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

The different preceding crops were compared in relation to soybean yield and nodulation during four years at the Faculdade de Agronomia e Medicina Veterinaria, in Passe Fundo, State of Rio Grande do Sul, Brazil. Four production systems with annual winter pastures were tested, in which soybean was sown after different winter crops (white oats, grazed black oats, grazed black oats + grazed common vetch, and wheat). Both in winter and summer the crops were grown under notillage. An experimental design of blocks at random, with three replications and plots with 500 m(2), was used. No significant differences between type of preceding crop and soybean yield were found in the 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.