Weed Seedbank in Rice Fields

The weed seedbank in the soil is the major source of weeds in rice fields. Therefore, information on ecological aspects of weeds occurring in rice, including their potential seed production, is crucial for weed management. The size of the weed seedbank in rice fields is highly variable depending on the climate, relief position, soil moisture content, depth of sampling, history of the areas and management practices used by farmers. As a survival strategy, colonization and persistence in the communities, most common weeds in rice fields produce huge number of seeds and vegetative propagules with physical and physiological dormancy mechanisms, insuring seed viability in the soil for long periods. A large proportion of weed seedbank remains generally on or close to the soil surface after seed rain. Sampling protocols involve the use soil cores at variable soil depths. Determination of the size of the weed seedbank can be made by seed direct extraction and germination methods. The latter is more precise with respect to enumeration of viable seeds in the soil. Weed management in rice fields should focus on methods suitable to decrease the weed population in the soil seedbank

Floristic and phytosociology of weeds in pastures in Maranhão State, Northeast Brazil

ABSTRACT Knowledge of weed floristic composition and phytosociology are key factors for improving weed management in pastures. Information on weed species that occur in pastures in Northeast Brazil, particularly in Maranhão State is very limited. It is, therefore, important, to search for information to help farmers to control weeds in livestock farming. This paper describes the weed flora diversity and community structure parameters, including density, frequency, abundance and importance value for each weed species found in five pastures of same age and management in Maranhão State, Northeast Brazil. The weed survey was carried out using a wooden frame (80 cm x 30 cm) placed randomly on the soil surface 30 times in each pasture (n = 150). Weeds were pulled out, separated by species and counted. The weed flora was represented by 996 individuals, from nine families, 15 genera and 19 species. Weed density within pastures was of 44.3 plants m-2. The weed flora was dominated by species of the Cyperaceae and Poaceae families. The most important weed species based on Importance Value were Eragrostis ciliaris (IV = 32.97), Cyperus rotundus (IV = 31,95), Cyperus luzulae (IV = 27,50), Cyperus sphacelatus (IV = 27,42), Pycreus lanceolatus (IV = 27,33) Cyperus haspan (IV = 25,72) and Eleusine indica (IV = 23,49). Weed diversity, based on Shannon Diversity Index was very high (H' = 4.37 nats ind-1). Our results could lead to improved weed management in pastures in Maranhão State, Northeast Brazil

Banco de sementes do solo em áreas de cultivo de subsistência na Floresta Ombrófila Aberta com Babaçu (Orbygnia phalerata Mart.) no Maranhão

Os objetivos desta pesquisa foram identificar e avaliar a estrutura das comunidades e a diversidade das espécies herbáceas invasoras presentes no banco de sementes do solo, em áreas de cultivo de subsistência nos Municípios de Bacabal, Lago Verde, São Luís Gonzaga e Vitorino Freire, localizados em trechos da Floresta Ombrófila Aberta com Babaçu, no Maranhão. Em cada município foram alocadas 15 parcelas de 50 m2, de onde foram retiradas 90 amostras de solo com um gabarito de metal vazado de 25 x 16 x 3 cm e colocadas em bandejas em casa telada. Foi avaliado o número de espécies e de indivíduos, bem como os valores relativos da densidade, frequência, abundância e o valor de importância de cada espécie. Os dados foram submetidos às Análises de Variância e de Coordenadas Principais. A diversidade foi calculada por meio do Índice de Diversidade de Shannon. O banco de sementes apresentou a maior riqueza florística em Bacabal, com 50 espécies de 34 gêneros e 17 famílias, bem como o maior número de indivíduos, 11.541. A maior similaridade florística foi observada entre Lago Verde e Vitorino Freire. As espécies predominantes, baseado no valor de importância, foram: Ludwigia octovalvis (VI = 34,8%) em Bacabal; Scleria lithosperma (VI = 37,0%), em Lago Verde; e Boerhavia erecta (VI = 40,4%), em São Luís Gonzaga; e (VI = 57,0%), em Vitorino Freire. A maior diversidade foi observada em Bacabal, com H’ = 2,66 nats ind-1. Os resultados podem ser aplicados na previsão de infestações de plantas invasoras nos municípios da região

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

The objective of this study was to compare the ex situ and in situ floristic diversity of the soil weed seed bank of a rice field in northeastern Brazil. In a rice field in the county of Bacabal, located in the state of Maranhão, thirty 25-m² plots were laid out. From 15 plots, soil samples (6/plot; n = 90) were taken with a soil probe (25 × 16 × 3 cm) and placed in aluminum trays in the greenhouse. From the remaining 15 plots, weed samples (6/plot; n = 90) were taken with the same soil probe. The number of seeds was estimated by germination. We evaluated the numbers of species and individuals, as well as the density, frequency, abundance and importance value (IV) for each species. Diversity was computed by the Shannon index (H'). We recorded 13,892 individuals (among 20 families, 40 genera and 60 species), of which 11,530 (among 50 species) germinated ex situ and 2,362 (among 34 species) germinated in situ. The family Cyperaceae had the highest number of species (16), followed by Poaceae (10). The dominant species, in situ and ex situ, were Schoenoplectus juncoides (IV=47.4%) and Ludwigia octovalvis (IV=34.8%), respectively. Floristic diversity was higher ex situ (H'=2.66). The information obtained here could help determine the infestation potential of these species, which could lead to improved management strategies

Soil weed seed bank in situ and ex situ at a smallholder field in Maranhão State, northeastern Brazil

The objective of this research was to assess the density, floristic composition, phytosociology and diversity of a soil weed seed bank ex situ by germination in a greenhouse and in situ by weed sampling on a smallholder corn field located in Lago Verde County, Maranhão State. Fifteen pairs of 25 m2 plots were designated. In half of these plots, 90 soil samples were collected with an open metal template measuring 25 x 16 x 3 cm and placed in a greenhouse to germinate. In the other half, 90 weed samples were collected using the same metal template. We recorded a total of 1,998 individuals from 40 species, 31 genera and 16 families, from which 659 individuals germinated in situ and 1,339 ex situ. Density was higher ex situ, with 372 plants m-2. The Cyperaceae family had the highest floristic richness with nine species, followed by the Poaceae with six. The dominant species based on the Importance Value Index were Lindernia crustacea (IVI 27.7%) in situ and Scleria lithosperma (IVI 37.0%) ex situ. Floristic diversity was higher ex situ, with H' = 2.66 nats ind-1. These results could help predict infestation potential and could lead to improved weed management strategies in corn-growing areas on smallholdings in Maranhão State, northeastern Brazil

Avaliação da função sistólica longitudinal na insuficiência cardíaca com fração de ejeção normal

FUNDAMENTO: A insuficiência cardíaca com fração de ejeção normal (ICFEN) é hoje o modelo mais prevalente de IC em diferentes estudos epidemiológicos, e anormalidades na função sistólica de grau leve (subclínica) têm sido observadas nesses pacientes quando a contratilidade do ventrículo esquerdo (VE) é avaliada no eixo longitudinal (S') pelo ecocardiograma Doppler tecidual (EDT), mesmo na presença de fração de ejeção do VE normal. OBJETIVO: Avaliar se pacientes com diagnóstico de ICFEN, de acordo com os novos critérios da Sociedade Europeia de Cardiologia, apresentam alterações da função sistólica constatada pela medida de S' quando comparados com os pacientes em que a ICFEN não foi confirmada. MÉTODOS: Cento e dezoito pacientes com sinais ou sintomas de IC foram submetidos a dosagem de BNP e ao EDT com medidas da velocidade do eixo longitudinal na sístole (S') e diástole (E') e medidas do fluxo transmitral durante a diástole (E,A). RESULTADOS: ICFEN foi confirmada em 38 pacientes (32,2%). O pico da velocidade miocárdica durante a sístole (S') e a velocidade miocárdica no inicio da diástole (E') estavam significativamente diminuídas em pacientes com ICFEN em relação aos pacientes em que a ICFEN foi excluída (7,8 ± 2,3 cm/s vs 9,4 ± 2,5 cm/s p=0,002 - 7,7 ± 2,6 cm/s vs 9,4 ± 2,5 cm/s-p=0,001). Valores médios de BNP foram mais elevados em pacientes com ICFEN (140,5 ± 122,4 pg/ml vs 23,1 ± 25,0 pg/ml p< 0,0001). S' se correlacionou de modo significativo com E' (r=0,457 - p< 0,0001) mostrando uma forte ligação entre contração e relaxamento ventricular. CONCLUSÃO: Nossos achados mostram redução da função sistólica, quando avaliada pelo S', na ICFEN, existindo correlação linear entre o grau de disfunção sistólica (S') e diastólica (E/E'e E')