Rapid population growth puts tremendous pressure on natural resources, and the demand for increased and high-quality food is the most important concern for fulfilling food and nutritional security today. People in low-income countries are highly prone to risk owing to unprecedented land degradation. The objective is thus to achieve a state of land degradation neutrality for sustainable agriculture [1]. To achieve land degradation neutrality, land must be maintained in such a way that it can support biological activities and produce enough food for human consumption [2]. In accordance with one of the United Nations’ Sustainable Development Goals (Target 15.3 for 2030), which specifies the need to fight desertification, it is important to rehabilitate degraded land and soil, particularly land affected by desertification and drought, in order to establish a land degradation-neutral world [1]. This indicates the need for developing and utilizing the land, especially previously overlooked areas. In this respect, the large soil resources of arid regions provide a potential agricultural habitat and comprise around 16% of the planet’s land surface [3]. Most developing nations with rapid population expansion are located in arid and semi-arid regions. However, since 1950, aridity has risen across the majority of the Earth’s surface, a trend that has been exacerbated by the ongoing effects of current global warming [4]. Because of limited natural water resources, arid areas are extremely susceptible to climate variability and extreme occurrences such as droughts and heatwaves, and as a result they experience rapid environmental and land degradation. Insidious land degradation, whether induced by natural forces or human mismanagement, has the potential to challenge the resilience of natural ecosystems, produce permanent alterations in their states, and in the worst situations, bring about permanent desertification [5]. Expanding and intensively using agricultural lands, improper irrigation methods, forest clearing, and overgrazing are all human activities that lead to desertification. These unsustainable practices place a heavy burden on the land by influencing its soil chemistry and hydrology in undesirable ways. The expected drier and warmer climate will have significant effects on biomass accumulation, decomposition, and C storage in a variety of ways, and eventually disturb the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), resulting in a reduction in the provision of important services provided by arid ecosystems [6].

2. Concept and Distribution of Arid Zone

There are several classifications of arid zones, as shown in Figure 1. Meigs [7] classified arid regions based on whether they have hot or cold winters (Table 1). The Food and Agriculture Organization (FAO) defines arid zones as those having a length of growing period (LGP) of 0–179 days [8], while the United Nations Convention to Combat Desertification (UNCCD) uses the ratio of yearly precipitation to potential evapotranspiration (P/PET) as a criterion for its classifications. Based on the criteria established by UNCCD, arid regions have a P/PET ratio between 0.05 and 0.65. For the purposes of this rstudy, wesearch, used the classification from UNCCD was used. The aridity index (AI) was used to categorise and define arid regions as hyper-arid (AI < 0.05), arid (AI = 0.05–0.20), semi-arid (AI = 0.20–0.50), or sub-humid zones (AI = 0.5–0.65) [9]. Arid regions account for 10.6% of the Earth’s land area, but semi-arid regions are much larger, covering 15.2% of the land area, and may be found on all seven continents. Finally, dry sub humid regions account for just 8.7% of the land area [10]. More than a third of the world’s population lives in dryland regions, which cover 5.36 million km² (41%) of the Earth’s land area ^[15][11]. There are extensive arid zones between 15° and 30° latitude in both the Northern and Southern hemispheres, including in North and South America, North Africa, the Sahelian region, Africa south of the Equator, the Near East, Asia, and the Pacific ^[16][12]. Africa possesses 37% of the world’s arid zones, making it the continent most at risk from land degradation and desertification, given that 66% of its territory is classified as desert or arid. Asia, home to 33% of the world’s arid zones, also experiences these consequences to a great extent.

3. Characteristics of an Arid Ecosystem and Its Soil Constraints

Arid environments are characterized by a higher evaporation than precipitation, as well as persistent water shortages, frequent droughts, high climate variability, and high wind velocity. When desertification occurs and previously non-arid areas become arid, a loss of biodiversity can also occur. The concept of aridity is based on the ratio of available water to the total amount of water used. Because of atmospheric stability, precipitation is often lower than evapotranspiration in arid regions, and frigid winters are typical. Dry, stable air masses that resist convective currents are a common source of aridity. The absence of storm systems, which cause convergence, generate unstable conditions, and supply the upward movement of air required for precipitation, can also lead to aridity. Most of the precipitation in hot deserts occurs in strong convectional showers that do not cover large areas, making widespread rains virtually unheard of in these regions. In low-latitude deserts, the skies are usually clear, allowing for plenty of sunshine. A low latitude desert’s annual temperature range is greater than that of any other tropical climate. Water is commonly lost as runoff in arid regions because the soils cannot absorb all of the rain that falls during heavy storms [17]. In other cases, when rain falls on dry land, much of the precipitation is lost to evaporation. As much as 90% of rainfall in arid settings evaporates back into the atmosphere, leaving only 10% for productive transpiration [18]. Low precipitation and high temperatures result in high evaporation in arid regions, which also leads to aridic and xeric soil moisture regimes.

3.1. Scarcity of Water

Water scarcity is a major limiting factor of agricultural production in arid locations. Because of low precipitation and high evapotranspiration, good quality water is in scarce supply in arid areas. This problem is aggravated by the current state of global climate change, which brings extreme weather events and prolonged dry seasons. Optimizing farming practices for production and water management improves soil, water, and product quality [19]. Because of the scarcity of water, the soils in arid regions have a poor natural primary production and low soil fertility. Arid soils typically have an alkaline pH and accumulate significant amounts of potassium (K), salt, calcium (Ca), and other minerals, which can be detrimental to plant growth. Furthermore, gypsic crusts are also formed in some arid soils that could support specialized species of plants. Therefore, low soil fertility has negatively affected plant growth and biodiversity in arid soils [20]. Because of the existence of subtle environmental conditions, which were not taken into account by the soil fertility assessment systems developed by researchers and scientists for temperate and humid areas, Hag Husein et al. [21] concluded that the conventional systems have a low potential for adoption in arid areas. Therefore, soil fertility assessment tools tailored to arid areas should be developed to ensure widespread adoption and actual application.

Management to Cope with Water Scarcity

There are two different aspects of arid regions, namely (i) arid regions with a persistent lack of precipitation (absolute deserts) and (ii) arid regions with erratic precipitation (periodic drought of unpredictable severity and duration). The selection of crops, their composition and rotation, and, especially, the quantitative needs of fields and water requirement, schedule of watering, and the combination of watering with atmospheric precipitation all depend on an accurate assessment of the hydrothermal conditions of the region. In general, during the growing season, non-saline soils should not have a relative humidity that falls below 65–70% of the field moisture capacity. When watering non-saline soils, only a deficit level of the field moisture capacity should be applied [22]. In fact, the high potential productivity of irrigated agriculture in arid lands has been realised, and admiring remarks by visitors from temperate lands may be found in the classical literature. In 1800, Napoleon’s savants conducted a survey that included a quantitative analysis of the productivity of traditional irrigated agriculture in Egypt. Based on the relative yields of the wheat crop, they concluded that Egypt’s agricultural output was more than double that of France [23]. In arid areas, it is challenging to meet the agriculture water demand solely by utilising conventional water sources. Fader et al. [24] reported that by implementing more efficient irrigation and conveyance systems, the Mediterranean region could save up to 35% of water used. Wastewater reuse or low-quality water could be a potential option in the region. Recovering and reusing large quantities of low-quality water for irrigation, such as that from urban and industrial wastewater treatment plants, has the potential to reduce the need for groundwater. However, there are potential drawbacks associated with their usage in irrigation, including pollutants and crop toxicity, soil quality decline, parasite transmission, and system flaws ^[25][26][25,26]. The toxicity, solubility, and concentration of the chemicals will determine the severity of the potential effects. The rate and frequency of wastewater application, the type of crop and the desired yields, the inherent soil properties and condition, the prevailing weather patterns, the farmers’ level of technological capabilities, and their socioeconomic standing are also significant. In the arid western United States, sites irrigated with recycled wastewater have shown 187% higher electrical conductivity and 481% higher sodium adsorption ratio (SAR) compared with the sites irrigated with fresh water [27]. Poor irrigation management and inadequate soil drainage systems are the primary causes of persistent soil salinity and/or sodicity issues caused by the use of saline irrigation water [28], which is more prevalent in arid areas. However, the proper choice of crops is necessary in this regard. For example, in the arid Mediterranean region, the yield of maize grown using drip irrigation is around 25% higher than that of maize grown with surface irrigation [29]. Using a drip irrigation system with salt water with an electrical conductivity of 12 dS/m, the maize produced yields that were comparable to those obtained using fresh water. Compared wih barley, which has a yield threshold of 8 dS/m, bread wheat (Triticum aestivum L.) is only moderately salt tolerant, with a threshold of 6 dS/m; durum wheat (Triticum durum Desf.) is even less salt tolerant than bread wheat [30]. When compared with other legume species in the arid Mediterranean region, faba beans score the highest in their ability to thrive in dry conditions due to their rapid growth, early flowering, and maturity, which allow them to avoid drying up and dying [31]. However, lentils (Lens culinaris Medicus) also have osmotic adjustment, can escape drought through being tolerant to a low temperature, have rapidly filling seed, and mature early, while chickpeas (Cicer arietinum L.) have deep roots, osmotic adjustment, and a generally high level of drought resistance and cold tolerance. One of the crops chosen to ensure food security in the 21st century is quinoa (Chenopodium quinoa Willdenow) [32]. The intrinsic low osmotic potential and the plant’s capacity for growth plasticity and tissue elasticity [33] allow quinoa to survive in dry environments [34]. As a result of the plant’s deep root system, reduced leaf area, vesicular bladders, small and thick-walled cells suited to losses of water without loss of turgor, and stomatal closure, the crop is protected against the detrimental effects of drought [34]. Moreover, there is an addition of excessive nitrogen through wastewater irrigation, causing eutrophication in arid areas [35]. Selecting crops that can take advantage of high concentrations of nutrients, such as fodder grass [36], or employing the method of crop rotation to permit the removal of any excess nutrients, could help to reduce the need for the excessive supply of nutrients, especially nitrogen. According to Hamilton et al. [35], the possibility of nitrate leaching into groundwater can be significantly lowered through careful adaptation of crop and plant production systems in alignment with local weather patterns and effluent characteristics. When it comes to reducing nitrate leaching, for instance in arid regions, high yielding crops with substantial concentrations of nitrogen in their biomass (such as leafy vegetable and fodder grass) are likely to be more beneficial than tree plantations ^[35][36][35,36]. A strong need exists for the development of regional decision tools to determine the most appropriate agricultural management strategies (i.e., crop choice, sowing time, management of soil cover, timings, and rates of fertilizer application, etc.) according to the amount of water held in the soil, especially given the inconsistency of rainfall in most arid areas. In order to boost biomass production and, as a consequence, both above- and below-ground inputs of C to the soil, it is necessary to increase the amount of plant-available water. This can be achieved by optimising the amount of precipitation collected, the amount of water retained by the soil, and the efficiency with which crops use available water. Capturing rainwater is highly dependent on the soil structure, as well as the presence and connectivity of macropores at the soil surface; however, improvement in the soil structure in the arid region is quite a challenging task, amidst less crop biomass and low organic input addition. Understanding the complex ecological processes associated with vegetation on soil moisture is vital for vegetation restoration in arid environments, even though the impacts of vegetation on soil moisture are multifarious. Vegetation growth and succession are influenced by soil moisture at the root zone [37], and vegetation in turn influences the soil capacity for storing, transferring, and evaporating water at the canopy level [38]. Canopy interception and stem flow are two ways in which vegetation re-distributes precipitation and hence alters post-rainfall infiltration processes ^[39][40][39,40]. Recent years have seen an increase in the usage of highly hydrophilic superabsorbent polymers (SAPs) in agriculture, where they are believed to function as a reservoir for both nutrients and water [41]. Some researchers have indicated that after being applied to farms, these SAPs can maintain soil moisture and store some nutrients for up to five years [42]. These polymers have been shown to enhance the physical properties of soil and especially soil aggregation, hence enhancing the quality and quantity of many agricultural products (Table 2) [43]. The benefits to the soil have been well documented, and include increased water penetration into the soil, decreased soil erosion, decreased soil bulk density [44], improved nutrient intake efficiency [45], reduced evaporation rate from the soil surface [46], better weathering, reduced leaching of soil nutrients, and increased activity and proliferation of mycorrhizal fungi and other soil microorganisms [47]. Jahan and Nassiri Mahallati [41] conducted a meta-analysis to understand whether the application of SAPs has been effective at enhancing the crop production in arid soils of Iran. It was found that the average seed yield for cereals increased by 15.2% after being treated with 83 kg ha⁻¹ of SAPs in arid soils compared with untreated seeds. Plastic film mulching has been shown to be an invaluable tool for increasing crop yields and adapting farming practices in arid regions [57]. For example, wheat yield and water use efficiency on the arid Loess Plateau of Northwest China were much higher when plastic film mulching was used as opposed to straw mulching [58]. Plastic mulching is an excellent way to prevent soil moisture from being lost through evaporation and to maximize the use of scarce rainfall, which can help drought-stricken areas in arid regions [59]. However, some studies have found that using plastic mulch reduced the crop yields. Plastic mulching, for instance, altered the water and temperature conditions outside the range of crop adaptation in low-lying areas with an abundance of resources, leading to poorer yields [60]. Film mulching can also increase the root growth ability during the early growth stage, which led to an overabundance of soil moisture being used. Inadequate coupled with late-season precipitation and soil moisture led to an imbalance between vegetative and reproductive growth, which resulted in a lower crop production and water use efficiency [59]. However, Gao et al. [57] found that both crop yield and water use efficiency were improved in China’s arid regions when farmers began using transparent plastic and ridge row mulching.

3.2. Soil Organic and Inorganic Carbon

SOC/SOM is a primary component influencing both the composition and structure of soil. SOM also contributes to greater drought resilience in arid regions and higher crop yields. Because of climate constraints, the soils in arid regions have an inherently low stock of organic C (Table 3). However, they also have a lot of inorganic C, mostly in the form of soil carbonates (Table 3) [61]. On average, Lal [62] reported that dryland ecosystems sequestered between 0.1 and 0.2 Mg ha⁻¹ year⁻¹ of soil inorganic C. In addition to acting as a sink for atmospheric CO₂, inorganic C in soil may also play a positive function in soil aggregation via the interaction of carbonates with SOM. Moreover, SOM controls the positive effect of carbonates in the soil structure [63]. Water stability of soil macroaggregates is highly associated with the carbonate content at low SOM values [64]. The importance of vegetative coverings in preventing soil erosion and maintaining soil organic C in arid areas has been well recognized. The presence of a sufficient protection of the soil surface is hampered by conventional management practices, including intensive tillage, feed needs for animal production, and excessive grazing ^[65][66][67][65,66,67]. Soil quality and long-term food security are threatened by the extractive nature of using crop residues as fodder for cattle and animal manure as a cooking fuel in emerging countries of Asia and Africa [68]. The loss of SOC in these nations must be prevented by increasing the quantity of crop residues generated. However, in some emerging regions, such as West Africa, fertilisation is necessary to stimulate sufficient biomass production due to the highly weathered nature of soils [69]. Appropriate crop rotations, which encourage a greater diversity of plants, typically result in an increase in above-ground biomass and a preference for a more diversified root system (i.e., below-ground C allocation), with varying effects on the soil organic C by root-derived products [70]. Soil C stock can be improved with the use of deep rooting plants [71]. The selection of species and cultivars with deeper and better root systems, as well as other measures for optimal use of the complete soil profile, are all important factors to consider when functioning with rain-fed arid agriculture. Improvements in soil productivity, agricultural profitability, and environmental sustainability can be achieved through the rotation of controlled perennial grass or grass–legume mixtures (ley) with annual crops [72]. Adding a perennial grass–legume to a crop and livestock rotation can boost landscape diversity while maintaining or improving yields compared with less varied systems [73]. The fluctuation between soil organic C (Cs) and soil organic N (Ns) is a feature that is characteristic of crop–pasture rotating systems. Carbon and nitrogen levels drop during the annual cropping phase, but swiftly recover during the perennial pasture phase [74]. Perennial plant species contribute three to seven times more C and N to the litter pool than annual species through greater root production [75]; these roots are also placed deeper in the soil profile, which explains the Cs and Ns recovery during the pasture phase [76]. The majority of Ns improvement can be attributed to biological nitrogen fixation. The demand for N fertiliser for non-legume annual crops is reduced, as N stored during the grazing phase is gradually mineralized throughout the annual phase. This slow process of N mineralization is thought to enhance the synchronisation between N supply and N intake, hence decreasing N loss opportunities and allowing for greater productivity. Even when annual crops are maintained with no-till, the yield ceiling might drop and the yield gap can widen when pastures are removed from the rotation, as has been demonstrated for wheat [77].

3.3. Salinity

In arid regions, soil salinization has emerged as a serious environmental constraint threatening soil productivity, agricultural sustainability, and food security [79]. When water-soluble salts are retained in the soil, it becomes saline. It can occur naturally or as a result of poor anthropogenic activities, most often related to agricultural operations. Dry climates and low precipitations cause soil salinization because they prevent excess salts from being washed from the soil. High evaporation rates increase salts on the ground surface. Poor drainage or waterlogging prevents salts from being washed because of a lack of water transportation. Irrigation with salt-rich water increases the salt content in soil. The removal of deep-rooted vegetation elevates the water table. Saltwater intrusion into groundwater, coastal breezes transporting salty air masses inland, seawater submergence followed by salt evaporation, seawater submergence, and improper fertiliser use all contribute to soil salinization. At present, saline soils can be found in at least 100 different countries, with a total area of 932.2 Mha [79]. This includes particularly large areas in Pakistan, China, the United States, India, Argentina, the Sudan, and many nations in Central and Western Asia, as well as along the Mediterranean Coast [79]. Wichelns and Qadir et al. [80] estimated that the agricultural industry loses $27.3 million per year due to salinization in agricultural lands. According to Bridges and Oldeman [81], secondary salinization causes between 10 and 20 million hectares of irrigated land to become unproductive every year. This translates to 3 ha of arable land becoming unproductive every minute around the world. As the world’s population is predicted to grow to 9.8 billion by 2050 [82], soil salinization will continue to be a major barrier to food production and the satisfaction of people’s hunger. As salinization can have a significant economic impact on crops, farmers that face this issue often switch to a different cropping system. The land is either abandoned or attempts are made to mitigate the effects of salinization [83]. There are four main approaches to reducing secondary salinization in agricultural land [84] (Figure 2). The first method integrates a variety of agronomic practices with the goal of reducing the detrimental effects of salinity on crop yield and quality. The second strategy aims to reduce the rate of salinization by enhancing drainage and making use of higher-quality irrigation water. The third strategy includes growing salt-resistant plants to remove excess salts. The mechanical extraction of salts such as scraping from soils is the fourth and final method (Table 4). One of the most important methods for preventing topsoil erosion due to soil salinization is the regulation of irrigation and fertiliser application. If farmers can still make a profit growing crops that can tolerate low to moderate levels of salt, then it may be worth considering growing salt-tolerant varieties. So far, biosaline agriculture has been seen as a last choice for situations in which substantial levels of salts develop in the root zone of the soil. When plants are grown in groundwater and/or soil that is high in salt, this method is known as biosaline agriculture. While there is a rising interest in cultivating crops that can survive in highly salty environments, only a few of these crops are commercially viable [79]. By flushing salts from the top horizons into the lower soil layers, leaching can help minimise soil salinity. The idea is to drain the salts down below the root zone and to keep them dissolved. Under limited water supply of an inferior quality, farmers must choose between giving all irrigation water so as to plant the maximum area possible without applying a leaching fraction, thus assuming a decrease in crop yield per unit area, or reducing the cultivated area while allocating some water for leaching, thus boosting the crop yield per unit area in the long run [85]. In areas where leaching is done, improved drainage is necessary to remove the surplus of drainage water (which contains salts), hence minimising or eliminating the resulting evaporation of salts. A proper drainage system is thus required in order to make leaching work properly. In addition to implementing subsurface tile drainage [83], a number of researchers have advocated dry drainage (reserving a portion of the available land for the evaporation of excess water and transporting the accompanying salt as a partial remedy for groundwater salinization) [86] and bio-drainage (cultivating specific plant species whose primary water needs can be met by the canal seepage water or the capillary fringe immediately above it) [87]. Cultivating deep-rooted salt-tolerant plants can partially and temporarily restore salt-affected land. The replacement of deep-rooted perennials with shallow-rooted annuals has produced widespread salinization in Australia [88]. Replacing native permanent evergreen vegetation with annual crops and inactive fallows disrupts the hydrological equilibrium and increases the soil profile drainage. Salt is then leached deeper in the profile, raising water tables and delivering salt to the lower land. Modifying the original flora generates long-term effects that are difficult to understand, but the result is bare, erosion-prone soil and salinized streams. The over-optimization of irrigation systems contributes to the salinization problem; hence it is important to change farmers’ perspectives on the worth of water. Water pricing has improved, especially in arid regions where water is scarce [89]. Economically efficient irrigation will become the new irrigation management paradigm due to water scarcity and poor quality. Under the limited availability of irrigation water, reducing the cultivation area to distribute leaching water is more profitable. Economic efficiency demands decision-makers to openly weigh costs, revenues, and water opportunity costs. Carefully limiting fertigation permits water savings, decreases the direct and indirect effects of the fertilizers, lowers production costs, and delivers a higher net return for the farmer. Straw mulching, which reduces soil water evaporation and modulates soil water and salt transport [90], is a potential solution for farmers seeking to control soil salinity. Straw mulching can significantly reduce salt levels in the top 40 cm of soil [91]. Straw mulching appears to lower the soil’s surface salt concentration and also controls the vertical distribution of salt, which in turn may lessen salt damage to crops, increase crop yields, and lessen the likelihood of soil salinization and erosion. Under the changing climate scenario, the use of salt tolerant plants is trending as one of the management approaches of salt-affected soils [92]. Plants that can survive moderate salinity (glycophytes) are distinguished from those that have a adapted to highly salty soils (halophytes). However, most agricultural crops are glycophytes and can only tolerate low to moderate salinity. The term “halophyte” is only applied to a select few crops. Some crop varieties are more resistant to salinization than others, regardless of the species planted. This is because their phenology makes it possible for them to avoid salinity-inducing conditions. Thus, it is crucial to cultivate cultivars that can withstand high levels of salt throughout their lifecycle, without compromising production [93]. Soil microbiological diversity can be improved and the effects of salinity on plant growth can be reduced by exploitation and using beneficial microorganisms that are native to arid soils [94]. There are two main approaches in the management of soil microbial diversity in cultivated soils [95]. Firstly, an untargeted long-term approach includes a low-input agricultural system such as organic farming, conservation agriculture, and intercropping, increasing landscape diversity and agroforestry. The second approach is a targeted strategy including the use of biofertilizers, biostimulants, microbial consortium, biopesticides, etc. Improvements in soil quality are facilitated by cyanobacteria and biocrusts, which function as agents that alleviate soil salinity [96]. The “salt-out mechanism” is a known cyanobacterial reaction to an excessive salt concentration, and it involves the accumulation of suitable solutes within the cell that do not disrupt metabolic activities, as well as the active exporting of Na⁺ and Cl⁻ [97]. Most cyanobacteria thrive in neutral to alkaline soils, with an optimal pH of 7.5 to 10, which means that arid soils can be inoculated with specific cyanobacteria strains for soil improvement and plant growth [97]. Water movement and subsequent crop root growth can be enhanced by cultivating perennial plants with deep roots that are tolerant of saline soil [98]. Reduced soil pH and enhanced CaCO₃ dissolution from increased root respiration can also contribute to higher soil Ca levels. The potential exists for a decrease in exchangeable Na percentage and electrical conductivity in the root zone where these alterations improve profile leaching. Na leaching from the root zone can take a lot longer in rainfed systems, and the method is hampered in many places by a lack of knowledge on how to practically and economically include perennial species in cropping rotations [99]. Transgenic crops are another possible answer to the problem of salinized soils. No matter the strategy chosen, the actions proposed to halt the salinization of agricultural areas must always consider acceptability by the relevant stakeholders.