Effects of sowing time and sowing density on the growth of subterranean clover at Adelaide

Abstract

Growth curves have been constructed for undefoliated swards of subterranean clover (cv. Woogenellup) established at three plant densities (1,2 and 4 x l0³ plants per m²) at three times of the year (May, June and August). The swards grew without any apparent water stress, until early December. The time course of shoot dry matter increase is examined by the use of a logistic function and by the recognition of three growth stages.

Maximum crop growth rates ranged from 10 to 15 gm^-2 day^-1. The rate decreased with increase in density but increased with lateness of sowing, so that the highest crop growth rate was obtained with the lowest plant density sown in August. Estimated end-of-season yields were independent of density but decreased from about 1500 g m^-2 for May sowing to 1000 g m^-2 for August sowing. Effects of sowing density on the growth pattern persisted throughout the whole season.

Swards took 70–100 days to attain a leaf area index (LAI) of 3, after which crop growth rates were almost constant with time and independent of short-term fluctuations in the level of daily solar radiation and average daily temperature. Swards reached a maximum LAI of about 6, LAI being linearly related to the amount of shoot dry matter up to about 600 gm^-2 independent of density and sowing time. No evidence was found of an optimal relationship between crop growth rate and LAI.

It is concluded that end-of-season yield is independent of plant density above 1000 established plants per m², and that swards established as late as August have the capacity to attain a yield of 10 tonnes ha^-1 provided the growing season is extended.