The impact of winter cover crops prior to no-tillage corn on aggregate stability was evaluated throughout the agricultural year of May 1991 - May 1992, in a Hapludalf (Red-Yellow Podzolic). The experiment was carried out at the Federal University of Santa Maria-RS, using the following winter cover crops as treatments: Lathyrus (Lathyrus sativus L.); Lupine (Lupinus angustifolius L.); hairy vetch (Vicia sativa L.); black oat (Avena strigosa Schieb) and winter bare soil. Water aggregate stability, organic carbon, microbial activity, soil moisture and soil cover were measured monthly from the start of the winter cover crop seeding until corn harvesting. For each plot, composed samples at 0 to 5 cm depth were used in duplicate to measure aggregate stability and in five replications to measure microbial activity and soil moisture. The winter cover crops induced a temporal variation of aggregate stability throughout the measured period. Black oat induced higher aggregate stability throughout winter or cover crops growing season and lupine induced higher values during summer months or corn growing season. These were attributed to oat root system and to decomposition rate of lupine straw imposing favorable conditions for aggregation effected by roots, soil cover, organic carbon addition and conservation of soil moisture favoring soil microorganism action. These effects certainly induced formation and conservation of soil aggregates.
temporal variation; legumes; gramineae; corn; no-tillage