THE ROLE OF SOIL STRUCTURE ON THE PORE FUNCTIONALITY OF AN ULTISOL

A Typic Hapludult was used to evaluate the effect of soil structure and different bulk densities (reached after the destruction of macro aggregates) on functional characteristics of the pore system. The water retention curve, pore-size distribution, shrinkage curve and index were determined in disturbed and structured samples. To evaluate the effect of soil structure on the continuity of the pore system the air permeability at different matrix potentials was measured. From the relationship between the air permeability and air-filled porosity, pore continuity indexes were calculated. The destruction of the soil structure affects the function of its pores. The amount of air-filled pores increased with the reduction of the bulk density, however, the stability and continuity of these pores are low, which affects their functionality. Therefore, the formation of a stable and continuous pore system allows the soil to conduct air, even though they have a restrictive amount of air-filled pores. On the other hand, the soil structure plays a key role in pore stability during drying and, consequently, on the equilibrium between phases. Finally, the highest bulk density (1.1 Mg m(-3)) does not reach critical values (compaction). However, depending on the bulk density of the soil, it is possible to reach restrictive values of air capacity which affects the air transport in the soil, especially if the porous media is not continuous.