A physiological analysis of the effect of sowing density on the growth rate of subterranean clover

Abstract

The initial planting density of subterranean clover swards is known to affect the subsequent crop growth rate in such a way that a low density crop reaches the same final yield as does one sown at high density. To explain this phenomenon, daily carbon influxes and effluxes were measured during the growth of 'low' and 'high' density swards in a constant environment. The growth characteristics of individual plants in the sward and the photosynthetic responses of individual leaves to light were measured during ontogeny. Good agreement was found between the growth curves reconstructed from daily carbon increment and growth curves previously derived from dry matter sampling. The crop growth rate of a low density sward was found to be higher than that of a high density sward, and this is shown to be due to a lower respiratory loss. The high respiration rate of a high density crop can be attributed to plant mortality when dry matter density is higher than 400 g m-2. The photosynthetic light response curves of individual leaves at the top of the canopy were not found to be affected by the initial planting density, which suggests that subterranean clover plants are extremely well adapted to growth under sward conditions.