Expansive Soils

  • Khan Towhid Osman


Soils that contain a large amount of clay – at least more than 30 percent, a large proportion of fine clay in the clay fraction, and the clay fraction generally dominated by 2:1 expanding type of smectitic clay, chiefly montmorillonite, expand in volume when wetted and shrink when dried; they shrink so severely that deep and wide cracks, through which soil materials can slide downward, develop in the dry season. These clay soils are known as expansive soils, shrink-swell soils, cracking soils, or vertic soils. Some clay soils contain high proportion of exchangeable sodium in colloidal surfaces. They remain dispersed and are called dispersive clay soils. Their consistence – very sticky when wet and very hard when dry, their cracks, and their contraction and expansion in volume with changes in soil moisture offer severe limitations to their agricultural and engineering uses. Unique morphological features such as slickensides in the middle of the profile and circular or polygonal landscape features known as gilgai often develop on the surface soil due to their alternate swelling and shrinking behavior. These soils are classified in the Vertisols order of Soil Taxonomy and Vertisol Reference Soil Group of World Reference Base for Soil Resources. These soils were earlier called Regur, Gilgai, Margalite, Tirs, Black Cotton Soils, etc. The major areas of Vertisols are found in Australia, India, Sudan, Chad and Ethiopia. For their profitable and sustainable agricultural use potential, the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), International Livestock Centre for Africa (ILCA), and the Agricultural Research Centre for the Semi-arid Tropics (CPATSA) have been developing innovative management packages including broad bed and furrow system, reduced tillage systems and their modifications.


Expansive clays Vertisols Shrink-swell soils Cracking soils Gilgai Pedoturbation Slickensides Broad bed and furrow Broad bed maker 

6.1 Types and Distribution of Expansive Soils

Expansive soils are clay soils that expand in volume when wetted. They usually contain more than 30 percent clay to a minimum depth of 50 cm, and in majority of the cases, the dominant clay is the swelling type 2:1 smectites (chiefly montmorillonite). These soils are alternatively known as shrink-swell soils because they are contracted as well when dried. When they are dried, they shrink so greatly that very wide and deep cracks develop on the surface to depths often extending more than a meter downward. They are thus called deeply and widely cracking soils, or simply cracking soils. Due to alternate swelling and shrinking, polygonal (or circular) mounds often develop in many of such shrink-swell soils as a distinct landscape feature. These micro-relief features are called “gilgai”. Expanding clay soils that contain high proportion of exchangeable Na+ ions become dispersed, and are then called dispersive soils or dispersive clay soils. Expansive and dispersive clay soils have usually a dark appearance due to dispersed clay-humus complexes and reduced manganese compounds.

In Soil Taxonomy (Soil Survey Staff 1999), these soils are classified in the order Vertisols. These soils are also grouped in the Reference Soil Group Vertisol of the World Reference Base for Soil Resources (FAO 2006). The name of Vertisols is derived from the Latin vertere meaning to invert (Dengiz et al. 2012) because soil materials are washed in (inverted) through the cracks downward. The soil order name itself implies the behavior of the soils, such as cracking and the presence of slickensides (a slickenside is a surface of the cracks produced in soils containing a high proportion of swelling clays. Pedogenic slickensides are convex-concave slip surfaces that form during expansion/contraction in expansive clay soils or Vertisols. Slickensides are found in association with other pedogenic features, such as clay-skinned peds, in-situ calcareous nodules, and root impressions). However, before recognizing Vertisols as an order of the new system of soil classification in 1960 by the Soil Survey Staff of USDA, these soils were called by different names in different parts of the world. At least some 50 local names could be identified in different regions of the world; the most familiar ones were: Regur (India), Adobe (USA, Philippines), Gilgai (Australia), Margalite (Indonesia), Tirs (Morocco), Black Clays, Black Cracking Clays, Black Cotton Soils, Dark Clay Soils (India, East and South Africa), Dian Pere (West Africa), Firki (Nigeria), Makande (Malawi), Mbuga (Tanzania), Mourcis (Mali), Badobes, Teen Suda (Sudan).

According to Soil Survey Staff (1999), Vertisols are mineral soils that have all of the following characteristics:

  1. 1.

    A layer 25 cm or thicker, with an upper boundary within 100 cm of the mineral soil surface, that has either slickensides close enough to intersect or wedge-shaped structural units that have their long axes tilted 10–60 degrees from the horizontal; and

  2. 2.

    A weighted average of 30 percent or more clay in the fine earth fraction either between the mineral soil surface and a depth of 18 cm or in an Ap horizon, whichever is thicker, and 30 percent or more clay in the fine-earth fraction of all horizons between a depth of 18 cm and either a depth of 50 cm or a densic, lithic, or paralithic contact, a duripan, or a petrocalcic horizon if shallower; and

  3. 3.

    Cracks that open and close periodically.


The order Vertisols have six sub-orders:


Vertisols with aquic soil moisture regime for most years and show redoximorphic features are grouped as Aquerts. Because of the high clay content, soil permeability is slow and moisture saturation prevails for a large part of the year. Under wet soil moisture conditions, iron and manganese are mobilized and reduced. The manganese may be partly responsible for the dark color of the soil profile.


They have a cryic soil temperature regime. Cryerts are most extensive in the grassland and forest-grassland transitions zones of the Canadian Prairies and at similar latitudes in Russia. These soils are not included in Vertisols of FAO Classification.


They have a thermic, mesic, or frigid soil temperature regime. They show cracks that are open at least 60 consecutive days during the summer, but are closed at least 60 consecutive days during winter. Xererts are most common in the eastern Mediterranean and some parts of California.


They have cracks that are closed for less than 60 consecutive days when the soil temperature at 50 cm is above 8 °C. These soils are not extensive in the USA, and occur mostly in west Texas, New Mexico, Arizona, and South Dakota, but are the most extensive suborder of Vertisols in Australia.


They have cracks that are open for at least 90 cumulative days per year. Globally, this suborder is the most extensive of the Vertisols order, encompassing the Vertisols of the tropics and monsoonal climates in Australia, India, and Africa.


They have cracks that are open less than 90 cumulative days per year and less than 60 consecutive days during the summer. In some areas, cracks open only in drought years. Uderts are of small extent globally, being most abundant in Uruguay and eastern Argentina, but also found in parts of Queensland and the “Black Belt” of Mississipi and Alabama.

FAO (2006) defined Vertisols specifically as “soils having, after the upper 18 cm have been mixed, 30 percent or more clay in all horizons to a depth of at least 50 cm; developing cracks from the soil surface downward which at some period in most years (unless the soil is irrigated) are at least 1 cm wide and extend to a depth of 50 cm: having intersecting slickensides or wedge-shaped or parallel-piped structural aggregates at some depth between 25 and 100 cm from the surface, with or without gilgai”. In the Australian Soil Classification system (CSIRO 2010), soils that consist of more than 35 percent clay throughout the solum, crack at some time in most years, and contain slickensides and/or wedge-shaped peds are recognized as Vertisols. According to FAO (2006) estimate, Vertisols cover 335 M ha worldwide. About 150 M ha is potential cropland. In the tropics, there are some 200 M ha; 25 percent of this is considered to be useful land. Most vertisols occur in the semi-arid tropics with an average annual rainfall of 500–1000 mm, but Vertisols are also found in the wet tropics, for example Trinidad. The largest Vertisols areas include South Africa, Sudan, India, Ethiopia, Australia, the southwest of the United States of America, Uruguay, Paraguay and Argentina. Two main types of Vertisols can be distinguished: lithomorphic Vertisols and topomorphic Vertisols. Lithomorphic Vertisols are formed on various parent rocks whose weathering generates base-rich environments favourable for smectite synthesis, while topomorphic Vertisols are formed mainly in low landscape positions which favor the accumulation of bases (FAO 2006). The global distribution of Vertisols is shown in Fig. 6.1 (map).
Fig. 6.1

Global distribution of Vertisols

6.2 Parent Materials of Vertisols

Vertisols develop on a variety of parent materials derived from igneous and sedimentary rocks. Vertisols can develop on igneous rocks including basalt, dolerite, ash, tuff and andesite in different regions all over the world. Vertisols have also developed from Rhyolites which are composed of volcanic glass, quartz crystals, orthoclases, biotites and hornblendes as accessories. Vertisols in Central Mexico are derived from basalts, which are abundant in the lowlands. In coastal area of the Gulf of Mexico, Vertisols developed from sedimentary parent materials, mainly from limestone. Sotelo-Ruitz et al. (2013) studied the mineralogical properties of some Vertisols developed on parent materials of igneous and sedimentary origins. Dominant minerals in the sand fraction of soils of igneous origin consisted of volcanic glass (47 percent), quartz (31 percent), and feldspars (22 percent). The clay fraction was dominated by amorphous materials, smectites, vermiculites, illites, and cristobalites. In contrast, the sand fraction in the soils of sedimentary origin was composed of calcite (64 percent), quartz (34 percent), and feldspars (2 percent). Smectites, vermiculites, quartzes, and feldspars composed the clay fraction. The parent material of the soils on igneous rock was rhyolite, while the sedimentary soils were derived from limestone and sediments with high calcium carbonate contents. Özsoy and Aksoy (2007) studied 11 different soil profiles formed on the neogene aged calcareous marl parent materials. Among these soils the Vertisols were deep, dark colored with strong wedge-shaped structure, high in CEC and base saturation with calcium and magnesium occupying more than 90 percent of the exchange sites. Aydinalp (2010) reported the development of Vertisols in different parent materials in northwestern Turkey. These soils occur on flat to gently sloping plains of the region. Clay content is high in the studied sites. The high cation exchange capacity and CEC /clay ratios suggest montmorillonitic and mixed mineralogy of the clay fraction. Calcium was the most dominant extractable cation followed by magnesium. Dengiz et al. (2012) studied the morphological and physico-chemical characteristics of Vertisols formed on the alluvial delta Bafra Plain located in the central Black Sea region of Turkey. These Vertisols were all dark in color in surface soil; they were heavy clayey soils with hardpan (high bulk density and a high compaction) formation under top soil. Vertisols may form residually from weathered limestone or basalt. These soils are generally developed from parent materials that are rich in alkaline earth cations (Ca and Mg). The weathering of these rocks produces smectite type clays. Heidari et al. (2008) studied some Vertisols with diverse parent materials and climates from western Iran. The Vertisols of Fars Province, Lorestan Province and Kermanshah Province have formed on limestone or calcareous sediments. In Ardebil Province, Vertisols developed on volcanic sediments. Pierre et al. (2015) studied the mineralogical properties of some Vertisols of the Logone Valley in Cameroon. Clay minerals are dominated by smectites associated with some amount of kaolinite and illite. Dominant primary minerals are quartz and feldspars. These soils have high contents of SiO2 (61.07–77.78 percent), moderate content of Al2O3 (7.08–15.54 percent) and low amount of Fe2O3 (1.78–6.92 percent).

6.3 Properties of Expansive Soils

6.3.1 Morphological Features

The principal morphological features of Vertisols include deep and wide cracks (Fig. 6.2) in the dry season, pedoturbation, minimal horizon differentiation, and unique subsurface features called slickensides. These characteristics in soil develop due to the presence of high clay content (usually >30 percent), by the activity of expanding type of clay (usually smectite, but other clay types may also contribute), and alternate saturation and desaturation of soil with moisture in different seasons.
Fig. 6.2

Deep and wide cracks in expansive soils (Vertisols). (Photo courtesy of Professor Paul McDaniel, University of Idaho)

These soils exhibit minimal horizon differentiation as a result of pedoturbation. They are also very plastic and sticky when wet. For high clay contents and their high surface area, the soil volume changes with the variation in moisture content, i.e. swells when wet and shrinks when dried. The shrink–swell process can generate pressures that cause vertical movement (heaving) on the order of 10–20 cm (Miller and Bragg 2007). Extreme heaves of 45–90 cm have also been found. The physical movement of Vertisols commonly results in the formation of surface mound and depression micro-relief features called gilgai (Miller et al. 2010). Gilgai (Fig. 6.3) is an Australian aborigine term meaning “little water hole”.
Fig. 6.3

Gilgai in Laewest clay, Calhoun County, USA. (Image courtesy of USDA)

Tamfuh et al. (2011) studied the morphological properties of some Vertisols of the Sudano-Sahelian Region of North Cameroon. They observed that with a depth of about 2–2.5 m above the water table, these soils show four main horizons from bottom to top: a dark grey horizon with hydromorphic patches (B3g), dark grey horizon (B21), dark grey horizon with slickensides (B1) and a surficial grey humiferous horizon (A1) with desiccation cracks. Also, they show a heavy clayey texture, very massive structure, high bulk density, very low porosity and a high compacity. The microfabric of the soils is marked by abundant plasmas, isotic at the surface but birefringent at depth, with numerous stress cutans.

Gilgai is composed of mounds and depressions; the bottom part of the depression is known as microlow. The microlow can retain water during rainfall and many hydrophytic and mesophytic plants may grow there. The surrounding top convex ridge-like part is called microhigh. The microhigh is usually drier, and generally xerophytic plants grow on microhighs. The area between the lower level of microlow to the upper part of the microhigh is called microslope (Miller et al. 2005). The microlow is concave, the microhigh is convex and the microslope is slightly sloping. The microlow is about 2–5 m deep. Miller and Bragg (2007) reported that in forested Vertisols trees tend to grow on microhighs, and mixed forbes and grasses occupy the microlows. Özsoy and Aksoy (2007) observed deep, dark colored Vertisols with strong wedge-shaped structure to develop on calcareous marl parent material.

Extensive shrinking produces wide (>1 cm) and deep (>50 cm) cracks that split and merge periodically. Soil materials are washed downward through the cracks and produce slickensides. Shrinking and swelling followed by pedoturbation creates wedge-shaped structural aggregates that are tilted with an angle from the horizon. Shrink-swell processes in soils are related to total clay content, fine clay content and minerals. Smectite and ‘mixed layer’ clays comprise an important proportion of the clay fraction in most Vertisols (Özsoy and Aksoy 2007). The shrink-swell phenomenon is responsible for the genesis and behavior of the Vertisols. Expressions of this phenomenon are linear and normal gilgai, cylic horizons, surface cracks and slickensides. Sotelo-Ruitz et al. (2013) suggested that the presence of smectites is responsible for morphological variations in Vertisols. Dengiz et al. (2012) observed prominent slickensides at the middle part of the profiles and a poor differentiation of horizons in Vertisols. The degree and frequency of changes in moisture content of the soil are perhaps the most important parameters that control cracking intensity. Vertisols are typically developed on alluvial material in flat inland areas. A dry layer of fine granules are usually found at the surface of Vertisols in varying thicknesses from several millimeters to a few centimeters. During grazing in the dry season or at the begging of rains, this layer slides into the cracks. Surface soil and sub-surface soil are mixed in this way, a process known as ‘churning’ or pedoturbation (Deckers et al. 2001).Cracks cause an increased loss of soil moisture with depth, through evaporation from the crack surface, even though this loss may be significantly reduced under fully established crops. Cracks are also the reason for a considerable increase in the irrigation water requirement at the time of the first irrigation after dry season. Cracks may also be the source of tunnel erosion in the semi-arid regions, especially in events of heavy irrigation or high rainfalls. Soil cracks may cause physical damage to crop roots (Elias et al. 2001). Pierre et al. (2015) studied morphological, physical and chemical properties of some Vertisols of the Logone Valley in Cameroon. These Vertisols are characterized by dark color, clayey texture, massive structure, deep and open superficial desiccation cracks and micro-reliefs (gilgai).

6.3.2 Physical Properties

Vertisols have high clay contents, ranging from 40 to 60 percent in most cases, but it may reach to even 80 percent in some instances. As outlined in Soil Taxonomy, clay content in Vertisols generally increases downward to the subsoil. The clay content remains over 35 percent throughout the profile to a minimum depth of 50 cm. Vertisols can store huge water in the root zone. Moisture content generally determines the physical behavior of Vertisols. These soils become very sticky upon wetting, and they are not workable for tillage under wet conditions. Again, they become very hard when dry. Therefore, cultivation of Vertisols under too wet and too dry conditions makes the soil puddled and cloddy respectively. Under such conditions achieving a good tilth cannot be expected. Tillage and seedbed preparation in Vertisols are possible only within a very narrow range of moisture contents. Trafficking in very wet conditions of Vertisols causes structural damage and compaction. On the other hand, tilling is also difficult in very hard soil conditions and it results in seedbeds with large clods. Vertisols swell when wet and shrink when dry. The extent of shrinking and swelling depends on the amount and type of clay, moisture conditions, landscape positions and vegetation type. Hydration and dehydration cause alternate swelling and shrinking and also depend on mineralogical, chemical, and physicochemical properties of soil (Ben-Hur et al. 2009; Lado and Ben-Hur 2004). The presence of high amount of smectite clay, high exchangeable sodium percentage (ESP ) and a low electrolyte concentration in the soil solution causes greater swelling.

Dinka (2011) studied shrik-swell dynamics of Vertisol catenae under different land uses in order to:(1) determine if variability in soil cracking on a Vertisol catena, having the same soil and land cover, could be explained by the shrink-swell potential of the soil and changes in soil water content; (2) characterize the temporal and spatial variability of the shrinkage of a Vertisol under different land uses; and (3) determine the relationship between specific volume and water content of soils, particularly between saturation and field capacity. Maximum soil subsidence was 120 mm in the grazed pasture, 75 mm in the native prairie, and 76 mm in the row cropped field. Shrinkage of the whole soil was not equidimensional, and the study generally indicated more horizontal shrinkage than vertical shrinkage. He suggested that a soil layer can subside up to 4 percent while drying from saturation to field capacity. Wide and deep cracks have the capacity to enhance rapid flow of water and nutrients into the subsoil, affecting the hydrology of the soils (Bandyopadhyay et al. 2003). Shrink-swell properties of Vertisols spatially vary with soil properties, micro-climate, topography, vegetation, cropping patterns, and soil management practices (Vaught et al. 2006). Soil properties important to shrink-swell that vary in space include clay content, clay mineralogy, and water holding capacity (Azam et al. 2000). High concentrations of clay in a soil, mainly fine clay fraction, result in high specific surface area that helps store water. As a result, the surface area of the fine clay and the bulk volume of the soil increase.

Swelling of clay particles increases the content of small, water-retaining pores at the expense of larger water-conducting pores. On the other hand, clay dispersion is an irreversible process, in which quasi crystals or domains (regions of parallel alignment of individual alumino-silicate lamellae in smectite minerals) break apart and disperse because of mutual-repulsion forces. Dispersion of soil clay occurs instantaneously once the electrolyte concentration of the soil solution falls below a threshold value, termed the flocculation value, and the dispersed clay particles may migrate and plug water-conducting pores, causing a reduction in saturated hydraulic conductivity (Ks) of soil. Clay dispersion is influenced by soil chemistry and mineralogy, and is enhanced primarily by a low electrolyte concentration in the soil solution and high ESP (exchangeable sodium percentage) of the soil (Lado et al. 2004; Laird 2006).

Soils usually contain more clay in lower landscape positions (Dinka and Lascano 2012). Large amounts of water may be present there because of higher clay content and surface or subsurface flow of water. According to Jovanov et al. (2012), very high retention of moisture in Vertisols depends on high clay content particularly montmorillonite, and on organic matter accumulation and pedoturbation. They observed that field capacity in Vertisoils of some regions of the Republic of Macedonia ranged from 22.47 to 40.47 percent by weight, but plants could not absorb much because the wilting point was also very high ranging from 13.55 to 24.68 percent by weight. The difference between field capacity and wilting point is considered as available water which was, on an average only 12.32 percent by weight in soils of their study. However, Vertisols have low hydraulic conductivity and infiltration rate under wet conditions and a high bulk density when dry (Tekluet al. 2004). Structural units in some Vertisols slake easily when wetted, and the soil surface becomes muddy and very sticky. Tewka et al. (2013) conducted a field study to assess the physico-chemical properties of the natural and cultivated soils of Savannah Vertisols in Ethiopia. They collected soil samples from four soil pedons, two from each fallow and cultivated soil. The soils contained about 70 percent clay. Bulk density ranged from 1.25 to 1.40 g cm−3 in the fallow soils and from 1.47 to 1.52 g cm−3 in the cultivated soils. Total porosity was about 43 percent in fallow soils and 40 percent in cultivated soils with the moisture content ranging from 65 to 80 percent. Their results indicated that cultivation of Vertisols caused considerable compaction of the soil.

In some Vertisols areas in Ethiopia, there are native Acacia seyal and Balanites aegyptiaca savannah vegetation . Many such lands have been cleared for agricultural crop production in the semi-arid Sahel regions. Shabtai et al. (2014) studied the effects of the changes in land uses on the structure and saturated hydraulic conductivity (Ks) of a Vertisol under sodic conditions. Exchangeable sodium percentage (ESP ) increased with soil depth, from 2 percent in the 0–15 cm layer to 8.1–10.6 percent in the 90–120 cm layer. Swelling and dispersion was more pronounced in the subsoil than in the topsoil due to the higher ESP values. In contrast, the topsoil was more sensitive to slaking forces than the subsoil, probably due to increased particle cohesion in the subsoil. This led to lower Ks values of the top soils under fast than slow prewetting. The steady-state Ks values under slow prewetting and leaching with deionized water were significantly higher in the savannah-woodland soil than in the cultivated soils, down to 120 cm depth. These differences in Ks values were associated with higher swelling values in the cultivated soils than in the savannah-woodland soil. Vertisols generally have low hydraulic conductivity, low infiltration rate and high moisture retention capacity ranging from 60 to 70 percent at field capacity because of their high clay content (Zewudie 2000). Marta (2012) analyzed some physical properties of a large number (n = 126, 0–150 cm depth) of Vertisol soil samples of Hungary. He obtained mean values of sand, silt and clay of 15.5, 39.0 and 45.5 percent respectively. Mean bulk density was 1.4 g cm−3 and co-efficient of linear extensibility (COLE) was 0.21. Asiedu et al. (2000) studied infiltration and sorptivity on the Accra Plains of Ghana under four different Vertisol management technologies including cambered bed, the Ethiopian bed, the ridge, and the flat bed. The initial values of both cumulative infiltration and infiltration rate were the highest in the cambered bed followed by the ridge, the Ethiopian bed, and the flat bed in the decreasing order. The terminal infiltration rates were quite similar for all the landforms and were about 0.05 ms−1. Field-measured sorptivity followed the order: cambered bed > ridge> Ethiopian bed > flat bed. Liu et al. (2010) suggested that if under a condition of no cracks, soil porosity of the entire soil column is 0.45m3 m−3 and soil moisture is 0.1m3 m−3, the soil porosity of the top soil layer may increase to 0.6m3 m−3 when cracks are open (while soil moisture is still assumed to be 0.1m3 m−3). The increase in soil porosity increases the proportion of air and decreases the fraction of soil within a unit volume.

6.3.3 Chemical and Mineralogical Properties

Vertisols occurring in India, Australia, Sudan, Ethiopia and other parts of Africa generally have a soil pH ranging between 7.5 and 8.5 in the soil profile due to the presence of high CaCO3 and high contents of exchangeable bases, especially calcium and magnesium. Some Vertisols in tropical areas under irrigation or in depressions may have a soil pH as high as 9.5 due to sodium saturation in the exchange complexes. Alkaline soil pH is conducive to volatilization loss of native and applied ammonia. Most Vertisols are calcareous with either almost uniform distribution throughout the profile or increasing downward. Gypsum has been found to occur in the sub-surface of the Vertisol profiles in relatively arid areas indicating the lack of leaching of the slightly soluble gypsum. Dengiz et al. (2012) observed that physico-chemically, the Vertisols on the alluvial plains in the central Black Sea region of Turkey were slightly basic to very basic, non-saline and poor in organic matter. These soils had high cation exchange capacity and total exchangeable bases, and very high base saturation percentage. Özsoy and Aksoy (2007) studied physico-chemical properties of some Vertisols developed on calcareous marl parent materials. These soils were high in CEC and base saturation with calcium and magnesium occupying more than 90 percent of the exchange site, low organic material but sufficient fertility. The agricultural potential of the soils were, however, limited due to high clay and CaCO3 contents of sub-surface horizons and a hard pan formation due to inappropriate soil tilling.

Although the dark color of the Vertisols could be suggestive of high organic matter content, it was found that most of the black cotton soils of India rarely have organic matter exceeding 1.0 percent. Jahknwa and Ray (2014) analyzed some chemical properties of Vertisols of Guyuk area of Nigeria. Soil pH and CEC are generally high in soils of the study site. They attributed these to the high clay content of the soil. Soil properties that exhibited very low values include soil organic matter and available phosphorus.

Pierre et al. (2015) studied chemical properties of some Vertisols of the Logone Valley in Cameroon. These soils are neutral to slightly alkaline in reaction (pH 6.4– 7.4), with low organic matter content, and an average CEC ~ 22.8 cmolc kg−1. Their exchangeable cations are dominated by Ca and K. Tewka et al. (2013) determined some chemical properties in natural and cultivated sites of the soils of Savannah Vertisols of Ethiopia. Soil pH in both soils was near neutral (6.1–7.2) with basic cations (K+, Ca2+ and Mg2+) dominating the exchange sites. High concentrations of Na+ ions were recorded at lower depths in both fallow and cultivated soils, indicating that the soils are potentially saline-sodic. Giday et al. (2015) found considerable variations in organic matter (0.05–4.39 percent), available P (0.86–22.50 mg kg−1) and total N (0.03–0.23 percent) contents in Vertisols of Southern Tigray, Ethiopia. The soils were slightly acidic to moderately alkaline in reaction (pH 6.5–8.20). The soil exchange complex was mainly dominated by Ca and Mg where the order of occurrence was Ca > Mg > K > Na. The CEC values were very high ranging from 41.42 to 50.37 cmolc kg−1. Marta (2012) analyzed chemical properties of a large number (n = 126, 0–150 cm depth) of Vertisol soil samples of Hungary. He obtained the following mean values of SOM, CaCO3, pH (H2O), and CEC: 1.5 percent, 3.2 percent, 7.5 and 35.6 cmolc kg−1 respectively. Exchangeable Ca2+, Mg2+, Na+ and K+ represented 72.9, 21.8, 3.1 and 2.3 percent of total exchangeable bases respectively. The mean organic matter content is relatively high; 1.5 percent in the 0–150 cm thick segment of the soils; the mean SOM value stays above 2.4 percent in the upper 40 cm; it is more than 1 percent in the upper 80 cm, and more than 0.5 percent at the depth of 150 cm too. The high mean CEC values are related to the high clay and SOM contents. Tamfuh et al. (2011) studied physico-chemical properties of some Vertisols of the Sudano-Sahelian Region of North Cameroon. These soils were high in cation exchange capacity (26–42 cmolc kg−1) and total sum of bases (74.30 and 94.23 cmolc kg−1), high base saturation, low organic carbon and a very high C/N ratio. Geochemically, Si and Al are the dominant elements, characterized by a Si/Al ratio range of 2.27 and 2.94. According to this rate, 2:1 clay minerals, namely smectite, are predominant and their presence confirms the shrink-swell behavior of the soils. Based on their smectite content, these soils present numerous interesting economic potentials in the chemical industry, pharmaceutics, agronomy and environmental protection (Nguetnkam 2004; Woumfo et al. 2006).

It was a general belief and there were plenty of evidences as well that the shrink-swell behavior of Vertisols is the manifestation of the activities of smectites (chiefly montmorillonite), the 2:1 expanding types of clay in the clay fraction. However, some investigations have shown that expansive layer silicates are not the only clay minerals present in Vertisols. Some studies revealed that it is the proportion of fine clay, regardless of the clay type, together with the wetting and drying cycle in the soil that can produce a high shrink-swell potential (Heidari et al. 2008). Heidari et al. (2008) observed the dominance of palygorskite-chlorite in the clay fraction of some Vertisols in Iran. They concluded that the inter particle pore size that is controlled by the size of primary particles, regardless of its nature, contributes to the shrink-swell potential in soils of their study. Despite the large body of information available today, showing that smectitic clays are by far the most dominant clay minerals (Shirsath al. 2000), these soils may be dominated by other minerals (Heidari et al. 2008). According to Thomas et al. (2000), a combination of physical, chemical, and mineralogical properties can best explain the shrink-swell behavior of soils. No single property can accurately predict shrink-swell potential for all soils. Pierre et al. (2015) observed the dominance of smectites and some amount of kaolinite and illite in the mineralogical properties of some Vertisols of the Logone Valley in Cameroon. Dominant primary minerals are quartz and feldspars. These soils have high contents of SiO2 (61.07–77.78 percent), moderate content of Al2O3 (7.08–15.54 percent) and low amount of Fe2O3 (1.78–6.92 percent). Mixed mineralogy has also been revealed in many studies (Shirsath al. 2000). Fassil (2009) studied the relationships of major physico-chemical properties of some Vertisols of northern highlands of Ethiopia. He observed that Si contents ranged from 79.8 to 87.5 g Si kg−1in the cultivated Vertisols of Adigudom, from 97.7 to 115.2 g Si kg−1 in Axum, from 113.7 to 117.2 g Si kg−1 in Maychew, from 130.0 to 133.9 g Si kg−1 in Shire and from 137.3 to 166.3 g Si kg−1 in Wukro. The highest concentration was found in areas where the sand content was the greatest.

Vertisols have a satisfactory level of fertility because of favorable pH, high cation exchange capacity and high base saturation percentage. Özsoy and Aksoy (2007) suggested that despite their high fertility under irrigated conditions, Vertisols are often undesirable for agricultural and some engineering purposes due to their high clay contents, puddling under wet and clodding dry conditions, easy slacking and the shrink-swell behavior, deep cracks and compactions.

6.3.4 Engineering Problems Associated with Expansive Soils

Expansive soils offer serious problems to the construction of foundations for roads and buildings. Civil engineers consider expansive soils as potential natural hazard. Expansion of soil can cause extensive damage to structures worldwide if appropriate measures are not taken (Bose 2012). Wide cracks in the wall, distortion of floor, heaving of beds in canal, and rutting of roads are the usual types of damages in expansive soils (Christodoulias 2015). The shrink-swell movement of the soil underneath causes these damages.

The damages due to expansive soils are sometimes minor maintenance issues but often they are much worse, causing major structural distress. In the United States, 10 percent of the 250,000 new houses built on expansive soils each year experience significant damage, some beyond repair (Lucian 2006; Al-Zoubi 2008). Many highway agencies, private organizations and researchers are studying the remedial measures because considerable land areas are covered with such soils in many countries (Radhakrishnan et al. 2014). The problem is of enormous financial proportions and is also a global phenomenon. Australia, Argentina, Canada, China, Cuba, Ethiopia, Great Britain, India, Israel, Kenya, Mexico, Myanmar, Spain and the United States are some of the countries which need to cope with expansive soils.

Expansive soils are responsible for a significant hazard to foundations for light buildings. They can damage foundations by uplifting as they swell with wetting. Swelling soils lift up and crack lightly-loaded, continuous strip footings, and frequently cause distress in floor slabs. The high shrink-swell potential and low bearing strength of fine-textured soils contribute to the failure of structures made of concrete and other non-flexible building materials. The stability and functionality of building foundations (basements), streets and sidewalks are impaired through the internal movement within the soil medium. Embankments and earth dams are thus susceptible to failure through internal slippage along planes of weakness, especially when saturated (Brierley et al. 2011). Expansive soils affect the lightweight structures very severely by high swelling pressure under wet conditions. Damages due to soil swelling or shrinking may be reduced by reducing the swelling pressure of the soil. Another measure can be to build structures resistant to damage from soil expansion.

Lime is commonly used to stabilize shrink-swell soils (Eisazadeh et al. 2012). Other chemical substances that can be used for the purpose include KCl, CaCl2 and FeCl3 instead of lime for their higher solubility in water (Prasada Raju 2001). Cokca (2001) reported that addition of CaCl2 and KOH reduced swelling of the expansive soils. Flyash can also act as a stabilizer (Phanikumar and Sharma 2004). Flyash is produced by coal-fired power plants during the combustion of coal (Hasan 2012). Radhakrishnan et al. (2014) recommended flyash and aluminum chloride (AlCl3) to increase the strength of expansive soils.

Clay particles in some Vertisols can be highly dispersed because of sodium saturation of the exchange complexes. They are dispersive clay soils. Serious engineering problems are caused by these dispersive clay soils when used in hydraulic structures, embankment dams, or other structures such as roadway embankments. Some natural clay soils disperse or deflocculate in the presence of relatively pure water and are, therefore, highly susceptible to erosion and piping (Zorluer et al. 2010). The amount and type of clay, pH, organic matter, temperature, water content, thixotropy and type and concentration of ions in the pore and eroding fluids are the factors that affect the critical shear stress required to initiate erosion (Umesha et al. 2011). So, dispersive clay soil erodes in the presence of flowing water starting in a drying crack, settlement crack, hydraulic fracture crack, or other channels of high permeability in a soil mass. Dispersive clays have a high proportion of exchangeable sodium whereas other non-dispersive clays may have a predominance of calcium, potassium, and magnesium cations in exchange positions and in the pore water.

6.4 Agricultural Uses of Expansive Soils

Vertisols of the arid areas, are generally under natural grassland and associated vegetation and are used for mainly cattle raising. Where irrigation can be applied, these soils can be used to grow a variety of tropical crops. The predominant crops in African Vertisols are barleys, faba beans, wheat, field peas, oats, lentils, linseed, niger seed, chickpeas, sorghum and rough pea. In Nigeria, many Vertisol soils are used for grazing and for growing a wide range of food crops, such as maize, yams and vegetables. These soils are primarily used in India for raising cereals (sorghum and millets), pulses (pigeon pea, chickpea, mung beans, lentil, etc.), oilseeds (groundnut, mustard, sesame, etc.), and commercially important crops like cotton, chilies, soybeans, sunflower, safflower, etc. In large tracts of Central India, wheat is also grown on the Vertisols. When irrigation is available, crops such as cotton, wheat, sorghum and rice can be grown. Vertisols are especially suitable for rice because they are almost impermeable when saturated.

Yield of crops under traditional management in Vertisols are quite low. Average yields of crops are 846 kg ha−1 for barley, 1295 kg ha−1 for faba bean, 964 kg ha−1 for wheat, 846 kg ha−1 for field peas, and 300 kg ha−1 for niger seed (Gryseels and Anderson 1983). Rainfed farming is very difficult because of the narrow range of soil moisture when they can be worked on. Vertisols in Australia are highly regarded because they are among the few soils that are not acutely deficient in available phosphorus. The potential productivity of Vertisols may be high because of nearly neutral or slightly alkaline pH, high CEC, high base saturation percentage, high water holding capacity, etc. Unproductive Vertisols can be made productive through improved drainage, fertilizer and adopting suitable crop management practices. Both yield and soil quality can be improved by improved management. Large Vertisol areas are still uncultivated, and some are intensively grazed. Agricultural use of Vertisols in Africa ranges from grazing, firewood production and charcoal burning through small holder post-rainy season crop production (millet, sorghum, cotton), to small-scale (rice), and large-scale irrigated crop production (cotton, wheat, barley, sorghum, and sugarcane).

Most Vertisols in Africa are not cultivated, and are used as grazing grounds. These areas carry large number of domesticated and wild animals. Here, Vertisols can be transformed into productive crop land if their management addresses their inherent physical problems. For example, improvements in tillage quality will lead to higher crop yields on clay soils compared to light soils. Heavy clay soils are very difficult to till by hand; their tillage for cropping tends to be either mechanized or animal powered. Crop/ livestock interactions are strong there, where animal power is used for soil cultivation and where more livestock can be fed on the basis of the enhanced production of crop residues and by-products. More manure and composts could be available too. In small farm holdings, animal power, crop diversity, residue management, and utilization of soil moisture for crop production have benefitted farmers. Most of the Vertisols in the highlands of Ethiopia suffer from excess water and poor workability. They are underutilized, and are largely used for dry season grazing. Only 25 percent of the 7.6 million hectares Vertisols in the highlands are cultivated. The common crops grown on Vertisols are tef (Eragros tistef), wheat (Triticum spp.), barley ( Hordeum vulgare ), faba bean ( Vicia faba ), field pea ( Pisum sativum ), grass pea ( Lathyrus sativus ), chikpea ( Cicer arietinum ), lentils ( Lens culinaris ), lineseed ( Linum usitaissium ), noug ( Guizotia abyssinica ) and fenugreek (Trigonella foenum-graecum). But the yields of these crops are quite low (Ayele 2004).

6.5 Limitations of Expansive Soils to Agricultural Uses

Agricultural management problems of Vertisols include extreme stickiness of the soils when wet and their intractability when dry and the lack of appropriate tillage implements. If tilled in wet condition, the soil is puddled, compacted and crusted; and if tilled in dry condition, which require much energy, large clods are produced. Having a satisfactory tilth in the seedbed in Vertisols under both wet and dry conditions is hardly possible. The soil is workable within a narrow range of soil moisture that can reach for a short span of time between rains. Soil preparation should be done at this time during initial substantial rains or in the post rainy season. The soils can remain saturated for a large part of the rainy season; often in flat lands they are flooded and are highly eroded in slopes. In India, Vertisols are particularly subject to soil loss by water erosion under the traditional systems of bare-fallowing during the rainy season. Losses are promoted by the combination of intense storms and lack of plant cover. In most Vertisols, infiltration and permeability are both very low and internal drainage is impeded. Artificial subsurface drainage systems do not work well. Nutrient deficiencies, especially micro-nutrient deficiencies, sodicity in irrigated fields and soil erosion, are other problems of Vertisols. Sodic Vertisols have dual problems – sodicity (high pH, ammonia volatilization, P and micro-nutrient deficiency) and inappropriate soil consistence. In Nigeria many Vertisols soils are non-saline, but are mildly to strongly sodic, especially the subsoils. They are high in basic cationic nutrients, but are generally low in organic matter, N, P and Cu. The potential productivity of some Vertisols soils is probably quite high, but a number of management problems must be solved before this potential can be fully exploited.

6.6 Integrated Soil and Crop Management for Expansive Soils

A good number of investigations had been carried out about the Vertisols of Ethiopia, particularly in soils of the high lands (ILCA 1990; Astatke and Jabbar 2001; Astatke et al. 2002; Teklu and Gezahegn 2003), regarding their culvation for crop production. According to Astatke and Jabbar (2001) and Teklu and Gezahegn (2003), farmers prepare lands early with the moisture obtained during early short rains and keep the land fallow for 2–3 months. They occasionally till the land and plant seedlings immediately after the rainy season so that the crop thrives on residual moisture. Farmers use five to nine cultivations prior to planting seedlings for making a fine seed bed and controlling weed. Such intensive cultivation disrupts aggregates, increases aeration, and mixes organic residues with soil resulting in higher soil organic matter decomposition and loss. Astatke et al. (2002) suggested that over tillage increases erosion. This is an acute environmental problem of the Ethiopian highlands. Waterlogging is always a problem in Vertisols in the rainy season, so improving surface drainage can advance planting date and increasing crop growing period. Making broad beds and furrows (BBF) is a strategy followed for centuries by women farmers of the Inewari area in the Central Highlands of Ethiopia. International Livestock Centre for Africa has adopted and modified BBF to fit to the smallholder systems in Ethiopia (ILCA 1990).

Improved management practices have been designed to overcome the problems of Vertisols. These practices include drainage of excess water through safe waterways, choice of suitable crops incorporating legumes in rotations, monitoring soil moisture and preparing seedbed in the optimum soil moisture content (nearer but less than field capacity) between or after rains, supplemental irrigation to avoid water stress, dry seeding, double cropping in semi-arid tropics, fallowing during monsoon or cultivating wetland crops (such as rice) in humid conditions, etc. Subsurface drainage is not usually feasible in Vertisols for slow permeability after closing the cracks by wetting. So, special attention has been given to improved surface drainage systems, including cambered beds, ridges, furrows, bunds, and broad banks in Ghana, India, Indonesia, Trinidad, USA and Venezuela.

For sustainable agriculture in Vertisol areas of India, the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) has developed, almost after a decade of research, some management practices known as Vertisol Technology. In regions of Vertisols where rainfall is dependable but the lands are left fallow in the rainy season, ICRISAT adopted a series of improved practices to increase agricultural productivity. Joshi et al. (2002) reported a system of management where micro-watersheds of 1.5–3 ha size were taken as units for land and water management and agronomic practices. The bed-furrow (ridge-furrow) cultivation system was followed to conserve moisture and to facilitate draining runoff water in a controlled manner.

Important elements of ICRISAT farming system include (i) growing the same crop in both rainy and post-rainy seasons, (ii) using improved crop varieties and improved cropping systems that may include solo, sequential and intercropping systems as the farmers find suitable, and (iii) using appropriate fertilizers. The basic elements of the ICRISAT system are: (i) adoption of a combination of broad bed and furrow (BBF) system and grassed waterways to avoid waterlogging and disposing of excess water safely, (ii) plowing the land roughly after the previous crop is harvested and some moisture is left in the soil, (iii) completion of seedbed preparation after the first pre-monsoon rain, and (iv) appropriate seed and fertilizer placement.

The ICRISAT has modernized the old concept of broad bed and furrow system which encourages controlled surface drainage by forming the soil surface into beds. An old version of this system called “rigg and furrow” was used in the medieval times in Britain for improving pastures; it had been used in the past in North America and in Central Africa. A variation known as the camber-bed system was used in Kenya. ICRISAT recommends broad beds about 100 cm wide, separated by sunken furrows about 50 cm wide with the preference of slope along the furrow between 0.4 and 0.8 percent. Two, three, or four rows of the crop can be grown on the broad bed, and the bed width and crop geometry can be changed if needed (Fig. 6.4). A view of a crop field finished with broad bed making is shown in Fig. 6.5.
Fig. 6.4

Broad bed and furrows for different cropping systems. (Adapted from FAO Corporate Document Repository; soil and water conservation in semi-arid areas)


A section of a crop field prepared with broad bed and furrow. (Image courtesy of FAO )

Broad beds can be made on a gentle grade by ox-drawn wheeled broad bed makers. Very simple and cheap broad bed makers are used in Ethiopia.

Broad bed and furrow system work best in deep Vertisols with dependable rainfall averaging 750 mm or more. It has not been as productive in areas of less dependable rainfall, or on Alfisols or shallower black soils although, in the latter case, more productivity is achieved than with traditional farming methods. Sometimes, maize can be planted on the beds and rice in the furrows (Fig. 6.6). Waterlogging will not affect maize in beds, and rice will thrive well in furrows.
Fig. 6.6

Sketch showing double-row maize in broad bed and rice in furrow

Improved management systems were able to increase crop productivity and enhance soil quality in Vertisols of India where average annual rainfall is 800 mm, the average minimum temperature is 19 °C and maximum temperature is 32 °C. Rainfall is variable spatially and temporally and also occurs in torrential downpours. Such erratic rainfall results in spells of excess moisture and drought during the crop growing period. The improved system consisted of a broad-bed and furrow landform treatment. The beds were 1.2 m wide with a 0.3 m furrow prepared at 0.4 ± 0.6 percent gradient using a bullock-drawn bed-maker mounted on a tropicultor. The land was cultivated soon after the harvesting of the post-rainy season crop and, after unseasonal rains, the beds were formed again. Field traffic was confined to the furrows. Excess rainfall drained along the furrows and discharged into grassed waterways. Seeds of high-yielding varieties of pigeon pea, sorghum and maize were dry-sown on the bed with variable spacing for different species. Sorghum and pigeon pea together recorded an average grain yield of 4.7 t ha−1 year.−1 compared with the 0.9 t ha−1 year.−1 average yield of sole sorghum in the traditional system (Wani et al. 2003). It appears that the control of soil moisture is the key to sustainable management of Vertisols. Behera et al. (2006) observed that irrigation schedules and frequencies at certain crop growth stages improved yield of wheat (Triticum aestivum) and durum wheat (Triticum durum) on Vertisols in Central India.

Rajput et al. (2009) described the benefits of community based crop management systems in Vertisols of Central India. They observed that the raised-sunken bed system (RSBS) of land treatment enhanced in-situ rainwater conservation and minimized soil erosion and nutrient losses. Grain yields of wheat (Triticum aestivum) and chickpeas ( Cicer arietinum ) were higher in this system than in the flatbed system (FBS) of planting. Soybean ( Glycine max ) yield increased nearly 100 percent with the ridge-furrow system (RFS) and about 55 percent in broad-bed and furrow system (BBFS) compared with the FBS. The adoption of integrated nutrient management based on soil testing increased soybean and wheat yields by 71 percent over farmers’ practice at Narsinghpur compared with about 100 percent for soybean and 187 percent for wheat at Hoshangabad. The intercropping of soybean with pigeon pea ( Cajanus cajan ) in 4:2 ratio produced higher net return and benefit-cost ratio (3.3:1) than either of the monocropping systems. In this area aquaculture in the ponded water in the bunded field is done during monsoon and growing of wheat or chickpeas is done in the winter season. This system was also profitable.

The Joint Vertisol Project has developed a package composed of the following elements to better utilize Vertisols in the highlands of Ethiopia (JVP 2000):
  • A broad bed maker (BBM) by modifying local mareshas (wooden plough ) to drain excess water from Vertisols plots to allow early planting compared to current practice;

  • Wheat variety suitable for early planting on Vertisols;

  • Seed rate and fertilizer rate for optimal yield;

  • Planting dates for optimal plant growth and yield;

  • Weed and pest management recommendations.

Among these, the Broad Bed and Furrow based implement (BBM) is the main element of Vertisols technology. The other components are improved varieties or management practices that can be used along with BBM or traditional practices that could resist waterlogging problems and give better yields.

A field experiment was carried out for 6 years between 1998 and 2003 at CaffeeDoonsa in the central highlands of Ethiopia to evaluate alternative land preparation methods on the performance of wheat (Triticum durum Desf.), lentil (Lens culinaries Medik L) and tef (Eragrostis tef L) grown in rotation (Teklu et al. 2006). Four land preparation methods (broad bed and furrow, green manure, ridge and furrow and reduced tillage) were arranged in a randomized complete block design. Broad bed and furrow (BBF) significantly increased the grain yield of lentils by 59 percent (from 1029 to 1632 kg ha−1) as compared to the control. On the other hand, reduced tillage (RT) resulted in the highest grain yield of wheat (1862 kg ha−1) and tef (1378 kg ha−1) as compared to 1698 kg ha−1 of wheat and 1274 kg ha−1 of tef for the control although the increase was not statistically significant. A gross margin analysis showed that BBF is the most profitable option for lentil with 65 percent increase in total gross margin. On the other hand, RT resulted in 11 and 8 percent increase in gross margin of wheat and tef respectively as compared to the control. Best combinations of crop and land preparation methods were: lentil sown on broad bed and furrow, and wheat and tef sown after reduced tillage.

Kebede and Bekelle (2008) conducted a field experiment to observe effectiveness of flat seedbed, traditional drainage system, and broad bed and furrow with 100 cm (BBF-100 cm) and broadbed and furrow with 80 cm(BBF- 80 cm) on the yield of wheat. Results revealed that BBF-100 cm, BBF-80 cm and traditional drainage system significantly increased the grain yield of wheat by 51.4 percent, 41.6 percent and 11.2 percent compared to the control respectively. Bhaambe et al. (2001) conducted field experiments to study the effect of sub-surface drain spacing and crop residue incorporation on reclamation of salt-affected Vertisols under soybean-wheat cropping system. Sub-surface drains at 25, 50 and 75 m spacing installed at 1.3 m depth with corrugated PVC perforated pipe efficiently drained out excess water and significantly increased productivity of soybean and wheat crops. They also improved soil physical properties, including bulk density, infiltration rate, hydraulic conductivity, and decreased soil salinity. Crop residues (sugarcane trash @ 5 t ha−1 or green manuring with dhaincha – Sesbania bispinosa ) significantly increased crop productivity and reduced salinity of salt affected Vertisols.

Integrating BBF system with minimum tillage can be a better option for the management of Vertisols. This could be implemented first by constructing broad bed and furrows with an animal drawn broad bed maker (BBM), and then the broad beds could be maintained for several cropping seasons with the minimum tillage practice. In making the land for subsequent seasons with the same practice, BBF will have to be rehabilitated. Retaining the BBFs for repeated use with minimum tillage and row seeding rather than broadcasting conserves soil and increases nutrient use efficiency. It reduces seed rates by the placement of seed uniformly at optimum soil depth and also reduces fertilizer rate by improving nutrient uptake. Crop residues are retained on the soil surface as mulch and the soils get permanent soil cover so as to reduce the extent of land degradation and promote sustainable natural resource management .

6.7 Conservation Tillage in Vertisols

Proper water management is a major component of Vertisol management. Rapid changes in moisture status lead to limitations in use while slow changes could allow for longer periods of soil properties which favor plant growth. FAO (2008) reported that the elimination of runoff can result in waterlogged conditions in Vertisols. On the other hand, reduced tillage and residue management can promote infiltration, improve structure, prevent surface sealing, and decrease evaporational losses in Vertisols. Management techniques for safely redirecting runoff include use of grassed waterways. On-farm tillage research in Ethiopian highland Vertisol area demonstrated that the minimum tillage on participatory basis could be an effective intervention for soil conservation due to the early-vegetative cover of the soil. Application of ash on Vertisols at Chefe Donsa significantly increased grain and straw yields of wheat (Astatke et al. 2004). Results from a factorial experiment including the factors like no-tillage, minimum tillage, full tillage and conventional tillage on growth of soybean under dry farming conditions in the arid or semi-arid region of Iran indicated that root growth and grain yield increased significantly under no-tillage than the other tillage systems (Sani 2013). However, Duiker and Myers (2002) suggested that soils with very low infiltration rates including soils with high concentrations of expansive clays are not likely to show reduced runoff and may experience decreased yields with no-till. An experiment on farmer’s field in Northern Ethiopia was conducted to evaluate the short term changes in soil quality of a Vertisol due to the implementation of conservation agriculture practices and to assess their effect on runoff and soil loss, crop yield and yield components of tef (Eragrostis tef). The treatments were permanent bed, reduced tillage, and conventional tillage. Soil organic matter was significantly higher in permanent bed than conventional tillage and reduced tillage. A long-term tillage experiment has been carried out (2005–2009) on a Vertisol to observe changes in runoff, soil loss and crop yield due to conservation agriculture in the sub-humid DoguaTembien district of the Northern highlands of Ethiopia (Ugent et al. 2011). The tillage treatments were (i) permanent raised bed (PB) in a furrow and bed system with 30 percent standing crop residue retention and no-tillage on top of the bed, (ii) reduced tillage, locally called terwah (TER), with plowing once at sowing with 30 percent standing crop residue retention and contour furrows made at 1.5 m distance interval, and (iii) conventional tillage (CT) with a minimum of 3 tillage operations and the removal of crop residues. Crops planted during the 5 years were wheat, grass pea, wheat and barley sown together, and grass pea. Glyphosate was sprayed starting from the third year (2007) at 2 Lha−1 before planting to control pre-emergent weed in PB and TER. Runoff and soil loss were measured in plastic sheet lined collector trenches, which were located at the lower end of each plot. Significantly different (p < 0.05) soil losses of 12.7, 16.2 and 27.3 t ha−1 y−1 were recorded for PB, TER and CT respectively. Overall, the permanent raised bed and reduced tillage systems significantly reduced sediment loss and runoff and increased crop yield.

Tillage is done to make a seedbed or rootbed with good tilth, mix soil and crop residues to facilitate mineralization and release of nutrients, to make the soil porous, and above all to eradicate the weeds. The main disadvantages of tillage are deterioration of soil aggregation, loss of organic matter and enhanced erosion. If herbicides are used to control the weeds, intensity of tillage may be reduced considerably. In the reduced tillage system, only the portion of the land that is used for seeding or transplanting is tilled keeping the remaining land undisturbed. Moreover, a considerable proportion of the crop residues are retained on soil surface. The crop residues act as cover that conserves moisture and protects the soil against water and wind erosion.

6.8 Amendments in Vertisols

Soil quality of Vertisols could be improved by the application of organic waste products as amendments. Results of an incubation experiment under controlled temperature conditions, 30° C, on a Vertisol with 12 organic amendments resulted in a significant increase in soil-exchangeable K and Na over control. Some of the organic wastes, viz. cotton gin trash (10 Mg ha−1; mega gram per hectare = t ha−1), cattle manure (10 Mg ha−1), biosolids (10 Mg ha−1) and composted chicken manure (3 Mg ha−1) have value as a source of nutrients to soil and hence showed potential to improve Vertisol properties (Ghosh et al. 2010a). Ghosh et al. (2011) conducted another incubation experiment using five organic amendments at various rates and observed their effects on properties of a Vertisol. Cotton gin trash, cattle manure, biosolids (dry weight basis 7.5–120 Mg ha−1), chicken manure (dry weight basis 2.25–36 Mg ha−1) and a liquefied vermicast (60–960 L ha−1) modified soil chemical, physical and microbiological properties: higher light fraction of organic matter, higher N and P content and higher soil microbial activity. In Australia, the surface and subsurface soils of the majority of cotton growing regions are sodic. Application of organic amendments can be an option to stabilize the structure of these sodic Vertisols. To evaluate the possibility, Ghosh et al. (2010b) conducted an incubation experiment with soils of three different sodicity levels, i.e. nonsodic (ESP < 6), moderately sodic (ESP 6–15), and strongly sodic (ESP > 15), and incubated separately with cotton gin trash (60 Mg ha−1), cattle manure (60 Mg ha−1) and composted chicken manure (18 Mg ha−1), keeping an unamended control. The organic amendments improved the physical properties of both Vertisols by decreasing clay dispersion. In the field experiment conducted by Balemi (2012) on the effect of farmyard manure (FYM) and inorganic nitrogen (N) and phosphorus (P) fertilizers on the growth and tuber yield of potato ( Solanum tuberosum L.), the treatments consisted of a factorial combination of 4 levels of FYM (0, 10, 20 and 30 Mg ha−1) and 3 levels of inorganic NP fertilizers (0, 33.3 percent, 66.6 percent recommended rates) in a randomized complete block design with 3 replications. Results demonstrated that the application of 20 or 30 Mg ha−1 FYM + 66.6 percent of the recommended inorganic NP fertilizers significantly increased total tuber yield over the application of the full dose of inorganic NP fertilizers without FYM in Vertisols. Tolessa and Friesen (2001) reported that the application of 25 percent recommended inorganic NP fertilizers + enriched FYM resulted in the highest marginal rate of return in maize indicating that the integrated approach can enable to save up to 75 percent of commercial fertilizers. Likewise, Bayu et al.(2006) also reported the possibility of saving up to 50 percent of the recommended NP fertilizers due to amendment with 5–15 Mg ha−1 FYM to sorghum crop. Gypsum amendment is sometime used in Vertisols at a rate of 1.5–3.0 Mg ha−1. Gypsum amendment reduces water dispersible clay, ESP, pH, exchangeable Na, and Mg and improves hydraulic conductivity and exchangeable Ca and Ca/Mg ratio. However, the favorable changes that occur in soil physical and chemical properties are mostly found in the surface soil.

Study Questions

  1. 1.

    Explain the following terms: expansive soils, swell-shrink soils, cracking soils, and dispersive soils. Describe the unique morphological features of Vertisols.

  2. 2.

    Give an account of the physical properties of expansive soils. Justify that the physical properties of the Vertisols are responsible for their limitations to agricultural use.

  3. 3.

    Describe the chemical and mineralogical properties of Vertisols. Explain that the physical behavior of the Vertisols is the manifestation of their clay mineralogy.

  4. 4.

    Discuss the agricultural use of expansive soils. Write a note on engineering problems of shrink-swell soil.

  5. 5.

    Discuss briefly how expansive soils can be managed for better crop yield.



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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Khan Towhid Osman
    • 1
  1. 1.Department of Soil ScienceUniversity of ChittagongChittagongBangladesh

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