An Analysis of the Influence of Plant Density on the Growth ofVicia faba

Abstract

The competitive effects of varying the density on the development of Vicia faba have been studied in a series of multifactorial experiments where the spacing both between and within rows was simultaneously altered. Over densities ranging from 11 to 67 plants per metre2 seed production on an area basis tended to be maximal at 35-45 plants per metre2 in the winter type and at the highest density for the spring type. As the density increased the number of pods per plant and the extent of branching fell progressively but there was no appreciable change in either seed size or the number of seeds per pod : thus seed production was solely governed by the number of mature pods formed. The number of flowers per plant was more dependent on the number of inflorescences than on the number of flowers per inflorescence. Increasing the population diminished the number of nodes bearing inflorescences particularly in the upper part of the shoot, while the size of the inflorescence was decreased to a lesser extent. The number of flowers forming mature pods was very small (9-14 per cent.). At the top of the shoot the flowers were infertile, while above the middle node most of the pods formed were shed while still immature. Thus the primary effect of increasing density was to depress the number of nodes on the lower half of the stems which produced mature pods. By the time the flowering stage was reached plant height was already correlated with density due more to a change in internode length than an alteration in the number of differentiated nodes; at maturity the differences in height were smaller due to the greater number of nodes in the widely spaced plants. For a given density, alterations in the distance between rows had little influence on development. The possible physiological factors responsible for the changing pattern of development brought about by varying density are discussed.