Ventilation surface area: key to modify morphology, quality and photosynthetic activity of tomato crops in Mediterranean greenhouses

Natural ventilation is one of the most effective tools for climate control inside greenhouses, as it affects CO₂ flow, as well as decreasing temperature and humidity. Nowadays in the Mediterranean area, most of the commercial greenhouses have a ventilation surface area below 15%. The objective of this research work is to compare four greenhouses, transversally divided in two similar halves by a polyethylene sheet, with different ventilation surface (Sv/Sc, ventilation surface/greenhouse area). Three greenhouses were multispan (Sv/Sc equal to: greenhouse 1: 11.3 vs. 10.9%, 2: 32 vs. 17%, 3: 19.0 vs. 18.5%) and one Almería type with a structure in “raspa y amagado” (Sv/Sc, 15.0 vs. 9.8%). During the development of the research, the morphological parameters of the plants, fruit quality and photosynthetic activity of a tomato crop developed in two consecutive cycles were monitored. Because an increase in the ventilation surface area in both cycles, yield was greater in both greenhouse structures studied, either due to the increase in weight (from 94.7 to 103.2 g) and diameter (from 62.9 to 69.1 mm) of the fruits or because of the increase in the number of fruits. Although statistically there are no significant differences, the average photosynthetic activity (ranging from 10.6 to 13.5 μmol CO₂ m^‑2 s^‑1) was higher in the better-ventilated sectors. In the morphology of the plants in the first period, there were significant differences in stem diameter (from 11.90 to 12.70 mm) between the plants of the different sector of greenhouse 2, being higher in the sector with more ventilation. In general, it has been observed that enlarging the ventilation surface area (a low cost measure) produce morphological improvements, increases of photosynthetic activity and fruit quality that are closely related to the augmentation of yield of crops.