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Soil hydraulic properties have numerous sources of variability related to spatial, temporal, and management‐related processes. Soil type is considered to be the dominant source of variability, and parameterization is typically based on soil survey databases. This study evaluated the relative significance of other sources of variability: spatial and temporal at multiple scales, and management‐related factors. Identical field experiments were conducted for 3 yr at two sites in New York on clay loam and silt loam soils, and at two sites in Maryland on silt loam and sandy loam soils, all involving replicated plots with plow‐till and no‐till treatments. Infiltrability was determined from 2054 measurements using permeameters, and Campbell's a and b parameters were determined based on water‐retention data from 875 soil cores. Variance component analysis showed that differences among the sites were the most important source of variability for a (coefficient of variation, CV = 44%) and b (CV = 23%). Tillage practices were the most important source of variability for infiltrability (CV = 10%). For all properties, temporal variability was more significant than field‐scale spatial variability. Temporal and tillage effects were more significant for the medium‐ and fine‐textured soils, and correlated to initial soil water conditions. The parameterization of soil hydraulic properties solely based on soil type may not be appropriate for agricultural lands since soil‐management factors are more significant. For infiltrability, temporal factors also need to be explicitly recognized. Sampling procedures should give adequate recognition to soil‐management and temporal processes as significant sources of variability to avoid biased results.
Es et al. (Mon,) studied this question.