Tomato growth and fruitbearing depend to the highest degree on the conditions of growing.
The studies at the Complex Experiment Station in Sandanski showed that the average monthly temperature of the air in the greenhouse was 0.7 to 4.7°C higher compared with the open area and that of the soil to a depth of 10 cm was 0.6 to 6.5°C higher.
The 24 h air and soil temperatures in the greenhouse undergo greater fluctuations than in the open because they are directly dependent on sunlight intensity, restricted air circulation and polyethylene high infra-red rays permeability.
The mean 24 h water vapour content of the air in the greenhouse is 0.8 to 7.2 gm/m3 higher and on some days 10 to 12 gm/m3, and the average monthly relative air humidity is 2 to 18.5 per cent higher.
The fluctuations in air humidity in the greenhouse are less than those in the open owing to the restricted air circulation.
These peculiarities in the greenhouse microclimate have a definite effect on tomato growth and reproductive manifestations.
The study conducted with the variety No 10 x Bison showed that at simultaneous planting in the greenhouse and outdoors (5–10 April) the greenhouse plants develop at an accelerated rate and fruits maturate 2–7 days earlier than those of early outdoors-grown tomatoes.
Greenhouse-grown fruits maturate 10 to 13 days earlier when planted at the optimal date (25 March).
The growth dynamics is shown in fig. 1. Greater and faster vegetative biomass accumulation is observed in the greenhouse compared to that in the open.
On simultaneous planting, the dry weight of a plant in the phase red fruit at the third inflorescence in the open is 182.4 gm and in the greenhouse 242.2 gm.
The difference is 68.9 gm at the optimal planting date 25 March.
The dry weight difference between the second and third variants during the growing season varies, rising progressively from 9.3 gm on 3 May to 69.3 gm on 22 June.
The average daily mass increase from planting to the phase red fruit at the third inflorescence is 2.23 gm in the open and 3.26 gm in the greenhouse.
The daily increase in the greenhouse is bigger throughout the growing season, the maximal one amounting to 5.53 gm, and in the open 4.94 gm.
The increase in the root system and overground organs - leaves, stems and fruits - shows the same regularity, i.e. the dry weight is heavier and the average daily increase is higher in the greenhouse than in the open.
Data presented in fig. 1 reveal slowest growth and least daily increase in the roots, followed by stems and leaves and fastest increase in fruit weight.
After the transplanting of the plants till the 25th day, the leaves and roots increase most fast and the fruits most slowly.
During this period roots in the