Radiation use efficiency by tomato transplants grown under extended photoperiod

S. Rakutko¹*, A. Avotiņš², K. Berzina², E. Rakutko¹ and I. Alsina³

¹Federal Scientific Agroengineering Center VIM, branch in Saint Petersburg, Filtrovskoje Shosse, 3, p.o. Tiarlevo, RU196625 Saint Petersburg, Russia
²Riga Technical University, Faculty of Power and Electrical Engineering, Kalku street 1, LV-1658 Riga, Latvia
³Latvia University of Life Sciences and Technologies, Faculty of Agriculture, Institute of Plant and Soil Science, Liela street 2, LV–3001 Jelgava, Latvia
*Correspondence: sergej1964@yandex.ru

Abstract:

The study focused on the effect of an extended photoperiod on the radiation use efficiency (RUE) by the tomato transplants (Solanum lycopersicum L.) in the pre–reproductive period. In two consecutive series of experiments, the photoperiod was 16 and 22 hours. The photon irradiance at the plant tops was maintained at low, medium and high levels: 100, 170 and 240 μmol m^–2 s^–1, respectively. The plants were grown under two lighting systems with different light quality. The difference was 7% higher blue flux share in Spectrum II. The use of an extended photoperiod, especially in combination with high irradiance level, resulted in the plant leaf chlorosis. When varying the radiation dose components, the deviation from the reciprocity law was recorded. By the analysis results, the chlorophyll degradation was a response to the extended photoperiod rather than the radiation dose. Without additional blue flux, under a regular photoperiod, RUE reduced by 8% at the high irradiance level. Under extended photoperiod, the shift from the low to high irradiance level reduced RUE by 20–37%, with bigger reduction values being observed at higher irradiance levels. Seven percent addition of blue flux made it possible to increase RUE by 5–8% at the same and lower irradiance levels and under the regular photoperiod. With the extended photoperiod under these conditions, RUE decreased by 8–21%. The study results verify a great influence of an extended photoperiod on RUE, while the degree of influence depends on other parameters of light environment – light quality and irradiance level.

Key words:

biometry, chlorophyll, chlorosis, doze, irradiance, light quality, photoperiod, radiation use efficiency

New assessment tool for artificial plant lighting: case of tomato (Lycopersicon Esculentum Mill.)

S. Rakutko¹, A. Avotiņš², I. Alsina³ and K. Berzina²

¹Federal Scientific Agroengineering Center VIM, branch in Saint Petersburg, Tyarlevo, Pushkinsky distr., RU196625 St. Petersburg, Russia
²Riga Technical University, Faculty of Power and Electrical Engineering, Kalku street 1, LV-1658 Riga, Latvia
³Latvia University of Life Sciences and Technology, Faculty of Agriculture, Institute of Plant and Soil Science, Liela street 2, LV-3001 Jelgava, Latvia

Abstract:

Growing crops under artificial conditions need a very favourable environment, especially the spectral composition of radiation influencing the plant biometry greatly. The study objective was to find how to assess the closeness of real growing conditions to the optimal ones using a single coefficient, which would reflect several time dependencies of individual growth indicators. The plant growth friendliness factor (K_G)was proposed for this purpose. Tomato transplants (Lycopersicon Esculentum Mill., ‘Polonaise F₁’) were grown in a peat substrate under two lighting systems with different light quality.One system consisted of eight fluorescent lamps OSRAM L58W / 840 LUMILUX Cool White and eight lamps L58W / 77 FLUORA mounted on the standard frame, alternating the lamp types (Type I spectrum).In the other lighting system, the PCB Star LEDs with wavelengths of red 630 nm and far-red 735 nm were added(Type II spectrum). The irradiance level was maintained at 140 μmol m^-2 s^-1, the photoperiod was 16 h. The ratio of long-wave flux to the total flux K_L was calculated for these lighting systems (0.37 rel.units for Type I spectrum and 0.50 rel.units for Type II spectrum) and K_G factor was determined by the proposed formula. The value of K_G was found to be twice as small for Type I spectrum than for Type II spectrum. The significant difference in biometric parameters of tomato transplants grown under Type I and Type II spectra was revealed. The plants grown in the environment characterized by higher K_G, were higher; they had more significant wet mass and stem neck diameter.

Key words: