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Scaling Approach to Deduce Field Unsaturated Hydraulic Properties and Behavior from Laboratory Measurements on Small Cores
No full textHydraulic properties should be determined at the scale of the process
modeled. The methods to hydraulically characterize a soil in situ
remain extremely difficult to implement, requiring measurements of
water content and pressure head with adequate time–depth resolution.
We recently proposed a method that reduced the number of field
measurements required for complete field hydraulic characterization.
In this paper, we extend the previous method to cases where the
only available information consists of laboratory hydraulic properties,
along with a measurement of the maximum water content in the field,
whose value depends on the way the wetting of the porous medium is
performed. Specifically, the field hydraulic parameters were estimated
with a scaling procedure accounting for the ratio between the total
porosity estimated by the maximum water content in the laboratory
and the partial porosity effectively involved in the field, as estimated
by the field-measured maximum water content. The scaling method
was evaluated with data from four soils (three volcanic sandy loam
soils and one silty clay loam soil). Soil hydraulic properties were measured
both in situ by a field internal drainage test and in the laboratory
in an evaporation experiment (Wind’s method). Scaling-based hydraulic
properties were also compared with those estimated by applying
a simplified method based on the unit-gradient water flow
assumption where only water content measurements performed during
the internal drainage test were of concern. The hydraulic properties
estimated with the scaling method were compared with the
measured ones and with those from the unit-gradient method in terms
of the Relative Mean Error (RME) and Relative Root Square Mean
Error (RRMSE). The scaling method proved to be especially effective
when applied to the three sandy loam soils, where scaled retention and
hydraulic conductivity curves to a large extent reproduced those measured
in the field. For the silty clay loam soil, appropriate results were
observed only for the water retention curve, while poorer scaled hydraulic
conductivity was obtained
Methodological issues in combining pores micromorphometry and hydraulic functions in soil
No full text
SWAP, CropSyst and MACRO comparison in two contrasting soils cropped with maize in Northern Italy
No full textThe quantification of the water balance terms within soil-crop-climate systems is required to derive proper management for plant growth and irrigation. A large number of available models use the well known Richards’ equation for the simulation of water redistribution at field scale. Despite their common basis of the representation of water flow in the unsaturated zone, apparently similar hydrological models give different answers if applied in the same pedological, climatic and agronomic scenarios. The objective of the present study was evaluating and comparing the performance of three well known models (SWAP, MACRO and CropSyst) based on the solution of the Richards’ equation: in a structured fine soil (Calciustepts located in Cerese, Mantova, Italy) and in a structured fine loamy over sandy soil (Hapludalf located in Caviaga, Lodi, Italy), both cropped with maize. The models were compared on the basis of their reliability to predict soil water content, measured by TDR, at 10 depths over 2 years. We compared the three models on the basis of difference-based indexes (CRM and RMSE) and correlation statistics (r and EF): at three depths (0–0.15, −0.4 and −1.0 m), in terms of soil water content profile following a drainage process on bare soil and on soil water content over the whole soil profiles. Although water retention and hydraulic conductivity curves were properly measured in laboratory on undisturbed soil samples, all three models required calibration and validation to obtain good quality simulations. The performances of the three models were quite similar: the average of all (models, sites and depths) root mean square error (RMSE) was 0.032cm3 cm−3 (±0.007). Generally, SWAP had the best performance especially in simulating surface infiltration and drying processes, followed by CropSyst and then MACRO. The better performance of SWAP respect the other two models seemed rely on the hydraulic properties parameterization (van Genuchten-Mualem vs. Campbell equation), and to the different techniques used for the numerical solutions of Richards’ equation close to the bottom and upper boundaries. Moreover, despite its rather good performance, CropSyst, due to its internal numerical constraints in the parameterization of the retention and conductivity functions, needed a very strong calibration then loosing part of its “physical basis” towards an increasing of its empiricism
A comparative analysis of the pore system in volcanic soils by means of water retention measurements and image analysis.
No full textA modelling approach to discriminate contributions of soil hydrological properties and slope gradient to water stress in Mediterranean vineyards
No full textGrapevine is a widespread crop for grape and wine production, often cultivated on hilly areas. Moderate vine water stress plays an important role in determining high-quality viticulture. However, a precise quantification of the effect of hydraulic properties and slope gradient on hilly soil water balance and consequently on vine stress has not yet been addressed in the literature. The slope-gradient effect is generally taken for granted, without providing experiments validating such a qualitative assumption. We tested the hypothesis that soil hydraulic properties play a greater role than slope gradient in driving soil water status and vine stress. In two consecutive years, we studied an “Aglianico” vineyard grown along a 90 m slope, with up-slope soil having lower water holding capacity than down-slope. Up-slope vines were more stressed, as shown by lower leaf water potential, stomatal conductance, leaf CO2 assimilation and leaf area index, than down-slope vines. Water flow was simulated by using the Hydrus (2D/3D) model, calibrated and validated towards a two-year set of soil water content measurements. Significantly lower soil pressure head and higher transpiration occurred in the up- than the down-slope site. A viable procedure was developed to separate the effects of soil hydraulic properties and slope gradient by modelling soil water balance and therefore vine transpiration with and without the slope gradient. The simulations indicated that the difference in seasonal relative transpiration of 8% in 2011 and 5% in 2012 between the two sites was due to their differing soil hydraulic properties, and that the slope gradient had no contribution to this variation
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