Chapter 1. Present status of salt-affected and waterlogged soils in Dasht-e-Azadegan and management strategies for their sustainable utilization S.A.M. Cheraghi1*, N. Heydari2, Y. Hasheminejad1, M. Qadir3, H. Farahani3, and T. Oweis3 1National Salinity Research Center (NSRC), Yazd, Iran; 2Iranian Agricultural Engineering Research Institute, Karaj, Iran; 3International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria *Corresponding author: [email protected] 1 Introduction southwest Iran is potentially one of the most suitable regions for agricultural Salt-prone land and water resources production. However, salinization of are major impediments to the optimal land and water resources has become a utilization of crop production systems serious threat to efficient use of these in many arid and semi-arid regions of invaluable resources. It is estimated the world, including Iran (Alizadeh et that out of the total 6.7 Mha of the al. 2004; Moghaddam and Koocheki province, 1.2-1.5 Mha (18-22% of total 2004). The salinization of land and water area) are faced with the dual problems resources has been the consequence of of soil salinization and water logging both anthropogenic activities (causing (Anonymous 2000). human-induced or secondary salinity and/or sodicity) and naturally occurring The Karkheh river basin (KRB) is one of phenomena (causing primary fossil the major river basins in the Khuzestan salinity and/or sodicity) (Ghassemi et al. province, consisting of two main sub- 1995). The main cropping systems in the basins namely Karkheh Olia (upstream) country are based on irrigated agriculture and Karkheh Sofla (downstream). The where at least 50% area (4.1 Mha) fall KRB is, most notably, the eastern flank under different types of salt-affected of the ‘cradle of civilization’ (ancient soils (Cheraghi 2004). Therefore, the Mesopotamia) and a boundary between dependency on irrigated agriculture is the Arab and Persian cultures. This at stake in areas where salt-prone land major river system of western Iran has and degradation of water resources has unique agricultural and hydrological increased over time. aspects; but also much in common with other catchments around the world, Human-induced salinization of land and e.g. rural poverty and land degradation, water resources has occurred mostly in low water and agricultural productivity, unique topographic conditions of semi- a dry climate, and growing upstream- closed or closed intermountain basins downstream competition for water. where irrigated agriculture has been Agriculture in the upstream basin is practiced for centuries. The slightly mainly rain fed, while the downstream and moderately salt-affected soils are basin is mostly irrigated. The drainage mostly formed on the piedmonts at the outlet of the KRB, which also is a basin foot of the Elburz (Alborz) Mountains in outlet, is the Hoor-Al-Azim swamp in the northern part of the country. The southwest Iran and on the Iran-Iraq soils with severe to extreme salinity are border (Fig. 1.1). At present, there mostly located in the Central plateau, the are very limited modern irrigation and Khuzestan and southern coastal plains, drainage networks under operation within and the Caspian coastal plain (Koocheki the KRB and agriculture is yet to be fully and Moghaddam 2004). The extent and developed. However, the government characteristics of salt-affected soils in has started constructing irrigation Iran has been investigated by several and drainage networks with the goal researchers (Dewan and Famouri 1964; of improving the traditional irrigation Mahjoory 1979; Abtahi et al. 1979; systems, e.g. in the Dasht-e-Azadegan Matsumoto and Cho 1985; Banie 2001). (DA) plain in southern parts of the lower KRB (LKRB). It is in this area where this Owing to abundant water resources, project was carried out. This chapter fertile lands and sufficient extraterrestrial describes this area (Dasht-e-Azadegan) energy, Khuzestan province in in terms of its geology, soils, climate, and 3 Fig. 1.1. Karkheh River Basin (KRB) and Dasht-e-Azadegan (DA) region water resources. It also reviews salinity in thickness from zero at the foot of the and waterlogging problems based on mountains to 100 m in the west and previous studies carried out in the region. northern west of the plain in the vicinity Lastly, general recommendations for of Hoor-al-Azim. Information about the effective use of soil and water resources upper strata of plain reveals that there for crop production and environmental are many varieties and diverse features are given. as compared to the deeper part of plain. There, it can be seen that thin lens-like sand features in a clay-silty background Geology appear on a limited scale. These features are accompanied by transverse layers, Azadegan plain is a deep structural hole indicative of a different deltaic formation. covered by Quaternary sediments. The These events show that the river tributary deepest part of this cavern is in the west beds have undergone frequent changes and northwest of the region and around of position at times near the Holocene Hoor-Al-Azim. The outer edge of the plain epoch. Furthermore, fine sediments is in the east and northeast, where the such as silt and clay particles and to bedrocks have been uplifted to form the a lesser extent chemical sediments, Mishodagh and Allaoakbar mountains. organic matter, and vegetative material The deepest layers of the plain are provide evidence of vast Quaternary composed of the Kachsaran, Mishan, and marshes in the plain, particularly on the Aghajari (Fars group) formation, from west side of the plain, where marshes deep to shallow. These formations were along the western border of Iran can overlain by conglomerate rocks (Bakhtiari be seen. Sedimentary deposits of the formation). The semi-deep portion of the Holocene epoch covering the surface hole was filled by recent sediment, which of the plain include alluvial, fluvial, and covers Bakhtiari conglomerates. aeolian sediments. The alluvial and fluvial sediments of plain are products of the The whole of sedimentary deposits in the geodynamic action of the Karkheh river Azadegan plain were laid down during tributaries. the Quaternary period. Sediment ranges 4 Soils precipitation of the region has enhanced accumulation of secondary lime minerals The soils of the area are alluvial soils in the soil mineralogy control section so formed originally by the floods of the that the carbonatic or mixed (calcareous) river. These alluvial areas are flat and soil mineralogy classes are common in the permeability is low, with little slope and region. Based on the USDA Soil Taxonomy poor natural drainage. Azadegan plain is (Soil Survey Staff 2003), soils are mainly a flood plain with very weak topography. classified as orders of the Entisols and The maximum elevation of 12 m a.s.l. is Aridisols. The young (recently formed) around Sosangerd and the Sosangerd- Entisols of the region belong to two Hoveizeh highway. The lowest elevation suborders. Fluvents are characterized is on the northwest side of the plain; by either 0.2% or more organic carbon adjacent to Hoor-Al-Azim (3-4 m a.s.l.). of the Holocene age at a depth of 125 Azadegan plain is the terminal basin and cm below the mineral soil surface or all of tributaries of the Karkheh river end an irregular decrease in content of in this plain. Therefore, the plain is the organic carbon from a depth of 25 cm scene of constant accumulation of the to a depth of 125 cm, or to a densic, river sediment. lithic, or paralithic contact if shallower. These soils have wide distribution in The low precipitation has developed the the region so that seven soil series aridic soil moisture regime throughout the belong to this suborder. The Kout soil region. The moisture control section, in series, which is classified as Salorthidic normal years, is dry in all parts for more Torrifluvents, is a typical Solonchak than half of the cumulative days per year, profile. Fluvaquents also are identified in when the soil temperature at a depth the lowland physiographic region of the of 50 cm from the soil surface is above plain. Redoximorphic features (brown 5°C; and it is moist in some or all parts mottling in a pale green soil matrix) in for less than 90 consecutive days when Fluvaquents (Sarhangiyeh, Shahatt-e- the soil temperature at a depth of 50 cm Abbas and Machriyeh series) represent is above 8°C. These conditions cause hydric conditions (seasonally saturated) low availability of water for cropping and in young, flood plain soils. The coarse- as a result, soils are classified only in textured soils are extended around rivers the Aridisol and Entisol orders based on in Susangerd city so the Psaments can be development status of diagnostic horizons identified just in this region. Psaments, (Soil Survey Staff 2003). which occur only in the Susangerd soil series of the region, have good drainage As a result of the hot climate, the and have less than 35% (by volume) rock mean annual soil temperature is 22°C fragments and a texture of loamy fine or higher, and the difference between sand or coarser in all layers. mean summer and mean winter soil temperatures is more than 6°C, either at Medium- to coarse-textured soils exist a depth of 50 cm from the soil surface or in areas around the Karkheh river and at a densic, lithic, or paralithic contact, its tributaries, which have experienced whichever is shallower, so the soil frequent flooding in previous times. temperature regime is considered to be Soil series in this area show a distinct hyperthermic in all series. stratification, including sequences of different-size textured ranges from The carbonatic nature of the parent coarse to medium textured and in these material, in addition to the low areas the slope is gently perpendicular 5 to the river (natural levees).