The responses to defoliation of two strains of subterranean clover, differing in growth habit, when grown in swards

Abstract

Dense swards of two strains of T. subterraneum-herein referred to as C and P-were compared at two heights of cutting-1.5 cm (low) and 5.0 cm (high)-and two frequencies of defoliation- 1-weekly (frequent) and 4- or 5-weekly (infrequent). Strain C has smaller leaves than P and a compact, in contrast to a lax, growth habit. The swards (initial density of c. 25 plants/dm2) were grown in boxes, out of doors, at Perth from 27 April to 20 September. Mean daily solar radiation varied from c. 10 to 16 MJ/m2 and average daily maximum and minimum temperatures were c. 20¦ and 10¦C respectively. The principal finding was that under defoliation stress (i.e. low cutting) strain C yielded more than P, whereas at a lower level of stress (high cutting) there was usually little if any difference between these strains. This effect was established for the most part before the first harvest, at day 55; thereafter, with continued defoliation stress, strain P appeared to worsen slightly relative to C. The results provide support for the view that strains with a compact growth habit are less susceptible to defoliation (or grazing) stress than taller strains of lax growth habit. Generally, the total yield of tops and also the effective yield (as cut and removed material) decreased when cutting height was lowered. Also, infrequent cutting increased effective yield, particularly under low density (four plants/dm2) as observed in an ancillary experiment.