Effects of Lotus tenuis density upon the emergence, survival and cover of Cirsium vulgare

Abstract

After burning for raising the stocking rate, the Paspalum quadrifarium-dominated grass- lands of the Flooding Pampa become invaded by a forage legume, Lotus tenuis, and /or by Cirsium vulgare among other weed species. Aiming to compare the relative impact of L. tenuis on pre and post-emergence stages of C. vulgare, the emergence, survivorship and coverage of C. vulgare were evaluated in response to four sowing densities of L. tenuis (0.0; 0.25; 0.5 and 1.0 seeds/cm²) and two spatial patterns of C. vulgare (15 uniformly distributed seeds within a circle of 5 cm diameter or on a circle of 28 cm diameter), by using a factorial design under greenhouse conditions. The emergence of C. vulgare lineally declined with increasing densities of L. tenuis, independently of its spatial pattern of sowing. While the emergence of C. vulgare was reduced up to 40% by the presence of L. tenuis, the effects of this species on the seedling mortality of the emerged seedlings reached up to 270% of increment. In contrast with the emergence, which was mostly affected by the maximum densities of L. tenuis, the final coverage of C. vulgare was similarly reduced for the presence of L. tenuis irrespective of its density. These results confirm the occurrence of pre-emer- gent effects of L. tenuis seeds on C. vulgare seeds, as previously detected under laboratory condi- tions, even under potentially adverse conditions for the activity of allelopathic compounds..