Fine-scale spatial variability of physical and biological soil properties in Kingston, Rhode Island

We evaluated the fine-scale (cm) variability of bulk density (ρB), organic matter content (%OM), volumetric water content (θV), and carbon mineralization rate (Cmin) at specific values of water potential in an old field soil. We measured these variables in soil samples obtained using paired abutting, 5-cm diameter, 10-cm deep cores. To compare abutting core properties, abutting cores were randomly assigned to one of two groups, A or B, using permutation procedures in order to account for the possibility of chance effects. Comparisons were made using either 10 (θV and Cmin) or 40 (% OM and ρB) pairs of samples in May, August, and November of 1997 and March of 1998. No differences were observed in the distribution of values among groups of cores for all the variables measured. Furthermore, there were no seasonal differences in coefficient of variation for any of the variables. Values of coefficient of variation followed the order: Cmin>θV>% OM>ρB. The difference between paired cores relative to population means (RD) was highest for Cmin (29.7%), followed by %OM (12.3%), θV (9.1%) and ρB (5.9%). Our results indicate that variability in soil properties (RD) at the centimeter scale is lowest for physical properties (θV and ρB) and highest for biological properties (%OM and Cmin). The assumption of identity among adjacent cores does not appear to be justified for the soil properties evaluated in our study.