Improving the estimation of complete field soil water characteristic curves through field monitoring data

In this work, Soil Water Characteristic Curves (SWCCs) were reconstructed through simultaneous field
measurements of soil pore water pressure and water content. The objective was to evaluate whether
field-based monitoring can allow for the improvement of the accuracy in SWCCs estimation with respect
to the use of laboratory techniques. Moreover, field assessment of SWCCs allowed to: a) quantify the
hydrological hysteresis affecting SWCCs through field data; b) analyze the effect of different temporal
resolution of field measures; c) highlight the differences in SWCCs reconstructed for a particular soil during
different hydrological years; d) evaluate the reliability of field reconstructed SWCCs, by the comparison
between assessed and measured trends of a component of the soil water balance. These aspects were
fundamental for assessing the reliability of the field reconstructed SWCCs. Field data at two Italian testsites
were measured. These test-sites were used to evaluate the goodness of field reconstructed SWCCs
for soils characterized by different geomorphological, geological, physical and pedological features.
Field measured or laboratory measured SWCCs data of 5 soil horizons (3 in a predominantly silty soil,
2 in a predominantly clayey one) were fitted by Van Genuchten model. Different field drying and wetting
periods were identified, based on monthly meteorological conditions, in terms of rainfall and evapotranspiration
amounts, of different cycles. This method allowed for a correct discrimination of the main drying
and the main wetting paths from field data related and for a more reliable quantification of soil
hydrological properties with respect to laboratory methodologies. Particular patterns of changes in
SWCCs forms along depth could be also identified. Field SWCCs estimation is not affected by the temporal
resolution of the acquisition (hours or days), as testified by similar values of Van Genuchten equation fitting
parameters. Instead, hourly data may offer a clearer vision of the drying and wetting paths, due to
the highest number of experimental data points. Moreover, in temperate climate situations as those of
the test-sites, main drying curves and main wetting curves of a particular soil were substantially similar
also for different hydrological cycles with peculiar meteorological conditions. SWCCs parameters were
implemented in a numerical code (HYDRUS-1D) to simulate soil water storage for different soil horizons.
Field reconstructed SWCCs allowed for simulating with a higher precision these trends, confirming the
reliability of the reconstructed field curves by a quantitative point of view. Moreover, best results were
obtained considering hysteresis in the modeling.