Water holding properties and soil water types in fine textured Vertisol soils of Thrace region in Turkey

The study was carried out on 16 selected model soil profiles, located on lands covered with soils exhibiting vertic properties in Thrace Region of Turkey. Different horizons and/or sub-horizons of 16 characteristic soil profiles were evaluated in field or laboratory conditions in terms of water holding capacity and water types properties. Total of 105 soil samples were analyzed for routine physical characteristics. Soil water holding capacity was determined applying negative potentials (Ψ) of -0.33 bar, -15.5 bar and -31.5 bar (pF 2.54; 4.2 and 4.5), using a pressure-membrane extraction apparatus. In addition to gravitational, available, unavailable and hygroscopic soil water types, the soil samples were investigated also in terms of crystal-lattice water content. The highest amounts of the listed water types were determined in soils of Buyuk Mandira, Turkgeldi and Seymen containing the highest rates of smectite clay mineral. The mass percentage (Pw) rates of the mentioned water types of the investigated profies varied in the ranges of 29.1–66.3%, 10–2.15%, 22.0–32.4%, 6.0–9.0% and 5.6–8.6%, respectively. Though the mass percentages of enumerated water types in the soils of Osmanli and Yeni Mahalle, all owning high sand and lower clay content on the other hand, are between 28.9–40.6%, 6.1–15.5%, 7.4–16.8%, 2.4–4.8% and 1.7–4.4%, respectively.