Temperature and leaf growth in Lolium perenne. 1. The thermal microclimate: its measurement and relation to crop growth.
Temperatures were measured in a perennial ryegrass crop in the field and an attempt was made to relate temperature to growth. The instruments used are described. Air and soil temperature profiles were shown to be influenced by the stage of crop growth and prevailing weather conditions. Daily maximum, minimum and mean temperatures in the canopy differed from those measured in a meteorological screen. Temperature extremes and the maximum diurnal variation in each month through the year are tabulated, and weekly means of the day and night temperatures are given. Weekly measurements of dry weight and leaf area and daily measurements of leaf extension were made in the spring. Instantaneous temperature profiles and growth could not be related directly, and a poor correlation was found between mean temperatures and increase of dry weight or leaf area. However, daily mean temperature was highly correlated with leaf extension. Because temperatures at different levels in the crop were highly correlated it was not possible to establish the separate effects of soil and air temperature on the growth of the grass sward in the field.