Quantificacao do balanco hidrico de um solo regado na presenca de uma toalha freatica. Simulacao com o modelo Swatrer

Results from a study including experimental quantification and simulation of the hydrological behaviour of a irrigated soil is presented. It is an alluvial soil located in the Irrigation Perimeter of The Sorraia River, at the Antonio Teixeira Research Station. The components of the soil water balance were calculated in three plots with maize, under three surface irrigation regimes, one not irrigated and two with differents irrigation depths, respectively 154 mm and 214 mm. Root extraction was calculated as the rest term of the soil water balance equation, for different soil layers and at several days during the growing season; soil water depletion, for each layer, was obtained integrating the derivative of water content with time, calculated graphically from observed values; soil water fluxes, including cappilary rise from the watertable, were estimated with the generalized Darcy equation, using hydraulic gradients got graphically from observed hydraulic heads profiles and the relation between hydraulic conductivity and water content, measured in situ with the instantaneous profile methods, in soil monoliths. Soil evaporation was estimated using one modification of Ritchie model, which was calibrated with results from minilysimeters in a bare soil and under the canopy. The results show: i) the contribution to crop evapotranspiration from the water table and from the water stored in the soil depends on the irrigation frequency and depth; flow from the water table represented 42,7% in the non-irrigated plot, 28.1% in the plot irrigated with 154 mm and 18.7% in the plot irrigated with 214 mm; ii) greater intervals between irrigations induce a higher soil water depletion, reducing the hydraulic conductivity of the soil, preventing the risk of deep percolation of irrigation water; iii) the development of roots and root extraction depend on the irrigation regime, and the last depends on the soil water content, depth and changes along the crop cycle, diminishing due to sucessives periods of drying and rewettingAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga