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The interest was the seed longevity dynamics of annual ryegrass in natural conditions as an important tool to explain its dynamics in no tillage systems used in the South of Brazil. The species is commonly managed for natural re-sowing and, in this way, allows cattle grazing with reduced costs during the winter time. In February of 2003, twenty bags of nylon screen containing sterilised soil with 100 seeds in each were randomly buried in the field, 5 cm deep. Around every three or four months, four sacks were exhumed. Seeds were counted and tested using germination and tetrazolium tests.The seeds showed high primary dormancy, which was overcome very fast. After 108, 226, 326, 565 and 732 days of burial there were no significant differences as the secondary dormancy of the seeds that did not germinate in autumn was not high. The last exhumation period was significantly different from the others due to the strong decay on seed viability. As few seeds remained viable after 732 days, the soil seed bank was classified as transient, being evident that in annual pastures the transitory seed banks have a main role in the regeneration of the species.

O conhecimento da ecologia de bancos de sementes do solo (BSS) contribui para a proposição de técnicas de manejo dos BSS de plantas espontâneas em lavouras estabelecidas sobre campo nativo. O objetivo deste trabalho foi verificar o efeito de sistemas de cultivo, estabelecidos há três anos sobre campo nativo (Depressão Central do RS, 30º05'S, 51º40'O, altitude 46m e precipitação 1398mm), sobre o BSS. Num experimento com sete blocos, divididos em três parcelas (semeadura direta - SD, preparo reduzido - PR, e preparo convencional - PC), efetuaram-se duas avaliações (maio e outubro/2002) do BSS, em cada sistema. O BSS foi avaliado por meio de amostragem de solo, que foi posto a germinar em estufa, sendo as plântulas contadas e identificadas. Variáveis edáficas foram relacionadas com os dados de BSS. Os resultados indicam que diferentes sistemas de cultivo influenciam o BSS, e que determinadas espécies respondem diferentemente a estes efeitos. SD aumentou a riqueza do BSS, além de diminuir a quantidade de sementes de Brachiaria plantaginea, e aumentar Sida rhombifolia, sendo que para PR e PC ocorreu o inverso. A distribuição espacial do BSS, na área experimental, apresentou-se muito heterogênea. Variáveis edáficas, especialmente matéria orgânica, pH e fósforo, apresentaram associações com a variação da composição do BSS. Apesar das constatações, são necessários estudos de longo prazo para revelar a dinâmica dos BSS em cultivos na Depressão Central do RS. Knowledge of the ecology of soil seed banks (SSB) contributes to improving integrated weed SSB management systems in croplands established in natural grassland areas. The aim of this study was to evaluate the effect of different cropping systems, established in a natural grassland field (Depressão Central of Rio Grande do Sul, 30º05'S, 51º40'O, altude 46m, rainfall 1398mm), on the SSB. Three different tillage-crop rotation systems were imposed (no-tillage - NT, reduced tillage - RT, and conventional tillage - CT) in three plots arranged in seven blocks. Two SSB evaluations were carried out in each tillage system, one in May and the other in October/2002. The SSB was evaluated by sampling soil cores, which were germinated in a glasshouse, and seedlings were counted and identified. Edaphic variables were registered to relate with collected data. The results indicated that different tillage systems affected the SSB composition, and that certain species responded differently to these influences. The NT system resulted in higher BSS wealth, a lower number of Brachiaria plantaginea seeds, a higher number of Sida rhombifolia seeds, but inverse values were recorded for RT and CT systems. The spatial soil seed bank distribution presented high heterogeneity among cropping systems. Edaphic variables, specially organic matter, pH and phosphorous, showed associations with the variation in SSB composition. In spite of these findings, long-term studies are necessary to reveal the temporal dynamics of the soil seed bank on the cropping system conditions of the Central Lowland region in Rio Grande do Sul, Brazil.

This research aimed to determine the soil seed bank and its relationship with environmental factors that have an influence in the distribution of the vegetation above the ground in an excluded area of natural grassland in the South of Brazil. Most of the 122 identified species in the seed bank were perennials. Data analysis indicated three distinct community groups, according to the size and composition of the soil seed bank in lowlands with permanent wet soils, in lowlands and in other areas. In general, lowlands were characterized by low-fertility soils, high moisture and aluminum contents, being spatially homogeneous habitats and, therefore, more restricted to vegetation heterogeneity than other parts of the relief. Environmental factors most associated with soil seed bank size and composition were relief position and their co-related soil variables such as: soil moisture content, potassium content, organic matter, basic saturation of cation exchange soil capacity, exchangeable basics sum of the soil and clay soil content. According to that, relief position, associated with combined effects of soil chemical properties related to it, determines the observed variation pattern of the soil seed bank, as a reflection of the vegetation above the area. O trabalho objetivou determinar o banco de sementes presente em uma área excluída de campo natural localizado na região sul do Brasil e sua correspondência com fatores abióticos que possuem influência no desenvolvimento e distribuição da vegetação presente. Foram identificadas 122 espécies, sendo a maioria perenes. Observou-se uma nítida separação entre o banco de sementes dos campos uliginosos, o banco de sementes de áreas baixas não alagáveis do relevo e o banco de sementes das outras porções do relevo. Os extremo inferiores alagáveis do relevo (campos uliginosos) apresentaram solos menos férteis, com maiores graus de umidade e de alumínio, constituindo habitat espacialmente homogêneo e, portanto, mais restritivo à heterogeneidade da vegetação em relação às demais áreas. Os fatores do ambiente mais associados à composição e tamanho do banco de sementes do solo foram a posição do relevo e variáveis correlacionadas como: grau de umidade, teor de potássio, matéria orgânica, saturação da capacidade de troca catiônica por bases, soma de bases trocáveis e teor de argila do solo. Desta forma, a posição do relevo, associada aos efeitos combinados das propriedades químicas do solo dele decorrentes, determinaram o padrão de variação observado no banco de sementes do solo, através da influência na vegetação da área.

O trabalho objetivou determinar o banco de sementes presente em uma área excluída de campo natural localizado na região sul do Brasil e sua correspondência com fatores abióticos que possuem influência no desenvolvimento e distribuição da vegetação presente. Foram identificadas 122 espécies, sendo a maioria perenes. Observou-se uma nítida separação entre o banco de sementes dos campos uliginosos, o banco de sementes de áreas baixas não alagáveis do relevo e o banco de sementes das outras porções do relevo. Os extremo inferiores alagáveis do relevo (campos uliginosos) apresentaram solos menos férteis, com maiores graus de umidade e de alumínio, constituindo habitat espacialmente homogêneo e, portanto, mais restritivo à heterogeneidade da vegetação em relação às demais áreas. Os fatores do ambiente mais associados à composição e tamanho do banco de sementes do solo foram a posição do relevo e variáveis correlacionadas como: grau de umidade, teor de potássio, matéria orgânica, saturação da capacidade de troca catiônica por bases, soma de bases trocáveis e teor de argila do solo. Desta forma, a posição do relevo, associada aos efeitos combinados das propriedades químicas do solo dele decorrentes, determinaram o padrão de variação observado no banco de sementes do solo, através da influência na vegetação da área. This research aimed to determine the soil seed bank and its relationship with environmental factors that have an influence in the distribution of the vegetation above the ground in an excluded area of natural grassland in the South of Brazil. Most of the 122 identified species in the seed bank were perennials. Data analysis indicated three distinct community groups, according to the size and composition of the soil seed bank in lowlands with permanent wet soils, in lowlands and in other areas. In general, lowlands were characterized by low-fertility soils, high moisture and aluminum contents, being spatially homogeneous habitats and, therefore, more restricted to vegetation heterogeneity than other parts of the relief. Environmental factors most associated with soil seed bank size and composition were relief position and their co-related soil variables such as: soil moisture content, potassium content, organic matter, basic saturation of cation exchange soil capacity, exchangeable basics sum of the soil and clay soil content. According to that, relief position, associated with combined effects of soil chemical properties related to it, determines the observed variation pattern of the soil seed bank, as a reflection of the vegetation above the area.

Due to changing cropping practices in perennial grass seed crops in western Oregon, USA, alternative rotation systems are being considered to reduce weed infestations. Information is generally lacking regarding the effects of alternative agronomic operations and herbicide inputs on soil weed seed bank composition during this transition. Six crop rotation systems were imposed in 1992 on a field that had historically produced monoculture perennial ryegrass (Lolium perenne L.) seeds. Each system plot was 20 x 30 m, arranged in a randomized complete block design, replicated four times. Twenty to thirty soil cores were sampled in June 1997 from each plot. The weed species composition of the cores was determined by successive greenhouse grow-out assays. In addition to seed density, heterogeneity indices for species evenness, richness, and diversity were determined. The most abundant species were Juncus bufonius L. and Poa annua L. Changes in seed bank composition were due to the different herbicides used for the rotation crop components. Compared to the other rotation systems, no-tillage, spring-planted wheat (Triticum aestivum L.) and oat (Avena sativa L.) reduced overall weed seed density and richness, but did not affect weed species evenness or diversity. When meadowfoam (Limnanthes alba Hartweg ex Benth.) succeeded wheat in rotation, weed species richness was unaffected, but evenness and diversity were reduced, compared to the other rotation systems. For meadowfoam in sequence after white clover (Trifolium repens L.), crop establishment method (no-tillage and conventional tillage) had no effect on weed seed species density, evenness, or diversity.