Temporal changes in small depth-incremental soil bulk density

Farmers are concerned that soil compaction will be a problem in the first f ew years after conversion to strict no-till. The objective of this study wa s to determine if the changes in depth-incremental soil bulk density during transition to no-till were greater than density changes due to natural var iation. We sampled six locations from a no-till field and six locations fro m a disk field of a soybean [Glycine max (L.) Merr.]-corn (Zea mays L.) rot ation and took 12 samples at each of the 12 locations. The soil types sampl ed were Clarion (fine-loamy, mixed, superactive, mesic, Typic Hapludoll), N icollet (fine-loamy, mixed, superactive, mesic, Aquic Hapludoll), and Canis teo (fine-loamy, mixed, superactive, calcareous, mesic, Typic Endoaquoll) s oils. We divided each 300-mm soil sample into 15 depth-increments, and pole d the 12 samples for each location for each 20-mm depth-increment. Bulk den sities 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 la st sampling dates for the no-till field, no significant changes in bulk den sity were detected for any depth-increment; however, for the disk field, in creases in significant bulk density were detected in 10 out of 15 depth-inc rements. Natural causes probably contributed to the bulk density changes th at occurred over time in both fields. None of these bulk densities were hig h enough to restrict root growth. We concluded that concern about soil comp action under no-till management is inappropriate for these structured soils .