AGRONOMIC TRAITS AND CONTROL OF ROOT DISE ASES OF WHEAT, IN ROTATION WITH OTHER WINTER CROPS

During nine years, in Passe Fundo, RS, Brazil, the effect of crop rota tion systems on yield, root diseases, and some agronomic traits of whe at (Triticum aestivum L.) were assessed. Six rotation systems for whea t were studied: monoculture; one winter without wheat, from 1990 to 19 95; two winters without wheat; three winters without wheat; two winter s without wheat and two winters with wheat; and three winters without and two winters with wheat. The winter crops were sown to conventional ly prepared soil, and summer crops were set up under no-till. An exper imental design of blocks at random was used, with three replications a nd plots totalling 30 m(2). Crop rotation was efficient in reducing ro ot diseases and in increasing wheat yields. No significant differences were observed among the systems used, indicating that wheat can be so wn with one winter of crop rotation (wheat/soybean and common vetch/co rn) only. Additionally, wheat can be sown in two consecutive winters, if two winters are left in rotation (wheat/soybean, wheat/soybean, whi te oats/soybean, and common vetch/corn). When comparing with the rotat ion systems, it became evident that the number of spikes, number of gr ains, and grain weight were significantly reduced by monoculture.