Dermintion of Suitable Study Scale in Estimating Organic Carbon and Bulk Density in Paddy Soils

The precision of soil data at any region depends largely on the nature of their variation which often is described by studying of their spatial variability. The location should be considered when analyzing such data because variation of soil properties depends on many process that act in space and time scale، therefore، potentially depends on a scale. This research was carried out to study the effect of scale on estimation precession of organic carbon and bulk density in paddy soils. Three different scales of study were selected at the field of the Rice Research Institute Iran in Rasht. At the first scale، 172 soil samples were taken from the center of 200×50 meter plots. At the second and third scales، 357 and 72 samples were taken from the center of 100×50 and 3×4m plots، respectively. The measured soil properties were organic carbon content and bulk density. All data had non-normal distribution، except bulk density in the third scale. Organic carbon in the second scale and bulk density in the third scale had the maximum and minimum coefficient of variation، respectively. A spherical model was fitted to the varigrams of organic carbon in all scales، which indicated that a single main factor affected organic carbon variations. In the other hand for bulk density، a linear model was fitted to the variograms of first and second scales; a spherical model was fitted to the third scale. Results showed that the first scale with the sampling distance of 200m may be the best scale for studying of organic carbon، and the second scale of 100m distance seems the best for the bulk density.