R.P. Rigoli

Relative Competitive Ability of Wheat (Triticum aestivum) Intercropped with Italian Ryegrass (Lolium multiflorum) or Wild Radish (Raphanus raphanistrum)

Replacement series experiments make possible the study of inter and intraspecific competition, based on the fact that the yield of the species under competition can be determined by comparing with plants in monoculture. The objective of this work was to investigate the relative competitive ability of wheat crop with the weeds Italian ryegrass or wild radish. Three experiments were conducted under greenhouse at UFPel, in 2006. The treatments were conducted in a completely randomized design, with four replications, with the treatments arranged in replacement series. The proportions of wheat plants and competitors Italian ryegrass or wild radish were: 100/0, 75/25, 50/50, 25/75 and 0/100, always with a total population of 900 plants m-2. Competitiveness statistical analysis consisted in applying diagrams to the replacement series and interpreting the competitiveness indices. The competitive relationships between wheat and ryegrass or between wheat and wild radish plants are altered by the proportion of plants that compose the association. Wheat shows superior competitive ability to ryegrass but inferior to wild radish when the species have similar proportions of plants in the associations and when these species occur in the same ecological niche.

Período crítico de competição de plantas daninhas com a cultura do trigo

Several factors limit wheat crop yield, with competition imposed by weed plants being the most outstanding. The objective of this study was to determine the critical period of weed interference in wheat crop and the effects of competition on morphological variables and yield components. This field experiment was carried out at Centro Agropecuario da Palma, Capao do Leao, RS, Brazil. Factors tested were periods of coexistence and weed plant control in FUNDACEP 52 wheat cultivar. Periods of coexistence and/or control were: 0, 7, 14, 21, 28, 35, 42 and 126 days after emergence (DAE). Results obtained for variables at the end of each control period or coexistence, and at harvesting, showed that wheat yield components were not affected by competition with weed plants and that effective control measures should be taken between 12 and 24 days after emergence.

Competitividade relativa de soja com arroz-vermelho

To reduce weed plant infestation, especially red-rice, areas traditionally cultivated with flooded rice in Rio Grande do Sul, Brazil, are being intercropped with soybean under a rotation system. The objective of this study was to quantify competitive abilities between soybean crop and red-rice biotype. Treatments were arranged in substitution series, with five proportions being used (0:16, 4:12, 8:8, 12:4 and 16:0) of soybean and red-rice, in a randomized complete block design, with four replications. Air dry matter and leaf area of the plants were evaluated. Competitiveness was analyzed through diagrams applied to substitution experiments and competitiveness indexes. Soybean presents higher competitive ability for environment resources than red-rice. Soybean crop production increases when close to a red-rice plant than to a soybean plant.

Influência de doses reduzidas do glyphosate no tomateiro (Lycopersicon esculentum)

Tomato plant (Lycopersicon esculentum) is grown in all regions in Brazil since it is widely used in cooking, processed or fresh. Glyphosate drift has been found rcited as one of the factors interfering negatively in vegetables cultivated in areas adjacent to rice plantations. The objective of this study was to evaluate the effects of reduced rates of glyphosate on tomato plants, applied at of 0, 15, 30, 45, 60, 75 and 90% of the commercial dose (1.260 g ha-1) 30, 50 and 70 days after transplanting (DAT) the tomato plants. The variables analyzed were: phytotoxicity, plant height, number of flowering clusters, and flower and fruits/plant. The data were submitted to analysis of variance, the Tukey test and regression. Glyphosate application at rates higher than 378 g ha-1 affected the growth of the tomato plants negatively, regardless of their development stage.

Association of plant traits in oat cultivars with competitive ability

Morphological crop plant traits which confer greater competitive ability may integrate cultural weed management measures, thus reducing the use of herbicides. The aim of this study was to investigate whether a fast initial growth of oat cultivars relate to their competitive potential with concurrent plants. A field experiment was conducted at the Universidade Federal de Pelotas, in Capao do Leao-RS, during the 2006 growing season. The oat cultivars ALBASUL, CFT 1, UPFA 22, and URS 22, which were tested under three competition conditions (absence of concurrent plants, presence of flax or of wheat as competitors) were used. The experiment was arranged in a completely randomized design, with four replicates. Many morphological characteristics in oat plants were evaluated at the initial phase of their development, as well as other agronomic traits at the end of the oat cycle and of the cycle of its competitors. Oat cultivars reacted differently to the presence of concurrent plants. The UPFA 22 cultivar generally presented greater values for the morphological plant traits associated with competitive ability; whereas URS 22 showed deficiencies in traits advantageous to competition. The cultivars UPFA 22 and CFT 1 demonstrated a high potential to compete with concurrent plants. The morphological traits of oat cultivars evaluated at the beginning of their development, in general, did not sustain the competitive ability until the end of their cycles.

Potencial competitivo de cultivares de trigo em função do tempo de emergência

Morphophysiological characteristics of wheat cultivars define their capacity to compete naturally with weed plants. The objective of this study was to quantify variations in emergence time, growth and initial development of wheat cultivars with different cycles and plant heights. This greenhouse experiment was arranged in a completely randomized experimental design, with three replications at the Universidade Federal de Pelotas, in 2006. Treatments consisted of seven wheat cultivars; BRS Guatambu; BRS Taruma; BRS Timbauva; BRS Camboata; BRS Buriti; CD 105; BRS Camboim, and two weed plants, turnip and Italian ryegrass. Emergence time of the cultivars and weed plants was evaluated up to 10 days after sowing. Plant height was determined at 10, 20 and 35 days after emergence (DAE) and development stage at 20 and 35 DAE. Leaf area was measured at 35 DAE as well as dry matter of the aerial parts and roots, with data being submitted to analysis of variance and means compared by the Duncan test. Among the characteristics of the wheat cultivars evaluated, cycle duration and plant height did not affect emergence time with cultivars BRS Guatambu, BRS Timbauva and BRS Camboim, presenting the highest competitive potential at the beginning of the cycle and BRS Tarumat showing the lowest means for the morphological variables.

Controle de arroz-vermelho (Oryza sp.) com o herbicida nicosulfuron ou a mistura formulada de imazethapyr + imazapic

Red rice control efficacy using nicosulfuron or a formulated mixture of imazethapyr + imazapic was evaluated. A greenhouse experiment was carried out at Faculdade de Agronomia Eliseu Maciel (UFPel) in Capao do Leao (RS), during the 2005/2006 growing season, in a randomized complete block design and four replications. Treatments were arranged in a 2 x 7 factorial, with factor A being the herbicides and factor B the herbicide rates (0, 0.25, 0.50, 0.75, 1.0, 1.25 and 1.50 L ha-1). The herbicides were applied over red rice plants at the V4 development stage. Control, plant height and aerial dry mass were evaluated. There was a significant interaction for the variables between the factors studied. Increased herbicide rates resulted in increasing control responses and decreased plant height and dry biomass. Results showed that red rice is efficiently controlled by the herbicides. Control efficacy is not restricted to the formulated mixture of imazethapyr+imazapic, also occurring with nicosulfuron starting from 40 g ha-1.

Uso associado e contribuições relativas de genótipos de aveia e de práticas de manejo à competitividade da cultura com plantas concorrentes

The association of management practices, such as population level and forms of nitrogen fertilizer application, may increase the competitive potential of a crop against concurrent plants. The aim of this study was to establish the relative contributions of oat genotypes and management practices and their combined use in modifying the competitivity of the oat plant against concurrent plants. Thus, a field experiment was conducted at the Universidade Federal de Pelotas, in Capao do Leao-RS, during the winter season of 2006, in a completely randomized block design, with four replicates, in a 2 x 2 x 2 x 2 factorial scheme.The competition conditions were (absence of concurrent plants or presence of association of flax + wheat as concurrent plants), oat cultivars (ALBASUL or UPF 16), oat population (230 or 150 plants m-2), and forms of nitrogen splitting were (10 kg of N ha-1 at seeding time, 15 kg of N ha-1 at the four leaf stage, and 20 kg of N ha-1 at the seven leaf stage, or, alternatively, 20, 15, and 10 kg of N ha-1 at those same times) as the factors studied. Additionally, a comparative check was added comprising only the association flax + wheat. The morphological characteristics of the oat plants, as well as of their competitors were evaluated in the beginning of the development period and other traits at oat maturity. The oat cultivar UPF 16 showed a greater competitive potential, compared to ALBASUL, at the initial period of growth. .Larger oat plant population and increase of nitrogen application at seeding time favor oat grain yield increase as well as its competitive potential increase, stimulating the suppression of the concurrent species.