Temporal Variability of Bulk Density and Soil Water at Selected Field Sites

Soil bulk density is not a fixed property but varies spatially because of soil differences and temporally because of management and climate effects. The purposes of this study were to determine the relation of bulk density and water table depth with soil properties for wet and dry measurement dates and to compare the correlation of soil properties with mass and volumetric water content. Volumetric soil samples were collected at 15 or 16 field sites on 37 dates over 5 years. At the same time, water table depths were determined. The soil samples were used to determine volumetric and mass water contents and bulk densities. Other soil properties were used to develop orthogonal Principal Component 1 (PC1). The fractions of soil or landscape properties contributing to PC1 were as follows: sand, 0.40; silt, -0.38; clay, -0.39; color index, -0.38; distance above short-range low point, 0.35; distance above longer-range low point, 0.29; profile curvature, 0.27; and plane curvature, 0.34. Principal Component 1 was positively correlated with bulk density for 24 of 27 wet measurement dates, but only 4 of 10 dry dates. Volumetric soil-water content was negatively correlated with bulk density for 9 of the 10 dry dates, but only 19 of the 27 wet dates. Mass water content had slightly higher correlations with PC1 than did volumetric water content, but both were significantly correlated for 36 of the 37 measurement dates. Dividing measurement dates into "wet" and "dry" facilitated interpretation of bulk density variation at the 15 or 16 sample locations.