Tillage systems should create adequate conditions for plant development. The objective of this study was to evaluate the density, porosity and penetration resistance of a Yellow Ultisol in the semi-arid region of northeastern Brazil after tilling with four agricultural implements (chisel, tandem disc harrow, offset disc harrow with 0.56 m discs, offset disc harrow with 0.61 m discs) in one, two and three operations, using an area without tillage as control. Data of soil bulk density and porosity were analyzed by classical statistics and penetration resistance by geostatistics using a grid given by the width of the equipment and reaching depth of 0.40 m. The effect of tillage had little influence on the evaluated properties. Higher bulk density values were detected in the 0.10-0.20 m layer only for all tilling devices. Porosity varied according to tilling, i.e., values were highest in the untilled soil and lower in soil that was chisel-tilled and harrowed with 0.61 m offset discs; porosity was lowest in the 0.20-0.30 m layer. The values of penetration resistance were adequate at the reaching depth of each equipment and high in the layers underneath, except in chisel-tilled soil.
soil bulk density; tillage; geostatistics
