Banco de sementes e flora emergente de plantas daninhas

Abstract

RESUMO -Com o objetivo estudar a relação existente entre o banco de sementes e o posterior estabelecimento da flora emergente de plantas daninhas, sob sistema de semeadura direta e convencional, realizou-se uma pesquisa no município de Pedra Preta-MT. O banco de sementes e a flora emergente foram avaliados, em cada sistema de cultivo, em 50 células contíguas de 1 m². O banco de sementes foi determinado a partir de amostras de 2,4% da área de cada célula na profundidade de 0-5 cm, em setembro de 2003, por meio da técnica de flotação. A flora emergente foi avaliada por meio de seis levantamentos sucessivos, até novembro de 2004, realizados na área total de cada célula, com retirada dos indivíduos após cada avaliação. Esses dados foram utilizados para calcular os parâmetros fitossociológicos e também a correlação entre o banco de sementes e a flora emergente. A similaridade entre o banco de sementes e a flora emergente foi baixa tanto no sistema de semeadura direta quanto no convencional. Houve correlação significativa apenas para Amaranthus deflexus e Eleusine indica entre o banco de sementes e a flora emergente. Para A. deflexus a correlação foi significativa nos dois sistemas de semeadura e, para E. indica, somente para semeadura direta. Palavras-chave: Amaranthus deflexus, correlação, fitossociologia.ABSTRACT -A study was carried out in Pedra Petra-MT aiming to study the relation between seed bank and posterior aboveground weed in annual crop fields under no-till and tillage systems. The seed bank and weed flora were assessed in fifty contiguous 1 m² cells, under both cultivation systems. The seed bank was determined from soil samples from 4% of the area of each cell at 0-5 cm depth using the flotation technique. The aboveground weed vegetation was evaluated by six successive surveys until November 2004, carried out in the total area of each cell, with removal of the individuals from the area after each evaluation. These data were used to calculate the phytosociological parameters and the correlation between the seed bank and aboveground weed. The similarity between the bank seed and the aboveground vegetation was low for both systems. Only Amaranthus deflexus and Eleusine indica showed to have significant correlation between bank seeds and the aboveground weed vegetation. For A. deflexus, the correlation was significant in both cultivation systems, while for E. indica, only under no-till.

Floristic diversity of the soil weed seed bank in a rice-growing area of Brazil: in situ and ex situ evaluation

“…Another possible explanation for the differences observed in the present study is that occasional periods of soil water stress and losses (due to intraspecific and interspecific competition) resulted in germination failure, as observed by Herault & Hiernaux (2004) in a weed seed and population dynamics study carried out in Africa. Similar observations were reported by Isaac & Guimarães (2008), in a study of the weed seed bank and emergent flora in crop fields in the state of Mato Grosso, in western Brazil. In the greenhouse, our seeds were protected from predators and systematically irrigated, which did not happen in the field.…”

“…However, it is higher than the 451 seeds m −2 found by Gasparino et al (2006), in crop fields in the state of Paraná, in southern Brazil, and the 2,028 seeds m −2 found by Isaac & Guimarães (2008) in direct seeding in the state of Mato Grosso, in western Brazil.…”

“…Various studies recently conducted in the tropics have been aimed at identifying weed species in crop fields, in pastures and in the corresponding seed banks (Silva & Dias-Filho 2001;Lacerda et al 2005;Begum et al 2006;Lopes et al 2006;Ikeda et al 2008;Isaac & Guimarães 2008;Andrade et al 2009;Costa et al 2009;Kamoshita et al 2010). However those studies were focused on agribusiness rather than on generating scientific knowledge for use in subsistence farming.…”

Germinação das sementes de Conyza canadensis e Conyza bonariensis em função da disponibilidade hídrica no substrato

“…Após esse perío-do, todos os tratamentos foram transferidos para substrato umedecido com água destilada, sendo realizada a contagem das sementes germinadas por mais 10 dias. A viabilidade das sementes não germinadas foi verificada por meio do teste da "pressão ao toque", com pinça, considerando-se como viáveis as sementes firmes (Isaac & Guimarães, 2008).…”

Seed bank from soil of coffee plantations associated with grevillea trees

“…Correlation between bank seeds and tht aboveground weed vegetation must be studied to understanding how biotic and abiotic components act in this cycle. Isaac & Guimarães (2008) observed relation between seed bank and posterior aboveground weed i n annual crop fields under no-till and tillage systems only for Amaranthus deflexus and Eleusine indica. For A. deflexus, the correlation was significant in both cultivation systems, while for E. indica, only under no-till.…”