We aimed with this study to evaluate the
potential of oilseed crops planted following soybean, in terms of their ability
to inhibit the occurrence of weed species under Brazilian Savannah cropping
systems. The long-term experiment was installed in 2010 at Dourados, MS,
Brazil, and in completely randomized blocks design with five replications with
12 × 24 m plot size. For three consecutive years (2010/11, 2011/12 and
2012/13), soybeans were planted in all the area by October/November being
harvested in February/March, when previously marked plots were planted in April
with: (1) radish (Raphanus sativus); (2) rapeseed (Brassica napus);
(3) crambe (Crambe abyssinica); (4) winter fallow-no plantation after
soybeans. In all years the same crop was repeated at the same plots, with no
crop rotation. Phytosociological characterization of weed species was carried
out in winter (after oilseeds harvest), pre-planting and post-emergence of
soybean for the three years. Relative abundance, frequency and dominance, as
well as the importance value for each species, was obtained. Areas were also
intra-characterized by the coefficients of Simpson, Shannon-Weiner and Shannon-Weiner’s
Evenness Proportion, and areas were compared for species dissimilarity with
Jaccard’s presence-only coefficient, by multivariate cluster analysis. Oilseed
crops definitely contribute for sustainable weed management as a cultural tool.
The most important oilseed crop weeds in the Savannah-like region of Brazil
were Amaranthus hybridus, Richardia brasiliensis, Lepidium
virginicum, Leonotis nepetifolia and Hybanthus parviflorus.
After three years of repetitive crop succession, some weeds were selected, and
rotation in Winter is advised at least every two or three years.