Regeneration from seed affects species assembly in plant communities, and temperature is the most important environmental factor controlling the germination process. Thermal dependence of seed germination is thus associated with species occurrence in an ecosystem. Hence, we aimed to investigate the role of temperature on seed germination of ten tree species from the western Brazilian Amazon. Seeds were collected in the state of Rondônia, Brazil, and set to germinate under constant temperatures ranging from 10 to 40°C in germination chambers. We calculated germination capacity (G%), germination rate (GR50, reciprocal of germination time), and thermal parameters, such as cardinal temperatures and thermal time requirements. Most species had a large range of temperatures showing G% ≥80%, with optimal temperature varying from 20 to 40°C. Base temperature ranged from 6 to 12°C and ceiling temperatures were mainly >40°C. Astronium lecointei and Parkia nitida showed high germination capacity under temperatures of 35–40°C, while germination of Theobroma cacao dropped from 100% to zero under temperatures between 37 and 40°C. The climax species Cedrela fissilis had the slowest germination time (10 days) and highest thermal time requirement, while seeds of Enterolobium schomburgkii (a late-successional species) germinated within the first day of the experiment. Rapid recruitment of Amazon species could be favoured with treefall disturbance, which increases temperatures in the understory, but sharp limits might be found in the supra-optimal range of temperatures. Such patterns might indicate different regeneration strategies in the tropical rainforest, providing important information regarding seed germination among Amazon species.

RESUMO -O sistema plantio direto é uma estratégia sustentável de produção que preconiza a manutenção da cobertura vegetal como prática conservacionista do solo. Objetivou-se avaliar o efeito de plantas de cobertura sobre atributos fisiológicos e agronômicos do milho na região sudoeste da Amazônia. Foram avaliadas 15 estratégias de sucessões de culturas com o milho e a influência sobre o rendimento de biomassa, de grãos, altura de plantas e inserção da espiga, índice de espiga, massa de 100 grãos, teor foliar de nitrogênio e clorofilas total, a e b em plantas de milho.Observou-se efeito das plantas de cobertura sobre o rendimento de grãos, de biomassa fresca e seca, na massa de grãos e nos teores de clorofila. Os efeitos sobre os teores de clorofila foram mais pronunciados na clorofila b e nos estádios fenológicos finais da cultura. O feijão-de-porco promoveu as maiores produtividades de grãos (7.539,3 kg ha -1 ) e potencial de silagem (16,2 Mg ha -1 de biomassa seca). A adequada escolha das espécies que compõe um sistema de plantio direto é preponderante para o apropriado desempenho agronômico do milho na região sudoeste da Amazônia. Palavras-chave:Zea mays, intensificação ecológica, sustentabilidade, integração lavoura-pecuária, plantio direto. CROPPING SYSTEMS ON THE PERFORMANCE OF CORN PLANTS IN THE SOUTHWESTERN AMAZONABSTRACT-A sustainable strategy for agricultural systems is the use of cover crops in no-tillage systems, as a conservationist soil practice. This paper aimed to evaluate the short-term effects of different cover crops on some physiological and agronomic attributes of corn crop in the Southwestern Amazon region. The effects of 15 cover plants on the biomass and grains yield, plant height, ear insertion height, ear index, mass of 100 grains, leaf nitrogen content and a, b and total chlorophyll levels of corn plants were evaluated. A randomized complete block design was used with four replications. Grain yield, fresh and dry biomass yield, mass of 100 grains and chlorophyll content were affected by some cover crops. Jack bean promoted the highest grain yield (7,539.3 kg ha -1 ) and biomass yield (16.2 Mg ha -1 dry matter) among the options assessed. Cover crops provided different levels of total, a and b chlorophyll levels, on the corn plants. Some cover crops presented the potential to improve the agronomic performance of the succeeding corn crop in the Southwestern Amazon region. The proper agronomic performance of corn in a no-till system depends on the adequate choice of cover plants to compose the system. Sorgo, v.15, n.3, p. 531-542, 2016 RESUMO -O sistema plantio direto é uma estratégia sustentável de produção que preconiza a manutenção da cobertura vegetal como prática conservacionista do solo. Objetivou-se avaliar o efeito de plantas de cobertura sobre atributos fisiológicos e agronômicos do milho na região sudoeste da Amazônia. Foram avaliadas 15 estratégias de sucessões de culturas com o milho e a influência sobre o rendimento de biomassa, de grãos, altura de plantas e inserção da e...

Understanding the ecological dynamics of weed populations in no-tillage systems is important to establish strategies for integrated weed control capable of increasing agroecosystem sustainability. This study sought to evaluate the effect of succession systems on the seed bank in a no-tillage system. The effects of fifteen succession systems, composed of seven grasses, seven Leguminosae, and a fallow condition, were evaluated on the seed bank at two soil depths (0 to 10 and 10 to 20 cm). The species found in the seed bank were quantified and identified by species and family. The precision of sampling, density, dominance, the indices of diversity of Simpson and Shannon-Weiner; index of sustainability; analysis of groupings of dissimilarities; and the value of importance of each species were calculated. High weed diversity was observed; 29 species were counted, including members of 12 different families. The highest expression of weeds was observed at soil depths of 0 to 10 cm. The Simpson and Shannon-Weiner coefficients indicated high diversity in both systems of succession. The index of sustainability did not indicate significant alterations in the different systems of succession. The coefficients of confenetic correlation were 0.74% and 0.82% for the 0-10 and the 10-20 cm soil depths respectively. It is concluded that there is a high diversity of weeds in the agroecosystems of Amazonia, and different cover crops promote modifications in the community and expression of the weeds' seed bank.

potential of cover crops in control of shrubby false buttonweed ... ABSTRACT -Searching for alternatives to deal with weeds without the exclusive use of herbicides can increase the sustainability of agricultural production in the Amazon region. This study aimed to evaluate the allelopathic potential of cover crops on the weed shrubby false buttonweed (Spermacoce verticillata L.). Three straw levels (1; 2.5 and 5 mg cm -2 ) of thirteen cover crops (Cajanus cajan, Canavalia ensiformis, Crotalaria juncea, C. ochroleuca, C. spectabilis, Mucuna aterrima, M. cinereum, Pennisetum glaucum, Sorghum bicolor, S. sudanense, Urochloa brizanha cv. Xaraés, U. brizantha cv. Piatã and U. ruziziensis) were assessed on germination and initial growth of weed and lettuce. We carried out two experiments (weed and lettuce) in a factorial scheme (cover crops x straw levels) with additional treatment (control without straw) in a completely randomized experimental design, with four replicates. The straw of the cover crops inhibited the germination and initial growth of the target plants. The highest straw levels promoted 44.0 and 78.8% reductions in radicle length in relation to the lowest dose (1 mg cm -2 ), for lettuce and Spermacoce verticillata, respectively. The highest sensitivity to allelochemicals occurred on the radicle. The major suppressive effects on weed germination were promoted by Cajanus cajan, Urochloa brizanha cv. Xaraés, Mucuna cinereum, M. aterrima, Canavalia ensiformis, Crotalaria juncea, C. spectabilis and U. ruziziensis. Cover crops use is an integrated practice management to control Spermacoce verticillata under no-tillage system.RESUMO -A busca por alternativas no manejo de plantas daninhas sem a utilização exclusiva de herbicidas pode contribuir para aumento da sustentabilidade na produção agrícola na região Amazônica. Objetivou-se neste estudo avaliar o potencial alelopático de plantas de cobertura, sobre a planta daninha vassourinhade-botão (Spermacoce verticillata L.). Três níveis de palhada (1; 2,5 e 5 mg cm -2 ) de treze plantas de cobertura (Cajanus cajan, Canavalia ensiformis, Crotalaria juncea, C. ochroleuca, C. spectabilis, Mucuna aterrima, M. cinereum, Pennisetum glaucum, Sorghum bicolor, S. sudanense, Urochloa brizanha cv. Xaraés, U. brizantha cv. Piatã e U. ruziziensis) foram avaliados, sobre a germinação e o crescimento inicial da planta daninha e da alface. Dois experimentos foram instalados (planta daninha e alface) em esquema fatorial (plantas de cobertura x níveis de palhada) com tratamento adicional (testemunha sem palhada) em delineamento experimental inteiramente casualizado, com quatro repetições. As palhadas das plantas de cobertura inibiram a germinação e o crescimento inicial potential of cover crops in control of shrubby false buttonweed ... 2 das plantas alvo. Os maiores níveis de palhada promoveram reduções de 44,0 e 78,8% no comprimento da radícula em relação à menor dose (1 mg cm -2 ), para a alface e para a vassourinha-de-botão, respectivamente. A maior sensibilidade aos aleloq...