Utilizing soil quality index to assess soil susceptibility to desertification in the eastern Tigris area (al-Fatha-Udaim) /Iraq.

The aim of this study was to determine how vulnerable the land was to desertification along the eastern Tigris River by analyzing eight parameters directly connected to soil health. the study area is a part of the Salah Addin governorate and spans 5592.43 km2. The morphology of the study region was assessed using a soil quality index and maps generated using the ArcGIS v.10.5 software as well as Landsat image OLI from USGS combined with laboratory results and the MEDALUS model for evaluating soil quality indicators. The research concluded two distinct types of locations within the study region. About 43.78 %, with area equal to 2448.64 km2, falls under the first group, which is not particularly vulnerable to desertification. While the second group accounts for 56.22 % of the study area and encompasses 3143.79 km2, they are only somewhat vulnerable to desertification.


1-introduction
Desertification was described as land deterioration in arid, semi-arid, and dry sub-humid areas caused by a variety of factors, including climatic fluctuations and human activities at the Rio de Janeiro-Brazil Summit in 1992 (Abbas and Mahdi, 2019) [1].Desertification is one of the world's most serious environmental issues, resulting in land degradation and a lack of biological activity on land.This phenomenon occurs as a result of a decrease in flora and water in high-temperature locations, as well as an increase in salinity (Zwain et al., 2021) [2].The Salah Addin governorate is one of the most important parts of Iraq that produce Wheat and barley They are regarded as a major contributor to Iraq's food supply.
Land degradation is a very significant environmental issue that poses a major threat at several levels, including global, regional, and local dimensions [2].This phenomenon ultimately results in the reduction of soil fertility and subsequent decline in output.Approximately 33% of the Earth's arid regions have experienced a decline in their productive capacity exceeding 25%.Annually, the global The present study aimed to assess the environmental sensitivity of desertification and land degradation in the eastern Tigris represented from the Fatha to Alazim River in the south of Salah Al-Din Governorate / Iraq using the soil quality index that is a part of the Medulas model.

Study area:
The study area is located in the central region within the eastern part of Salah Al-Din Governorate, which in turn is located within the northern part of the central region of Iraq, specifically in the transitional region between the sedimentary plain, the island region, and the undulating semimountainous region, as shown in the figure (1).The study area is located between longitudes (43° 30`E and 44° 30`E) and latitudes (34° 03`N and 35° 00`N) as it is bordered by Tuz district and Diyala governorate from the east.The north side is bounded by the Kirkuk governorate as well as the Baiji district.from the west bounded with Tigris which extended from Baiji to Balad.'Figure 2' Different elements are used to assess soil quality indexes.
Soil data were obtained through field investigations after demining 28 Pedon station figure (3), digging holes to a depth of 35 cm, then taking samples from them and transporting them inside plastic containers to the laboratory, and then conducting laboratory tests to obtain data on the soil (physical and chemical), namely (texture, organic matter, pH, electrical conductivity, lime, gypsum, drainage and bulk density).Slope-gradient regression analysis based on demographic information from a satellite that measures digital elevation.The approach uses an average indicator value between 1 and 2 to determine categorization.Where T: texture, OM: Organic Mater, D: Drainage, BD: Bulk Density, S:Slope gradient, EC: Electrical Conductivity.According to the classifications indicated in Table (2), the categorization illustrates the assigned indices for distinct categories of each of the parameters.
Table 2. Structure of range and weight index soil quality indicator [14].
This clear difference in soil separator distribution and textures in the pedons and surface soils of the study area is due to environmental conditions and land use, which affected sedimentation and erosion processes at each site.Parent material and carrier factor effects.
Texture is the most constant property, making it a key element in soil categorization systems.

Bulk Density:
The results shows that bulk density values in the research region vary.Most pedons had higher bulk density and sand values.
Soil bulk density at the examined locations ranged from 1.32 to 1.69 mega g.m -3 as represented in figure (4).Some pedons have high lime and gypsum contents, which may explain this phenomenon.Calcium carbonate and gypsum fill soil pores and gaps.The high specific gravity of sandy soil grains is largely due to basic minerals.This supports 1982 Sopher and Baird research [15].

Electrical conductivity:
The measured EC values for the top layer varied from 0.61 to The low-salt type (S2), with a conductivity range of 4-8 dS/m, covered 582.39 km 2 , or 10.41% of the total area.The soil's aptitude for agriculture has led to its exploitation by irrigation and plowing, which has caused the decline.Capillary heat helps salinize and remove salts.The cyclical process of soil wetting and drying, irrigation, and the arid climate allow salts to rise by capillary action.

Organic Matter:
The results show that soil organic matter concentration varies between research regions.In particular, the upper surface layer had the largest organic matter concentration, 2.35g/kg, whereas the bottom level had 0.09g/kg.All research locations show a similar pattern of soil organic matter decreasing with depth.According to Awad (1986) [9].
The top layer has a higher concentration of organic matter from bacteria and roots than lower depths, reducing organic matter.The weak vegetation cover and dry climate of the study area likely cause the soil to lose organic matter through oxidation due to a lack of rainfall and high temperatures.

lime (CaCo3):
the results illustrate the various calcium carbonate contents found in the research pedons.Pedon P6 has the greatest concentration (296 g kg-1), and the lowest value was (49) in p11.It slides up and down together with the rest of the depths and the Pedon.As a result, we discover that, across the board, calcium carbonate levels and its distribution within the soil Pedon decline with depth.Since calcium carbonate salts are already among the least soluble salts, this is to be expected.This agrees with findings from other research such as (Herrero and Porta, 1987) and (Al-Janabi, 2010) [17] [18].The types found in the study area, the area occupied by each type, and its percentage are shown below table (3) &figure (6).[19].In a broad sense, it is seen that the soil within the designated research region has a notable abundance of gypsum, therefore classifying it as a gypsum soil table (4) as shown in figure (7).Furthermore, it is worth noting that this soil type displays irregularities in both its vertical and horizontal distribution.Vertical increases in gypsum content have been noted, mostly attributed to the presence of gypsum rocks in the original material.Additionally, the upward movement of water in the top layer facilitates the leaching of gypsum, resulting in its subsequent accumulation and deposition in the lower strata.Hence, it may be inferred that these soils are more susceptible to deterioration and desertification due to their chemical composition, parent material characteristics, and the adverse climatic conditions they experience.types identified.The high-quality soil covered an area of 2448.64 hectares, accounting for 43.78% of the total study area.In contrast, the moderate-quality soil occupied an area of 3143.79 km 2 , representing 56.22% of the total study area.These results are summarized in Table .
The variation in the types of index values can be attributed to the differences in the weighted index values assigned to the various soil characteristics under study.The index value observed divided into two zones is primarily a result of the elevated levels of gypsum, which negatively impacts the index value.Specifically, the weighted index values assigned to gypsum range between 1.5 and 2, with more than half of the organic matter samples receiving a weighted index value of 1.5.
Regarding the tissue samples, the weighted index (1) and the stability of the weighted index value for water drainage were found to be favorable, thereby positively influencing the value of the SQI.

4
determinant of biomass.The SQI in the study area that related in soil sensitivity Which was relied upon in the work methodology is eight parameters figure(2).

10 'Figure 4 '
Bulk Density distribution through the selected region.'Figure 5' Electrical conductivity.' Figure 6' lime.11 3.2 soil quality index Indicators, (T, BD, EC, caco3, S, D, Caso4, OM), the slope gradient was semi stable figure (8) so that it toked stable weight as well as the drainage were also stable because the soil of study area is well drained.Results revealed that the SQI values ranged from 1.25 to 1.43 across all samples within the study area.These values indicated varying degrees of soil quality, with both high and moderate-quality

Table ( 1) Range and weight index structure of the MEDALUS soil quality index [9] [10] [11] [12].
Table (1) explains the elements and signs that contribute to this level of susceptibility and sensitivity.
(5)]rved in the deeper layer were found to be highly similar to those of the surface layer, exhibiting a marginal rise.The classification of soil salinity in Iraq[16], as outlined in the 1982 classification of soils affected by salinity, categorizes soil salinity depending on the rate of salt concentration.This categorization is presented in the table The variability of soil salinity across different beds has been observed, with salinity levels either increasing or decreasing with depth.As represented in the figure(5)The reported salinity (S1) was low.These values were recorded across 5010.11km 2 at 89.58%.This shows that the research region's soil is low in salt.Any amount of precipitation helps salts leach and percolate into the ground.This occurs predominantly in well-drained soils and is regulated by the groundwater table distance.
6.98 dS/m, whereas for the subsurface layer, the range was 0.95 to 7.01 dS/m.The EC values

Table ( 3) Varieties and areas of calcium Carbonate and percentage of soil in the study area 3
.1.6gypsum:Theresultsdemonstrate that the Pedon P4 had the maximum gypsum concentration, measuring 735 g.kg -1 in the subsurface layer.Conversely, the top layer at p15 displayed the lowest gypsum value, measuring 86 g.kg -1 .This phenomenon can be attributed to the higher solubility of calcium sulfate salts compared to calcium carbonate salts, resulting in a greater probability of their rising in subterranean horizons as opposed to surface horizons.This conclusion aligns with the research conducted byBarazanji et al. (1980)

Table ( 4
) Varieties and areas of gypsum and percentage of soil in the study area

Table ( 5
) SQI classes for the studied region 'Figure9' Soil quality class map for the study area