Spatial Distribution of Some Soil Characteristics in the Fallujah and Karma Regions and Evaluation of Their Suitability for Agricultural Production

Soil is an important economic resource and an inexhaustible resource for all human activities throughout life. Agriculture is one of these activities, without which agriculture cannot thrive and fulfill its role properly to ensure high productivity [1]. Most soil studies have focused on the geographical distribution of soils and their spatial heterogeneity. Spatial variation of characteristics on the ground, as successful management of land suitability is based on optimal selection and appropriate strategy [2] and because this resource has its spatial distribution and is affected by its characteristics and properties, therefore it will be reflected in its performance according to suitability for different purposes, including agricultural purposes. Therefore, this suitability must be studied by identifying the important characteristics and properties of it and identifying the problems and obstacles it suffers from [3]. The suitability assessment is one of the objectives of land classification and its causes. Its objectives are to obtain the highest production while protecting the soil from degradation, and to determine the type of land use after determining its productive capacity for different uses by knowing the effect of climate factors and soil characteristics on the basis of which crops can be divided into soils. The causes of these problems are largely related to the improper use and exploitation of soil resources, which results in soil degradation and a reduction in its productive capacity. Consequently, soil evaluation is used to determine the efficiency, capability, and suitability of soils for different land uses, especially for agricultural and livestock production, through the application of various evaluation methods and classification systems [4]. The evaluation process is an important and sensitive function that expresses the requirements of crops and the characteristics of the soil and land [5]. The process of agricultural suitability requires many factors, the most important of which are climatic factors, in addition to the physical and chemical properties of the soil and fertility [6], While the role of humans is considered an influential and effective factor in the interconnected ecosystem that represents the relationship between (climate, soil, and plants) [7], and understanding the nature of preserving this relationship helps us preserve lands and meet future needs in a sustainable manner to improve production capacity at the lowest costs [8]. Also because agricultural activity is one of the largest and most extensive human activities, as it occupies large areas of arable land [9] the need has emerged at the present time to study and analyze the suitability of soils for agriculture and to state the problems and obstacles and the necessity of setting limits for them in order to meet current needs and preserve lands for future generations within the concept of sustainable development due to the increasing population growth [10]. Suitability is considered one of the main planning processes for the real and optimal use of land to achieve spatial stability [11]. For this purpose, this research was conducted to achieve the objectives, including describing and classifying the soils of the Fallujah and Karma regions, adopting the 2015 FAO global reference system, studying the spatial distribution of characteristics using geographic information systems, and evaluating the suitability of the region’s soils for agricultural purposes, adopting the SYS 1980 system.

The study area is located astronomically between latitudes $33.12^{\circ}$ N and $33.44^{\circ}$ N and longitudes $43.40^{\circ}$ E and $44.00^{\circ}$ E Spatially, it is located in western Iraq, surrounded to the north by Salah al-Din Governorate, to the northwest and west by Tharthar Lake, the Euphrates River, and Ramadi District, to the south by Al-Amiriya District, and to the east and southeast by Baghdad Governorate, as shown in Figure 1.

A Field Survey was conducted using the free method to investigate the impact of soil formation factors and processes and their repercussion on the formation and origin of the soils in the study area.

Several soil boreholes were drilled using augers at different locations within the boundaries of each district in the study area.

Three major soil subgroups were identified in the area, and one pedon was. Selected to represent each subgroup the Flu alluvium soil, desert alluvium soil and the developed gypsum subgroups, as shown in Figure 1.

Depending on the nature and type of agriculture exploitation, soil samples were taken from the surface horizon to a depth of 0−30 cm. Considered the effective depth of the root zone for most important agricultural crops.

The soil samples transported to the Laboratory were air-dried. Then ground and prepared for laboratory analysis.

Physical measurements. Particle size distribution of the soil samples was conducted using the suction method by pipet as described by Mohammed et al. [12].

The most important and effective soil formation factors in the study area are the parent material and topography. The parent material's influence is evident in the soil properties, as well as the influence of topography in terms of slope and its role in differential and anthropogenic sedimentation processes. The most important prevalent processes are gypsihcation (gypsum formation) and salinization processes. In addition to the calcination process, climatic conditions are a basic factor that determines the nature of the land’s production process and its suitability for agriculture [13]. The effect of climatic conditions is determined by the direct effect on soil temperature and moisture, as soils are affected by the factors of rain and temperature, as climate is considered a major influence. On the productivity of the main food crops [14]. The climate of the region is characterized by the climate of Iraq in general, as the nature of the climate in the region is characterized by extremism and great variation in temperatures, as it rises greatly in the summer at a monthly average of 45 ${ }^{\circ} \mathrm{C}$ in the month of July and decreases during the winter to reach 15 ${ }^{\circ} \mathrm{C}$ in the month of December. Due to the extremism in temperatures between the summer and winter months, which reaches more than 22 ${ }^{\circ} \mathrm{C}$, so the soil temperature is characterized within the Hyperthermic class, and dry moisture within the Aridic (Toric) class according to the United States Department of Agriculture (USDA) soil temperature and moisture classifications, and the region’s rainfall is characterized by being little and falling in the winter, with an annual average value ranging between (148.1−87 mm).

The soils in this group are symbolized by (3a/2-JC30), where the symbol JC refers to the symbol of the main soil unit in the symbol, meaning Calcareous Fluvisols [15]. These are sedimentary soils containing calcareous materials between 20−50 cm from the soil surface. The parent material for these soils is derived from river sediments. The number (30) represents the soil units associated with it and within the soil map unit, while the number (2) represents the medium texture class and number (3) represents the soft texture class, while the letter (a) represents the simple slope class flat to slightly wavy with a slope degree of 0.8%. This group is characterized by stratification patterns that reflect the history of irregular sedimentation processes.

This group corresponds to the newly formed Entisols soils in the modern American soil classification system and under the group Typic Torri fiavent. The soils of this group are distributed in the Saqlawiyah region (P10) and in the districts of (Al-Nasaf, Al-Bushjil, Al-Naimiyah and Al-Dafar) within the districts of (Al-Tawil, La’id, Al-Hitawin, Jamila, Al-Za’ana, Al-Shabni and Al-Musallamah) and are represented by the soil sections (P1, P2, P3, P4, P5). These soils are distributed on both sides of the Euphrates River basin and form an area estimated at 189 km$^2$ [16], as shown in Table 1.

The soils in this group are symbolized by (2/3a-Jc40). In the soil map unit, this symbol refers to the course, gravelly desert sedimentary soils, called Eutric Fluvisols. The number (40) indicates that the soil contains 40% rocky soils, while the number (2) represents the coarse texture, represented by sandy and sandy mixed textures. Number (3) refers to the medium texture such as sandy mixture, silty mixture, and clay mixture, and the letter (a) represents the degree of slope that is classified within the level (flat). The soils of this group are characterized by being undeveloped soils: they were formed by the action of ancient river sediments followed by a gravelly gypsum layer [17]. These soils are distributed within the districts of Al-Kaifa and towards the district of Al-Karma and up to the Al-Haswa area, and they are represented by the pedons (P6, P7, P8). This group forms an area estimated at an area estimated at 274 km$^2$, representing 12.7%, is represented by Figure 2. Table 2 shows a typical section of Bidun in the Al-Kaifa Distrac.

The soils in this group are symbolized by (Yy10-2ab), (Yy12-a), and (Yy13-a), and are represented by the pedons (P10, P11, P12). This group is represented by dry desert gypsic soils containing a gypsum horizon, corresponding to the American classification system for dry desert gypsies, typic gypsums. These soils extend from the city of Fallujah towards Al-Karma Island in the east and up to Al-Khalidiya Island in the west. These soils extend over flat to slightly undulating areas and their surface is covered with fine gravel that was formed after the withdrawal of the waters that covered the surface of Iraq and represents the remains of fossils [18]. These soils were affected by the floods of the Euphrates River in ancient times, and these soils are topped by a gypsum layer that sometimes reaches a thickness of more than a meter, and it is accompanied by other soils at a rate of up to 20,000. Table 3 shows a typical section of a pedun soil on the Al-Boushjel District [19].

Based on the proportions of the three classes of sand, silt, and clay shown in Table 4, this study found that the soil texture class was mapped onto the American soil texture triangle to extract the soil texture class. This class is important in soil management processes such as tillage, weeding, fertilization, and irrigation. The texture class indicates the softness and roughness of the soil. In addition to its importance in soil classification processes, the texture type is considered one of the fixed characteristics upon which classification is based and its relationship to engineering characteristics such as expansion and contraction. Table 4 shows the physical and chemical characteristics of the soils in the study area at a depth of 0–30 cm [20]. The names and types of soil texture in the study area are shown in Table 5. Figure 2 shows its location on the soil texture triangle the soils of the study area were divided into two groups: medium textured soils, most of which represent river basin areas, in addition to being affected by slow sedimentation processes: long time dimension, and coarse textured soils, which are often close to sedimentation sources and are affected by rapid differential sedimentation processes of short time dimension. Table 6 represents the distribution of texture types and their percentages, and Figure 3 shows the nature of that distribution [21].

Based on a field study of the region, it was possible to analyze the characteristics and properties of the soils in the region. The following describes and distributes these characteristics.

Soil salinity represents an important factor contributing to soil degradation, as it negatively affects the soil’s biological functions [22]. In addition, it reduces the soil's productive capacity because elevated salinity levels increase the electrical conductivity of the soil.

Soil salinity is one of the important chemical properties in the soil and is usually expressed by the amount of electrical conductivity and is measured in deciSiemens/m. The soil is classified as saline based on the American Salinity Classification (SOLAR) as the soils of the study area varied in the value of electrical conductivity by more than (4 deciSiemens/m) [23]. Based on that, the soils of the study area’s districts were classified as shown in Table 7, and the Figure 4 shows the nature of the spatial distribution of this characteristic.

Table 7 shows that the study area to cited with in(S0−S1) Class are Agriculturally exploited have low salinity, do not affect most plant, and often represent alluvial soils located within the river basin and river levee.

In region with moderate salinity, most vegetable crops are affected, as well as some groin crops, this effect is evident in the reduction of land Productivity by at least 30%.

The districts falling within salinity S3−S4 class characterized by low Productivity of vegetable crops and most grain crops and only some salt- tolerant tree shrubs grow there.

The high salinity is attributed to blocked drains and rising ground water level, which leads to salt acumination on the surface.

Calcium carbonate is a common salt found in most soils in arid and semi-arid regions. The source of carbonate in soil is the limestone parent material from which the soil originated, which was transported by river water, as well as by wind. Calcium carbonate affects soil properties, contributing to the filling of porosity between soil particles. In addition to its work on collecting soil materials, it also contributes to reducing the cation exchange capacity in the soil, and it also helps to raise the pH values in the soil and thus reduces the availability of trace elements in the soil and also contributes to the retention and precipitation of some other elements [24]. Its percentage in Iraqi soils generally ranges between (15%−35%). The soils of the study area are characterized by being very calcareous because the percentage of carbonates is more than (15%). Calcium carbonates are distributed in the districts of the study area, with a range of (20%−32.8%), as in Table 8 and Figure 5, it shows the nature of the geographical distribution of the calcium carbonate category in the study area.

These sulfate salts are among the salts that are widespread in the soils of arid and semi-arid regions, including the districts of the study area. Gypsum is either primary, resulting from the origin of gypsum, or secondary, which is deposited from irrigation water and groundwater [25]. The percentage of gypsum in the study area varies depending on the physiographic location [26]. Gypsum is distributed in the study area according to the following class, as shown in Table 9, and Figure 6 shows the distribution of gypsum in the study area.

Based on the characteristics and properties of the provinces' soils known in Table 10, and based on the 1980 SyS classification, and based on the following equation [27]:

where,

$Cs$ = capability suitable

$A$ = texture index

$B$ = lime index

$C$ = gypsum index

$D$ = salinity index

$E$ = drainage index

$F$ = ESP index

$G$ = depth index

$H$ = pedon development

$I$ = withering index

The standard multiplication method was adopted for the above attributes after taking their weighted value according to the work method. It was possible to obtain the results known in Table 10.

Based on the SYS 1980 designations for the suitability classes as shown in Table 11. According to Figure 7, it was possible to divide the districts of the study area into the following classes [28].

1. Class(S3): this class occupied 62.43% from study area and is considered moderately Suita for agricultural production, as the limitation are simple and can be improved to increase the lands productivity to second class.

2. Class(S4): this class occupied 3.80% from the study area and is considered few suitable for agricultural production as the limitation are moderate as salinity, high calcareous and gypsum content and low fertility.

3. Class (N): this class occupied 33.7% from the study area and is considered non suitable for agricultural production as the limitation are high as salinity Texture, high calcareous and gypsum content.

Natural processes, including climatic, topographical, and parent material factors, have significantly influenced the classification of the region's soils through the presence of gypsum and calcareous horizons. Geomorphological and pedogenic processes have also influenced the formation of sedimentary soils through the diversity of secondary geomorphological units, including river basins, river shoulders, river levees, point bars, and river crevasses.

The areas and types of soils varied according to their physical and chemical properties, and this is what was shown by their geographical distribution within the perspective of the land in the study area, and the equation (SYS 1980) succeeded in evaluating the suitability of the lands in the study area. After studying the results, it became clear that the study aims to identify the lands most suitable for agricultural production. After analyzing these results, it became clear that expanding the horizons of evaluation studies for land suitability by adopting evaluations and their preferences, and attention to aspects of soil management for the purpose of reducing its salinity by opening closed drains and attention to irrigation operations using modern methods such as sprinkler and drip irrigation. These recommendations are important as they provide a complete vision for decision makers to move towards integrated management of these lands and reach effective solutions that will develop and find solutions to the problems that the region's soils suffer from.