Hydraulic properties of the diagnostic horizon of Latosols of a regional toposequence across the Brazilian Central Plateau

International audience; The Brazilian Central Plateau covers about 40% of the Cerrados Biome and represents 24% of the Brazilian territory. The Latosols that correspond to about 40 % of the surface area of the Central Plateau are characterized by a poor horizonation, a weak macrostructure and a strong development of the fine granular structure composed of sub-rounded microaggregates 50 to 300 µm in size. In this study, we analyzed the hydraulic properties of a set of Latosols varying according to their clay content and mineralogy with respect to their location along a regional topossequence across the Brazilian Central Plateau. Ten Latosols (L) were selected on the South American Surface (L1 to L4) and Velhas Surface (L5 to L10) and we studied the properties of their diagnostic horizon (Bw). We measured their bulk density and particle density, and the soil-water retention properties at 1, 6, 10, 33, 300, and 1500 kPa by using the centrifugation method. We also determined the saturated hydraulic conductivity in the field using the Guelph permeameter procedure. Results showed that the total pore volume (Vp) ranged from 0.460 to 0.819 cm3 g-1 and 58.2 % of the variance was explained for by the clay content. According to Balbino et al. (2002), Vp was divided into a volume of intra-microaggregates pores (Vintra) and inter-microaggregates pores (Vinter). Results showed that Vintra ranged from 0.090 to 0.234 cm3 g-1 and Vinter from 0.305 to 0.585 cm3 g-1. Results showed also that Vp explained a proportion of the variance of the water retained that decreased with the water potential. On the other hand, the clay content explained a proportion of that variance that increases when the water potential decreased. The great proportion of variance (90.7 %) explained for by the clay content alone at 1500 kPa showed that there is little variability that can be attributed to clay mineralogy variation. The saturated hydraulic conductivity (Ks) was related to an effective porosity (Φe) defined as the volume proportion of pore with equivalent diameter > 300 µm. Finally, our results showed that water retention properties and saturated hydraulic conductivity varied mainly according to the clay content and development of large pores without any close link with the mineralogy of the clay fraction.