Population dynamics of weeds in no-tillage and conventional crop systems.

Population dynamics of weeds in successive maize and bean crops were evaluated in two soil management systems (conventional and no-tillage), for two maize applications (grain and silage), and in four consecutive growing seasons. Every year, conventional tillage consisted in plowing and harrowing before sowing. In no-tillage, chemical weed desiccation was made with the mixture glyphosate + 2.4-D. To control weeds, the mixture fluazifop-p-butil + fomesafen was applied on the bean crop in all the planting seasons, and the herbicides nicosulfuron + atrazine on maize after crop emergence (1998--1999, 1999--2000, 2001--2002) and atrazine + metolachlor before emergence (2000--2001). Purple nutsedge (Cyperus rotundus) was the most important species under conventional soil tillage; while in no-tillage the dicotyledonous weed species (Amaranthus deflexus, Bidens pilosa, Euphorbia heterophylla, Galinsoga parviflora Ipomoea grandifolia) were the most relevant. Regardless of the maize use, the C. rotundus population and tuber bank, with prevailingly dormant tubers, was considerably reduced in no-tillage compared with the conventional system.