Dynamics of competition between wild oats (Avena fatua L.) and winter cereals

This study examined the effects of competition on the growth of Avena fatua, winter wheat and winter barley. Plants were sampled at frequent intervals from replacement series experiments at two contrasting sites in the U.K. A. fatua was much slower to establish than the two cereals, but thereafter exhibited a faster rate of growth. In monoculture, it took a considerable time for A. fatua to reach a size equal to that of the cereals, but by the end of the experiments it was the largest of the three species. The change-over from cereal dominance in mixtures to A. fatua dominance was rapid, and in three cases coincided with cereal flag leaf emergence. In the fourth case, it appeared to coincide with the start of canopy height extension. At one site the order of competitiveness at anthesis was A. fatua = barley > wheat, and at the other site the order was A. fatua > wheat > barley. In order to explain and predict differences between years and sites, more studies are required on morphological development in relation to abiotic variables

Efeito de extratos aquosos de estruturas de grama-seda no desenvolvimento inicial de plântulas de arroz, milho e trigo Effects of aqueous extracts of bermudagrass structures on initial growth of rice, corn and wheat seedlings

Objetivou-se verificar os efeitos de extratos aquosos de estruturas de grama-seda (Cynodon dactylon (L.) Pers) e de exsudatos radiculares presentes no solo no qual a planta se desenvolveu, sobre a germinação e o crescimento inicial de arroz, trigo e milho. O extrato aquoso das estruturas da parte aérea, subterrâneas e da planta inteira, assim como do estolão, da folha + colmo, estolão + folha + colmo, rizoma, raiz e de rizoma + raiz de grama-seda foi elaborado a partir de 100 g L-1 de material seco. Foram avaliados a protrusão da radícula e os crescimentos da radícula e da plúmula de cada espécie. A inibição ou o estímulo do desenvolvimento inicial de plântulas foi dependente da espécie avaliada e da estrutura vegetal empregada na elaboração do extrato. A protrusão da radícula foi mais inibida que os crescimentos da radícula e da plúmula. O estímulo do desenvolvimento da radícula e da plúmula foi mais evidente quando o extrato foi elaborado a partir das estruturas do sistema radicular, da parte aérea e da planta inteira que de estruturas individualizadas de grama-seda. De modo geral, o arroz e o milho foram mais inibidos por extratos elaborados a partir da parte aérea e subterrânea, respectivamente. Para o trigo, a inibição ou o estímulo foi dependente da variável analisada. O desenvolvimento da radícula e da plúmula de arroz, milho e trigo foi estimulado por extrato elaborado a partir da planta inteira. O extrato produzido a partir da fração argila + silte estimulou o desenvolvimento da radícula do milho e da plúmula do trigo.<br>The objective of this work was to study the effects of aqueous extracts of Bermudagrass structures (Cynodon dactylon (L.) Pers) and soil exudates, on the germination and initial growth of rice, corn and wheat seedlings. The aqueous extracts of above-ground and subterranean parts and of the whole plant, as well as of stolons, leaves + culm, stolons + leaves + culm, rhizome, root and rhizome + root of Bermudagrass, were prepared from 100 g L-1 of dry plant material. It was also investigated if these extracts and the one obtained from soil removed from the rhizosphere of the subterranean plant parts, and of the stolons would show any interference. Inhibition or stimulation of the initial seedling development was dependent on the tested species and the structure employed in the preparation of the extract. Radicle protrusion was inhibited more than radicle and plumule growth. The stimulus of radicle and plumule growth was more evident when the extract was prepared from the root system structures, above-ground plant parts and whole plant than from the separated plant structures of Bermudagrass. Rice and corn were more inhibited by extracts prepared from the above-ground and subterranean plant part respectively. Wheat inhibition or stimulation effects were dependent on the variable analysed. The development of radicle and plumule of rice, corn and wheat was stimulated by extract prepared from the whole plant. The extract prepared from the clay + silt soil fraction in which the grass grew stimulated growth of corn radicle and wheat plumule