THE RELATIONSHIP BETWEEN COMPETITION AND DEFOLIATION IN PASTURE

Abstract

Field trials were carried out on a downland permanent pasture at the Grassland Research Institute, Hurley, between 1953 and 1955, to investigate the factors involved in competition in pasture undergoing periodic defoliation. Response to competition was estimated by comparing the yield of species units (either individual plants or close groups of shoots) growing normally in the pasture with the yield of matched units from which the surrounding herbage had been removed. The species studied were cocksfoot, red fescue, creeping bent, plantain, ox‐eye daisy and bulbous buttercup. In addition to the estimation of normal competition for environmental resources in pastures of differing height, two special effects upon species due to the presence of surrounding herbage were investigated following unusual results from competition tests in swards under periodic defoliation. First, the influence of surrounding herbage in modifying the growth habit of a species, causing it to grow in a more erect manner, and consequently to suffer more on defoliation at a specific height than in the absence of competition. Secondly, a decreased yield after defoliation, not associated with changes in the growth habit of the species, which was ascribed to an increase in top/root ratio brought about by shading during the preceding period of competitive growth. The effect of selective defoliation of a species in relation to the herbage surrounding it was also studied. Differences in the degree of defoliation of a species and its surrounding herbage had a marked effect upon the degree of competition exerted by the latter upon the former, increasing it when the species was preferentially defoliated and decreasing it when the surrounding herbage was preferentially defoliated. The factors involved in pasture competition under periodic defoliation are listed and discussed.