**3.3. Factor analysis**

The evaluation of soil degradation is difficult because of the diversity and complexity of soildegrading processes. Interrelations between the variables frequently obscure the evaluation of each soil-degrading process' contribution. Factor analysis is frequently used to reduce the number of variables in a dataset, and so we used factor analysis to identify the key variables of soil degradation in the study area.

All the studied soil properties namely EC, pH, P, K, SOM, CEC, B, Zn, Cu, Fe, Mn, Cd, sand, clay, silt, coarse material, hydraulic conductivity, soil erodibility (K) factor, crusting index, runoff, PAWC, soil loss, penetration resistance, and wheat yield were subjected to factor analysis (see **Table 7**).

*Topsoil:* The 24 variables were considered for the factor analysis of topsoils and grouped in nine factors accounting for 71.2% of the total variance (**Table 8**).

The variables clay, sand, and erodibility were loaded in Factor 1 and this factor was named as "erodibility factor". The "erodibility factor" accounted for 14.7% of the total variation. We found a negative correlation between clay content and soil erodibility. This was attributed to the effect of clay on soil aggregate strength, which decreases soil erodibility. Likewise, when we compared soil loss in clayey and sandy clay soils, clay soil was more resistant to erosion because of its stronger aggregates.


loss, SOM content, and concentrations of P, K, B, Zn, Mn, CM, and crusting index were noticeable among these variables. All these variables are known to control yield in wheat [22]. However, wheat yield interestingly showed low variation with a relatively normal distribution as indicated by moderate skewness and low kurtosis values. In contrast to subsoil, where most of the soil variables were slight to moderately skewed, the majority of the variables were highly skewed in topsoil. The variables Mn, P, K, B, Zn, and soil loss exhibited a considerably constant distribution in topsoil, as suggested by kurtosis values (**Table 6**). Therefore, this low variation

The P level was low (<10 mg kg−1) in 94% of the study area and was medium to high (>10 mg kg−1) in only 6% of the study area. By contrast, the K content was adequate in both soil depths in most of the study area. Combined with highly variable and skewed distribution of SOM, the low P content of the majority of soil indicated that P and N fertilizers

Microelement contents of the study soils were classified based on procedures [50]. Calculations showed that B and Zn contents were low due to parent material and that Cu, Mn, Fe, and Cd contents were adequate. Boron content was lower than 0.5 mg kg−1 in 85.5% of the cultivated areas and 82.9% of the grassland areas, and Zn was lower than 0.5 mg kg−1 in 99.7% of the entire study area. Both B and Zn are essential microelements in wheat production. This indicates that the use of B and Zn additive fertilizers is necessary. Also, the highly variable and skewed

The evaluation of soil degradation is difficult because of the diversity and complexity of soildegrading processes. Interrelations between the variables frequently obscure the evaluation of each soil-degrading process' contribution. Factor analysis is frequently used to reduce the number of variables in a dataset, and so we used factor analysis to identify the key variables

All the studied soil properties namely EC, pH, P, K, SOM, CEC, B, Zn, Cu, Fe, Mn, Cd, sand, clay, silt, coarse material, hydraulic conductivity, soil erodibility (K) factor, crusting index, runoff, PAWC, soil loss, penetration resistance, and wheat yield were subjected to factor

*Topsoil:* The 24 variables were considered for the factor analysis of topsoils and grouped in nine

The variables clay, sand, and erodibility were loaded in Factor 1 and this factor was named as "erodibility factor". The "erodibility factor" accounted for 14.7% of the total variation. We found a negative correlation between clay content and soil erodibility. This was attributed to the effect of clay on soil aggregate strength, which decreases soil erodibility. Likewise, when we compared soil loss in clayey and sandy clay soils, clay soil was more resistant to erosion

in wheat yield may be attributed to the application of fertilizers in the study area.

distribution of these elements should be considered in fertilizer application [22].

application should be site specific.

104 Land Degradation and Desertification - a Global Crisis

of soil degradation in the study area.

because of its stronger aggregates.

factors accounting for 71.2% of the total variance (**Table 8**).

**3.3. Factor analysis**

analysis (see **Table 7**).
