THE GROWTH AND DEVELOPMENT OF SOME GRASS SPECIES UNDER COMPETITIVE STRESS

Two pot experiments were carried out in a semi‐controlled environment to examine the response of individual plants to competitive stress in simple systems incorporating varying cutting frequencies and soil–nitrogen levels. A third experiment was set up outdoors to examine the effect of competition on individuals in an association, on the association as a whole, and to extend the controlled environment studies to a more complex model involving micro‐plots. Phalaris coerulescens , although its seedlings possessed a high competitive ability, showed a dramatic decline in competitive ability in later stages of the association, this decline being associated with extensive floral development. In micro–plots the effect of competition was so severe as to prevent the expression of seasonal growth characteristics by P. coerulescens . Considerable inter‐specific differences existed in the response to competition of leaf‐area production per tiller during periods of regrowth. Whilst P. coerulescens remained highly productive and maintained a dense tiller population in monocultures, its tiller regeneration following flowering was severely suppressed in competition with vegetative plants of HI ryegrass or Festuca arundinacea . The number of heads produced per plant, head length and time of head emergence were all affected by competitive stress, the former response being a reflection of the relative competitive abilities at the time of floral initiation. The response of the latter two characters reflected the decline in competitive ability which occurred during later stages of the growth and development of P. coerulescens .