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International audienc

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The effects of rice (Oryza sativa L.) cultivation under flooded conditions on soil's physical-hydraulic properties were studied in this article, using a new methodology based on a combined analysis on soil water retention curve (WRC) and pore size distribution (PSD). WRC analysis was carried out through the changes of van Genuchten's model parameters, the characteristics of WRC at the inflection point, and the specific water capacity curve. Analysis of PSD was performed on the volume changes of porosity fractions through a detailed pore size classification, while different pore size classifications based on their hydraulic and structural characteristics were also used. The methodology was applied using a small dataset obtained from fine-textured Entisol soils which were subjected to rice cultivation under flooded conditions in Axios River plain (Northern Greece). Measurements of WRC were obtained at four depths of the soil profile from two fields, before and after the growing season of rice. The analysis indicated that the van Genuchten's model parameters (θ s, a, and n) and the WRC characteristics at the inflection point (pressure head h i, pore equivalent diameter D i, and slope S i) significantly changed after the growing season following similar patterns, along the soil profile in both fields. The parameters θ s, a, D i, and S i were decreased, while n and h i were increased. The h i and a were the most sensitive parameters, while the values of (h i and 1/a) in each layer before and after the growing season for each field were linearly correlated and shifted to higher values because of compaction, indicating that it could be applied as a tool to evaluate the degree of soil compaction to similarly textured soils. The peaks of the specific water capacity curves were compressed (lower values of slope S i) and shifted to lower water potentials (h i) that corresponded to pores of equivalent diameter D i between 2 and 6 μm. The soils had few structural pores (>9 μm) and low air-filled porosity (>30 μm) before the growing season, which presented accessory reduction after the growing season in both fields. Total porosity was reduced at the expense of structural porosity along the soil profile, while the pore size class of 5-3 μm was identified as the threshold where the smaller pores' volume started to increase in all layers of both fields. The results indicated that the changes in the WRC and the PSD follow specific trends, which can be used in future studies to model temporal variability of soil's physical-hydraulic properties

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