Spatial and Temporal Variability of Soil Moisture Content.
sidney r. Vieira1, Célia R. Grego1, G.Clarke Topp2, and Walter Zebchuk2. (1) Instituto Agronômico, Avenida Barão de Itapura, 1481, Campinas, 13020-902, Brazil, (2) E. Cereal & Oilseed Res. Centre, 960 Carling Avenue, Ottawa, ON K1A0C6, Canada
The objective of this study was to assess the spatial variability as well as the temporal stability of spatial distribution for soil moisture content. The measurements were taken with a TDR at 15cm depth, in a nearly flat 1.2 ha field at the Central Experimental Farm of the Agriculture Canada, Ottawa. The soil is classified as a Rideau soil series, is primarily clay to silty clay texture and has an extensive macrostructure effectively stable in time. The field in approximately triangular measuring 110 by 220 meters. A square grid with 10m spacing was laid out, resulting in 164 sampling points at which two 28cm long TDR rods were installed at 45 degree angle to measure the moisture up to 20cm depth. Measurements were taken on 6 dates at the end of the summer of 1987, in 21 dates from May through Oc-tober 1988, and 6 dates between April and May 1989. During all the samplings the field was vegetated with natural grasses and legume pastures. The spatial variability was analyzed examining the scaled semivariograms, the statistical parameters and the parameters of the models fit to the individual semivariograms as a function of time. It was concluded that the field starts showing a parabolic trend when the soil gets dry probably due to hydraulic conductivity changes over the field and that the places were the mean value occur seem to be more stable in time when spatial dependence does not exist. Key words: TDR, temporal stability, semivariogram, geostatistics, precision agriculture.