The clay fraction mineralogy and the granular structure of Oxisols in the Cerrado (Brazilian savanna) are the reason for the great volume of large pores as well as of extremely small pores, but no significant medium pore volume, resulting in low available water for plants. This study aimed to characterize and model the behavior of water retention in Oxisols with different texture classes of the Cerrado region. Samples were collected from the Bw horizon of 10 Oxisols under native vegetation. Water retention was measured at matric potentials of 1, 2, 4, 6, 8, 10 kPa using a Richards plate, and the water retained in potentials of 1.500 and 300.000 kPa determined by a thermocouple psychrometer model WP4-T Dewpoint Potentia Meter. The double van Genuchten model was proposed to fit the experimental water retention data by non-linear fitting using software R 2.10.1. The relationship between the estimated model parameters and the inflection point with soil texture properties was evaluated also by the Pearson correlation test. Results indicated good fitting of the model and great prediction power and correlation between the soil clay content and equation parameters (Usat, Upmp, Ures), as well as with the slope of the second inflection point (Itex). Oxisol texture influenced the behavior of water retention curves. The water retention curves of Oxisols were bimodal in the studied range of water potential.
water content; Oxisol; mathematical model
