This study was carried out from 1994 to 1998 in the Agronomy experimental area at the University of Cruz Alta - UNICRUZ, Cruz Alta, State of Rio Grande do Sul, Brazil to evaluate the influence of five soil management systems on bulk density, porous space (total porosity, macro and microporosity) of an clayey Rhodic Hapludox, as well as their effect on soybean, wheat and corn yield. The experiment had a completely randomized block design with four replications. The following management systems were used: (1) continuous no-tillage-PDC; (2) no-tillage with chiseling every three years-PDSD; (3) summer no-tillage with autumn/winter chiseling -PDV; (4) reduced tillage systems: chiseling plus harrow disking-PCEG; and, (5) conventional tillage: disk plowing plus harrow disking-PCAG. Two samples were collected in each experimental unit at depths of 0.0-0.07, 0.07-0.14 and 0.14-0.21 m. In the three studied depths the soil bulk density was higher for the treatments with less soil mobilization (PDC and PDSD), while the total porosity and macroporosity showed an opposite behavior. With exception of PDV, the bulk density values, total porosity and macroporosity were practically constant in the other management systems during the three consecutive years at the three studied depths, indicating no soil compaction tendency over time. The yield of soybean and corn did not differ significantly among the management systems, demonstrating that for these crops the soil structure did not affect the yield. Wheat was sensitive to the structural state of the soil since the management systems with most soil mobilization (PCGA) provided more appropriate conditions. The results evidenced no need to mobilize the soil each year or every three years in the areas operated under no tillage systems.
porosity; bulk density; no-tillage; soybean; wheat; corn
