Introduction

In desert regions with limited recourse to surface water, groundwater is a valuable resource used to provide water for industrial, household, and agricultural uses (Liu et al. 2015). Most of the world's irrigated agriculture relies on groundwater resources (Arslan 2017; Perrone 2020). According to Yu et al. (2018), human health, socioeconomic well-being, and global food and nutritional security are directly correlated with soil viability and quality (Kopittke et al. 2019). Maximizing the use of natural resources for agricultural production is crucial as Egypt's population expands and there is a pressing need for food.

One of the essential goals of the national strategy to fulfill the enormous growth in the population's need for food is the horizontal expansion of agricultural land in the desert area. One of the most crucial regions for the horizontal expansion of agricultural land is the Western Desert. It has a lot of potential for agricultural growth and has numerous major oases (depressions), including El-Dakhla, El-Kharga, El-Bahariya, Siwa, and El-Farafra. Oases have been there for millennia, supporting human populations, trading routes, and agriculture. The Western Desert is about two-thirds of the country's area, which stretches from the Libyan border (25° E) to the Nile in the east (31° E), as well as from the Mediterranean coast interior (34° N) to the border with Sudan at latitude 22° N. The Nubian Sandstone Aquifer System (NSAS), the largest subsurface water reservoir known in the entire desert, generates isolated oases within an area of high aridity. To establish development priorities, it was required to research the land resources in those new locations and comprehend their spatial characteristics. For feasibility studies, design for land development projects, agricultural production, land users, planners, and various engineering works, it is crucial to assess the characteristics of the land and how it responds to agricultural service operations. Additionally, it is essential to grasp the benefits of using soil effectively for particular goals.

In El-Kharga and El-Farafra oases (Darwish et al. 2006; Wahba et al. 2007; El Bastawesy and Ali 2013; Kawy and El-Magd 2013; Kawy and Darwish 2014), the soils were classified, mapped, and assessed for their suitability and productivity for particular crops utilizing remote sensing and Geographic Information System (GIS) techniques. Typic Haplargids, Typic Torripasamments, Typic Torriorthents, Typic Haplotorrerts, and Vertic Torriorthents are the most prevalent soil classifications in the Oases, along with Salic Natrargids, Typic Natrargids, Sodic Haplosalids, and Sodic Haplocalcids. The investigations revealed that the most of oases soils are suitable for growing sugar beet, wheat, cotton, sunflower, maize, soya bean, potato, watermelon, olive, alfalfa, peach, and citrus in high, moderate, and marginal quantities. However, the soils of the Dakhla oasis have some characteristics that make them less conducive to agricultural cultivation, including high sodium saturation, soil salinity, high lime concentration, and soil depth. The integration of remote sensing and GIS is also beneficial for the development of sustainable agriculture. Several soil maps can provide an overview for decision-makers and individuals concerned about increasing agricultural growth in both oases.

The use of groundwater for irrigation is widespread in areas that suffer from water scarcity, especially in the regions trying to fill the food gap in areas that suffer from overpopulation. Due to the shortage of freshwater supplies in deserts, irrigation in arid and semiarid areas frequently uses groundwater. Moreover, it is not possible to reuse that water in those areas despite the misuse through surface irrigation. Groundwater is increasingly being used for irrigation in these places because wastewater treatment cannot keep up with the demand for food in those far-flung areas and the rise of urban areas (Running et al. 2019; Marvel et al. 2019).

Several social and environmental goals, such as boosting production or profits and reducing wastewater discharge to the environment, are achieved using groundwater for irrigation. In contrast, wastewater is thought to be a source of dangerous pathogens that contaminate surface and groundwater (Singh et al. 2004; Chen et al. 2005; Hamilton et al. 2007). Pure, wholesome, and clean water can be found in groundwater; contrarily, wastewater is full of contaminants, including viruses and HM, that are harmful to human, animal health, and the environment (Qadir et al. 2007). The accumulation of HM in soils is considerably facilitated by wastewater irrigation (Singh et al. 2004; Mapanda et al. 2005). The detrimental effects of HM deposition in soils affect crop output and quality as well as the atmosphere's and water's overall quality (Kabata-Pendias and Mukherjee 2007; Srinivasan and Reddy 2009). Because of their toxicity and endurance in the ecosystem, HM soil contamination is a severe concern (Micó et al. 2006; Facchinelli et al. 2001).

The study area's long-term and ongoing usage of a particular water source led to the deposition of numerous metals and impacted the pH and EC of the surface soils (AbdelRahman et al. 2019; Carrière et al. 2020; Ganiyu et al. 2020). Surface samples from different parts of the landscape were taken for this study to evaluate the availability of HM and micronutrients as a result of their long-term deposition. This is crucial to accomplishing sustainable groundwater irrigation goals and reducing the environmental harm caused by HM.

The science of sustainable groundwater irrigation continues to have a large gap regarding the long-term buildup of bioavailable forms of HM in soils (Bhuiyan et al. 2021; Senthilkumar et al. 2021; Kayode et al. 2022). Most individuals are unaware of how these chemicals behave in the environment and their potential risks to human health.

In the current study, we assess the impacts of irrigation with groundwater effluents on the characteristics of the soil. To attain sustainable groundwater irrigation goals, it is also necessary to produce spatial distribution maps that outline HM deposition in agroecosystems. The study's specific goals were to: (i) evaluate the effects of long-term irrigation with groundwater effluents on soil properties and accumulation of total and available forms of Al, As, B, Ba, Cd, Cr, Co, Cu, Fe, Mn, Ni, Pb, Sr, and Zn in soil and groundwater; (ii) use a GIS to create spatial distribution maps of those HM and micronutrients; and (iii) identify locations where soils have been contaminated with HM across the landscape.

Materials and methods

Study area

El-Kharga oasis

The largest oasis in the Western Desert of Egypt is El-Kharga. It is a large depression about 200 km long from north to south and 20–80 km wide in an east–west direction, covering 68,223 km2 and lying around 645 km SW of Cairo (Fig. 1).

Fig. 1
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El-Kharga oasis and its Digital Elevation Model

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Climate of El-Kharga oasis

According to EL-Kharga's climatological statistics, the mean annual temperature is 25–42 °C, with a significant variance between summer and winter temperatures. The temperature varies between 7.52 and 25.17 °C in the winter and between 22.69 and 41.21 °C in the summer. The lowest wind speeds at EL-Kharga were 7.87 km/h in January, and the highest speeds were 12.54 km/h in June. The yearly mean surface wind speed was 10.51 km/h. El-Kharga's predominant winds come from the north and northwest. The depression is affected negatively by the wind-driven sand flow. The average relative humidity of El-Kharga Oasis is 35.26% per year, with monthly mean values of 24.97% in June and 49.79% in December. Climate data indicate that the area's climate is particularly arid because dryness predominates for most of the year, and there are no wet seasons.

Gameh et al. (2017) stated that the study area’s climate is classified as having a hyperthermic temperature regime and a Torric moisture regime by the Soil Survey Staff (1999).

Landform and soils

The depression known as the El-Kharga oasis (Fig. 1) is filled with marine shale deposits and is covered in sheets of sand. Soil qualities changed dramatically after 10 years of cultivation (Gameh et al. 2017, 2018). The late Tertiary and early Quaternary geological periods, which were known for their humid climates, are thought to have produced the majority of the region's soils. The most prominent parent materials that have been affected by the climatic circumstances during these times are; the former terraces' alluvial sediments, The deposits of clay shale, The limestone rocks from the Eocene, Miocene, and Cretaceous eras, and the sandstone known as the Nubian formation (El-Barkouky 1979). The soils of the El-Kharga Oasis area are either deep clay or deep sand; the former represents old lacustrine deposits that were formed during the old geological wet periods in El-Kharga and Baris, while the latter refers to soils associated with the Nubian sandstone. Textural changes in the soil and the presence of sand and clay materials may indicate that depressions were formed under fluviatile Aeolian conditions (Gameh et al. 2017).

El-Farafra oasis

El-Farafra oasis is one of the promising regions for agricultural horizontal expansion in New Valley Governorate. It is approximately 650 km southwest of Cairo, in the Western Desert, as a depression known as El-Farafra oasis, which has an area of more than 10,000 km2 (Fig. 2). It had an asymmetrical triangle shape, with the north as its apex and the south as its increasing breadth.

Fig. 2
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El-Farafra oasis and its digital elevation model

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El-Farafra depression (Fig. 2) is an irregularly shaped, semi-closed basin that is bordered by escarpments on the north, east, and west sides. The plateau that provides the northern escarpment for the Dakhla and Abu Minqar Oases gradually climbs southward from the valley floor.

The slope gradient, according to the Digital Elevation Modal (DEM) analysis, ranged from 0 to 81%, indicating a flat to extremely steep slope gradient (FAO 2006). The aspect map shows that slopes facing north (north, northeast, and northwest) and south (south, southeast, and southwest) predominated in the study region.

Climate of El-Farafra oasis

The minimum temperature is 4.9 °C in January, and the highest is 38.5 °C in July, according to meteorological data obtained from El-Farafra station (latitude: 27°03′30" N: longitude: 27°59′21" E, elevation: 28.3 m) on average over 15 years from 2005 to 2020. The average annual temperature is 22.6 °C, and there is 21.4 mm of precipitation overall. Potential evapotranspiration (PET) has a mean annual value of 3.5 mm day−1. The yearly mean wind speed is 10.4 km/h−1, and the annual mean relative humidity is 39.8% on average. The region is hyper-arid, with an aridity index of less than 0.01 (Abuzaid et al. 2021). According to Soil Survey Staff (2014), the soil moisture regime is Torric while the soil temperature regime is hyperthermic (Mohamed and Omran 2019).

Landform and soils

The majority of the landform units are located on depressions, mudflats, outwash plains, foot slopes, and playa landforms. Most of the soils in these landforms are usually shallow (less than 0.5 m deep) (less than 0.5 m deep). Lithic Torrifluvents, Lithic Torriorthents, and Lithic Torripsamments are the names of these shallow soils. However, Vertic Torrifluvents and Typic Torrifluvents soils make up the majority of deep soils (between 1.5 and 1.7 m), which are used for "ancient" cultivation. Particularly in the soils of the Typic Haplocalcids, there is a relatively high concentration of calcium carbonate. This suggests that these soils' calcic layers have the potential to form a subsurface hardpan, which impedes the quick emergence of waterlogging problems. Furthermore, saline soils (Typic Haplosalids) are common in a variety of farmed fields (El Bastawesy and Ali 2013).

Land use/land cover (LULC)

Based on the visual interpretation of satellite images and land surveys, Three LULC units make up the majority of the area: bare land, vegetation (natural and farmed), and barren wet sabkha. The area occupied by these classifications was 1223.30, 220.84, and 1.52 km2, or 84.62, 15.28, and 0.10%, respectively, of the total area. Around the sabkha, there were sporadic patches of natural vegetation that were covered in halophytic plants (Chenopodiaceae). Field crops, orchards, and vegetable crops are all grown on croplands (Abuzaid et al. 2021). Given that low and very low vegetation quality classes made up about 97% of the total area, the vegetation condition in the study area would be a significant driver for land degradation. On the one hand, the bare ground made up around 85% of the entire area. On the other hand, annual crops (barely clover, wheat, maize, broad bean, sorghum, and groundnuts) make up 54% of the total cultivated area, while field crops (wheat, barely clover, wide bean, maize, sorghum, and groundnuts) account for 69% of the total cultivated area. Orchards (19%), mango, date palm, guava, and vegetable crops (13%), including potato, tomato, onion, and arugula, made up the majority of the remaining cultivated land. Since the soils are bare during the yearly field crops, the little plant cover they provide accelerates soil erosion. (Kosmas et al. 1999).

Soil and water analyses and land evaluations methods

All samples were analyzed using ICPMS-RQ at NARSS’ laboratory. The source of the threshold limits you used for assessing HM in soil and water according to WHO (1996).

Land capability was produced using the United State Soil conservation service (1958; 1959; 1963; 1992). Land suitability was followed the procedures of FAO (1976; 1985; 2007) as generated in the work of AbdelRahman et al. (2016). While soil fertility was assessed as produced in the work of AbdelRahman et al. (2021). Soil quality was assessed as recommended in the work of AbdelRahman and Tahoun (2019).

Spatial model

The spatial model (Fig. 3) was used to load the different layers of soil and water analysis with LULC, and the separation between deep wells and shallow wells to determine the source of pollution.

Fig. 3
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The spatial Model flowchart to determine sources of high contamination areas

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Results

The regions are consisting of five major LULC classes i.e., built-up area, sand sheets and dunes bare land, vegetation (natural and farmed), and barren wet and dry sabkhas. Based on the cultivated area and bare land, HM concentrations, soil characteristics, and microelement concentrations are distributed spatially. Figures 4 and 5 represent the geographical location of the sections with their physical boundaries.

Fig. 4
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Soil characteristics of El-Kharga oasis

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Fig. 5
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Soil characteristics of El-Farafra oasis

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Through visual interpretation of satellite images and land surveys, desertification and land degradation have caused chaos in El-Kharga Oasis, where 40 percent of the cultivated area has become barren in recent years. The deterioration caused by human activity complements the continuous tillage and monoculture, and the overexploitation of land and water resources helps to accelerate and increase wind and water erosion processes on the remaining 60% of the cultivated land. If this land is left untreated, it may suffer irreversible loss of soil organic matter (OM) as well as degradation of agroecosystems and their services. Farmers in El-Kharga Oasis agroecosystem face two main challenges: soil salinity and wind erosion.

The geospatial distribution of soil properties is presented in Figs. 4 and 5. The pH of the surface soil was neutral to alkaline in El-Kharga while found to be alkaline in the entire region of Farafra.

Soil salinity: In the hyper-arid El-Kharga oasis, groundwater from the Nubian sandstone aquifer and the carbonate aquifer is the only source of water. The salinity of the water ranges from low (150 ppm) to moderate (about 2000 ppm). The oases' agriculture follows the Egyptian agricultural pattern of summer and winter crops. The main orchard trees are date palms (Phoenix dactylifera L.) and olives (Olea europaea L.), which provide the oasis with the majority of its income. As a result, agriculture and vegetation in these areas depend primarily on groundwater. Large patches of agricultural land have become increasingly saline as a result of overflowing wells and an ineffective drainage system, resulting in severe salt-affected soils and the formation of salt marshes. Eventually, the lands that have been impacted are abandoned.

From the meteorological data, the wind flow velocity varies from season to season. It is at its low in August and reaches a peak from March to May. High wind speeds often cause sand storms, erosion, deposition, and dune migration, encroaching and threatening the oasis agroecosystems. High wind speed also directly impacts crop productivity by plucking and hindering pollination.

Studies on determining and controlling soil salinity indicate an increase in the concentration of salts in some areas of the study area, as shown in Fig. 4. Therefore, modern irrigation methods must be used to maintain soil productivity and mitigate the negative effects of salinity. Geomatics technologies can be efficiently used in this regard to monitoring soil salinity (Ismael 2020).

Analysis of irrigation water samples for HM revealed that the oases' water supplies are deemed safe for use in irrigation. The surface layer's buildup of high concentrations was greater than the maximum permissible soil concentrations. The high concentration was found to be in the parts adjacent to the built-up areas.

From the field study for collecting water samples, it was observed that in many cases, where deep groundwater is not available, shallow groundwater is the only source of irrigation. In some cases, deep and shallow groundwater can be used for irrigation. In many parts of El-Kharga Oasis, shallow groundwater is of poor quality as is evident from Fig. 6. Some sites contain enough salts to affect the extreme physical and chemical qualities of the soil, making the growth of crops difficult. Drilling deep wells and the energy needed to draw groundwater are both very expensive. Therefore, the shallow aquifer in El-Kharga Oasis could be a suitable solution to this problem, as the costs of shallow well drilling and the energy required to extract groundwater are very low (Hasanien et al. 2010). From the questionnaire of farmers in the field, it was observed that most farmers drill hand-dug wells. This is in agreement with the results obtained previously (Ghoubachi and Baraka 2006; Gameh et al. 2017).

Fig. 6
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Water characteristics of El-Kharga oasis

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The water table has significantly decreased due to excessive groundwater usage for agricultural purposes over the past two decades, necessitating the construction of an early and efficient management strategy (Moghazy and Kaluarachchi 2020). Due to heavy use and overexploitation, El-Kharga Oasis' groundwater levels decreased from 60 to 80 m bsl (below surface level) in the northern half, and from 40 to 60 m bsl in the southern half between 1967 and 2007 (Mekkawi et al. 2017). In addition, between 2003 and 2013, the number of deep wells climbed to 350, and the reservoir water level dropped by more than 90 m (Department of water resources in El-Kharga, Personal Communication). In dry and semiarid climates, meeting crops' total water requirements to maintain optimum growth and productivity is difficult. As a result, it's critical to figure out how to maintain optimal agricultural production during water shortages. Researchers have been looking for new irrigation technology, methods, and strategies to improve water efficiency as a result of this difficulty (Hamdy et al. 2003). Furthermore, irrigation systems are essential for reducing water losses and raising agricultural output productivity to meet future food demand increases. The irrigation sector, on the other hand, must be revived to reach its full potential by applying creative management approaches and changing its control (Kawy and El-Magd 2013; Kawy and Darwish 2014; Saber et al. 2022).

During fieldwork, it was observed that farmers frequently lamented the lack of irrigation water, high salt content in the soil and irrigation water, inadequate agricultural drainage, and sand encroachment. Additionally, farmers' inexperience in dealing with issues related to soil degradation and their inefficient management of water and soil, such as their reliance on surface irrigation.

All irrigation waters were neutral pH values. In the meantime, minimum salinity levels were observed south of El-Farafra while they were observed north of El-Kharga. For all groundwater, the concentrations of HM were less than the permissible level for irrigation (Figs. 6 and 7). Moreover, the highest HM concentrations were observed for the cultivated areas that suffer from poor drainage and are attached to built-up areas. The increase in the HM concentration for these patches may be attributed to Sewage leakage into shallow wells processes. This hypothesis needs further study to confirm this, but it is noted that the increase in these concentrations is only found in surface wells.

Fig. 7
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Water characteristics of El-Farafra oasis

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El-Farafra and El-Kharga Oases are among the natural depressions in the western desert of Egypt. Their lands conferred indications of promising agricultural expansion under hot arid circumstances. Their landforms include: depression floor, Peniplain, Chalky plain, Sand sheets, and Playa. Their soils are as follows: Gypsisalids; Calcisalids; Haplosalids; Haplogypsids; Calcigypsisalids; Torryluvants; Quartzipsamment; Torripsamment; Torriorthents; Aquisalids; and Gypsiargids. In the majority of the examined soil samples, gypsum and calcium carbonate accumulations were discovered in salinity-related conditions. In the majority of depressions, there are drainage issues and groundwater issues. The difficulty lies in understanding the issues and developing a proper management system for soil and water.

To identify the existing landforms, geological maps of El-Farafra oasis with the DEM were used. Fieldwork verified the presence of these units and described them. Locations of studied different soil profiles were preliminarily estimated to characterize the soils which occupy these units' surfaces. The geomorphologic lineaments exhibited in the studied region are the elevated plateau, El-Farafra oasis depression, and the foothill slopes. The latter includes local marshes, ridges, lacustrine deposits, sand dunes, crescentic, sand sheets, and hills. These results are in solidarity with the previous description of the region in previous studies (El-Shazly 1976; UNDP/UNESCO 2001; El Bastawesy and Ali 2013; El-Hamdi et al. 2018). The depression floor landform provides the best unit for development plans in terms of its soils.

The soil of chalky plain: These eroded remnants of the chalk, which come in a variety of sizes and shapes, can be found on El-Farafra depression floor. This depression's floor is an exposed chalky plain, which spreads across a considerable area close to the El-Gunna plateau, Ain Hinnis Bir Bidni, and north Ain El-Maqfi. The surface of the land is nearly level, the examined soils are poorly drained, and the texture of the soils varies from sand loamy to loamy sand. The percentages of sand, clay, and silt Fractions range from 25 to 59%, 5 to 13%, and 12 to 29%, respectively. The content of calcium carbonate ranged from 19 to 63%, with a tendency to increase as soil profile depth increases. OM was low and varied between 0.1 and 0.4%. pH varied from (8.1 to 8.4) neutral to slightly alkaline. EC values indicate strongly to very extremely saline soil.

The soil of sand sheets and sand dunes: These are among El-Farafra oasis' most distinctive topographic features. Huge swaths of the El-Farafra depression are covered in patches of sand dunes and drifts that run parallel to the prevailing wind and longitudinally throughout the region. These sand dunes are typical of an open, somewhat flat desert that has almost no precipitation and is blown by a reasonably continuous, unidirectional wind that comes from an infinite supply of sand. The northern depression floor has some sand accumulations, particularly in Wadi Hemis and Wadi Maqfi. These are little sand dunes along the NNW-SSE direction along the Abu Monqar scarps in the southern portion of the oasis. The land surface is almost leveled. Soils are poorly drained, with a loamy sand texture. Sand fraction ranges from 84 to 93%, silt from 3 to 6%, and clay fraction from 7 to 9. Soil pH (8.1 to 8.3) is slightly alkaline. EC values indicate strongly to very extremely saline soil. The parent material is sandstone and weathering is physical rather than chemical. Calcium carbonate content ranges from 10 to 33%, while organic matter content is very low from 0.1 to 0.5%.

The soil of playa: They exist mostly at the outlet of the Wadis whose sediment is derived mainly from the surrounding plateau. Playas are characterized by smooth flat surfaces with a very gentle slope toward their edges. Therefore, they have convex shapes with an elevation ranging from 30–70 m asl (above sea level) and cracks on their surface, and brownish color with few shrubs and grasses, especially near their edges. The unit has soil texture in general loamy sand. The sand fraction ranges from 79 to 83%, silt from 3 to 5%, and clay fraction from 9 to 17%. Calcium carbonate content ranges from 3 to 19%, while organic matter content is very low from 0.1 to 0.3%. Soil has neutral to slightly alkaline as indicated by pH values which range from 7.7 to 8.3. The soils are slightly to extremely saline.

The soil of dry wadis: The Wadi is covered with alluvial material developed through weathering of parent rock structure and transported by floodwater to the lowlands. Soil texture is sandy clay loam to clay. CaCO3 content ranged from 7 to 14%, while OM is very low not exceeding 0.4%. Soil pH values (7.1 to 7.7) are neutral to slightly alkaline. EC values are highly saline to extremely saline.

Recognizing land forms helped in the understanding of the interrelations between physical, chemical, and morphological characteristics of soil attributes. Some physical and chemical characteristics of the soils were affected by their location on landforms. The differences in physical and chemical properties of the studied soils are reflecting the circumstances of the landforms. Different degrees of studied pedogenic features are tied to the relationship between the soil and the age of the landform. Most of the examined soil profiles are derived from the clayey and sandy members of El-Farafra formations, overlying hard calcareous beds, and in places on the basaltic rocks. The high CaCO3 content of some profiles is associated with calcareous parent material. The presence of groundwater and the problem of drainage is common in most of the depression. The challenge is to be aware of the problems and to design a proper and appropriate soil and water management system.

Water quality for irrigation purposes: The quality of water used for irrigation is an important factor for crop productivity and the effect on soil. The classification of the groundwater samples according to their EC values (FAO 1976, 1985). Results of such groundwater samples reveal that it is highly suitable for irrigation as shown in Figs. 5 and 7.

Soils that are represented geomorphological by Playa and Pediplain, have a landscape of flat with a nearly level sloping surface, moderate to deep (80–140 cm), calcareous to moderately calcareous with EC values ranging from non to saline, and organic matter content is low.

While Pediplain interferes with sand sheets units are characterized by the landscape, generally flat to gently undulating with a flat to gently sloping surface. Deep profiles with an effective soil depth of 100–150 cm, non-calcareous to strongly calcareous, and low values of EC and organic matter.

Land capability, land suitability, soil fertility, and soil quality were assessed as shown in Tables 1 and 2 and Figs. 8 and 9. The main limitations were soil salinity, drainage, soil texture, and soil depth. The most restricting chemical component that needs to be taken into account is soil salinity, which can be reduced by reclaiming these soils through leaching, especially because good irrigation water is readily available and management methods are being implemented that can lower the salinity.

Table 1 Land assessment of El-Kharga for LCC, LSC, SQ, and SF
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Table 2 Land assessment of El-Farafra for LCC, LSC, SQ, and SF
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Fig. 8
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Land capability classification (LCC), Land suitability classification (LSC), Soil fertility (SF), and Soil quality (SQ) of El-Kharga oasis

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Fig. 9
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Land capability classification (LCC), Land suitability classification (LSC), Soil fertility (SF), and Soil quality (SQ) of El-Farafra oasis

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The studied soils have two orders (S and N), and four classes (S2, S3, N1, and N2) were recognized in the studied soils. S2: soils have a moderate intensity of topography, texture, and a slight intensity of salinity and CaCO3. S3: soils suffer from the moderate intensity of profile depth, texture, topography, salinity, and alkalinity. N1: soils have severed intensity of depth, salinity, and texture. N2: areas are rocky land, shallow and very shallow soils, and extremely saline soils. These areas are permanently not suitable for agriculture.

After carrying out the necessary substantial land improvements, land utilization is applicable. Increased soil efficiency is needed in the study area to manage the severity of existing restrictions, including leveling of the gently undulating land in high and low areas, installing drip and sprinkler irrigation systems to save irrigation water and prevent the formation or rise of the groundwater table, removing salinity and reclaiming alkalinity, and adding organic fertilizers, green manures, and soil conditioners. The prospective capability will grow as a result of these advancements.

The main limiting factors were texture and salinity, which can be improved using good management practices such as salt leaching, use of organic matter amendments, construction of a good drainage system, and following good agriculture practices for crops. These improvements will develop the potential suitability.

Discussion

A shortage of irrigation water, excessive levels of salts in irrigation water and soil, poor agricultural drainage, and sand creeping are all obstacles to the Governorate's agricultural growth. In addition, illogical water and soil management, such as dependency on surface irrigation, haphazard well drilling, farmers' lack of expertise in dealing with soil degradation concerns, and ultimately, insufficient agricultural extension services, exacerbate the Governorate's agricultural situation (Gad et al. 2016; Gameh et al. 2018; Soliman 2020).

The soil in El-Farafra oasis was categorized as Typic Calcigypsids, Calcic Aquisalids, Gypsic Aquisalida, Calcic Aquisalida, Typic Torripsaments, and Typic Quartzipsamments based on its morphological description, climatic conditions, physical & chemical properties, depending on USDA Soil Taxonomy. The collected results show that the studied crops could be identified and grouped into the following classes based on their soil suitability: sunflower, melon, corn, and olives. These results are in agreement with the results obtained by Wahba et al. (2007) who arranged the crops as follows olives < peach < sunflower, melon, and corn for their soil suitability in Sahal Baraka at Farafra. However, the peach was found not suitable because of its physiological climatic requirements. It can be inferred that soil texture, drainage quality, and sodium saturation are the most influential soil criteria that affect the appropriateness categorization in the research region. It concluded that the Typic Haplogypsids showed the highest agricultural soil suitability for the selected analyzed crops with soil texture limitation. On the other hand, area limited of Haplo-soil is suitable for cultivation, while only one soil unit in Typic Haplogypsids is highly suitable for wheat, potato, sunflower, alfalfa, and citrus with soil texture as a limiting factor and the rest of this order are low suitable.

Due to physical and chemical soil factors such as soil texture, effective soil depth, and drainage situation, the majority of the agricultural region was divided into low suitable to nearly not suitable for studying crops. The most restricting chemical component that must be taken into account is soil salinity, which can be reduced by reclaiming these soils through leaching, especially when good irrigation water is readily available and management strategies are being used to reduce the salinity. On the other hand, the soil maps created in this study for agricultural suitability can be useful in this management (Darwish et al. 2006; Wahba et al. 2007).

Through the field study and some analysis results obtained, salinization/alkalinity, waterlogging and wind erosion are the most effective drivers of land degradation in irrigated desert oases (Elbeih and Zaghloul 2021; Liu et al. 2020; King and Thomas 2014). Therefore, early and timely detection of vulnerability to land degradation is critical for sustainable agricultural production in these areas (Barman et al. 2021).

Wind erosion risk is a common phenomenon in dryland soils (Osman 2018), especially under hyper-arid climates (Fargette et al. 2019; Pei et al. 2015). Due to the high climate erosivity, poor vegetation cover, and extremely erodible soil portion, this has happened (Fenta et al. 2020; Borrelli et al. 2014). Climate erosivity is exacerbated by infrequent rainfall, high evapotranspiration rates, and strong wind speeds (Osman 2018). The separation of soil particles by wind impact is facilitated by low clay and organic matter concentration in soils (Guo et al. 2017). The lack of thick vegetation promotes the mass movement of soil (Sharma and Singh 2017). As a result, 88% of the land was at high risk for erosion, while 9% was at moderate risk. According to the Egyptian National Action Program to Combat Desertification (Desert Research Center 2005), wind erosion hazards in the western desert oases range from moderate to severe, with an average soil loss rate ranging from 4.5 to 66.9 Mg ha−1 year−1. These findings are in line with those reported in that program. In the examined area, increasing plant cover appears to be the most effective method for reducing wind erosion (Abuzaid et al. 2021).

The present study's in-depth studies demonstrate that it provides background knowledge on the parameters affecting soil and groundwater quality as well as the factors that affect these parameters. This article can help water resource planners develop management strategies to protect the health of the local people. The findings of the HM measurements in the area indicate that one of the elements influencing the accumulation of HM is the pH of the soil. The pH minimum and maximum in the area range from 7.67 to 9.07. All of the samples are therefore fully immobile and in an alkaline environment. The study concludes that there are issues with soil degradation and contamination in the area due to the preponderance of human activities that have the potential to accumulate dangerous chemicals and HM that could have an adverse effect on the environment and human health.

Conclusion

With the availability of dry conditions in the region, it is necessary to carefully select the cultivated crops and their locations due to the prevailing dry climate, since the water source in these areas is not renewable. Except for the sand sheets unit, the high level of the water table in the lands representing the different soil units is a problem that necessitates drainage and periodic analyses of soil salinity. The study area is suitable (S2) and moderately suitable (S3) in some soils for a wide range of crops such as annual and semi-annual and perennial crops. The results presented in the study show an accumulation of certain elements. Despite the accumulations of these elements are within safe limits for human consumption. Salinity, lime content, sodicity, and soil depth are the main limiting elements. The region is distinguished by good water quality, making it a priority in attempts to expand agriculture.

Recommendations

By implementing these soil management techniques, the land's capacity can be increased.

  • Use modified surface irrigation to leach salt, and grow crops that can withstand salt. No deep plowing is allowed due to the underlying salts.

  • Increase soil permeability by occasionally adding sand to the soil. Using organic fertilizer to increase nutrient availability, CEC, and permeability using contemporary irrigation techniques, reducing the watering times to prevent the formation of salt crust on the soil surface.

  • To enhance the physical qualities of sandy soils or to increase the permeability of heavy clay soils, non-saline dredging clay or sand materials are applied.

  • Accurate fertilization management also improves soil fertility.