SEASONAL VARIATION IN THE WATER LOSS FROM GLASSHOUSE TOMATOES

Using a weighing machine in a small glasshouse (0.01 acre). Morris et al (1953 and 1957) found that the rate of water loss from crops of tomato, lettuce and carnation, together with the associated soil, was closely correlated with the intensity of the incident solar radiation. This applied both to hourly values within a day and to daily values within a month. With tomatoes the proportion of the radiation used in evaporating water increased with increasing stem length, possibly because of corresponding increases in the leaf area and in the amount of solar radiation intercepted by the vertical sides of the plant array.

Rothwell and Jones (1961) used drainage lysimeters to find the quantitative relation between water loss and radiation for December-sown tomatoes grown on a commercial scale in a 0.1 acre single-span glasshouse, orientated N-S, at Fairfield Experimental Horticulture Station. The proportion of radiation used in evaporating water again became greater as the length of the stems increased during March, April and May, but in this larger glasshouse the proportion of solar radiation intercepted by the vertical sides of the plant array was relatively small.

As all these tomato crops were planted out in early Spring, it remains possible that the change in the ratio of water loss to radiation was partly due to a seasonal change in some other weather factor.

Lake et al (1965) used weighing machines to