EFFECT OF TEMPERATURE ON INTERCEPTION AND CONVERSION OF SOLAR-RADIATION BY STANDS OF GROUNDNUT

Stands of groundnut were grown in controlled environment glasshouses at air temperatures of 19, 22, 25, 28, and 31-degrees-C. Leaf area index (L) increased with rise of temperature, and after 85 d was about 10-fold larger at 31-degrees-C than 19-degrees-C. Over most of the range of temperature, both L and fractional interception of solar radiation (f) were functions of thermal time accumulated from sowing (above a base of 10-degrees-C). In this respect, they were tightly coupled to developmental rate at the main apex. In one experiment, only 38% of seeds emerged at 22-degrees-C and 21% at 19-degrees-C, compared with more than 70% at 25-degrees-C and 31-degrees-C, but the low population density was compensated by faster leaf expansion by each plant (at 22-degrees-C only) and a greater fraction of solar radiation intercepted by unit leaf area. The amount of solar radiation intercepted by stands increased with rise in temperature, but the greatest differences between treatments occurred before the canopies achieved complete ground cover (i.e. f > 0.9) and the relative effect of a rise in temperature diminished the longer the duration of growth. The dry matter produced for unit solar radiation intercepted was not strongly affected by temperature between 22-degrees-C and 31-degrees-C. where the mean was 2.1 g MJ-1; the value at 19-degrees-C was uncertain since the stands were sparse throughout the experiment. After 85 d, the stand at 31-degrees-C had produced eight times the dry matter of that at 19-degrees-C-a difference caused mainly by the effect of temperature on the rates of development and expansion.