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Características morfofisiológicas diferenciais de plantas podem influenciar as relações de competição entre cultura e plantas daninhas. O objetivo do presente trabalho foi avaliar a influência das características de plantas de quatro cultivares de soja sob competição ou não com outros dois cultivares de soja, simulando espécies daninhas dicotiledôneas, durante a fase vegetativa de crescimento. Para isso, conduziram-se dois experimentos: um em vasos, visando fornecer subsídios quanto ao crescimento inicial das plantas de soja; e outro em campo, a fim de acompanhar características de crescimento das plantas. Em campo, foram comparados os seguintes fatores e tratamentos: três condições de competição (ausência de plantas concorrentes; presença de plantas dos cultivares de soja BRS 205 ou Cobb); e quatro cultivares reagentes de soja à competição (IAS 5, BR-16, CD 205 e Fepagro RS-10). Cultivares de soja apresentaram variações na velocidade de emergência e de crescimento inicial de plantas. A presença de plantas concorrentes, independentemente das características próprias, afetou a ramificação da soja. Os cultivares Fepagro RS-10 e BR-16 apresentaram rápido crescimento durante a fase inicial de desenvolvimento; CD 205, ao contrário, mostrou lento crescimento nesta fase. Cultivares de soja de ciclo precoce cobriram com mais rapidez o solo durante os primeiros 45 dias do que os tardios.Differential morphological plant characteristics may influence competition relations between crop and weeds. The aim of this study was to evaluate the influence of plants of four soybean cultivars and two other soybean cultivars, mimicking dicotyledonous weed species, on their relationships during the vegetative growth period. Thus, two experiments were carried out: one in pots, to provide data for initial soybean plant growth; and the other in the field, to monitor plant growth characteristics. The following factors and treatments were tested in the field: three competition conditions (absence of competing plants or presence of the soybean cultivars BRS 205 or Cobb), and four soybean cultivars reagent to competition (IAS 5, BR-16, CD 205, and Fepagro RS-10). Soybean cultivars showed varied emergence speed and initial plant growth. The presence of the concurrent plants, regardless of their plant characteristics, affected soybean branching. Fepagro RS-10 and BR-16 cultivars had a fast growth during the initial development period; CD 205, on the contrary, showed slow growth during this phase. Early maturity soybean cultivars cover the soil more rapidly than late maturity cultivars, during the first 45 days of growth.

As perdas de produtividade das culturas em decorrência da competição de plantas concorrentes geralmente aumentam quanto mais semelhantes forem suas características morfofisiológicas. O objetivo deste trabalho foi avaliar os efeitos da competição de cultivares de soja, simulando espécies daninhas dicotiledôneas, sobre cultivares de soja portadores de características diferenciais de planta. Para isso, conduziu-se um experimento em campo, em Eldorado do Sul-RS. Os fatores e tratamentos comparados foram: três condições de competição (ausência de plantas de soja concorrentes e presença de plantas concorrentes do cultivar de soja BRS 205 ou Cobb); e quatro cultivares reagentes de soja à competição (IAS 5, BR-16, CD 205 e Fepagro RS-10). Avaliaram-se variáveis relacionadas à produtividade dos cultivares e outras correlatas. Características dissimilares em plantas de cultivares de soja, como estatura e ciclo, resultaram em habilidade competitiva diferenciada com plantas concorrentes. O cultivar de soja CD 205, de estatura elevada e ciclo tardio, mostrou alta habilidade competitiva; IAS 5, de baixa estatura e ciclo precoce, apresentou baixa tolerância à competição, enquanto BR-16 e Fepagro RS-10 são intermediários. Cultivares com elevada habilidade competitiva, além de tolerarem a competição, preservando o potencial de produtividade, também suprimem a produção de grãos das plantas concorrentes.Due to concurrent plant competition, crop yield losses generally increase as their morphophysiological characteristics become more similar. The objective of this research was to evaluate the competitive effects of soybean cultivars mimicking dicotyledonous weed species on soybean cultivars holding dissimilar plant characteristics. Thus, a field experiment was carried out in Eldorado do Sul-RS. The factors and treatments compared were: three competition conditions (absence of competing plants and presence of the soybean cultivar "BRS 205" or "Cobb"), and four soybean cultivars reagents to competition ("IAS 5", "BR-16", "CD 205", and "Fepagro RS-10"). Variables related to cultivar yield and other correlatives were evaluated. Dissimilar characteristics in soybean plant cultivars such as height and maturity length, resulted in differentiated competitive ability with concurrent plants. The cultivar CD 205 of high stature and late maturity showed high competitive ability while IAS 5, of low stature and early maturity, showed low tolerance to competition, and BR16 and Fepagro RS-10 showed intermediate tolerance. Soybean cultivars holding high competitive ability as well as tolerance to competition, thus preserving their yield potential, also suppressed grain yield of competing plants.

ABSTRACT: The presence of volunteer corn plants in coexistence with soybean has been increasing since the introduction of glyphosate-resistant corn hybrids. This study aimed to evaluate the effect of interference of volunteer RR® corn plants at different densities on two RR® soybean cultivars. The experiment was conducted in Rio Verde, GO. The experimental design was a randomized block design in a factorial arrangement (2×5), with four replications. Factor A consisted of two soybean cultivars (BMX Potência RR® and M8210 IPRO®), while five densities of RR® corn plants per m2 (0, 4, 8, 12, and 16) were adopted for factor B. The following evaluations were carried out for soybean: plant height, SPAD index, percentage of interrow closure, shoot dry matter, first pod height, number of pods per plant, 100 grain weight, and grain yield of grains. Soybean plant height presented a linear and positive relationship with the increased density of corn plants. Shoot dry matter, 100 grain weight, number of pods per plant, and grain yield were negatively affected by the increased density of volunteer corn infestation. The soybean cultivar M8210 IPRO® was more susceptible to corn plant interference when compared to the cultivar BMX Potência RR®.