Abstract

The influence of soil structure dynamics on spatiotemporal variability in soil water flows and distribution is generally omitted in hydrological modeling across scales. Soils like Andosols exhibit important structural dynamics, which affects the accurate representation of soil water distribution and solute transport. This study aimed to describe spatiotemporal variability of soil water retention (SWR) functions in a variably compacted Andosol. Laboratory and field observations were conducted at 10-, 20-, and 60-cm depths in a grassland in southern Chile. We studied 10-min resolution time series from 48 soil moisture contents and 18 matric potential sensors across six monitoring stations from June 2020 to June 2022. Wet and dry period dynamics were delineated based on soil moisture states. Wetting/drying cycles were identified using time derivatives of soil moisture content. Unimodal (vG) and bimodal (dualvG) formulations of the van Genuchten equation were fitted. This study provides insights into how soil structural dynamics, as affected by variable water-filled pore volumes, influence the SWR parameters across different compaction levels and depths. Laboratory and field observations represented different conditions, describing expected contrasts. The dualvG performed better than vG for lab data, showing lower Akaike information criterion (AIC) and root mean squared error (RMSE), and high R2. Soil compaction influenced the dualvG parameters and decreased the diversity of field SWR behavior. Wetting and drying cycles did not affect model parameters. However, it allowed for describing peaks of homogeneity and heterogeneity when wet and dry period dynamics were considered. Non-systematic hysteretic behaviors in the data suggested the occurrence of non-uniform flows.