Recovery of physical attributes of an ultisol as affected by soil tillage and sowing time in no-tillage

The improvement in the structural soil quality under continuous no-tillage occurs concomitantly to soil (re)acidification. Surface compaction can sometimes occur, owing to machinery traffic, which has to be corrected by soil tilling. In a 12-year experiment under different soil management systems we evaluated the time it takes to recover the initial soil physical attributes that are affected by soil tillage by the occasion of lime reapplication. The experiment was set up on a Rhodic Paleudult (Ultisol) at the Agronomical Experimental Station- UFRGS, in Eldorado do Sul, state of Rio Grande do Sul, Brazil, for 12 years under conventional and 4, 8 and 12 years under no-tillage systems. The soil physical attributes (bulk density, porosity and aggregate stability) and organic carbon content were evaluated in three (0-2.5, 2.5-7.5 and 7.5-15.0 cm) soil layers, just before and 6, 12, 24, 36 and 48 months after the third lime application. By tilling the soil at lime incorporation after four years of no-tillage, bulk density and porosity improved, but the aggregate stability decreased. Four years under no-tillage were necessary to recover the original aggregate stability condition. Soil physical attributes were more uniform in conventional tillage, but the aggregate stability in the surface layer was lower, and was related to the organic carbon content.