Winter Oilseed Crops after Soybeans as Tools for Weed Management in Brazilian Savannah Cropping Systems

摘要

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.