HEADING DATES OF S24 PERENNIAL RYEGRASS AND SPRING TEMPERATURES

For spaced plants of Lolium perenne cv. S24 at the Welsh Plant Breeding Station, Aberystwyth, and at the National Institute of Agricultural Botany, Cambridge, linear relationships were obtained between the recorded heading dates and (a) mean March earth temperatures at 30 cm depth and (b) mean March plus mean April earth temperatures at 30 cm depth. The residual standard deviations were ±2.97 days and ±2.65 days, respectively, A mean March earth temperature of 8°C predicted heading on 5 May, 6° C predicted heading on 12 May, and 4°C predicted heading on 20 May. For sites with an average April temperature significantly below 8.7°C a correction of +2 days per degree mean temperature difference in April had to be applied to these dates. These equations could be used to predict dates for 50% ear emergence in swards with a 50% confidence limit of ±22 days for sites in Central and Southern England and Wales. In certain years, cold, wet weather in May appeared to delay heading considerably at two Scottish sites.