## 1 Introduction  
Soil erosion has environmental and socioeconomic significances due to loss of a natural resource. Many arid soils are characterized by bare surfaces that are exposed directly to the erosive forces. The erosion depends on the physicochemical properties of the soil that are reflected in the soil aggregation [1]. Thus, the soil aggregation provides information on soil fertility and soil stability to erosion forces [1; 2; 3; 4]. Soil aggregation refers to the adhesion of two or more soil particles by organic and inorganic cementing materials [5; 6]. The size and stability of soil aggregates depend on the type and content of the cementing materials [1]. One of the most important elements that bonds between soil particles and forms aggregates is the clay minerals. The clays are characterized by a high specific surface area (SSA) and high cation-exchange capacity (CEC), which generates strong forces of cohesion [7]. Studies have shown that there is a connection between the clay content and the aggregate size and stability [8; 9; 10; 11]. Aggregate diameters can range between less than 2 \(\upmu\)m to a few millimeters [1; 12] with specific aggregate size distribution in a soil sample. It is generally assumed that soils with a greater amount of large aggregates will be more fertile and have stronger resistance against erosion [1]. One of the most popular indices for determination of aggregate size distribution in the soil is the mean weight diameter (MWD), which represents the relative part of each size segment of the aggregates in the soil [13]. This index can also be a representative and convenient measure of the comparison between different soils. Another common index is the division of the aggregates into different groups of sizes with a gross distribution into macro aggregates (>250 \(\upmu\)m) and micro aggregates (<250 \(\upmu\)m) based on the hierarchy concept of [PERSON] [12]. It was found that macroaggregates were composed of much higher organic matter compared with microaggregates [14]. In wind erosion, the soil erodibility is mostly associated with the aggregates that are smaller than 840 \(\upmu\)m [15]. Erodible fraction (EF) index presents a quantitative value that expresses the weight of the small aggregates (<840 \(\upmu\)m) relatively to the total weight of the soil sample. The dry aggregate stability (DAS) also examines the stability of the soil to wind erosion which calculates the proportion between the weight of the small aggregates (<840 \(\upmu\)m) and the weight of the large aggregates (>840 \(\upmu\)m) [15]. These indices and the soil stability are affected by the cementing materials such as organic matter, clay content and carbonates [16]. Several studies have showed a clear relationship between aggregate and the mean weight diameter (MWD) value and soil stability to wind erosion [17]. [PERSON] at el. [18] showed negative correlation between MWD and dust emission expressed by particulate matter that is <10 \(\upmu\)m in diameter (PM10) in agricultural soils. Dust-PM10 emissions can be minimized by reducing soil tillage that prevents breakage of aggregates, thus reducing the soil erosion by wind [19]. In soils with small aggregates, the horizontal sediment fluxes are higher and thus so is the soil erosion [20]. Dust emission is enabled under a critical value of wind (shear) velocity (u*) at which the aerodynamic force is enough to dislodge particles from the surface [21]. The dust entrainment from the soil is strongly connected with the saltation process. Saltation is initiated when the wind stress is sufficient to lift sand-sized particles (63-500 \(\upmu\)m) into the fluid stream. Lifted particles undergo ballistic trajectories to impact the surface. The resulting impacts can eject, or splash, new particles into the stream [22; 23]. [PERSON] [24] and [PERSON] et al.