The role of time of emergence in determining the growth of individual plants in swards of subterranean clover ( Trifolium subterraneum L.)

An experiment was carried out which enabled a separate assessment to be made of the influence of, firstly, pre-emergence growth rate, and secondly, the competitive environment at emergence on the subsequent growth of individual plants of subterranean clover. Swards of the Bacchus Marsh variety were grown in large seed boxes at the Waite Agricultural Research Institute, Adelaide. Four different sowing treatments were applied whereby the sowing of alternate plants in a checkerboard grid was delayed by 0, 2, 4, and 8 days. Emergence date and final dry weight were recorded individually for each plant in the experimental swards. There was considerable overlap in emergence times between the earlier and the later-sown plants. Consequently by a comparison of the separate regressions for earlier and later-sown plants of yield per plant on day of emergence for each treatment, it could be demonstrated that plants with very different pre-emergence growth rates but emerging on the same day in the same sward, and hence into the same competitive environment, gave essentially the same subsequent growth. In other words, in the absence of differential competitive effects, there was no detectable influence of pre-emergence growth rate on subsequent growth. On the other hand, the final dry weights of individual plants were very strongly related to day of emergence. A delay in emergence of 5 days brought about a reduction in final yield of about 50%, and a delay of 8 or 9 days of at least 75%. In view of the negligible influence of pre-emergence growth rate, per se, this reduction is attributable solely to the increased severity of competition from plants already emerged. In spite of the wide variation in emergence patterns, the total yields of all swards were very similar, indicating an almost complete compensation between plants in the utilization of available growth factors.