Funções de pedotransferência para a estimativa de propriedades físico-hídricas de solos cascalhentos sob povoamentos florestais

Abstract

Saturated soil hydraulic conductivity (ksat), field capacity (FC), permanent wilting point (PWP) and available water (AW) are properties commonly used as input in models to predict hydrological and erosive processes. in watersheds. The determination of these properties demands a long time of sampling and analysis and the results can have high spatial variability and low representativeness due to the small sampling density, mainly in watersheds and in soils with the presence of coarse fractions in different horizons. Therefore, the use of pedotransfer functions (PTFs) can be a good strategy to obtain soil physical-hydric properties to be used as input for models to predict hydrological and erosive processes in watersheds with soils originated from of intrusive igneous rocks. The objective with this study was to establish pedotransfer functions to estimate ksat, FC, PWP and AW for soils derived from intrusive igneous rocks in a forest watershed in Rio Grande do Sul. The study was carried out in a forest watershed (0.94 km2 ) located in Eldorado do Sul-RS. The ksat, soil bulk density, total porosity, soil moisture at the water tensions of 1, 6, 10, 33, 100, 500, 1000 and 1500 kPa, and particle size distribution (9 classes: < 0,002, 0,002-0,05, 0,05-0,250, 0,250-2,00, 2,00- 2,36, 2,36-2,80, 2,80-3,35, 3,35-4,00, > 4,00 mm) were determined for each horizon of 24 soil profiles. Statistical analysis was performed using Spearman's correlation and multiple regression analysis, followed by robust regression analysis to generate and validate punctual PTFs to estimate ksat using four sets of predictor variables, and to estimate FC, PWP and AW, using three sets of predictor variables. The ksat is dependent on the soil granulometric fractions, with greater influence of the gravel+pebbles fraction and PTFs composed with the fractions > 4 mm, silt and soil clay can be used to estimate the ksat in horizons with presence of gravel fractions, while not being recommended to use for less permeable horizons due to the overestimation of ksat in these horizons. The FC, PWP and AW are dependent on soil granulometric fractions, being more influenced by the gravel+pebbles fraction. The FC and PWP can be estimated using PTFs using some soil granulometric fractions. The PTFs for estimating the AW have very low accuracy and should not be used, being recommended as an alternative the use of the PTFs for estimating the FC and PWP and, then, the calculation of the AW by the difference between these two soil physicalhydric properties.