Spatial Variability of Field‐measured Soil‐water Characteristics

One hundred neutron access pipes were placed 1‐m apart along a 100‐m transect together with tensiometers located at soil depths of 0.3 and 0.6 m. After ponding the experimental site with water for at least 4 d, the site was allowed to drain and covered with 0.3 m of straw to reduce evaporation. Measurements of soil‐water content θ and soil‐water pressure head ( h ) initially made at 2‐h intervals were made less frequently as redistribution proceeded. The (θ, h|t )—observations were fitted to the five‐parameter van Genuchten model. Spatial autocorrelations and cross‐correlations of θ, h , and percentage sand manifested significant coefficients for distances as great as 10 m. The practical significance of this research is that it addresses the impact of the separation distance between a tensiometer and a neutron meter access tube on the precision of the measured soil‐water characteristic curve. Greater precision is obtained for separation distances < 10 m.