Effects of Defoliation Height and Time of Initital Defoliation on Regrowth Components in a Poa pratensis- dominated sward

Two experiments on swards dominated by Poa pratensis L. were conducted in 2 climatically contrasting (wann/dry and cold/wet) years. There were either 4 or 3 initial defoliation dates in spring and 3 defoliation heights (2, 6 and 10 cm). Regrowths were harvested 4 weeks after the initial defoliation. The swards received a total of 80 kg/ha nitrogen split into 2 dressings. Regrowth characteristics, based on samples cut to ground level, depended on weather conditions. The yield of vegetative shoots was affected most by shoot size, which in turn was determined by initial defoliation date, in the dry year. In the wet year, however, the factor most influencing yield was shoot number, which increased with close defoliation, Close spring defoliation resulted in the lowest production of reproductive tissues. Neither the time of initial defoliation in spring nor the defoliation height had any impact on the total production of vegetative shoots in the wet year.