Competitividade relativa de cultivares de arroz irrigado com Aeschynomene denticulata

Abstract

This study evaluated the relative competitive ability of rice cultivars in the presence of a joint-vetch (Aeschynomene denticulata) biotype, at different replacement levels of plants in the association. The experiments were conducted in a randomized complete block design with four replications. First, it was determined the population of plants in which the final dry mass remains constant, both for the rice and for the joint-vetch (24 plants per pot). Later, two experiments were carried out to evaluate the competitiveness of the rice cultivars BRS Querência and BRS Sinuelo CL with joint-vetch plants, both conducted in replacement series, in different crop and weed combinations, varying the relative proportions of plants per pot (24:0, 18:6, 12:12, 6:18 and 0:24). Competitiveness of each species was analyzed by diagrams applied to replacement experiments and by the relative competitiveness indices. Fifty days after the emergence, tillering or number of leaves, height, leaf area and shoot dry mass were determined. Competition occurred between the rice cultivars and the joint-vetch, both were adversely affected, irrespective of the plant proportion. This resulted in reductions in all evaluated variables. Different competitive abilities were observed between rice cultivars in the presence of joint-vetch. The 'BRS Querência' was more competitive than the 'BRS Sinuelo CL' for all plant proportions and variables tested.

Competitive Ability of Canola Hybrids With Weeds

“…It is noteworthy that, in substitutive experiments, there is little evidence of having qualitative changes due to population increase, i.e., the dominance of one species over another rarely changes with the change of the population (Cousens & O'Neill, 1993). The results observed in this study are corroborated by the ones verified by Agostinetto et al (2008), Fleck et al (2008), Agostinetto et al (2009) and Galon et al (2011Galon et al ( , 2015. However, conflicting results have been verified by Agostinetto et al (2013), who found different behavior when rice and soybeans competed with cockspur, and the crops, in this case, were more competitive than the weeds, therefore occurring differences between species in competition.…”

“…Similar results occurred when wheat grew with ryegrass (Rigoli et al, 2008); barley, when infested by ryegrass (Galon et al, 2011); and rice, in the presence of Aeschynomene denticulata (common names vary regionally) (Galon et al, 2015).…”

“…The probable cause for canola having higher growth than weeds and having been more competitive than these may be related to the population of plants that competed with the crop, since the weeds showed greater competitive ability when in high population densities and not individually (Rigoli et al, 2008;Agostinetto et al, 2013;Galon et al, 2015). It is noteworthy that, in substitutive experiments, there is little evidence of having qualitative changes due to population increase, i.e., the dominance of one species over another rarely changes with the change of the population (Cousens & O'Neill, 1993).…”

“…However, in some works the weeds have shown greater competitive ability than: irrigated rice versus gulf cockspur grass (Agostinetto et al, 2008) versus red rice (Fleck et al, 2008) and Aeschynomene denticulata (common names vary regionally) (Galon et al, 2015); barley versus ryegrass (Galon et al, 2011); and soybeans versus turnip (Bianchi et al, 2006). It is noteworthy that in a community of plants there is benefit in the competition for resources for those which are established first, or for intrinsic characteristics of each cultivar or hybrids regarding the competitive ability (height, growth rate, number of tillers, leaf area, dry matter, among others); thus, smaller amounts of resources will be available in the environment, which leads to increased damage to the competitor or the crop (Agostinetto et al, 2013).…”

“…It also stands out that for the canola crop in competition with turnip and/or ryegrass no studies were found in the literature that have quantified the competitive ability of canola hybrids infested by these weeds. Many studies using the substitutive method show that there are differences in the competitive ability of other crops such as; rice versus red rice, gulf cockspur grass and Aeschynomene denticulata (common names vary regionally) (Fleck et al, 2008;Agostinetto et al, 2008;Galon et al, 2015), soybeans versus turnip, plantain signalgrass and cockspur (or cockspur grass), barnyard millet, Japanese millet, water grass, common barnyard grass, or simply "barnyard grass") (Bianchi et al, 2006;Agostinetto et al, 2009Agostinetto et al, , 2013, barley versus ryegrass (Galon et al, 2011), among others.…”