Soil compaction is an undesirable consequence of land use for crop production, especially under cultivation with minimum soil turnover as in the no-tillage system (NTS). However, the compaction caused by machine traffic on soils under NTS does not make crop production unviable, indicating that some intrinsic mechanisms promote the reversion of soil compaction. In this study, the influence of alternate contraction and expansion cycles was evaluated with regard to the bulk density (ρ) of a Latossolo Vermelho argiloso (clayey Oxisol) (0.57 kg kg-1 clay, and 0.12 kg kg-1 sand) and the temporal change in ρ in the field. Soil samples were compacted in the laboratory to reach a ρ of 1,464 kg m-3 and subjected to five cycles of contraction (air drying) and expansion (saturation). During the contraction process, soil gravimetric water content and ρ were monitored. Soil ρ was also measured in the field in the years 2010, 2011, and 2013. A decrease in soil water content in the samples increased the ρ according to a sigmoid function with two asymptotes, and the increase in ρ was significant at water contents lower than that of the permanent wilting point (1.5 MPa). Although there was an increase in ρ during contraction, successive contraction and expansion events steadily reduced ρ from 1,713 to 1,570 kg m-3 (end of contraction), and from 1,464 to 1,385 kg m-3 (near saturation). In the field, a decline in ρ was observed in compacted soil (from 1,406 to 1,327 kg m-3) at a rate of -26 kg m-3 yr-1. We conclude that the decrease in the state of field compaction is largely linked to the same mechanisms that cause the decrease in compaction in the samples in the laboratory. We conclude that for the soil used in this study, contraction and expansion cycles may reverse most of the compaction that machine traffic causes to the soil.
soil compaction; resiliency; no-tillage
