Comportamento espacial e temporal da umidade do solo em uma bacia hidrográfica da região sul de Minas Gerais

Abstract

The structure of conceptual hydrological models is highly dependent on studies of soil physical-hydric attributes at a watershed scale. The present study was developed in a small watershed of 14 ha of area, which is located at the campus of the Federal University of Lavras. In this watershed, there are Latosols, Argisols, Cambisols and Gleissol as pedological unit, and the land uses are annual (corn) and perennial (coffee) crops, and Tropical Mountain Semideciduous Forest (FESM). This dissertation is structured in two chapters. In the first one, it was evaluated the spatial continuity of the physical-water attributes of the soil in the depths of 10, 20, 30 and 40 cm, and later mapping by ordinary kriging. Specifically, it was evaluated: soil bulk density (D s ), particle density (D p ), total porosity (P), macroporosity (Map), microporosity (Mip), soil moisture at the permanent wilting point (θ PMP ), organic matter (OM), saturated hydraulic conductivity (k) and percentage of sand, silt and clay fractions. In the second chapter, soil moisture spatial dependence structure at depths of 10, 20, 30 and 40 cm was studied during the hydrological year 2016/201, Temporal stability was also evaluated from three methodologies, being mean relatives difference, time stability indicator (TSIij) and nonparametric Spearman test. Variographic analysis showed that the majority of the studied attributes presented spatial dependence structure. Yet, soil moisture presented a strong spatial dependence structure during the monitoring period. The interpretation of the maps showed the relationship between soil physical-hydric attributes, soil classes, land use and relief. The FESM area showed the lowest values of D s in the watershed, and the highest values of MO, P, Map and k, being interpreted as a propitious area for the occurrence of soil recharge process. However, in the areas destined to the annual and perennial crops, the highest values of D s and Mip, and the shortest ones for MO, P, Map and k were observed. So it was possible to verify in these land uses a greater difficulty for water movement in the soil, when compared to the FESM area. Regarding the temporal variation of soil moisture, it was verified, that it is directly related to the rainfall regime. The areas of lower soil moisture in the watershed tended to be placed at the region of occurrence of Haplic Cambisol and Haplic Gleisol, which predominantly has FESM as the land use. However the areas of higher values of soil moisture were concentrated in the region of Latosols, in which the land use is annual crop. Soil moisture temporal stability in depth was verified. It was greater in the superficial layers (10 cm and 20 cm), than the others (30 cm and 40 cm). It was possible to identify representative points of the temporal behavior of the soil moisture in the watershed. They were all located in the FESM area and mostly in Argisols. It is observed that the FESM favors soil physicalhydric attributes, which favors a water movement in soil, being important for hydrological processes, especially for underground recharge, although this is an area with permanence of lower humidity throughout the period, when compared to the other land uses in the watershed.