MODIFIED HAINES' FUNNEL: SOIL WATER RETENTION CURVES OF SOIL SAMPLES NEAR SATURATION

Water movement through the soil matrix is generally modeled using equations of Darcy, Darcy-Buckingham and Richards, which are based on the knowledge of some soil physical properties such as, soil pore size distribution and water retention characteristics. Soil water retention is determined by the soil water retention curve (SWRC) of the soil. The first objective of this study is to develop a simple apparatus by a modification of the Haines' funnel, to obtain detailed SWRC of near-saturation soil samples, samples in matric potentials (psi(m)) varying from 0 to -12 kPa (water column 120 cm). Soil aggregates of a Dystrophic Red Latosol (LVd) from Parana were investigated, with an average diameter between 1.6 and 5.7 cm, soil bulk density between 1.01 and 1.31 g cm(-3) respectively, and reconstituted sand samples, with a mean sand size of 0.106 mu m to 2.000 mm, with fractal fragmentation dimensions (D-f) varying from 2.5 to 3.0. A second objective was to analyze the soil pore size distribution of the soil samples. For this purpose the van Genuchten interpolation equation parameters were used to establish the water storage function (WSF) of the samples. In conclusion, an analysis of the WSFs showed that the soil aggregates had a more complex soil pore system; that the soil particle distribution of the sandy soil is directly related to their water retention properties; and finally, that bulk density did not significantly affect soil water retention of the soil aggregates.