The arrangement of plants is a management practice that has been studied
over the years and shows, in soybean, an association with the spatial
distribution modification and the increase of yield per area.
Phytosociological surveys in crop area are of great importance, as they
provide which species are highlighted. These indices allow the knowledge
of the most important weeds within the weed community, for which we must
determine management alternatives or even changes in the system, in
order to enable its control. The objective of this study was to evaluate the
effects of different densities of soybean plants on agronomic characteristics
and also to identify weeds in different management areas of soil
preparation for soybean cultivation in the Cerrado of Roraima. The
experiments were implemented and conducted in cerrado area, in the
experimental field Água Boa of Embrapa Roraima. For the plant
arrangement experiments, a randomized block design was used in a 2x4
factorial scheme, with four replications. The treatments consisted of two
years of soybean cultivation, sown in four plant densities. The following
agronomic characteristics were evaluated: plant height; height of the first
pod insertion; stem diameter; number of node on stem; number of pods per
plant; number of branches per plant; dry mass of the plant; crop index and
grain yield. The data obtained from the measured variables were submitted
to analysis of variance with application of the F test at 5% probability. The
values referring to the means of the cultivars were compared by the Tukey
test at 5% of probability and those referring to the effects of plant densities
were measured by polynomial regression analysis. The weed
phytosociology experiment was carried out in three different areas. For the
samplings a square of welded iron was used in the ends with dimensions of
0.50 x 0.50 m. It was identified the class, family, scientific name, common
name and described the type of propagation, growth habit, life cycle and
dry mass (%). A descriptive analysis of the phytosociological parameters
was carried out: relative density, relative frequency, relative dominance,
importance value index and relative importance index. The Weed Similarity
Index was calculated for the areas. The highest average yield of BRS 8381
soybeans is obtained with the population of 387,448 plants per hectare and
BRS Tracajá soybean is obtained with 240,000 plants per hectare in the
cerrado of Roraima. The treatments used favored the appearance of new
weed species. Among the species collected in the area, the botanical
families Poaceae, Cyperaceae, Fabaceae and Rubiaceae are the most
representative.
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