Management versus inherent soil properties effects on bulk density and relative compaction

Bulk density (D-b) is a soil physical parameter used extensively to quantify soil compactness. The D-b varies with management as well as with inherent soil properties. Because of its dependence on inherent soil properties, measurements of D-b are of limited value as a measure of the effect of management on soil compaction when soils with different inherent characteristics are compared. Researchers have used the concept of relative compaction or relative bulk density, (Db-rel), the ratio of the D-b of a soil to the D-b under some standard compaction treatment (Db-ref), in order to compare the response of different soils to stresses arising from management. This research was conducted to determine D-b, Db-ref and Db-rel across a range of soils under different tillage practices and to assess the relative importance of texture, organic matter content and management on these parameters. Thirty-six paired sampling sites were located along two parallel transects in a side by side comparison of no-tillage and conventional tillage treatments. The transects crossed three soil types: Aquic Hapludalfs, Psammentic Hapludalfs, and Typic Hapludalfs. Clay content (CLAY) varied from 5.8 to 42.3%, and organic matter (OM) varied from 1.4 to 11.6%. Multiple regression analyses showed that D-b was related (R-2 = 0.83) with CLAY, OM, tillage, position, and the interactions OM*CLAY and tillage*position, whereas the Db-ref was related (R-2 = 0.86) with OM, CLAY, and tillage. Normalizing D-b with respect to Db-ref, effectively eliminated the influence of CLAY, OM and their interaction on Db-rel. The analyses indicated that it is possible to quantify the separate effects of inherent soil properties and management on D-b, when soils derived from similar parent materials and under similar climatic conditions are considered, either by using multiple regression analyses to describe D-b, or by normmalizing D-b with respect to Db-ref. (C) 1997 Elsevier Science B.V.