Role of seedling growth on weed-crop competition

The paper focus on relationships between early growth and competitivity of weed species. A seedling is defined as a young plant from its emergence until the end of exponential growth. Factors affecting seedling growth are reviewed and relationships among species characteristics, environmental and agronomic factors are discussed. In most experiments seedling relative growth rate is negatively correlated with seed weight, its main determinant being specific leaf area. The first results of experiments conducted by the authors show that seedling weight at the end of exponential growth appears to be related to parameter I of Cousens' hyperbola. The relative size of the plants when competition starts, determined by the relative time of plant emergence, initial seedling weight and relative growth rates, is concluded to be of paramount importance in defining plant competitive ability. The paper emphasises that further insight into the mechanisms which drive early plant growth could enhance our predictive ability. The study of simple attributes of seeds and seedlings that could be used to predict their adult plant behaviour and the grouping of weed species in 'functional groups' with homogeneous competitive traits is suggested as a way to expand applicability and predictability of decision-making programmes.