Numéro #148

Study of the spring growth of perennial ryegrass cultivars in relation to cumulated temperatures

Early spring growth is particularly important in the Belgian highlands (Ardenne), where the climate is sub-mountainous. Start of growth and rate of biomass constitution during the first growth cycle were observed in 6 cultivars of perennial ryegrass with different heading dates. The parameters of the linear relationship between yield and the cumulated temperatures (base 0°C) from 1st February onwards were determined during 2 consecutive years. The cultivars tested, when classified according to their growth rate, fell into 2 significantly different groups. The first group contained the early-heading cultivars, i.e. Barvestra, Bastion and Barlano, with an average growth rate, expressed in kg DM/degree-days/ha, of 9,5 in 1991 and of 12,7 in 1992. The second group contained the late-heading cultivars (Meltra, Condesa, Barenza) and had an average growth rate of 6,2 in 1991 and of 6,6 in 1992 (expressed in the same units). The cumulated temperatures required by Bastion to reach a harvestable biomass of 1 500 kg DM amounted to 434 degree-days in 1991 and to 482 degree-days in 1992. To reach the same yield level, Barenza needs 580 degree-days in both years. Since the average temperature was 10°C during this period, a difference from 10 to 15 days was thus observed between to two cultivars.