forgan, Shaw, Owr and Kabish and their main tributaries. These Wadis contribute to the huge annual discharge which is estimated to be about 3 - 5 Mm3. The lower basin of Um Bayada is the areas selected for this study and makes a total area of about 225 km2 (approximately 54,000 feddans). Administratively the area belongs to Al-Maliha locality. Al Malha, the main town of the locality (42,132 inhabitants – 1993 Census) lies about 60 km North West of the study area (el Sammani 1997). The major sources of water supply during the rainy season are wadis and few natural depressions (Rahads). Ground water from deep boreholes and spring water (at the bottom of rock fissures along upper Wadis) are the main source during the dry period. The emergence of settlements in the area depends largely on water availability. Settlement comprise of villages of different size scattered throughout the area with population of less than 1000 persons for small villages to more than 2,000 for large ones. The major settlements within the study area are Um Bayada Hemaira, Um Bayada Ziraiga, Tarroom, Hattan, Al Hadadeyat, Al Fouda, Ganbagley and Angro villages. The dominant tribal inhabitants are the Meidob with other tribal communities which include Kababish, Berti, Zayadiya and Kawahla (El Sammani 1997). The local populations are mainly sedentarists and semi-nomadic residing in small scattered villages and huts. The area as well includes some nomadic tribes from neighboring regions. Most of the sedentary population practice subsistence agriculture, with some keeping livestock plus other minor activities. Most of the young population, particularly men, has left the area to look for jobs at Khartoum or even outside the country. 1.2

The Environment 1.2.1 Geology and geomorphology The region is part of the northern edge of the African shield, a tectonically stable region which forms the core of the African continent. The region was probably part of a land mass for most of its existence since Pre-Cambrian times. The Pre-Cambrian basement complex is therefore covered only by thin and discontinuous sediments, largely of continental origin (HTS, 1975).

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Block faulting and warping are the two events since the Pre-Cambrian which have a profound effect on the geology of the region and probably associated with the formation of the great Rifts of East Africa and outburst of volcanic activity in Tertiary times. The faulting and warping created a number of basins of deposition which have been filled with fluviatile, often coarse, sediments.

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Al Meidob Hills Qoz

N

Jebel Mogran Qoz Mogran Jebel Argud Qoz Argud

Um Bayada basin ( the dark area surrounded by the dashed white line) and the Wadis mainly originating from Meidob Hills in the North.

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Qoz Graywid

Qozlands on South and East areas



The Pre-Cambrian Basement complex is covered by sandy cross-bedded continental sedimentary rocks (the Nubian sandstone formation). The sediments that later formed the Nubian Sandstone formation were deposited across a broad plain under fluviatile conditions, mainly during Cretaceous. The tertiary volcanicity has been responsible for the formation of the dominant topographic feature of the region, the Meidob volcanic dome. In turn, this together with other volcanic centres, such as Meidob dome, has profoundly influenced the drainage pattern of the area and subsequent deposition and soil formation (see satellite image Figure 2). 1.2.1.1 Structure and strategraphy The area lies in at the interaction of two major lines of weakness; one of them is represented by an east-north east alignment of volcanic rocks and fracture zones. It extends from Cameroon through Jebel Marra – Meidob Hills – Wadi El-Milk and Bayoda volcanic centres to the northern Red Sea Hills. This zone of weakness is thought to be Post Mesozoic (Whiteman, 1971). The second fracture zone is also associated with volcanic activity and the form of depositional troughs. It extends south-south east from Libya to Jebel Marra and continues to the East African Rift valley system. The effect of interactions of these two lines is reflected in the major fractures and dykes (undifferentiated) in the area and the Tertiary volcanic eruption which created Jebel Marra massif. The massif lava was extended onto the uplifted eroded Basement Complex land Surface (HTS, 1977B). The study area is composed of four major Lithology; namely the PreCambrian Basement Complex, the Cretaceous Nubian sandstone formation, the Tertiary Meidob volcanics and the Quaternary Superficial (Alluvial and Aeolian) Sediments. I. Basement Complex (Pre-Cambrain) It includes all the igneous and metamorphic rocks and thus forming erosion surface on which quazi-horizontal continental sediments rest. The igneous rocks which include granites, gneisses, quartzite and schists have been fractured and folded. This gives a complex structural pattern in which the degree of deformation varies considerably. The Basement rocks are in general resistant to weathering and erosion. About 150 km east of Jebel Marra the Basement complex becomes covered by Nubian Sandstones or the Quaternary Superficial deposits of varying types and depths. When exposed, the basement rocks show evidence of exfoliation and severe weathering in most cases. This indicates that the sedimentary rocks were either deposited in discontinuous basins or were partially removed by erosion prior to volcanic activity. II. Nubian Sandstone (Cretaceous) These are sandy cross-bedded continental sedimentary rocks covering the Pre-Cambrian Basement complex. The sediments that later formed the Nubian Sandstone formations were deposited across a broad plain under 7

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fluviatile conditions, mainly during Cretaceous. The Nubian Sandstone covers most of the study area from the volcanic massif interiors and down to Wadis and depressional basins (Lebon and Robertson, 1961). The formation seems to be extensive in the middle and lower parts basin. There is some evidence that the Nubian sandstone formation extend further to Al Malha and El-Fasher. The latter site is intruded and capped by basalt. In many parts of the study area the Nubian Sandstones are covered by thick deposits (mainly Aeolian) and whenever exposed they are severely weathered, dissected and faulted. III. Meidob Volcanics ( Tertiary) The volcanic rocks are confined to the upper-most parts of the Wadis at Meidob dome an area where the dome rises in a gentle relief consisting of trachytes, basalt and pyroclastics. The stratigraphy of the volcanic dome is highly related to the phases of its formation in earlier times. Several phases of formation were pointed out by HTS (1958) for Jabal Marra volcanism and since both occurred at the same time, this could applied to Meidob volcanics. The "first eruption phase" resulted in the accumulation of great thickness of basalt and trachytes lava to form the dome itself. The earlier flows were more basic, and extremely fluid, they flowed for long distances from the source down existing drainage channels before coming to rest and solidify. The later flows became progressively more acid in composition and consequently less fluid, solidifying close to their source and building up the Lava Mountains, which forms the bases of the present volcanoes. A period of relative quiescence followed in which the newly formed mountain was subjected to intense sub-aerial erosion. This resulted in of the formation of the extensive current bedded piedmont alluvial and colluvial deposition. A "second eruption phase" occurred, during which small quantities of basaltic lavas were intercalated in or capped the pediment deposits. These flows followed the newly-formed drainage channels, so that in some cases they are found in the valley bottoms. The "explosion phase" is typified by the emission of considerable quantities of ash, tuff and welded tuff, and possibly the formation of the Calera of the Malha craters. The "intrusion phase" is expressed by the numerous plugs and a few basic dykes. IV. Superficial Deposits (Quaternary) Superficial deposits of both fluviatile and aeolian origin are widespread in the area (Lebon and Robertson, 1961) and they are broadly represented by Umm Bayada basin and the surrounding Wadis and Qoz lands. These deposits can be classified into the following: a) The Alluvial Sediments The alluvial sediments vary in composition from relatively stony coarse beds of alluvial sands and clays in the upper catchments of the Wadis to fine silts, clays in the lower basin. The alluvial material is derived either from the Meidob volcanic or the Basement Complex. The largest deposits lie in the lower reaches of the Wadis and their tributaries at Umm Bayada which represent the 8 __________________________________________________________________________________________________________________ Sudan University of Science and Technology (SUST)




main depositional basin. Although Wadi Mogran and Angro are the main Wadis but the rest of the Wadis (Seyal, Bado, Forgan, Shaw, Owr and Kabish) resemble them in material, sources, time and conditions of deposition. The thickness of sediments underlying Al Bayada area lies on Umm Bayada basin ranges down to more than 1000 m. They are mainly of the Nubian sandstone formation, but also perhaps including up to about 100 m of alluvium. The great thickness of these sediments suggests a subsidiary basin probably with fault boundaries in the Basement floor. The considerable thickness of the alluvium suggests that subsidence may have continued until recent times. Moreover recent borehole evidence showed that the sediments at Umm Bayada are particularly so loose and permeable. Accordingly it has been postulated that these deposits are not in situ formed materials but rather they are a more recent deposits of the reworked Nubian materials. The clay plain of Um Bayada is thought to be formed by sheet floods. This is suggested probably due to the similarity of the condition of formation. Shallow alluvial deposits are found in all the other small Wadis away from Umm Bayada basin and its main Wadi channels and the dome foothills. The ratio of fine to coarse sediments varies considerably with distance away from the source. During deposition of the alluvium, the Wadi channels have not shown considerable change through time. This resulted in relatively homogenous flood plain sediments. b) The Aeolian Deposits The Qoz land or Dune land represents the Aeolian deposits and covers most of the lower half of the basin. The Qozland which is believed to have been formed during the arid phases of the Pleistocene, deposited in many forms e.g. sand dunes and sand sheets. These deposits have consolidated or stabilized by some cementing material and vegetation but recently they are moving in response to very severe desertification factors aggravated by the increasing human pressure on the land. The sand deposits vary in thickness from more than 100 m in the Southern, Western and North Eastern parts of the basin to less than 50 cm in its contact zone with the basin and Wads clay plains. 1.2.1.2

The Geochronology

Wickens (1975), HTS (1977b) and Lebon and Robertson (1961) described the chronological sequence of geological and geomorphological events in the area as follows:

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a) Cretaceous This is the deposition of continental Nubian sandstone formation in basins of the Basement Complex formations. b) Lower Cretaceous Regional uplift led to almost complete erosion of the Nubian Sandstone formations c) Mid-Tertiary This is the initial major eruption of Jebel Marra volcanic complex that have causes uplifting and building of the massif. d) Mio-Pliocene This is the peneplanation and formation of the shallow basins in the surrounding areas. This coupled with the dissection of the volcanic massif and deposition of pediment alluvial and colluvial sediments. e) Plio-Pleistocene Regional uplift and the second lava eruption with the formation of the Al Malha crater (HTS, 1977b). This formed new drainage channels and an initial dissection started. The uplift is believed to have resulted in the formation of Um Ruwaba series of Kordofan (Wickens, 1975). A further built up of pediment deposits followed the initial dissection and channel fills. Peneplanation and the formation of the grey clay plains, took place during the pluvial period the (Pleistocene). During this period there was also further region uplift and the onset of a period of desiccation. The formation of the Qoz land as a result of sand invasion, took place during several Pleistocene arid phases. The source of the Qoz deposits was the direct weathering and disintegration of Nubian Sandstone (Andrew, 1948). The initial dissection of the clay plains and the pediment and the reconstruction of the upper Wadi parts took place during this period. f) Recent Further uplift occurred during recent times with further dissection of all the previously mentioned formations. Major beds of the wadis and low flat basins were established.

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TABLE 1


Geological and hydrological setting of Meidob region

GEOCHRONOLOGY

LITHOSTRATIGRAPHY

QUATERNARY TERTIARY

Superficial Deposits

TERTIARY

LITHOLOGY

HYDROGEOLOGY

aeolian sands (Qoz); alluvium, slope- good aquifer, permeability from low to high, thickness of the aquifer varies Recent unconsolidated formations, wash, residual deposits alluvial, aeolian and evaporitic sediments. poor aquifer Volcanics Basic to intermediate laves and tuffs poor aquifer, an aquifer in zones limited to fractured zones

CRETACEOUS

Nubian Sandstone Series

Fine sandstone with little limestone and good aquifer if it is at shallow depth conglomerates with subordinate mudstone Dolomite with shale, marl, sandstone and clay.

PRECAMBRIAN

Basement Complex

schists, gneisses, granites, poor aquifer in general, may form an amphibolites, quartzites, phyllites, etc. aquifer if fractured near the surface

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Wind direction

Wadis (Mogran, Angro, Seyal, Bado, Forgan, Shaw, Owr and Kabish)

Sloping Upper Parts


Nearly flat middle, basin

Low basin bottom

Qoz Argud

Meidob Hills (southern Slopes) Deep, slightly cracking Clay & Silty Clay materials with overblown & mulch

Schematic diagram across Um Bayada Basin (North-South) showing different Landforms

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Jebel Argud



1.2.2 Climate Climatic zonations were proposed for Sudan by Van der Kevie (1976). This proposal was primarily based on water balance, using monthly rainfall and potential evapotranspiration data. Kevie pointed that the differentiating criteria are significant for agriculture, whilst the zones also correspond rather well with vegetation zones. The definitions of the major zones have been adopted fro Papadakis, but certain amendments were made e.g. in some of the dry climate zones and the dry monsoon zone, subdivisions were made based on lower temperature in winter. The dry zones were also divided in areas with winter or summer rainfall, or with no marked seasons. Although in consequence, the study area lies within the major Semi-Desert zone. Van der Kevie gave the following description for the major climatic zone and its subdivisions. Table (2) provides a summary for sub-divisions: Semi-Desert climate (summer rain, cool winter) : Maximum temperatures of the hottest month (April or May) are 40 – 42 o C and mean minimum of the coldest month (January) is 8 - 13 o C. The average annual rainfall, ranging from 100 – 225 mm, is less than 50 % of the annual potential evapotranspiration in all months, but at least in one month the rainfall is more than 20 percent of the evapotranspiration.. Vegetation is sparse Acacia desert scrub. There is summer grazing in Wadis and even some extensive cultivation of rainfed sorghum or Dukhn on water receiving rather sandy soils. Main potential is irrigated farming along big Wadis and basins or depressions.

Table ( 2 ) Climatic Factors in the climatic zone of the study area (Van der Kevie 1976) Climatic Zone

Semi-desert Summer rain, cool winter

Humid Dry Growing months months season

0

11

1

Average annual rainfall mm 100 to 225

Mean Mean Max. Max. Diagnostic temp. in temp. in characterhottest coldest ization month month 40 - 42 8 - 13 Rw =2.00.5E Tc >13

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180 160 140 120 Monthly rainfall mm Monthly PET mm

100 80 60 40 20 0 J

Figure 1:

F

M

A

M

J

J

A

S

O

N

D

Rainfall and potential evapotranspiration representing stations which lies within the semi-desert climate (summer rain, cool winter) 1.2.3

Vegetation The degradation forms resulting from drought, over cultivation, overgrazing, and clearing of woodland have changed the natural vegetation to such an extent that a zonation of natural plant associations is rendered entirely questionable. The occurrence, type and distribution of natural vegetation within an area is controlled by water availability – a prime factor of climate, lithology and landforms. Vegetation cover in the study area is of sparse to densely distribution. The vegetation has been greatly affected in the last three decades by land use practices and drought. The several attempts to make vegetation zones were primarily based on either rainfall amount or soillandform type (Jackson and Harrison 1956, Lebon 1965, Barbour 1961a and Ibrahim 1980). The following are the three identified vegetation types differentiated according to pedo-geomorphological units as follows:

i. The Qoz vegetation At the Qoz around of Um Bayada, the dominant vegetation types are: Acacia nubica (Al laot), Maerua erassifolia (Al sareh), Acacia tortilis (Al seyal) and Acacia mellifera (Al Kitr) as individual or small group stands. Aristida sieberna (Gaw), Aristida plumose (Bayad), Blepharis linariifolia (Begheil), Ergrositis Termula (Al banu) and Triulus terrestris (Dereisa) are the dominant grasses. 14

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ii. The Basement vegetation This zone s confined to the northern quarter of the basin and the adjacent severely dissected dome foothills soils. Acacia mellifera (Ktir), Commifora africana (Gafal), Acacia nubica (Laot), and Cappars deciduas (Tundub) are the dominant trees and bushes in this area. Harrison and Jackson (1958) described this part as hill catena with individual or grouped bare and eroded hills where erosion is active and soils are shallow. At the foot of the steep slopes the soils are hard surface and impervious. Terminalia brownie (Sobag) and Boswellia papyrifera (Tarag-tarag) the main tree stands. The main grass types are; Andropogon gayanus (Abu rachis, Marahbieb), Pennisetum pedicellatum (Umm difolo), Pennisetum pedicellatum (Umm difolo), Tristachya (Gaw) and other Aristida species. iii. The alluvium vegetation Variety of tree species exist in this zone as well as those found on both the Qoz and the Basement vegetation zones. Acacia mellifera (Kitr), Acacia seyal var. Seyal (Talih), Acacia tortilis sub sp. radiana (Seyal), Acacia nilotica (sunut) Acacia nubica (Laot), Balanites aegyptiaca, Boscica senegalensis (Mukheit) and Capparis deciduas (Tundub) are the dominant tree stands for this part. Cassia italica (Senna-senna) and Cassia occidentals (Sim Ed Dabib) are dominant perennial grass while Aristida spp. and Cenchrus biflorus (Haskaneet) occur as annuals along water courses (Harrison and Jackson, (1958); Lebon and Robertson (1961)). 1.2.4

Water resources 1.2.4.1 Surface water The Wadis are the main surface hydrologic system in the study area that is very much influenced by the presence of Meidob dome since its main catchment area lies within the southern slopes Meidob hills. With the considerable length of the dome, numerous tributaries and branches join the main Wadi from different parts until it reaches Um Bayada basin (Figure 3). The main Wadis like Mogran, Angro, Seyal, Bado, Forgan, Shaw, Owr and Kabish enter Um Bayada basin at foothill zones up stream areas. Numerous small tributaries join these systems at different stages. Due to these large amounts of water converging into Um Bayada basin, the main channel down stream becomes over loaded and often over spills its banks. The flood size and lateral distance in the basin vary from year to another. The hydrologic characteristics of the Wadis at Meidob area are attributed to the following determinants: i. The location of the basin in relation rainfall regime. ii. Al Meidob hills which influences runoff, evaporation and infiltration. iii. Lithology variations within the basin influences runoff and loss of water iv. Variations in vegetation cover 15

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v. The braiding nature of the Wadi 1.2.4.2 Underground water Um Bayada area and the surroundings are underlain by a great thickness of coarse clastic rocks, most of which occur below the water table, thus constituting a major aquifer. The configuration of the aquifer is determined by the depositional history of the strata. It occurs in a great basin formed by down warping and/or faulting of the Basement complex. Although at present its entire surface is covered by superficial deposits of Qoz and alluvium, its geometry and nature of its deposits have been studied by surface geophysical methods and borehole drilling (FMAF & SMARRI 2004). According to Hunting Hydrological map (1970) for the central part in Northern Darfur, it shows some basins of irregular shape of over 1000 sq Km surface area with a very uneven basement complex floor. There are several deeps and shallows but over most of the thickness of sedimentary strata is greater than 200m. As for underground water quality for agricultural purposes some related water properties for Um Bayada aquifer have been measured by the former RWC (Rural Water Corporation -Khartoum). Water samples from similar areas showed that the ground water is generally of medium salinity with few samples in the high salinity range (EC greater than 750 micro mhos/ cm. Hunting (1970) concluded that leaching will therefore be required to avoid any build up of soil salinity and this could be a problem since the soils are probably of very low permeability and have a low infiltration intake capacity. Hunting (1970) discussed the US Salinity Laboratory irrigation water classification in terms of total salinity expressed by electrical conductivity and alkalinity or sodicity as expressed by Sodium Adsorption Ratio (SAR) defined as follows: Na+ SAR = Ca++ + Mg ++ 2 This was applied to Um Bayada aquifer and showed that the water samples fall within the medium to high salinity/ low sodium hazard classes. Eaton's Residual Sodium Carbonate (RSC) measure for irrigation water sodicity was also being calculated and discussed. This is defined by the equation: RSC = (CO3 - - + HCO3 -) - (Ca++ + Mg ++) (All concentrations are expressed in milliequivalents per liter). The results show that many of the water from sag Um Bayada have high RCS values. Despite this high sodium levels, Hunting did not anticipated further soil permeability problems to be brought the presence of the sodium, since the soils are inherently of low permeability and the present Na concentrations are not toxic to plants. 16

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1.3


Major land use types The main occupations in the area are.  Traditional farming (rainfed)  Traditional animal breeding  Wood cutting Most sedentary inhabitants practice rainfed cultivation and livestock rearing. Due to poor soil characteristic in some parts and lack of dependable source of water, cultivation is discontinuous and people are more dispersed. Limited traditional rainfed is practiced to grow Millet, Sorghum and water Mellons. Beside rainfed cultivation, Cattle, goats and sheep are raised in large numbers. Tree-felling and wood cutting for fuel and building purposes dominate as an activity. In Qozland rainfed cultivation (shifting) is practiced. The main crops grown include: millet, sesame, groundnuts and water melons. In the rest of the uncultivated Qozland animals of both sedentary and nomadic population are grazed (lebon and Robertson 1961). Recent attempts were being made to improve crop production within Um Bayada area by implementing new methods for water harvesting and management and as well introducing modern means for mechanized farming (e.g. Um Bayada pilot project). Due to natural devastating seasonal floods, mismanagement coupled with local conflicts and regional civil war these attempts were brought to an end.

1.4

Infrastructure Most of the roads within the area are seasonal and difficult to drive along during rainy season. The earth road which connects Al Malha and Hamrat Al Sheikh in North Kordofan passes through the study area. After Hamrat Al sheikh this road continues to connect Sodari, Gabra Al Sheikh and ends at Um Dorman. Some sort of basic health and schooling services are available at large villages. Al Malha Locality head quarter is situated in Malha town together with relevant government and non-government offices. Active trading and essential services start to develop through out the area.

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CHAPTER 2 SOIL CHARACTERISTICS AND CLASSIFICATION

2.1

Soil characteristics 2.1.1

Previous work

Numerous land resources studies were carried through out the North Darfur, but the areas around Al Meidob and in particular at the present study area had the smallest gain. Most of these studies were done with the objective of providing data for rural land use planning projects and hence investigations concentrate on water resources and land uses. In this regard little emphases were given for soils characterization and arable farming since the major kind of land use is grazing. The soil information provided in the majority of these studies lacks some basic soil information related to land assessment for agricultural development. Although it was reported that some soil samples from the pilot project at Um Bayada were collected and analyzed (Abdalla 1972), but it seems that no professional attempt was done to characterize and assess the soils at Um Bayada basin in depth for agricultural development. 2.1.2

Morphological and Physical characteristics a) Parent materials and genesis The parent materials of the soils of Umm Bayada basin are part of the alluvial, aeolian and local residuum deposits covering most parts of the region. The alluvium deposits were laid down by eight Wadis (Mogran, Angro, Seyal, Bado, Forgan, Shaw, Owr and Kabish) at upper slopes of the basin. They are mainly composed of stratified silt loams, clay loams and silty clay with variable thickness. The low duneland lies on the northern and southern parts of the basin and as the whole area including Wadi Abu Hamra is affected by wind blowing, some of the sandy materials are found throughout the area. Aeolian deposits are seasonally reworked by Wadi flood waters and mixed with other alluvium or deposited as thin sandy layers. The old residuum sandstone materials are part of the intensively weathered peneplains and plateaus which have some exposed rock outcrops and gravelly surfaces. These are the erosional plains mostly at the upper or middle slopes of the basin. The presence of weak pedogenetic features in the alluvium soils of Um Bayada was expected in such the soils of the Wadis. Absence of pedogenetic features in similar alluvium soils has already been reported by Dawoud (1974) at Saq Al Na’,am area, and as well being confirmed through some field observations at Abu Hamra basin (Taha 1999). These immature soils are not expected to develop under the present arid climatic conditions. Evidence of calcium carbonate movement within the profile was not reported. Soil texture and some structural development are the main criteria used to differentiate the soils of Um Bayada due to the absence of clear pedogenetic features. Some more 18

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characteristics, closely related to texture and structure, were also used to differentiate soils (e.g. porosity, cracks, and distribution of the roots). In Um Bayada area although there are some deep, homogenous, relatively thick layers which might probably indicate anthropic deposition (spate irrigation), but it is believed that most soils were developed in natural deposits. b) Stratifications and texture These alluvium soils have layers with homogenous textures throughout their profiles. At Um Bayada the profiles generally have 4 - 5 layers. Thickness of layers range from 20 to 40 cm, but few have layers of more than 40 cm thickness. Textures are dominantly silty clay and clay with very few layers of clay loam and sandy clay loam. Clayey stratified textures of clay and sandy clay loam are localized at upper reaches of the wadis. Fine clay is the dominant particle size, mixed with variable amounts of silt, coarse silt and very fine and fine sand. c) Soil color Under the prevailing arid conditions, the organic matter content of the coarse textured soils is negligible and no translocation of clay and carbonates would occur. Therefore, the soil color reflects the color of the textural particles only. Very little variation in color exists among most coarse textures, but generally heavy textured soils have darker colors than lighter ones. All hues were reported as 10YR, with values ranging between 7 and 4 while the chroma is between 4 and 2. In some profile dark mottles were reported. d) Structure and porosity Since these alluvial soils are clayey and moderately stratified, common blocky structures with limited porosity are dominant under these arid conditions. Soil structure refers to the nature and degree of aggregation of soil particles and porosity refers to the amount of voids between and within these aggregates. Homogenized soils with dense layers at different depths will definitely affect water infiltration and permeability. e)

Soil-Water relationships i. Infiltration rate and permeability The least pervious layer in a profile regulates the vertical permeability, and thus controls the infiltration rate (FAO 1986). Optimum infiltration rates for gravity irrigation are between 0.7 and 3.5 cm/hr. Structure, sodicity and bulk density all influence the infiltration rate through their relation to pore size and cleavage plane. The average hydraulic conductivity of a soil profile is used to determine subsurface drainage and to evaluate the possibility of perched water table developing. In some strongly homogenized soils such as found at Um Bayada, the minimum hydraulic conductivity values depend on the depth of the slowly permeable layer. The development of a water table is also influenced by the frequency of irrigation and/or heavy rainfall during the cropping season. To obtain high yields, the upper rooting zone should in general not be saturated for more than 48 hours during most of the crop 19

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growth period, although this depends to some extent also on the crop being grown, with some crops (such as sesame) being more sensitive to water logging than others (such as sorghum after seedling stage). Field determinations for both parameters were not done and it was suggested to be carried as part of the research for the soil and irrigation section in the future. The following data was selected from a previous work in Abu Hamra area. The data shown in table 4 indicate that fine textures (silty clay and clay) have a significant effect on the infiltration rate and permeability. These representative characteristics fairly represent Um Bayada soils despite some expected variation in textures and other related soil properties. Table 4 Representative Physical characteristics of Soils Infiltration And permeability Cm/hr

Total pore space %

Apparent Specific gravity

Field Capacity %

Permanent Wilting %

Weight

Volume

Cm/m

Silty Clay

0.25 (0.03–0.5)

51 (49-53)

1.30 (1.3-1.4)

31 (27- 35)

15 (13 - 17)

16 (14-18)

21 (18-23)

21 (18-23)

Clay

0.05 (0.01-1.0)

53 (51-55)

1.25 (1.2-1.3)

35 (31-39)

17 (15-19)

18 (16-20)

23 (20-25)

23 (20-25)

5 (2.5-25)

38 (32-42)

1.65 (1.5-1.8)

9 (6 - 12)

4 (2 - 6)

5 (4 - 6)

8 (6 – 10)

8 (6 – 10)

Soil Texture

Loamy Sand

Total available Moisture

ii. Available water As the homogenized Um Bayada soils have both fine textures within most profiles, it seems that average values represent these soils fairly well. Table 5 shows the average minimum (water at 1/3 atm. minus water at 15 atm.) and the average maximum (water at 1/10 atm. minus water at 15 atm.) and as well the average available water for dominant textures in Um Bayada area. Table 5

Average available water for some selected textures (Doka 1979) Available Water (cm water per 100 cm soil)

Textural Class

Range (minimum - maximum)

Average

3.9 - 7.9

5.9

Clay

19.5 – 23.6

21.6

Silty Clay Loam

22.8 - 28.0

25.4

Loamy Sand

20

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Table 6 shows the calculated available water capacities for some profiles representing the soil series in Um Bayada area. The data show clear differences between the four, dominantly fine textured soils (e.g Morgan, Um Bayada, Fouda and Alfaki) and the sandy soils (Argud).

Table 6. Available water in profiles representing the soils of Um Bayada Soil Series (representative profile)

Available Water Holding Capacity (cm water per 100 cm soil)

2.1.3

Mogran

(UBD….)

22.4

Um Bayada

(UBD….)

23.3

Fouda

(UBD…)

21.8

Argud

(UBD…)

10.0

Al Faki

(UBD….)

21.5

Chemical characteristics a) Total Carbonates Due to the low content of carbonates in the soils of Um Bayada in the form of CaCO3 they are not visible in the soil profile. Soft aggregates, streaks and hard concretions were not observed in most soil profiles. The chemical analysis showed that almost all horizons have between 5 and 30 g/kg CaCO3, and very few with more than 30 g/kg. The carbonate in recent alluvium soils often occurs in the silt and clay fractions where they have direct effect on soil texture and related properties. This seems to apply to Um Bayada soils as well. b) Fertility status Organic carbon, Nitrogen, phosphorus has been analyzed in the topsoil. In all previous work as well as in this report, the organic matter percentage was calculated from organic carbon figures (Organic carbon g/kg X 1.724). An average from all previous topsoil results showed that they are extremely low with less than 1.5 % organic matter. Nitrogen is also extremely low (0.01 - to 0.05 %), and on average even less than what was reported in similar studies (Doka 1979), which ranged from 0.01 % to 0.13 % (average 0.05 %). Available phosphorus levels (dominantly between 4 - 8 ppm) are fairly adequate for some crops like cereals, but moderately deficient for cotton and highly deficient for vegetables (Table 7). This is most probably attributed to the calcareousness of the soils of Um Bayada, which can fix high amounts of phosphorus. Previous data from Dawoud (1973) for similar alluvium soils indicated that an average of about 5000 ppm total extractable potassium for Sag El Na'am soils, which seems adequate. Previous data on boron revealed that the figures obtained are below toxicity levels.

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Table: 7 General interpretation of available phosphorus determined by Olsen's method (Landon 1991) Characteristic crop demand

Indicative available P Values (ppm)

Examples

Deficient

Questionable

Adequate

Low P

Grass, cereals, soybeans, maize

8

Moderate P

Lucerne, cotton, sweet corn, tomatoes

14

High P

Sugar beet, potatoes, celery, onions

< 11

12 - 20

> 21

c) Salinity and Alkalinity The result of the chemical analysis shows that most soils are slightly saline and few are moderately saline and alkaline. In similar situation at Saq El-Na'am Dawoud (1973) reported that 95 % of its sites are none to slightly saline, 5 % moderately saline and alkaline and no strongly saline or alkaline soils were reported. This corresponds very well with the situation in Um Bayada where the moderately saline –alkaline soils are found at lowest sites within the Depressional areas. Vertical distribution of salinity within the profile seems to be controlled mainly by moisture movement and to some extent by texture. Homogenous fine textured soils have regular distribution of slight salinity within the profile with some increase of salts in the topsoil. In Depressional soils the heavy textured layers in the topsoil, substratum or inside the profile always have moderate concentration of salts. Land use is an important influence in controlling salts as it was reported that abandoned fields tend to become slightly to moderately saline through time. Intensive cropping and elimination of long fallows resulted in increased water use in the recharge area, decreased seepage flow and therefore a reduced salinity problem (FAO 1988). The degree of alkalinity is reflected in the percentage of exchangeable sodium (ESP). Some soils have ESP of less than 10, but high values were reported at soils with depressional sites (Um and Bayada, Fouda series). The pH is relatively high, which can also be an indication of high Na levels, although its range is less wide (8.0 - 8.4). Most soils are slightly and moderately alkaline, which might have been caused by long term concentration of sodium from flood water with its low levels of sodium.

2.2

Soil classification 2.2.1

Soil classification system

The soils of Um Bayada were classified according to the Soil Taxonomy of the United States Department of Agriculture (1994), and correlated with the FAO/UNESCO Soil Map of the World classification (1988). At regional level, the soils were classified to 22

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the subgroup level and lately correlated with the existing soil families and series already established in previous soil surveys. a) b) 2.2.2

USDA Soil Taxonomy FAO Classification

Soil classes identified

Five soil series have been identified in Um Bayada area. The parent materials have been characterized as depositional - "terminal alluvium" and "aeolian sands" - due to their mode of formation. Different taxonomic units (soil series) have been named in this study. The definition of a soil series is “a group of soils having soil horizons similar in differentiating characteristics and arrangement in the soil profile, except for the texture of the surface soil, and developed from a particular type of parent material. The soils within a series are essentially homogenous in all soil profile characteristics except texture, principally of the surface horizon, and slope, stoniness, degree of erosion, topographic position and depth to bedrock where these features do not modify greatly the kind and arrangement of soil horizons". However, since 'soil series' is traditionally restricted to soils in which profiles are differentiated by a sequence of morphological features resulting from a pedogenetic process, it was preferred to modify the term for soils which are pedogenetically inactive. Hence the term 'depositional series' was used. They are mainly stratified alluvium deposits laid down by wadis. A soil variant is defined as a soil unit closely related to a soil series but departing from it in at least one differentiating characteristic at series level. It is used to avoid establishing a separate series. The variant was used in Abu Hamra study area to allow mapping areas of limited extent and slightly different than one of the defined soil series. The soils series identified fall within either Entisols or Inceptisols orders with clayey textural class families according to the USDA Soil Taxonomy (1994). Derived from the conclusions made by Kevie (1976) which were based on the soil temperature data from limited meteorological stations in Sudan, it was realized that El Fasher soil temperature regime is isohyperthermic. Accordingly the soil temperature regime in Al Bayada is classified as hyperthermic in which the mean annual soil temperatures are of 22C or higher with a difference of less than 5oC between mean summer and mean winter soil temperatures. The soils are assumed to have mixed clay mineralogy as they were washed by water from different locations having variable parent materials. Since all soils are calcareous, calcareousness was not indicated in the family name. Physiographic position, stratifications, irregular decrease of organic carbon with depth, soil texture and some morphological features are the main criteria to identify these taxonomic units. According to the FAO soil classification (1988) and the World Reference Base (WRB) for Soil Resources (1994) all taxonomic units were classified as Vertic Cambisols, Calcaric Cambisols or Haplic Arenosols. Series should be defined in the same way everywhere, regardless of the immediate purpose of the survey. Where detailed interpretations are required, the series can be subdivided into phases according to any characteristics significant to land use, for example depth, surface texture, stoniness, slopes or salinity. The phase is not a unit of taxonomic classification. It can be used at any categorical level to draw attention to differences of practical significance. 23

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All the soil series were being established during Al Bayada soil survey. If similar soils are being identified anywhere in Sudan, they will have the same name. All soil series (Al Bayada, Fouda, Mogran, Alfaki and Argud) were described below and the differentiating characteristics were summarized in Table 8.

Mogran series Mogran Vertic Torrifluvents soils are occupying slightly higher position between the upper Wadi fans and the clay plain as it also occurs in the fringes of the stabilized dunes tonguing in the clay plain. They members of fine loamy, mixed isohyperthermic family. They are well drained and moderately permeable when wet. The structure of A horizon ranges from strong coarse and moderate subangular blocky to weak, very coarse and medium subangular blocky. Subsoil is generally massive or weakly developed. The soil is hard and compacted when dry and friable when moist. Carbonate content is very low and the soil matrix is slightly calcareous. Mogran soils are associated with soils of Um Bayada. Typical profile : UMBD14

Um Bayada series UM Bayada soils are Vertic Cambisols occurring on flat level plain and at some places they might occupy relatively low lying sites. They are members of very fine clayey, isohyperthermic family. They are cracking clays, imperfectly drained and associated with Gilgae micro-relief. Thy have a homogenous very deep profile with dark yellowish brown colors of strong to moderate very coarse and coarse subangular blocky structures at surface and subsurface. The substratum is generally massive with slickensides and parallelepiped structural components. The soil matrix is noncalcareous and non-saline. Um Bayada soils are associated with soils of Mogran and Fouda series. Typical profile: UMBD01

Fouda series Fouda soils are Calcaric Cambisols similar in characteristics to Um Bayada, but occupying slightly depressional sites and they are imperfectly drained specially at substratum. They are members of very fine, clayey, isohyperthermic family. These soils are slightly cracking with thick surface mulch. Surface horizons are homogenously dark brown while subsurface forms tongues of gray colors. Subsoil shows contrast layer of dark gray color (10 YR 4/1). The structure of A horizon is moderate to strong Subangular blocky subangular and the subsoil is massive with slickensides and pressure faces. The soil matrix is non-calcareous and slightly alkaline. Fouda soils are associated with Mogran and Umm Bayada soils. Typical profile: UMBD11

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AL Faki series Al Faki Vertic Torrifluvents soils with stony topsoil, occupying higher position as part of the Wadi fans in the fringes the of clay plain as it also occurs close to the stabilized dunes tonguing in the clay plain at the northern part. They members of fine loamy, mixed isohyperthermic family with common rounded volcanic stones (pumice) on the surface and topsoil. They are well drained and moderately permeable when wet. The structure of A horizon ranges from strong coarse and moderate sub-angular blocky to weak, very coarse and medium sub-angular blocky. Subsoil is generally massive or weakly developed. The soil is hard and compacted when dry and friable when moist. Carbonate content is very low and the soil matrix is slightly calcareous. Mogran soils are associated with soils of Um Bayada. Typical profile: UMBD10

Argud series Argud soils are Typic Quatzipsamments occupying convex and sloping positions on gently undulating sandy plains. They are members of coarse sandy, siliceous isohyperthermic family. They are developed on very deep, well sorted aeolian sand dunes. They are generally excessively drained with the exception of some inter-dune sites which are moderately well drained.. The soils have yellowish brown and yellowish red colors. Texture of control section is sand and loamy sand and the substratum is loamy sand. The soil matrix is non-calcareous, non-saline and mildly alkaline. Argud soils are associated with soils of Al Bayada and Fouda series. Typical profile: Ditto Series OH02 (Soil Survey Admin, 1973)

2.2.3

Soil profile descriptions and analytical data

Representative profile descriptions together with the analytical data for each soil series are shown at appendix 1. These were described in the field during a semi-detailed soil survey study at Um Bayada area.

25

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Table 8 : Differentiating soil characteristics for Soil Taxonomic units (soil series and soil variants) in Um Bayada study area Water Capacity cm/100cm Soil Available Taxonomic Particle size Units distribution Sand 1. Mogran (MG) 2. Um Bayada (UB) 3. Fouda (FD) 4. Al Faki (FK) 5. Argud (AG)

Texture

Family Textural Class

pH (1:5 )

Silt

Clay

14

33

53

Silty clay

Clayey (fine)

7.6 – 9.1

12

40

48

Silty Clay

Clayey (fine)

8.5 – 9.2

13

42

45

Silty Clay

Clayey (fine)

8.3 – 9.0

12

59

29

Silty Clay

Fine Loamy

7.8 – 8.7

77

15

8

Loamy sand

Sandy

5.9 – 6.9

ESP * SAR