Relationships Between Soil Particles and Pores Size Distributions of Coarse Textured Soils

The aim of this study was to characterize the particles and pores size distributions of coarse textured soils and to relate them with the indicators for soil physical quality. Four sites in the region of Blagoevgrad, southwestern Bulgaria were selected. The dominant plants grown in the region are tobacco and vegetables on coarse textured Eutric Leptic Cambisols and Fluvisols. The analyzed soil physical properties were particles size distribution, soil water retention curves (SWRC), pore size distribution, soil aggregate size distribution and water stability of soil aggregates. The particles’ size distribution was approximated by the two-parameter equation of Rosin and Rammler (Eq. 1), and the pore size distribution was derived from the SWRC using the capillary rise equation of Young–Laplace. The SWRCs were approximated with the van Genuchten equation (Eq. 2) (van Genuchten, 1980). Several indicators of soil physical quality were also derived from the obtained experimental data. The studied soils have lower relative field capacity (0.43–0.53) than the optimal value and a high aeration capacity (23–29% volume of air-filled pores at matric potential pF1.7). A statistically significant relationship was found between the measures of particles size spread (β in Eq. 1) and of pores size distribution (n in Eq. 2) as well between W at pF2.5 (pores < 9 μm) and the coarseness of particles (α* in Eq. 1).