MEASURING AREAL SOIL-MOISTURE DISTRIBUTION WITH THE TDR METHOD

Time domain reflectometry (TDR) was used for measuring surface (0-10 cm) soil moisture content distribution of a field plot 6 m x 10 m in size. Within a regular grid, 273 points were measured by TDR and sampled for gravimetric (GM) moisture content determination, after harvest of a barley crop. Soil moisture content values were proven to be trended. The areal distributions of soil moisture contents were analyzed by semivariograms. The areal pattern of TDR moisture content values. but not of the gravimetric data, reflected the effect of the vehicle traffic during the harvest on the sample plot. The significant statistical difference found between the original TDR and GM moisture content values was attributed to the soil bulk density pattern existing on the study plot. Semivariograms of the detrended residuals show isotropy and no spatial structure. The standard error of the mean as a function of sample size was calculated for the detrended data. The study illustrates the good in situ applicability of the TDR method and examples how soil bulk density might appear in field measured TDR soil moisture content.