| Abstract: | Continuous hourly measurements of air and soil temperatures, irradiance and wind velocity, and less frequent measurements of soil water status and dry matter (DM) yield were recorded over two growing seasons and the intervening winter 1978–79 for an enclosed upland grassland in Cumbria, with the aim of establishing realistic combinations of environmental factors for the design of experiments under controlled conditions. Important features of the microclimate included high diurnal and day-to-day variation in environmental temperature, relatively high winter soil temperatures, variation between years in the influence of altitude upon irradiance, low wind velocity throughout the year at plant height and the loss of DM yield in the early summer of 1978 due to severe drought. Combinations of environmental factors throughout the 2 years can be obtained from the figures presented; in particular, the records indicate that in growth-cabinet or greenhouse experiments associated with the breeding or selection of cultivars for earlier DM production in spring, it is important to combine low temperatures (≤ 10°C) with realistic levels of irradiance (≥200 W m−2) and daylength (12.5–15 h). |
