Abundance and dominance of soil arthropods in dry bean grown under different soil management systems and cover crops

The cropping systems and the type of cover used in the off season are of great importance in maintaining the balance of the food web of soil arthropod communities and may be used as an instrument to maintain the balance between pests and their natural enemies. The aim of this study was to determine the effects of soil management systems and cover crops planted in the winter, on population of soil arthropods in different agroecossystems of Brazilian savanna. Arthropod populations were monitored in two systems of soil management (no tillage and conventional) in the area of Embrapa Rice and Beans, in the summers of 2004 and 2005. Pitfalls were used to assess the diversity of the arthropod fauna of beans. The crop was sown after crotalaria and sorghum. None of plots received any chemical treatment throughout the study. Evaluations were performed weekly from the third week after planting. The experimental design was randomized blocks in four replications. The dominance and relative abundance were determined by the method of Kato. Species were considered dominant if abundance was above the limit of dominance calculated by DL = (1 / S) x 100 where: DL = limit of dominance, S = total number of species per sample. Of the total number of species collected, the groups considered dominant were Carabidae Scarabeidae, Chrysomelidae, Cincidelidae, Tenebrionidae, Formicidae and Aranea, with relative abundance of 14.77%, 7.95%, 10.23%, 4.55%, 5.68%, 17.05% and 5.68% respectively. Considering the population of arthropods, it was found that there was no significant difference (P> 0.05) of the number of individuals collected in pitfall traps. These results indicate that there was no preference for occupation in different coverage in conventional or no tillage systems. The treatments (cover crops) little interfered in the richness of the soil fauna arthropods in the management conditions studied, indicating that cover crops does not affect the arthropod activity in agrosystem. Key words: Brazilian savanna; Phaseolus vulgaris, pitfall