Spatial and Statistical Similarities of Local Soil Water Fluxes

Abstract

Understanding the spatial and statistical distribution of soil water flux in a field is fundamental for stochastic modeling soil water flow and chemical transport in spatially variable soils. The objective of this study was to examine the persistence of the spatial pattern and statistical distribution of local soil water flux for different application rates during constant flux rainfall infiltrations. A series of constant flux-infiltration experiments were conducted in a spatially variable field. The local soil water fluxes for each of the 0- to 0.2-, 0- to 0.4-, 0- to 0.6-, and 0- to 0.8-m depths were determined from the change of water storage as a function of time before the wetting front passes the end of vertically installed time domain reflectometry (TDR) probes. The spatial similarity (persistent spatial pattern) of the measured soil water flux for different application rates at four depths was examined using Spearman rank correlation coefficient. Results showed that there was no persistent spatial similarity among measured soil water fluxes for the 0- to 0.2-, 0- to 0.4-, 0- to 0.6-, and 0- to 0.8-m depths. This indicates that transient infiltration experiments with different application rates have different flow pathways for each of the 0- to 0.2-, 0- to 0.4-, 0- to 0.6-, and 0- to 0.8-m depths. The statistical similarity (persistent statistical distribution) of soil water flux for different application rates was examined using histograms. Chi-square tests indicated that the histograms of soil water flux for different application rates were different for each of the 0- to 0.2-, 0- to 0.4-, 0- to 0.6-, and 0- to 0.8-m depths, suggesting the stochastic convective flow model may not be used to predict flow and transport in this field for different application rates.