Separação de competição e alelopatia em associações entre capim-annoni-2 (Eragrostis plana) e braquiária (Brachiaria brizantha cv. Marandu) em cultivo hidropônico

Abstract

The capim-annoni-2 (Eragrostis plana Nees), is an exotic grassland that represents a great threat to brazilian ranchers, due to its high competitive capacity and liberation of allelochemicals. In the field, the competitive and allelopathic effects of its presence occur simultaneously, making it impossible to distinguish it, so it is necessary to develop methodologies that allow determining its relative importance in the ecological interactions between the invader and the cultivated species. The aim of this work was to determine the relative importance of the allelopathic and competitive effects in the process of interference between capim-annoni-2 and brachiaria (Brachiaria brizantha cv. Marandu). The experiment was conducted in two stages, in a completely randomized design, with three replications. The first stage identified the full interference between the two species, and the treatments were composed of densities of 05 and 10 plants of each species, both in monoculture and in association. The second stage determined the allelopathic effect caused by allelochemicals released by capim-annoni-2 in the hydroponic solution on brachiaria plants. This effect was measured after replacement of N, P, K consumed in the solution containing capim-annoni-2. The assessments were: shoot length (SL), root length (RL), shoot matter (SM) and root matter (RM) and shoot dry matter (SDM) and root dry matter (RDM). Data were submitted to analysis of variance by the F test and the means were compared by the Tukey test. At the end of the two steps the calculations for the relative importance indices were performed. In the first stage, 10 brachiaria plants reduced RL, SL, RL and DSM of 5 capim-annoni-2 plants compared to monoculture. However, 10 plants of capim-annoni-2 increased RL, SM and SDM and RDM of 05 brachiaria plants, characterizing high plastic capacity of brachiaria plants under interference. In the second stage, there was a reduction of SL, RM and RSM of brachiaria plants developed in a solution previously occupied by 05 capimannoni-2 plants, evidencing allelopathic interference. Through the calculations of relative competition index (RCI) and competitive ratio (CR), it was observed that brachiaria plants are facilitated with the presence of capim-annoni-2 and at the same time are highly competitive to capim-annoni-2, causing reductions in development variables. The RNE evidenced competition when the density of capim-annoni-2 was reduced brachiaria increased, when compared to the other treatments, evidencing that beyond interspecific competition there is intraspecific competition for brachiaria. There was an allelopathic effect of capim annoni-2 on the brachiaria, but this did not overcome the stimulatory effect observed in the total interference. Further studies should investigate the stimulatory effect exerted by capim-annoni-2 on brachiaria plants.