The Effect of the Irradiation Dose and Time Factors on Producing Capacity of Lettuce and Leaf Vegetables in Photo-Culture Conditions

Abstract

Optimisation of the irradiation dose and duration factors in conditions of lettuce-and-leaf vegetable photo-culture matches the goals of development of controllable plant cultivation systems for greenhouses and other protected-ground facilities. Based on the literature of the last years, it is specified that the DLI (Daily Light Integral) factor is paid great attention to in development of sustainable industrial phyto-technology with use of online meteorological and satellite-navigation data. The opportunities of control of the factors under consideration are demonstrated through the example of the author’s experiment in photo-culture conditions of two lettuce cultivars (Frisee and Adamant) made using an automated multi-layer City Farm installation in a room with controlled environment. During the experiment, the variable values of PPFD (photosynthetic photon flux density) in range (180–220) μmol/(m2s), daily photoperiod τф from 13 to 21 hours, vegetation duration t about 24 to 30 days were used with constant VLI, which is the new concept of vegetation light integral (VLI), was introduced similarly to DLI. It is found that the principle of reciprocity of irradiance parameters and time (the Bunsen-Roscoe law) is not met at constant dose. In terms of average producing capacity, it was possible to increase the level of biomass synthesis by 30 % for Frisee lettuce and by 36 % for Adamant lettuce. A series of partial dependences relating producing capacity of lettuce cultivars to DLI, photoperiod, and vegetation duration was obtained (the authors understand producing capacity as biomass over the vegetation period). The experiment results may be used as input data for the Virtual Agronomist software developed for controlled plant cultivation.