Study of time dependency of factors affecting the spatial distribution of soil water content in a field-plot

Temporal and spatial variability of water content in soil results from a complex interaction of different factors such as duration and frequency of rainfall, soil layering, vegetation, and topography. The objectives of this study were (i) to use a resistant median-polishing scheme to quantify the temporal variability of a depth and a horizontal location factor in an additive model, and (ii) to investigate the time stability of those two factors at a detailed temporal scale during different infiltration and redistributions cycles. Time series of water content were measured at 5 depths and 12 locations along a transect of 6 m using Time Domain Reflectometry (TDR). Measurements were repeated every 2-hours for 168 days under natural boundary conditions. At each time step, the mean water content of the soil profile, 5 depth factors and 12 location factors were estimated. The time series of these factors were qualitatively interpreted and related to the atmospheric and prevailing soil conditions. It was found that micro-heterogeneity plays an important role, even at this small plot-scale. The relative contributions of the factors were dependent on the antecedent soil moisture conditions. Also, the ratio of the deterministic variance, i.e., variance explained by the deterministic factors, of water content to the observed variance is variable in time.