Keywords

1 Introduction

The World Bank Data on the MENA region reports 21 countries/territories as MENA: Algeria, Bahrain, Djibouti, Egypt, Iran, Iraq, Israel, Jordan, Kuwait, Lebanon, Libya, Malta, Morocco, Oman, Qatar, Saudi Arabia, Syrian Arab Republic, Tunisia, United Arab Emirates, West Bank and Gaza (Palestine); Yemen (https://data.worldbank.org/). Large areas of Libya, Egypt, Bahrain, Kuwait, Qatar and the United Arab Emirates are entirely desert (FAO 2013). The region possesses 1.6% of the world’s water resources and hosts 6% of the world’s population (Khater 2002), about the same population as the European Union (EU). The three smallest countries (Bahrain 1,472,674, Djibouti 1,000,000 and Qatar 2,986,953) have the lowest population in the region (about 5.5 million inhabitants). Of the total land area of the MENA region, only one-third is agricultural land (cropland and pastures), while only 5% is arable (cropland). The rest of the land is either urban or desert. Due to the dry climate, about 40% of the cropped area in the region requires irrigation. The region is one of the most land and water-constrained regions of the world and is predicted to become hotter and drier in the future due to climate change that will put more pressure on soil and water resources for agriculture. Only 4% of land in the region has soils of high or good suitability for rain-fed cereal cultivation and 55% is unsuitable (OECD-FAO 2018). The soils currently used for farming are severely degraded to the point where their productivity is estimated to have been reduced by up to 30 to 35% of potential productivity. Soil degradation in rain-fed systems is caused by wind and water erosion, while in irrigated systems the farming practices themselves are responsible for soil salinity and sodicity (OECD-FAO 2018). Thus, the soil salinity in the MENA region is a major concern for the sustainability of irrigated agriculture and water management.

The unsustainable use of soil and water resources will lead the region’s arable land and water resources to reduce and the region will be a difficult environment for agriculture, as it also suffers from severe land constraints. In two-thirds of the countries, less than 5% of the land is arable, while Saudi Arabia, Lebanon, Tunisia, Morocco, Yemen, Mauritania and Syria have huge desert pastures for livestock grazing. The productivity of water use is only half the world average. The need for the region to address these challenges, with limited land and water resources, will be further compounded by the expected impact of more frequent extreme climate-related events.

The MENA region countries/territories are located in different environmental conditions, where rainfall patterns, temperature and frequency are heterogeneous, as well as soil types. In general, MENA is a water and arable land-scarce region and the crop production is less than those of the developed countries. Due to water scarcity in the MENA region, agriculture is accomplished through irrigation to offset the crop water requirements. The use of saline water causes salinity zones under different irrigation systems (Shahid 2014). Due to the dry climate, about 40% of cropped area in the region requires irrigation. For good crop production, it is essential to irrigate the crops with a suitable quality of water, which is scarce in the region, therefore, marginal quality water (saline/brackish) is used for irrigation. This causes salinity build-up in soils. A pre-screening of soils against different salinity and sodicity waters is suggested to assess the fate of soils against irrigation cycles with salty water (Shahid and Jenkins 1992a, c; Shahid 1993) and to determine after how many irrigation cycle’s soils become saline, sodic, or saline-sodic.

Soil and water salinity is common in the countries of the MENA region and is affecting the national production. Losses from salinity alone across the region are estimated at US$ 1 billion annually, or US$ 1,600 to US$ 2,750 per hectare of affected lands (UNEP 2020). In order to use the soil and water resources sustainably, it is essential to address the salinity issue in a holistic way to understand and manage it properly. In this chapter, salinity issues, their impacts on agriculture and the environment, as well as potential options to manage salinity are presented and discussed. It is hoped that countless numbers of scientists and institutions will benefit from the information presented in this chapter.

2 Geographical Location of the MENA Region

The 21 countries in the MENA region cover some territory in Asia, Africa and Europe and include the Mediterranean and Red Sea and Arabian Gulf. The MENA occupies an area of 15 million square kilometers (Fig. 1).

Fig. 1
A map of the Middle East and North Africa. The regions listed are northern regions namely Morocco, Tunisia, Lebanon, Palestine, Syria, Israel, Jordan, Iraq, Iran, and Kuwait. Southern regions namely Mauritania, Sudan, Djibouti, Yemen, and Oman. Central regions namely Algeria, Libya, Egypt, Saudi Arabia, Bahrain, Qatar, and U A E.

Map of Middle East and North Africa region

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3 Climate of the MENA Region

Due to the geographic location of various countries in the MENA region close to the seas and the continental areas, there are differences in the climate. However, in general, the region is mainly located in the arid, semi-arid and desert environment, where there is insufficient rainfall and high temperature, and thus soils are dry most of the year. The summers present temperatures above 40 °C, winters are mild in the coastal areas, and inland deserts become very cold (even below 0 °C). Specifically, the Middle East (ME) has a hot and arid climate, and in some countries, irrigation is accomplished by river waters, e.g., the Nile delta in Egypt, the Tigris and Euphrates watersheds. In these countries, drought is increasing compared to previous decades. The MENA is a transitional area between equatorial and mid-latitude climates.

4 Water Resources of the MENA Region

The MENA region is a water-scarce region, where the annual water share per person is about 1,274 m3, in a few countries water share is up to 50 m3 per capita per year. In general, 50% of the MENA countries have below 500 m3 available water per capita per year. Irrigation is managed through conventional and modern irrigation systems and 85% of fresh water is used for agriculture. The region is the most water-stressed in the world, and two-thirds of countries continue to use groundwater at rates exceeding renewable internal freshwater resources, which over time become saline/brackish, and the recycling for irrigated agriculture will cause severe soil salinization and sodication problems and crops yield decline.

5 Soils of the MENA Region

Of the total land of the MENA region, only one-third is agricultural land (cropland and pastures), while only 5% is arable (cropland). The soils in the region are heterogeneous based on the differences in the soil formation factors (climate, organisms, relief, parent material and time) and the processes (transformation, translocation, losses and additions). In the Jenny Equation (Jenny 1941), which is S = f(cl, o, r, p, t,…), the “S” represents soil formation, “cl” is climate, “o” is organisms in the soil, “r” is relief such as the topography, “p” is the parent material. In the MENA region, in general, the aridity, drought and desertification are main environmental concerns, limiting the soil formation, and hence in some countries soils are poorly developed, such as psamments (sandy soils) classified as Entisols (Soil Survey Staff 2014) or Arenosols (WRB 2015). Following is the summary of soil types in some of the MENA region countries (FAO-ITPS 2015) (Table 1).

Table 1 Major soil types in the MENA region countries
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6 Facts About Soil Salinity Extent in Some MENA Region Countries

Iran—About 235,000 km2 (or 14.2% of the total area of the country) is salt-affected, which is equivalent to about 50% of irrigated lands in Iran (Pazira 1999; Fathi and Rezaei 2013). Another estimate revealed 34 million hectares (Mha) or nearly 20% of the surface area of the country is salt-affected. This includes 25.5 Mha of slightly to moderately and 8.5 Mha of severely salt-affected soils (Cheraghi et al. 2007).

Kuwait—209,000 hectares are affected by salinity (Hamdallah 1997; Burezq et al. 2021).

UAE—In general 80% of agricultural land in Abu Dhabi Emirate is affected by salinization (EAD 2018); out of 76,858 hectares of farming area in Abu Dhabi emirate, 69,348 farmland hectares are salinized (EAD 2018) at 0–25 cm depth which is 90% of the total farmland (EAD 2018).

Oman—44% of the total geographical area is affected by varying degrees of salinity (Ahmed et al. 2013).

Egypt—Saline, saline-sodic and sodic soils have a strong presence in the Nile delta land and represent an average of 37% of the total cultivated soils. The north delta contains the highest area of saline and saline-sodic soils reaching 46% (Mohamed 2016).

Hachicha and Abdelgawed (2003) have summarized the extent of salt-affected soils in some Arab countries as below:

  • Syria—532,000 ha, 40% of the total irrigated areas, are salt-affected soils.

  • Iraq—Salt-affected soils: 1.3 Mha slightly affected, 6.7 Mha severely affected.

  • Saudi Arabia—about 2 Mha are sabkhas (salt scalds) and about 3,641 Mha is affected by salinity, 50,000 ha severely, 1.7 Mha moderately, 1,977 Mha slightly and 13,675 ha very slightly affected.

  • Qatar—70,124 ha affected, 6,517 ha slightly and the rest severely affected.

  • Bahrain—41,273 ha are affected, 17,540 ha slightly and 22,473 ha are severely affected.

  • Kuwait—85,000 ha affected and 65,827 ha slightly affected.

  • Oman—9,442 Mha affected, about 30% of the total area of Oman (309,500 km2).

  • Yemen—483,467 ha affected.

  • Jordan—In the Jordan Valley, 6,500 ha affected, 1,400 ha slightly, 1,600 ha moderately, and the rest severely affected.

  • Libya—Salt-affected soils are about 700,700 ha: 199,300 slight, 174,400 moderate, 327,000 severe sabkhas, and sodic soils. The area affected by salinity and water logging is about 250,000 ha.

  • Algeria—Irrigated area is about 350,000 ha and 25% are salt-affected soils. About 8% of the irrigation waters are very saline and 21% have moderate salinity.

  • Morocco—Irrigated area is 1 Mha, about 21% are salt-affected and 57% of the Gharb irrigated area. Salt-affected soils are 350,000 ha. Another estimate presents, 5% of agricultural soils are affected by salinization to different degrees, reducing thus their productivity.

  • Mauritania—Salt-affected soils: cover 86.3 Mha (38.3%). Most of the irrigated area along the Senegal River is affected.

  • Tunisia—Salt-affected soils are about 1.5 Mha, 10% of the total area. Irrigated areas cover about 375,000 ha. Salinization and waterlogging affected about 50% of the areas, and 10% are severely affected.

7 Potential Threats to the Soils of the MENA Region

Globally ten threats to soils have been reported (erosion, compaction, acidification, contamination, sealing, salinization, waterlogging, nutrient imbalance, loss of organic matter and of biodiversity) (FAO-ITPS 2015). In the MENA region, both rain-fed and irrigated land in use suffers from ongoing degradation caused by wind and water erosion and unsustainable farming practices. Three-quarters of the region’s 30 million ha of rain-fed cropland is estimated to be degraded. In addition, soils currently used for farming are severely degraded to the point where their productivity is estimated to have been reduced by up to 30 to 35% of potential productivity. Soil degradation in rain-fed systems is caused by wind and water erosion, while in irrigated systems the farming practices themselves are responsible for soil salinity and sodicity. Losses from salinity alone across the region are estimated at US$ 1 billion annually or US$ 1,600 to US$ 2,750 per ha of affected lands. Recent studies have estimated the economic cost of land degradation in the region at US$ 9 billion each year (between 2% and 7% of individual countries’ GDP).

The review of the soils of the MENA region and potential threats has revealed that the soils of the MENA region are subjected dominantly to nine threats at various locations, the exception is for acidification which is not common as the soils of arid and semi-arid regions are alkaline in reaction (pH > 7.0). Therefore, the soil problems in MENA region are complex and require a holistic approach for sustainable use and management, through investing in soils. The key objective should be to promote “Sustainable Soil Management” to improve soil productivity for crop intensification, provide ecosystem services, improve food and nutrition security and combat desertification towards sustainable national and regional development (Table 2).

Table 2 Potential threats to the soils of the MENA region, influences on soils, crops and environment and management options
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8 The UN Sustainable Development Goal 2 in the Context of the MENA Region

Globally, there are 17 ambitious UN SDGs with 169 targets that all UN Member States have agreed to work towards achieving by the year 2030 (Pedersen 2018). Soils contribute, directly or indirectly, to a number of SDGs (numbers 2, 3, 6, 13 and 15) pertaining to hunger (SDG 2), human health through nutrition (SDG 3), clean water (SDG 6), climate change (SDG 13) and life on land (SDG 15).

The SDG 2 directly relates to agriculture, food production and soils “To end hunger, achieve food security and improved nutrition and promote sustainable agriculture”. Among 5 targets under the SDG 2, targets 2.3 and 2.4 directly relate to food and soil quality.

  • SDG 2—End hunger, achieve food security and improved nutrition and promote sustainable agriculture.

  • Target 2.3: by 2030 double the agricultural productivity and the income of small-scale food producers.

  • Target 2.4: by 2030 ensure sustainable food production systems and implement resilient agricultural practices that progressively improve land and soil quality.

The SDG 2 and the associated targets are highly relevant to the MENA region due to continuous soil degradation and increasing water scarcity and prolonged droughts. To achieve the above-cited SDG and the activities by 2030 in the MENA region, it is essential to adopt Sustainable Soil Management (SSM) through investing in soils, especially enhancing understanding of spatial salinity distribution (salinity mapping and regular monitoring) to create salinity-based crops zones “that is what we must attempt to achieve in the context of MENA region affected with salinity ailment”. Should the MENA region not address the salinity problem in irrigated agriculture holistically, there would be a danger that farm productivity will decline and that may increase food imports costing billions of dollars. This strongly suggests the need to understand the salinity impact on irrigated agriculture and assess at the national level to give national strategies to manage the salinity problem to enhance farm productivity, to increase local production and to support national food security. Therefore, it is essential to measure soil salinity to manage on scientific grounds.

9 Soil Salinity Assessment—Procedural Matters

Soil salinity can be measured in the field at different soil:water ratios (1:1, 1:2.5, 1:5), and in the laboratory by collecting extract from a saturated soil paste. The soil salinity measured at different soil:water ratios must be correlated to ECe (laboratory measurement), which is considered standard from a salinity management and crop selection point of view (Shahid 2013; Shahid et al. 2018a, b). Field measurement procedures are briefly described below:

  • 10 g soil + 10 ml distilled (deionized) water (1:1)

  • 10 g soil + 25 ml distilled (deionized) water (1:2.5)

  • 10 g soil + 50 ml distilled (deionized) water (1:5).

There is no standard factor to convert EC (1:1, 1:2.5, 1:5) to ECe values. Table 3 provides a general guide when location and country-specific factors are not available. To be accurate it is recommended that each country in the MENA region should develop its own factors for rapid salinity assessment without sending soil samples to the laboratory, to avoid delays in decision-making. The use of a modern salinity monitoring system allows instant salinity measurement through an automated dynamic salinity logging system (Shahid et al. 2008).

Table 3 Conversion factor to convert EC (1:1, 1:2.5, 1:5) into ECe (Shahid et al. 2018a, b)
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9.1 Field Assessment of Soil Sodicity (Qualitative Test)

Field assessment of soil sodicity can be determined through the use of a turbidity test with soil:water (1:5) suspensions (Shahid et al. 2018a, b).

  • Clear suspension—non-sodic

  • Partly cloudy—medium sodicity

  • Very cloudy—high sodicity.

The relative sodicity can be further assessed by placing a white plastic spoon in these suspensions.

  • The spoon is clearly visible—non-sodic

  • The spoon is partly visible (medium sodicity)

  • The spoon is not visible (high sodicity).

9.2 Electromagnetic Induction (EMI) Characterization of Saline Soils

McNeill (1980) was among the first investigators to describe how electromagnetic induction (EMI) method can be used in assessing soil salinity. The EMI is a technique to effectively measure apparent electrical conductivity using EM38 equipment and is presented as mS/m (Cameron et al. 1981). The EM38 is specifically designed for salinity measurement in agricultural farm surveys. The EM38 measures EC for a maximum depth of 1.5 m (vertical mode) and 75 cm in horizontal mode. The salinity data can be stored in the datalogger and through integration with GIS, georeferenced salinity maps can be created, showing salinity heterogeneity in the farm or the landscape (Cook et al. 1992). The salinity map will allow farmers to develop more precise management zones and salt-tolerant crops to obtain higher yields. It should be noted that EM38 provides apparent EC (field), which must be converted to ECe (measured in the lab), therefore, a location-specific correlation between EC-EM8 and ECe is desirable for data interpretation, salinity management and crops selection, which will be location and soil type specific.

9.3 Laboratory Assessment of Soil Sodicity—Procedural Matters

Soil sodicity can be measured by analyzing extract from a saturated soil paste for Na, Ca and Mg to calculate the sodium adsorption ratio (SAR), which is then used in a standard equation to calculate the Exchangeable Sodium Percentage (ESP). The ESP can also be measured using exchangeable sodium (ES) and cation exchange capacity (CEC), both expressed in meq/100 g soil.

The Sodium Adsorption Ratio

$${\text{SAR }} = {\text{ Na}}/\left( {{\text{Ca}} + {\text{Mg}}/{2}} \right)^{{0.{5}}}$$
(1)

where Na, Ca and Mg are in meq/l unit.

ESP calculation by using SAR

$$ESP = [100 (-0.0126 + 0.01475 * SAR)]$$
(2)

ESP calculation by using exchangeable sodium (ES) and cation exchange capacity (CEC)

$${\text{ESP }} = \, \left( {{\text{ES}}/{\text{CEC}}} \right) \, \times { 1}00$$
(3)

where ES and CEC are represented as meq/100 g or cmoles/kg.

An ESP of 15 is the threshold for designating soil as being sodic (Richards 1954). At this level, the soil structure starts degrading and negative effects on plant growth appear.

10 Soil Salinity Classification

The Soil Science Division Staff (2017) presented the latest salinity classes (Table 4), where the lowest soil salinity value is set at 2 dS/m compared to the saline soil limit set up by Richards (1954) as ECe 4 dS/m. Even though the lowest ECe limit is set at 2 dS/m, at this salinity level many salt-sensitive crops can reduce their yields (Tables 1 and 2). However, these salinity limits are appropriate for national, regional and global salinity mapping.

Table 4 Soil salinity classes based on the EC of extract from saturated soil paste (Soil Science Division Staff 2017)
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Regarding the soil sodicity (ESP limits to define sodic soil) there is a general consensus among global scientists to define soil as sodic when the ESP reaches 15. However, in Australia since the review by Northcote and Skene (1972), an ESP 6 had been widely used as an acritical limit for the adverse effects of sodicity.

10.1 Classification of Salt-Affected Soils (Richards 1954)

Three classes are defined to present the salinity and sodicity of the soils.

Saline soil (ECe ≥ 4 dS/m, ESP < 15)

Saline-sodic soil (ECe ≥ 4 dS/m, ESP ≥ 1 5)

Sodic soil (ECe < 4 dS/m, ESP ≥ 15)

Soil pH is not a criterion in the classification of salt-affected soils; however, at high ESP, pH is also increased which can affect nutrient availability to plants (P, and micronutrients except Mo).

11 Salt-Affected Soils in the Global and Regional Context

Of 310 million hectares of global irrigated areas, 20% (62 million hectares) is salt-affected, costing US$ 441 per hectare, with total economic losses of US$ 27.3 billion (Qadir et al. 2014). Further, it has been cautioned that “Every day for more than 20 years, an average of 2,000 hectares of irrigated land in arid and semi-arid areas across 75 countries have been degraded by salt”, reported by the UNU Institute for Water, Environment and Health (https://unu.edu/media-relations/releases/world-losing-2000-hectares-of-farm-soil-daily-to-salt-induced-degradation.html). Currently 20% (62 million hectares) of 310 million hectares of irrigated lands are salt-affected. Globally, if immediate action is not taken to address salinity problems, we will lose 25% of 310 million hectares of irrigated lands by 2100, when the population will rise many folds. These figures alert us all that irrigated agriculture resources are being depleted at a rate that will certainly not allow the future population of 9.3 billion by 2050 to meet their own food demands, unless we adopt new, innovative and regenerative approaches to manage these marginal resources.

Salinity is not only neglected on irrigated agricultural farms but also in plant ecology and biogeography (Bui 2013). There is an immediate need to initiate or enhance systematic salinity research programs at national levels from assessment, to monitoring and management in agricultural farms. The most appropriate way is to delineate agricultural farms into crop zones based on groundwater and soil salinity levels and provide guidance to the farmers to grow appropriate salt-tolerant crops to improve farm productivity. This will ultimately lead to reduce the gap between local production and food import and support food security.

The food security for a growing population can only be assured if a sufficient area of fertile soil and water will be available for food production (Montanarella and Vargas 2012) and through global governance of soil resources as a necessary condition for sustainable development.

However, it has been observed that the available cropland area has decreased from 0.45 ha/person in 1960 to below 0.25 ha/person by 2008. In the regional context, recent estimates of the extent of salt-affected soils in the MENA do not exist, a few countries have assessed their soils and soil salinization levels at the national level, such as Kuwait (Shahid et al. 2002), but not in the farming areas, Abu Dhabi emirate (EAD 2009, 2018; EAD-MoEW 2012), Middle East (Hussein 2001; Shahid et al. 2010) and Oman (MAF 2012) have assessed soil salinity. However, most of these estimates are on a national level where in some countries salinization effects on agricultural farms have not been explored, and salinity concerns are not answered. Only the Abu Dhabi emirate (EAD 2018) and Oman (MAF 2012) have completed the salinity assessment of agricultural farms. Earlier, an estimated area of 209,000 hectares has been reported as being salinized in Kuwait (Hamdallah 1997), which is roughly 11.7% of the total Kuwait land area.

In recognition of the significant effects of salinity on irrigated agriculture, the UN-FAO-sponsored Global Soil Partnership (GSP) has currently published The world map of salt-affected soils (https://www.fao.org/soils-portal/data-hub/soil-maps-and-databases/global-map-of-salt-affected-soils/en/) and assessed the current salinity extent and scale to better understand the constraints to world food security for solutions-oriented management schemes. In addition, considering the importance of salt-affected soils and their management GSP has officially launched the “International Network of Salt-Affected Soils (INSAS)” in November 2019 at the International Center for Biosaline Agriculture (ICBA first Global Forum on Innovations for Marginal Environment-GFIME) (https://www.fao.org/global-soil-partnership/insas). This international consortium also encourages the National Agricultural Research Systems (NARS) to work within their boundaries to publish geo-referenced soil salinity atlases of agriculture farms for informed decisions on crop selection to achieve higher production from the improvised farms.

12 Soil Salinity and Plant Growth

Plants are more sensitive to high salinity during seedling stages, immediately after transplanting, or at germination. As soil salinity increases, the osmotic potential is increased and the plants extract water less easily, aggravating water stress conditions. During plant growth, the water moves into plant roots by a process known as osmosis, which is controlled by the level of salts in the soil water and in the water contained in the plant. If the level of salts in the soil water is too high, water may flow from the plant roots back into the soil resulting in dehydration of the plant, causing drying or even death of the plant (Physiological drought). The salt tolerance of a specific crop depends on its ability to extract water from salinized soils. Crop yield losses may occur even though the effects of salinity may not be obvious (salinity is silent killer). However, it is a general saying that “if salinity can be measured it can be managed”.

12.1 Salts Affects on Plants and Adjustments

The salts affect plants in two ways, i.e., (i) osmotic effects and (ii) specific ion effect.

Osmotic effect—water moves through osmosis (from higher to lower concentration), however, when salts are high in soil water, the water in the plant’s cells is pulled out by the saline soil environment resulting in decreased turgor pressure in the cell leading to wilting of plants and plant death.

Specific ion effect—at higher salt levels, plant’s metabolic process is decreased. This can be explained by the reduction of enzyme activities in plants.

There are three ways by which the plants adjust salts during plant growth.

  1. (i)

    Salts excretion from leaves—salts absorbed from the saline soil environment after passing through the plants are excreted by salt glands (e.g., saltbush—Atriplex; and halophyte grasses and mangroves) in the leaves (Fig. 2)

    Fig. 2
    A photograph of a small mangrove branch with leaves. All the leaves have tiny spots on the dorsal side that indicate salt secretion.

    Salts secretion from mangrove leaves (Shahid 2012)

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  2. (ii)

    Salts exclusion at the roots level—while plants are taking water from the soil, the salts are filtered at the roots level, thus, accumulation of salts occurs in the very near vicinity of the roots.

  3. (iii)

    Accumulation of salts in cell vacuoles—the salts move from the cytoplasm to the large vacuoles. The vacuoles have lower metabolism relative to the cytoplasm.

12.2 Farm’s Productivity Decline Due to Salinity

The choice of crops becomes limited and yield declines linearly as salts in the irrigation water and soil increase (Shahid et al. 2018a). In Oman, farm productivity decreased due to soil salinity which has led to a significant reduction in farm profitability (MAF 2012). While the farms irrigated with fresh water make gross profits of about US$ 2,860/0.42 hectare, this falls to US$ 2,080 for low salinity water, US$ 1,222 for moderate salinity farms and only US$ 1,118 for high salinity farms (MAF 2012). Hussain (2005) reported 18.9–36.0 million US$ annual losses due to only salinity in Oman. The Oman Salinity Strategy (MAF 2012) survey data exhibit a spectrum of crops that are abandoned with the increase of salinity. Thus, for example, some vegetable crops start to be abandoned when salinity goes above 1,500 ppm. Between 3,000 and 5,000 ppm tree crops such as lemon and mango are abandoned. While even fodder crops and dates are being abandoned progressively over the salinity range 5,000 to 10,000 ppm. The main cause of abandonment was stated to be falling incomes caused by decreasing yields and product quality as the salinity of irrigation water increased. These studies (EAD 2018; MAF 2012) cautioned the effects of salinity on crops, farm abandonment, and stress to assess salinity problems at the national level if agriculture has to be sustained, such as the case of countries in the MENA region, a water and arable land scarce region.

In the Abu Dhabi Emirate (EAD 2009), an area of 35.5% (2,034,000 ha) has been depicted to be affected by varying degrees of soil salinity, where the highly saline soils on the soil salinity map are confined to the coastal land (King et al. 2013), and inland sabkha (salt scald) where the groundwater levels approach the surface, creating large areas of aquisalids at the great group level of US soil taxonomy (Soil Survey Staff 2014; Shahid et al. 2013, 2014). These estimates are mainly from general salinity assessment and do not present the salinity status of the irrigated agricultural farms. Considering the importance of salinity management in irrigated agriculture farms to enhance farms productivity and increase domestic agriculture production, the Environment Agency Abu Dhabi (EAD) conducted an Abu Dhabi emirate-wide multi-million-dollar salinity assessment of agricultural farms project (EAD 2018). After analyzing 16,000 soil samples from over 4,000 agricultural farms, it has been observed that the soil salinity of irrigated agricultural farms was significantly higher than the salinity of neighboring native soils of the same origin. Where the salinity effects are alarming, for example, over 6,000 agricultural farms have been abandoned in the Abu Dhabi emirate alone, due to the salinity problem, thus reducing the national capacity of domestic food production. The survey showed about 90% of the irrigated farmland was affected by soil salinity of varying degrees (EAD 2018). Such agriculture farm-based salinity information is not known in most of the MENA region countries, but the situation may be alarming.

In the case of Kuwait, the country-wide soil/water salinity status of agricultural farms is not known (Al-Menaie et al. 2018), but soil salinity has been indicated (Al-Rashed and Al-Senafy 2004) in Abdali farms ranging from 5 to 25 dS/m levels, imposing serious constraint to crop production in Kuwait cultivated land and in general it is reported as an early warning of land degradation (Shahid et al. 1998). Later, Al-Rashed and Al-Senafy (2004) clearly stated that since the establishment of Abdali farms, there was a clear increase in soil salinity levels. In the same study in Abdali, groundwater Total Dissolved Solids (TDS) were reported to range between 5,700 and 14,900 mg/l during summer and between 5,200 and 17,500 mg/l in winter. While interpreting soil survey data, Shahid et al. (2002) concluded that in Kuwait an area of 12.1% was affected by varying degrees of salinity, this salinized area does not include agriculture farms. Therefore, the farmers are not aware of the salinity levels of their farm soils and irrigation waters and continue farming various crops without knowing their salt-tolerance levels, and are likely to have low crop productivity. If, however, the farmers select crops based on the salinity tolerance levels, maximum production can be achieved.

12.3 General Guideline About the Crop Response to Root Zone Soil Salinity

No effect of soil salinity on crop yield declines until soil salinity (ECe) reaches a threshold level (ECt). Above this, there is a linear decline in crop yield “slope” (s) as soil salinity increases (Maas and Grattan 1999). To understand the possibility of expected crop yield decline at certain soil salinity (ECe) levels relative to yield from normal soil, the following relationship is globally used:

$${\text{Yr }} = { 1}00 \, - {\text{ s}}\left( {{\text{ECe}}{-\!\!-}{\text{ECt}}} \right)$$
(4)

where Yr is yield under saline soil environment relative to non-saline environment, i.e., at or below ECt level; s = is the slope (% linear decline in yield with each unit increase of soil salinity (ECe) above ECt; ECe = Average root zone soil salinity during crop season; ECt = threshold soil salinity of crop.

The above equation can be explained by giving the following example.

Example: Average soil salinity (ECe) of irrigated field is 8 dS/m. What are the relative yields of barley (forage) and alfalfa crops?

Barley (Hordeum vulgare)

ECe (8 dS/m); ECt (8 dS/m); S (5%) Barley yield relative to non-saline soil = 100%

Alfalfa (Medicago sativa)

ECe (8dS/m); ECt (2 dS/m); S (7.3%) Alfalfa yield relative to non-saline soil = 56.2%

Conclusion: Farmer should grow barley for higher yield and profitability. If he grows alfalfa farmer is likely to lose 43.8% yield.

13 Facts About Soil Salinity, Crop Salt-tolerance and Management

Crop selection based on the expected root zone soil salinity during crop season is the best choice to moderate salt effects. Extra leaching has to be accomplished in access to crop water requirements to keep the root zone salinity at an acceptable level (threshold salinity). Plants are sensitive to salinity at an early stage, the mature plants are more tolerant to salts. Salt tolerance in general increases from Fruits → vegetables → field crops → forage crops. Regular monitoring of root zone salinity is a must to take necessary action to maintain soil salinity at a safe limit.

14 A Paradigm Shift in the Classification of Salt-Affected Soils in Relation to Crop Types

The most used classification of salt-affected soil is the one published in 1954 by US Salinity Lab Staff (1954) and later in 2017 (Soil Science Division Staff 2017). In the former classification, saline soil presents electrical conductivity of extract from saturated soil paste (ECe) more than or equal to 4 dS/m (ECe ≥ 4 dS/m). This limit was set up with the understanding that at this level, salinity starts showing its impact on soil properties and plant growth. However, it is not true for salt-sensitive crops, such as, maize, broccoli, tomato, cucumber, spinach, celery, cabbage, potato, pepper, lettuce, radish, onion, carrot etc., these crops start showing effects of soil salinity on plant growth even at less than ECe 2 dS/m. The Soil Science Division Staff (2017) classify soils with ECe < 2 dS/m as non-saline, even though salt-sensitive crops show yield decrease in this range. These definitions (Richards 1954; Soil Science Division Staff 2017) are creating confusion among scientists and farmers, in the sense that how a non-saline soil can cause a significant effect on plant growth. The authors of this chapter believe that the level of soil salinity in the context of its impact on crops to be set up at the salinity threshold level of the specific crop. If this paradigm shift in understanding the effects of salinity to crop is well received and appreciated specifically in the MENA region, and in general globally, this will lead to enlighten the gray area (between salinity thresholds of crops below ECe 4 dS/m) and provide more insights to the salinity problems and their objective-oriented long-lasting management through the selection of salinity level oriented appropriate salt-tolerant crops. To guide the researchers, extension workers and farmers, a comprehensive information is prepared (Tables 5 and 6) showing the crops in relation to salinity threshold level (t), slope (s) and the minimum (ECe) and maximum (ECe) salinity levels for each crop, with explanation as a footnote, relative reduction of crop yield in saline soils compared to non-saline soil and comprehensive salinity/sodicity management practices. All these crops (Table 5) show significant crop yield reduction at ECe 4 dS/m (a level considered non-saline soil). Therefore, the saline soil definition (EC ≥ 4 dS/m) of Richards (1954) should be considered very general, perhaps suitable for regional and global soil salinity mapping, but not from the crop point of view of crop selection considering the salinity level is safe for crops.

Table 5 List of crops with salinity thresholds (ECe) less than 4 dS/m
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Table 6 Relative yield reduction of important field, vegetables, forage and fruit crops as affected by soil salinity (ECe) (Ayers and Westcot 1994)
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15 Soil and Salinity Management Options in the MENA Region

Due to the complexity of soil, water and environmental problems in the MENA region, sustainable soil management requires a mix of best soil management practices tested and proved successful under local conditions or on similar soils and environmental conditions for adoption. In summary, it requires proper tillage to conserve soil moisture and organic carbon, efficient nutrient and water management, crop residue management to transform to compost, organic and biofertilizers, irrigation and weed management as well as crop rotation by including crops having the character of biological nitrogen fixation (BNF) to maintain soil fertility. Negligence of any of the above may reduce soil’s capability to produce to its full capacity and compromise soil quality and crop performance as well as lead to soil and groundwater pollution. In addition, due to differences in climatic conditions (temperature, rainfall), soil parent material, intensity of soil formation factors and processes, the soils within the national boundaries and across the region are of different types (https://www.fao.org/soils-portal/data-hub/soil-maps-and-databases/harmonized-world-soil-database-v12/en/). The groundwater used for irrigation is not of the same quality, but possess heterogeneous levels of salinity and sodicity, thus the vulnerability of the irrigated lands to salinity/sodicity is different. This led to the conclusion that there is no single or combination of techniques universally applicable to manage soil salinity in the MENA region. Therefore, the salinity management in irrigated agriculture should be diagnostics-based, crop and location-specific. In this context, a comprehensive analysis is made to come up with potential salinity/sodicity problems in the region, their influences and objective-oriented management solutions are enlisted (Table 7). This comprehensive table provides all types of problems in the countries of the MENA region and the suggested mitigation options, these are not specific for any country but can be used on a case by case basis based on diagnostics of the problems.

Table 7 Salinity and sodicity-related problems, their influences and potential management solutions
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