Temporal Changes in Small Depth‐Incremental Soil Bulk Density

Farmers are concerned that soil compaction will be a problem in the first few years after conversion to strict no‐till. The objective of this study was to determine if the changes in depth‐incremental soil bulk density during transition to no‐till were greater than density changes due to natural variation. We sampled six locations from a no‐till field and six locations from a disk field of a soybean [ Glycine max (L.) Merr.]–corn ( Zea mays L.) rotation and took 12 samples at each of the 12 locations. The soil types sampled were Clarion (fine‐loamy, mixed, superactive, mesic, Typic Hapludoll), Nicollet (fine‐loamy, mixed, superactive, mesic, Aquic Hapludoll), and Canisteo (fine‐loamy, mixed, superactive, calcareous, mesic, Typic Endoaquoll) soils. We divided each 300‐mm soil sample into 15 depth‐increments, and pooled the 12 samples for each location for each 20‐mm depth‐increment. Bulk densities ranged from 0.9 to 1.3 Mg m −3 in the top 0 to 20 mm, and 1.2 to 1.6 Mg m −3 for the depth‐increments below 20 mm. Comparing the first and last sampling dates for the no‐till field, no significant changes in bulk density were detected for any depth‐increment; however, for the disk field, increases in significant bulk density were detected in 10 out of 15 depth‐increments. Natural causes probably contributed to the bulk density changes that occurred over time in both fields. None of these bulk densities were high enough to restrict root growth. We concluded that concern about soil compaction under no‐till management is inappropriate for these structured soils.