How does no-till affect soil-profile compactibility in the long term?

Abstract

How no-till management affects soil-profile compactibility in the long-term is unknown. The few previous studies measured soil compactibility for the upper 20 cm soil depth, which limits a complete understanding of the potential changes in compactibility for deeper depths. The objective of this study was to determine Proctor bulk density at different soil water contents, Proctor maximum bulk density (MaxBD), water content at MaxBD termed as critical water content (CWC), and relationships of MaxBD and CWC with soil organic C (SOC) and mean weight diameter of water-stable aggregates (MWD) for the 0–15, 15–30, and 30–60 cm depths in two long-term (32 and 36 yr) tillage experiments in the western US Corn Belt on silty clay loam soils. Treatments were: moldboard plow, disk, and no-till under continuous corn (Zea mays L.) and corn-soybean (Glycine max L.) rotation at the 32-yr site, and moldboard plow, chisel plow, double disk, and no-till under corn-soybean rotation at the 36-yr site. No-till reduced Proctor bulk density and MaxBD only at the 32-yr site and shallow depth (0–15 cm) by 5% compared with moldboard plow. However, disking reduced Proctor bulk density compared with plowed systems to 60 cm depth at the 32-yr site and to 30 cm depth at the 36-yr site. Disking at both sites reduced MaxBD by 7% (0.10 Mg m−3) to 30 cm depth compared with plowed treatments. Compared with moldboard plow, disk till increased CWC by 3% for the 30–60 cm depth at the 32-yr site, while both disk and no-till increased CWC by 5% at the 0–15 cm depth at the 36-yr site. Maximum compactibility decreased as SOC concentration and MWD increased, while CWC increased as SOC concentration increased at most soil depths. No-till reduces soil compactibility only near the surface compared with plowed systems but reduced till (disk) reduces compactibility to deeper depths in the profile, suggesting it can be more effective than no-till at reducing compactibility.