SD, standard deviation; CV, coefficient of variation; EC, electrical conductivity; SOM, soil organic matter; CEC, cation exchange capacity; CM, coarse material; HC, hydraulic conductivity; CI, crusting index; PAWC, plant-available water content; PR, penetration resistance.

**Table 6.** Descriptive statistics of some soil properties in topsoil (0–0.3 m) of study area (*n* = 142).

The soil textural components, coarse material, soil organic matter, and Cd were highly variable in topsoil, and P, B, hydraulic conductivity (Ks), and some micronutrients (e.g., boron) were highly varied in subsoil. On the other hand, wheat yield showed low variation with a relatively normal distribution as indicated by moderate skewness and low kurtosis values (**Table 6**). This was attributed to fertilizer applications for a long time. In contrast to subsoil, where most of the variables were slight to moderately skewed, the majority of the variables were highly skewed in topsoil, which may be attributed to the existence of many irregular slopes with erosion and/or depression localities. Extreme values are likely to occur at these localities. Soil 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 in wheat yield may be attributed to the application of fertilizers in the study area.

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 application should be site specific.

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