6533b86dfe1ef96bd12ca978

RESEARCH PRODUCT

Alternative analysis of transient infiltration experiment to estimate soil water repellency

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The repellency index (RI) defined as the adjusted ratio between soil‐ethanol, Se, and soil‐water, Sw, sorptivities estimated from minidisk infiltrometer experiments has been used instead of the widely used water drop penetration time and molarity of ethanol drop tests to assess soil water repellency. However, sorptivity calculated by the usual early‐time infiltration equation may be overestimated as the effects of gravity and lateral capillary are neglected. With the aim to establish the best applicative procedure to assess RI, different approaches to estimate Se and Sw were compared that make use of both the early‐time infiltration equation (namely, the 1 min, S1, and the short‐time linearization approaches), and the two‐term axisymmetric infiltration equation, valid for early to intermediate times (namely, the cumulative linearization and differentiated linearization approaches). The dataset included 85 minidisk infiltrometer tests conducted in three sites in Italy and Spain under different vegetation habitats (forest of Pinus pinaster and Pinus halepensis, burned pine forest, and annual grasses), soil horizons (organic and mineral), postfire treatments, and initial soil water contents. The S1 approach was inapplicable in 42% of experiments as water infiltration did not start in the first minute. The short‐time linearization approach yielded a systematic overestimation of Se and Sw that resulted in an overestimation of RI by a factor of 1.57 and 1.23 as compared with the cumulative linearization and differentiated linearization approaches. A new repellency index, RIs, was proposed as the ratio between the slopes of the linearized data for the wettable and hydrophobic stages obtained by a single water infiltration test. For the experimental conditions considered, RIs was significantly correlated with RI and WDPT. Compared with RI, RIs includes information on both soil sorptivity and hydraulic conductivity and, therefore, it can be considered more physically linked to the hydrological processes affected by soil water repellency This study was supported by grants from the Università degli Studi di Palermo (Dottorato di Ricerca in Scienze Agrarie, Forestali e Ambientali, ciclo XXIX, D50002D13+1012 Ministero dell'Istruzione, dell'Università e della Ricerca (PRIN 2015 project GREEN4WATER B72F16000550005) the Slovak Research and Development Agency APVV (project APVV‐15‐0160), Ministerio de Economía and Competitividad of Spanish Government (project CGL2013‐47862‐ C2‐1‐R), Botánica Mediterránea S.L., and Montgó Natural Park Field data in Italy and Spain were collected by V. Alagna. All authors analysed the data and contributed to write the manuscript