An increase in the use of winter mixed cover crops has been observed in Southern Brazil during the last years. As a new agricultural practice, it is important to evaluate its potential benefits in dry matter production and nutrient accumulation. A field experiment was carried out from 1998 to 2000, in UFSM (RS), on a Typic Paludalf soil. Black oat (Avena strigosa Schieb) + common vetch (Vicia sativa L.) and black oat + oilseed radish (Raphanus sativus L. var. oleiferus Metzg.) were cultivated in different proportions of seed mixing. There were nine treatments: (1) 100 % black oat (AP), (2) 100 % common vetch (EC), (3) 100 % oilseed radish (NF), (4) 15 % AP + 85 % EC, (5) 30 % AP + 70 % EC, (6) 45 % AP + 55 % EC, (7) 15 % AP + 85 % NF, (8) 30 % AP + 70 % NF, and (9) fallow (spontaneous vegetation). Dry matter (DM) and the concentrations of nitrogen, phosphorus, potassium and carbon in cover crop biomass were determined. The crop mixture DM yield was similar to that of single oat and single oilseed radish and greater than single vetch. Nitrogen in the biomass of oat + vetch mixtures did not differ from that of single vetch, and was, on average, 32 kg ha-1 of N higher than that of single oat in the three years. The C/N ratio of oat + common vetch was 67 % higher compared to the single vetch crop. The cover crops provided greater DM and were more efficient in N, P and K accumulation than the winter fallow spontaneous vegetation. Results of this study indicated that the cultivation of a mixture of oat + common vetch and oat + oilseed radish is more efficient than single crops are, since it combines the high biomass production capacity of black oat and oilseed radish with the ability of common vetch to fix atmospheric N2.
oat; vetch; oilseed radish; grass-legume; bicultures; no-tillage
