Yield and Quality of Romaine Lettuce at Different Daily Light Integral in an Indoor Controlled Environment

Abstract

In this study, the effect of different photosynthetic photon flux density (PPFD) provided by LEDs (Light Emitting Diodes) and photoperiod on biomass production, morphological traits, photosynthetic performance, sensory attributes, and image texture parameters of indoor cultivated romaine lettuce was evaluated. Two cultivars of lettuce Lactuca sativa var. longifolium namely ‘Casual’ (Syngenta)—midi romaine lettuce with medium-compact heads—and ‘Elizium’ (Enza Zaden)—a mini type (Little Gem) with compact heavy heads—were used. PPFD of 160 and 240 µmol m−2 s−1 and photoperiod of 16 and 20 h were applied, and Daily Light Integral (DLI) values were 9.2, 11.5, 13.8, and 17.3 mol m−2 day−1. The experiment lasted 30 days in the Indoor Controlled Environment Agriculture facility. DLI equal to 17.3 mol m−2 per day for cv. ‘Casual’ and 11.5–17.3 mol m−2 per day for cv. ‘Elizium’ allowed to obtain a very high fresh weight, 350 and 240 g, respectively, within 30 days of cultivation in an indoor plant production facility. The application of the lowest PPFD 160 µmol m−2 s−1 and 16 h photoperiod (9.2 mol m−2 per day DLI) resulted in the lowest fresh weight, the number of leaves and head circumference. The level of nitrate, even at the lowest DLI, was below the limit imposed by European Community Regulation. The cv. ‘Elizium’ lettuce grown at PPFD 240 µmol m−2 s−1 and 16 h photoperiod had the highest overall sensory quality. The cv. ‘Casual’ lettuce grown at PPFD 160 µmol m−2 s−1 and 20 h photoperiod had the lowest sensory quality. The samples subjected to different photoperiod and PPFD were also successively distinguished in an objective and non-destructive way using image features and machine learning algorithms. The average accuracy for the leaf samples of cv. ‘Casual’ lettuce reached 98.75% and for cv. ‘Elizium’ cultivar—86.25%. The obtained relationship between DLI and yield, as well as the quality of romaine lettuce, can be used in practice to improve romaine lettuce production in an Indoor Controlled Environment.

Enhancing Pigment Phenotyping and Classification in Lettuce through the Integration of Reflectance Spectroscopy and AI Algorithms

“…Despite the expectation that HC, LDA, KNN, Log-Reg, Nai-Bay, RF, SGD, SVM, and Tree [ 12 , 31 ] would have the highest precision and accuracy, our study found otherwise. Instead, SVM, PLS, and RF algorithms showed the highest accuracy for lettuce pigment phenotyping when used with a regression model [ 20 , 36 ].…”

“…Accordingly, the results showed that STEPW and VIP are useful in phenotyping plants, as reported in previous studies [ 31 , 33 , 37 ]. However, it has been noted that these methods have limitations, such as low accuracy and biases in the output.…”

“…However, it has been noted that these methods have limitations, such as low accuracy and biases in the output. On average, our findings indicate that 11.5% of the STEPW and VIP values were shared among the range of data, with VIP values ranging from 5.1 to 20.6%, as reported in [ 1 , 26 , 31 ].…”

“…The 700–1300 nm range has been found to have higher reflectance values and is believed to reflect differences in the molecular, biochemical, anatomical, and physiological characteristics of plants [ 1 , 3 ]. For instance, previous studies have correlated variations in the thickness of parenchyma cells in different lettuce varieties to differences in radiation scattering [ 31 , 32 ]. On the other hand, SWIR bands, composed mainly of organic compounds such as structural carbohydrates, amino acids, and proteins also demonstrate major variations in vibrational spectra [ 20 ].…”

The embodied carbon emissions of lettuce production in vertical farming, greenhouse horticulture, and open-field farming in the Netherlands

“…The studied CBVF uses 91 W m − 2 LED with a PPFD of 140 μmol m − 2 s − 1 , resulting in a very low molar efficacy of 1.54 μmol J − 1 . The best performance in terms of quality and yield for lettuce production requires approximately 240 μmol m − 2 s − 1 and a 16 h photoperiod (Matysiak et al, 2022); a daily light integral (DLI) of 13.8 mol m − 2 d − 1 compared to 10.1 mol m − 2 d − 1 in the VF studied. To obtain more insight into the performance of the studied VF the yearly amount of photosynthetic active photons reaching the crops to produce a kg FW were presented in Fig.…”