Soybean yield and nodulation in different annual winter crops under no-tillage

The different preceding crops were compared in relation to soybean yield an d nodulation during four years at the Faculdade de Agronomia e Medicina Vet erinaria, in Passe Fundo, State of Rio Grande do Sul, Brazil. Four producti on systems with annual winter pastures were tested, in which soybean was so wn after different winter crops (white oats, grazed black oats, grazed blac k oats + grazed common vetch, and wheat). Both in winter and summer the cro ps were grown under notillage. An experimental design of blocks at random, with three replications and plots with 500 m(2), was used. No significant d ifferences between type of preceding crop and soybean yield were found in t he mean of years. After five years of no-tillage, an abundant nodulation in soybean was observed in all production systems. Soybean grown after white oats, grazed black oats, grazed black oats + grazed common vetch, and wheat may be included, without any loss, in the different systems studied.