The objective of this study was to assess the spatial variability for soil water content as a function of time, in two distinct land uses. In order to do that, soil moisture measurements were taken in two adjacent plots, one of which was cultivated and the other was kept with natural vegetation, in Galicia, Spain. The water content was measured using a TDR at 15 cm depth. The soil was classified as an Umbrisol (FAO) and measurements were taken on a regular square grid of 1m on a flat 190 m² plot, half of which was cultivated and comprised 100 sampling points and the other half was with natural vegetation and comprised 90 samplings points. Dates of sampling were 29/October/1993, 16/March/1994 and 13/October/1994. The spatial variability was analyzed by the semivariograms, and by kriging estimation maps for each date and land use, and assessing temporal stability of the places where values close to the mean value occur. It was concluded that cultivation and cover crop affect the spatial dependence for soil water content since on the cultivated plot the spatial dependence tended to disappear as the water content increased. The reverse was found for the natural vegetation plot since it showed spatial dependence for larger distances as the water content increased. The time stability of soil water content was higher when spatial dependence among samples was lower.
Soil moisture; TDR; geostatistics; Umbrisol
