-Plants compete for resources present below and above the soil surface. The objective of this work was to separate the individual effects of the competition for resources between soybean and corn as competitor plants. The experiment was conducted in a greenhouse, in 2014/2015. The treatments consisted of soybean cultivars (TEC 5718 and TEC 6029) in competition conditions with corn (no competition, competition for soil resources, competition for solar radiation and total competition). The variables evaluated were plant height at 7, 14, 21, 28, 35 and 42 days after emergence (DAE), stem/culm diameter, leaf area, shoot dry mass, root dry mass and the chlorophyll index, at 42 (DAE). The competition for soil resources between soybean and corn is pronounced, being that short cultivars with determinate growth habit, such as TEC 5718, invest more in root biomass, specific leaf area and leaf area ratio when in competition. The soybean cultivars do not suppress corn, but allow it to benefit when associated to its root system, increasing the shoot and root dry mass, leaf area and chlorophyll index.Keywords: Glycine max, Zea mays, water, competitiveness, solar radiation, competitor plant. de plantas, aos 7, 14, 21, 28, 35 RESUMO -As plantas competem por recursos presentes abaixo e acima da superfície do solo. O objetivo deste trabalho foi separar os efeitos individuais da competição por recursos entre a soja e o milho como planta competidora. O experimento foi conduzido em casa de vegetação, em 2014/15. Os tratamentos consistiram de cultivares de soja (TEC 5718 e TEC 6029) sob condições de competição com milho (ausência de competição, competição por recursos do solo, competição por radiação solar e competição total). As variáveis avaliadas foram estatura

Article AbstractSpontaneous corn plants in soybean crop are considered weeds because they compete for the same environmental resources. The objective of this study was to evaluate the competitive ability of soybean cultivars when in coexistence with spontaneous corn plants.A field experiment was conducted in CCGLTEC, Cruz Alta/RS, in 2014/15, in a split-plot design, with the main plot being composed of four different cultivars (CD 2694, BMX 7166, TEC 5718, TEC 6029) and the subplots of interference conditions (without the presence of corn volunteer plants, in the presence of corn until the V 3 , V 6 , V 9 stages, or for the entire soybean cycle. Leaf area, shoot dry mass, plant height, chlorophyll index, and development stage were determined at 15, 30, and 49 DAE; we also determined apparent biological productivity, apparent harvest index, and components of productivity and grain yield. The cultivars showed losses in leaf area and shoot dry mass when in coexistence with corn (8 plants m-2) in the three periods evaluated. All cultivars showed losses in apparent biological productivity, apparent harvest index, and final grain yield when growing under competition throughout the cycle. Cultivars with a medium/long growth cycle, such as CD 2694 (maturity groups (GM): 6.9) and BMX 7166 (GM: 6.6), show a higher competitive ability up to V 9 stage in contrast to cultivars with a short cycle, such as TEC 5718 (GM: 5.9) and TEC 6029 (GM: 5.7).

No abstract

The usage of cover crops is an adopted cultural measure that shows positive effects when associated with the no-till system and weed management. During the cycle of the plants there might be competition within them for water, solar radiation and nutrients and effects of allelopathic substances released by leaching, volatilization and/or root exudation in the environment might also coexist. The study aimed to quantify the floristic composition of weed species in an cultivated area with cover crops during winter and summer, for two years, 2011/12 and 2012/13, in an experimental area of UFSM, Campus of Frederico Westphalen – RS state, Brazil. The treatments consisted of Italian ryegrass, wild radish, black oat, vetch, wheat and uncultivated, in winter, and, sorghum, sunflower, black velvet bean, dwarf velvet bean, gray velvet bean and green velvet bean in the summer. In the first year of the experiment, a diversity of weeds in winter was observed, especially occuring Stellaria media and Bowlesia incana. In summer, the weeds of higher importance were Ipomoea spp. and Bidens spp., both of utter importance in agricultural systems. Winter cover crops of wild radish and Italian ryegrass and summer cover crops of sorghum and sunflower provided a lower weed infestation