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Development and functional evaluation of laboratory methods to determine soil hydraulic properties and their relation to crop water availability

Abstract

There is a lack of information on the fundamental hydraulic properties (conductivity and retention) of Brazilian soils, essential in hydrological modeling and for the quantification crop water availability. Retention curves are routinely determined in soil samples using suction / pressure equipment, but, according to recent literature, such measurements may be flawed. Another bottleneck in the hydraulic characterization of soils is the unsaturated hydraulic conductivity which is hardly ever determined. The technique of inverse modeling applied to laboratory evaporation experiments may facilitate the determination of these properties. To apply this technique, water potentials can be measured by mini-tensiometers (as in the commercial Hyprop equipment) or, allowing measurement in the drier soil, by gamma-ray attenuation. This research proposal aims to improve and validate inverse modeling methods for the determination of soil hydraulic properties and to interpret their results in the context of the water availability limits of some soils of the State of São Paulo, also contributing to the formation of a database of unsaturated hydraulic properties of Brazilian soils. The hydraulic properties will be determined in undisturbed samples of some representative soils by inverse modeling of water redistribution data obtained using measurements in laboratory evaporation experiments monitored by tensiometry and by gamma radiation attenuation. The performance and uncertainties associated with each of the methods will be evaluated by statistical and stochastic-functional methods, and the consistency of the measurements obtained with the traditional porous plate pressure chamber method will be verified. From the determined hydraulic properties, the characteristic water conditions (field capacity, critical condition and permanent wilting condition) will be quantified by interpretation of the corresponding dynamic processes. Finally, it is expected that the project contributes to the diffusion of advances in the methodology for obtaining and interpreting the hydraulic properties of Brazilian soils. (AU)