A 6-year (1997/98-2002/03) study was undertaken in Passo Fundo, Rio Grande do Sul, Brazil, to assess the effects of soil tillage systems and crop rotation systems on soyabean grain yield and its components. The treatments comprised 4 soil tillage systems: (1) no-tillage, (2) minimum tillage in winter and no-tillage in summer, (3) conventional tillage with a disc plough in winter and no-tillage in summer, and (4) tillage using a mouldboard plough in winter and no-tillage in summer; and 3 crop rotation systems (I) wheat/soyabean, (II) wheat/soyabean and common vetch [ Vicia sativa]/maize or sorghum, and (III) wheat/soyabean, common vetch/maize or sorghum and white oats/soyabean. The yield and weight of 1000 kernels of soyabean grown under no-tillage and minimum tillage was higher than those grown under conventional soil tillage with a disc plough and a mouldboard plough. Plant height was greater in the no-tillage system. The yield of soyabean grown after wheat in system II was higher than in soyabean grown after white oats and wheat in system III and after wheat in system I. The lowest soyabean yield, grain weight per plant and weight of 1000 kernels were obtained in monoculture (wheat/soyabean).
