Transpiration of glasshouse tomatoes, lettuce and carnations.

Abstract

A deep rectangular box filled with soil (total weight ca 500 kg) and containing the experimental plants was supported on a weighing machine sensitive to 10g, correspond-ding to an evaporation of 0.013 mm water. Total radiation was measured by a Moll-type thermopile, originally connected to a poten-tiometric recorder printing every 33.3 sec, the resulting trace being later integrated with respect to time; in the later experiments, to save this labour, it was connected to the input of a magnetic amplifier driving an integrated motor counting unit. Daily values of evaporation and radiation were plotted for all crops, and some hourly values for 2-day periods in summer are presented for the last experiments, on tomato and carnations. In the first experiments, on tomato and winter lettuce, only 16% of the total area of the house was occupied. Evaporation and radiation varied similarly, their ratio being >1 for tomatoes, and widening as the season advanced: for lettuce the ratio was