BANK OF WEED SEEDS IN AGROSYSTEMS IN THE BRAZILIAN CERRADO

ABSTRACT The seed bank is the reserve of viable seeds found in the soil and is related to diversity and abundance of species that make up the weed populations. This study aimed to determine the seed bank in four distinct environments (grazing area, area of vegetables, annual crop area and perennial crop area) in two seasons (rainy and dry season). To determine the seed bank, each environment was divided into four sub-areas of 0.2 hectares, considering that each area was a repetition, totaling 16 experimental units. Samples of 0.8 kg were taken from each area, and each sample was distributed on a plastic tray and allowed to germinate in a greenhouse. The density of the individuals was determined by observing the number of emerging seedlings in the trays, performing the counting at every 18 days. Evaluations were made for ninety days in each season. The germination curve was calculated, as well as the Shannon diversity index (H'), the Sorensen similarity index and the relative importance. The seven main species identified in the environments were Cyperus rotundus, Nicandra physaloides, Galinsoga parviflora, Alternanthera tenella, Panicum maximum, Portulaca oleracea and Eleusine indica. Among the studied environments, during the rainy season, the highest number of individuals was found in annual crop and the greatest diversity in the evergreen environment. During the dry season, the number and diversity of individuals were lower and similar in all environments. RESUMO O banco de sementes é a reserva de sementes viáveis encontradas no solo e está relacionado à diversidade e abundância das espécies que compõem as populações de plantas daninhas. Com este estudo, objetivou-se determinar o banco de sementes em quatro ambientes distintos (área de pastagem, área de hortaliças, área de cultura anual e área de cultura perene), em duas épocas do ano (estação das chuvas e da seca). Para determinação do banco de sementes, cada ambiente foi dividido em quatro subáreas de 0,2 ha, sendo cada uma delas uma repetição, totalizando 16 unidades experimentais. Retiraram-se amostras de 0,8 kg em cada subárea, as quais foram distribuídas em bandeja plástica e levadas para germinar em casa de vegetação. Foi determinada a densidade de indivíduos, observando-se o número de plântulas emergentes nas bandejas, realizando-se a contagem a cada 18 dias. As avaliações foram feitas durante 90 dias em cada estação. Foram calculados a curva de germinação, o índice de diversidade de Shannon (H')