Response of growth, yield, and quality of edible-podded snow peas to supplemental LED lighting during winter greenhouse production

The occurrence of low natural light levels during winter months is a major limiting factor for greenhouse plant production in northern regions. To determine the effects of supplemental lighting (SL) on winter greenhouse production of pea pods, plant growth, pod yield, and quality were investigated under SL at a photosyn thetic photon flux density (PPFD) of 50, 80, 110, and 140 mu mol m(-2) s(-1), plus a no-SL control treatment, inside a Canadian greenhouse from January to March. Light-emitting diodes with a red-to-blue PPFD ratio of 4:1 and a 16 h photoperiod were used for the lighting treatments. During the trial period, the average natural daily light integral (DLI) inside the greenhouse was 6.6 mol m(-2) d(-1) and the average daily temperature was around 13 degrees C. Compared with the control, SL treatments increased pod yield and promoted plant growth, as demonstrated by faster main stem extension and greater aerial biomass. Also, total pod yield (g plant(-1) or no. plant(-1)) and some growth traits (e.g., stem diameter, branch number, leaf thickness, and leaf chlorophyll content) were proportional to supplemental PPFD within the range of 0-140 mu mol m(-2) s(-1). However, SL levels of 50-80 mu mol m(-2) s(-1), corresponding to a total (natural + supplemental) DLI of 9.4-11.1 mol m(-2 )d(-1), resulted in the best pod quality based on evaluations of individual fresh mass, length, soluble solids content, succulence, and firmness. Therefore, a total DLI ranging between 9.4 and 11.1 mol m(-2 )d(-1) can be recommended as a target light level for greenhouse production of pea pods using SL under winter environment conditions.