ECOLOGICAL SUSTAINABILITY AND WEED SELECTION IN LONG-TERM CROP ROTATION INVOLVING OFF-SEASON MAIZE IN TROPICAL BRAZIL

Abstract

Maize is important in crop rotation in Tropical Brazil, with vast off-season following soybeans. Off-season maize is being grown intercropped with forages to supply pastures to cattle after maize harvest and to help with weed suppression. There is, however, scarce information on weed dynamics in the soybean and maize + forage cropping system, mainly in the long term. The objective was to evaluate weed infestation and the ecological sustainability of successive years of off-season maize cultivation, under crop succession with soybean. The phytosociological method was used to assess the importance value of weed infestation in five areas: T1 four years of soybean/off-season maize + brachiaria; T2 four years of soybean/cowpea bean; T3 four years of soybean/off-season maize; T4 six years of soybean/off-season maize; T5 nine years of soybean/off-season maize. In general, T1 had lower absolute infestation, and the longer the maize-soybean succession, the more weeds there were. The main species found were Digitaria horizontalis, Gnaphalium coarctatum,Commelina benghalensis, and Conyza ssp., all occurring only in areas with longer maize and soybean succession. Therefore, different cropping systems influence weed composition and absolute infestation levels. The use of maize intercropped with brachiaria can be a tool in weed control for maize producers.