Subsoil Compaction: The Intensity of Manifestation in Silty Clayey Calcic Pantofluvic Fluvisols of the Iğdır Region (Eastern Turkey)

The formation of compacted subsoil layer under the impact heavy machines is a global problem in soil science, soil physics, and agrotechnology because of the numerous and significant effects on the water, air, and thermal regimes of soils, their permeability for root systems of plants, etc. For recent calcareous alluvial soils (Calcic Fluvisols) in the foothill areas of eastern Turkey, this problem is particularly important, because these soils were formed as a result of floods of the Aras River. These soils represent unconsolidated homogeneous formations and have a compacted horizon at the depth of 30 to 65 cm, which was formed during dozens of years. Its density almost reaches critical values for loamy soils (>1.5 g/cm3), and its penetration resistance is also high: close to 5 MPa. The studied soils are heavy loamy throughout the profile with a predominance of silt fractions (1–3 and 4–6 µm), have a low content of soil organic matter (up to 0.5% in the plow layer). In the layers of 0–30 cm and 70–150 cm, soil density and penetration resistance are not high: 1.3 g/cm3 and 2 MPa, respectively. Such a fast and deeply penetrating soil compaction is associated with the initial loose state of the soils, their heavy texture, and low content of soil organic matter—the main protector from the subsoil compaction. To prevent further development of subsoil compaction, it is recommended to optimize agrogenic loads, stop using heavy machines under conditions of the high soil water content, and to apply organic fertilizers.