Resumo

VENCE, Lilia Beatriz; VALENZUELA, Osvaldo Rubén; SVARTZ, Héctor Alejandro  e  CONTI, Marta Elvira. Water retention curves as a tool in the selection of a plant-growing substrate and the watering scheme. Cienc. suelo [online]. 2013, vol.31, n.2, pp.153-164. ISSN 1850-2067.

The relationship between the volumetric water content (θ) and the water potential (ψ) is represented by the function θ = f (ψ) which depicts a water retention curve representing the process of water desorption in a porous media. This model, according to van-Genuchten, represents the pore-size distribution associated with air-water steady state. However, water availability for root uptake is a function of substrate resistance to water flowing. In this framework, the objectives of this study are to 1) determine the parameters which indicate both the static and dynamic properties referred to the air-water relationship in two substrates and 2) select the basic criteria for the proper timing of irrigation as well as the selection of the substrate-container height. Water holding capacity, available water and water buffering capacity were determined in: M1: 80% of perlite + 20% Sphagnum peat moss from Tierra del Fuego and M2: 20% of perlite + 80% of Sphagnum peat moss from Tierra del Fuego. The water retention and unsaturated hydraulic conductivity curves were graphed according to the volumetric water content and adjusted according to the van-Genuchten model. The physical parameters of both substrates were used to estimate their air-water behavior. However, when the adjusted curves were drawn, more detailed information was obtained on the air-entry tension, higher in M2 than in M1, associated to the ''water table'' which is formed in the container bottom. Thus, the water retention curve was also used in modeling the unsaturated hydraulic conductivity which allowed quantifying the irrigation thresholds. All information obtained was appropriate for the selection of the substrate and the proper container and irrigation management scheme. Thewater retention curve is a good tool for selecting both factors with a systematic view. These results should be calibrated for every crop.

Palavras-chave : Water release curves; Volumetric water content; Matric potential; Hydraulic conductivity.

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