Abstract

GONCALVES, M. C. et al. Effect of soil water quality in a Fluvisol in Alentejo. Rev. de Ciências Agrárias [online]. 2009, vol.32, n.1, pp.79-92. ISSN 0871-018X.

Three soil lysimeters (A, B, and C) were built in a Fluvisol located in Alvalade-Sado (Alentejo). The soil lysimeters were irrigated from 2001 to 2005 with waters of different quality (May to August), and subjected to atmospheric conditions during the remaining months of the year. A total depth of 500 mm was applied every year in each soil lysimeter. The quality of the irrigation waters varied by increasing the concentration of NaCl, CaCl2 e MgCl2 in its composition. The electrical conductivity (EC) of the irrigation waters applied varied between 0.3 and 3.2 dS m^-1, with the best quality waters being applied in soil lysimeter A, and the worse quality waters being applied in soil lysimeter C. The sodium adsorption ratio (SAR) was 1, 3 and 6 (meq L^-1)^0.5, always maintaining a relation Ca:Mg = 1:2 in the irrigation waters. Effects on soil salinization/sodification resulting from applying those irrigation waters were evaluated in the end of each irrigation season, in the end of each leaching season, and in the end of the experiment (December 2005). The parameters monitored were the EC and soluble cations in the saturation extract, extractable cations, the cation exchange capacity, SAR and the exchangeable sodium percentage (ESP). Soil hydraulic properties and soil microagregation stability was also monitored in the end of the experiment. A mass balance for salt concentration along the different seasons was also calculated. In the end of the experiment, EC values although higher than the values presented in the initial conditions, were inferior to 2 dS m^-1 . Rainfall was enough to leach salts mainly until 40 cm depth. SAR increased with irrigation notoriously until 40 cm depth, not being evident the effect of rainfall on leaching. Final values were 4, 5 and 9 times higher than the initial ones in soil lysimeters A, B and C, respectively. ESP behaviour was similar to SAR. Final values were not high enough to cause soil sodification (only 6% in the most unfavorable conditions). The salt balance showed an accumulation of sodium 2.5 to 4 times higher than the initial conditions in soil lysimeters B, and C, respectively. An important amount of sodium was leached from soil lysimeter C. No changes were observed in soil hydraulic properties and soil microagregation stability. The small variations present were due to spatial variability of those soil properties.

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