GROWTH AND YIELD OF GREENHOUSE TOMATO WITH CONSTANT OR INTERMITTENT HEATING OF THE ROOT AND SHOOT

What is the effect of constant compared to intermittent heating of the shoot and root on growth, nutrient status, and yield of greenhouse tomato (Lycopersicon esculentum Mill)? Seedlings were transplanted early, on 4 Mar. 1994 and 1 Mar. 1995, or late, on 25 Mar. 1994 and 31 Mar. 1995, into troughs of peat-lite mix. The troughs were heated to 21C by buried tubing, either constantly, or for 12 h during the day or the night, or they were not heated. The greenhouses had either 14/14C or 22/6C day/night minimum air temperatures. After 2 weeks, early transplants had the greatest leaf weight with constant root heat and least with no heat. Root weight was greater for 14/14C than 22/6C air heat. With 14/14C air heat, only the no-root heat reduced leaf weight, whereas with 22/6C air heat, root heat ranking was constant > day > night ≈no heat. With late transplants, only the no heat reduced leaf weight. Most nutrient concentrations were less in late than in early transplants. Number of fruit, and number and weight of marketable fruit produced by 1 July from early transplants was affected by root heat; the ranking was constant heat > day > night > no heat. The 22/6C air heat increased marketable yield because of fewer small, irregular and blossom end rot fruit. Root heat had no effect on yield of late transplants.