Prevention of additional compaction in eucalyptus and pasture land uses, considering soil moisture and bulk density

Soil compaction is harmful to agricultural and forestry areas, and strategies to avoid soil deformation are of great interest. The objective of this study was to evaluate the compressibility of a soil submitted to different land uses in an area located in southern Brazil. The land uses assessed were a) Anthropized Forest: constituted by tree and shrub species; b) Pasture: five years old; c) Eucalyptus 20: twenty years old; and d) Eucalyptus 4.5: conducted in 2nd rotation, and 4.5 years old, with Eucalyptus harvesting in the first cut made manually with a chainsaw and wood extraction with a Forwarder. Undisturbed soil samples were taken in 2006, and they were submitted to the uniaxial compression test. Bulk density and volumetric moisture were calculated before the test, as well as soil deformation, compression index and precompression stress at the end of the test. Anthropized Forest and Pasture soils presented the highest volumetric soil moisture, a mean of, respectively, 0.301 and 0.304 m3 m- 3. Euca-lyptus 20 had the lowest bulk density (mean of 1.15 Mg m-3), and Eucalyptus 4.5 the highest bulk density (mean of 1.47 Mg m-3). Precompression stress is low for all soil land uses, ranging from 31.24 to 50.92 kPa, and care should be taken to avoid further compaction. Load-bearing capacity of the soil presented positive and negative relationship with, respectively, bulk density and volumetric moisture, but the low coefficient of correlation (r) and determination (r2) shows the need of further studies for a better adjustment of the data. From the knowledge of volumetric soil moisture, it is possible to monitor and define the most suitable soil condition for traffic of machinery and animals trampling into the areas to avoid additional compaction, while the load-bearing capacity of the soil can be estimated by bulk density, being useful to monitor the occurrence or not of additional compaction.