SUSTENTABILIDADE DE SISTEMAS ORGÂNICOS COM PLANTAS DE COBERTURA NA CULTURA DO ARROZ, POR MEIO DE ALTERAÇÕES FÍSICAS DO SOLO

To evaluate the influence of cover crops on Oxisol physical attributes, in an organic production system with conventional tillage, a study was conducted at Embrapa Arroz e Feijao, Santo Antonio de Goias, Goias State, Brazil, for two years, in a succession cover crops-rice, in which cover crops were sown in the autumn/winter and the subsequent crop, rice cultivar Aimore, was sown in the summer. Five cover crops were used: Velvet bean ( Mucuna aterrima ), Sunn hemp ( Crotalaria juncea ), Pigeon pea ( Cajanus cajan ), Broom sorghum ( Sorghum technicum ), and spontaneous vegetation fallowing. A randomized blocks design with four replications was used. In the second year of experimentation (2005), soil samples were collected from plots and from a close forest, at depths of 0.00-0.10 m, 0.10-0.20 m, and 0.20-0.30 m, to determine organic matter content (SOC), soil physical properties, S index, and soil aggregation. The cover crops management was carried out at the flowering stage and its biomass incorporated into soil profile. For total porosity, microporosity and bulk density, there were no significant differences among depths, for different cover crops. For S index, for all treatments at the 0.00-0.10 m layer depth, values between 0.020 and 0.035, characterizing intermediate soil physical quality, were found. The percentage of aggregates with a diameter larger than 2 mm and the weighted average diameter of aggregates were higher at the 0.10-0.20 m layer depth. SOC decreased with depth, independently of cover crops. KEY-WORDS: Cover crops; soil tillage; porosity; aggregate stability.