Competition, growth and yield of faba bean (Vicia faba L.)

This paper reviews current knowledge regarding the influence of plant density on the growth and yield of the faba bean crop (Vicia faba L.). An analysis is also made of sowing rate and other factors that may modify optimum plant density, including environmental conditions; in this sense, should be made a differentiation between faba crops grown in temperate conditions and those grown in Mediterranean and semi-arid conditions. The genotype also prompts variations in optimum plant density, depending on the botanical type (mayor, equina or minor) and the growth habit (determinate versus indeterminate) of the cultivar selected. Sowing date also influences optimum seeding rate, which is lower for autumn-winter sowing under temperate and Mediterranean conditions and increases as the sowing date is delayed. For the spring-sown crops typical of temperate conditions, optimum plant density will be higher due to the shorter growing season. With a longer growing season and under optimum environmental conditions, there is normally no additional response to densities over 20 plants m−2, while in suboptimal conditions, optimum plant density may increase to over 60 plants m−2. Although the faba bean crop displays considerable plasticity in response to variations in plant density, mainly with regard to number of pods per square meter, it is not wholly clear to which component of yield this should really be ascribed. Number of stems per plant appears to be the most influential factor, although further research is required to confirm this.