Ocorrência, dinâmica de sementes e estabelecimento inicial de Aeschynomene spp. em arroz irrigado no Rio Grande do Sul

Abstract

The jointvetch (Aeschynomene spp.) is a semi-aquatic weed from the Fabaceae family with C3 photosynthetic metabolism, characterized by paripinnate composite leaves, cortical stem, yellow-reddish papilionaceous flowers and articulated legumes, called loments. Some of the 49 species that are present in Brazil occur in rice fields from Santa Catarina and Rio Grande do Sul states, being considered the main broadleaved weed on the crop. Knowledge of ecophysiologic aspects of weeds are essentials to develop integrated management practices. Hence, this work hypothesis is that the survival of the Aeschynomene species in irrigated rice fields is due to soil seed bank dormancy and viability and, germination under flood conditions, and it’s objective is to clarify which are the characteristics and the process that allow the Aeschynomene species to establish and reproduce in irrigated rice fields. That said, four studies were conducted: 1) survey of Aeschynomene species occurring in Rio Grande do Sul, its distribution in rice production regions and practices adopted by farmers for its management; 2) determination of the seed dormancy and the most efficient method to break it; 3) determining the longevity of the seed bank in the soil; and, 4) elucidation of the effect of flood conditions, soil moisture, temperature and photoperiod in the emergence and establishment of this weed. Four species were identified in rice fields from RS: A. denticulata, A. indica, A. rudis e A. sensitiva, the first being the most frequent and, the irrigation deficiency was pointed out by farmers as the main reason for the species perpetuation. Seeds of A. denticulata and A. indica presented exogenous dormancy, which can be break using mechanical scarification on the seed coat. A. denticulata and A. indica seed bank underwent reduction of 46% and 97% in an one year period, respectively. Flood presence prevented A. denticulata and A. indica seedling emergence, that found the most favorable conditions for emergence on the temperatures and photoperiods of the simulated sowing seasons of October and November, regardless of soil moisture at field capacity or saturation, even after removing flood presence.