Development of planting-density growth harvest (PGH) charts for lettuce grown in a plant factory with artificial lighting

Easy estimation of crop growth and productivity in relation to cultivation parameters is crucial when designing cultivation strategies in vertical farms. Planting-density Growth Harvest (PGH) charts facilitate the easy estimation of crop growth and harvest parameters, including crop growth rate, relative growth rate, shoot fresh weight, harvesting time, and yield. In this study, a PGH chart was developed for lettuce (Lactuca sativa L.) grown in a plant factory with artificial lighting. The plants were provided with Hoagland nutrient solution (EC 1.5 dS<middle dot>m-1) using a nutrient film technique with a photosynthetic photon flux density of 270 mu mol<middle dot>m-2<middle dot>s-1 and a 16-h/8-h (day/night) photoperiod using light-emitting diodes. Three planting densities of 15 x 8 cm (83 plants/m2), 15 x 16 cm (42 plants/m2), and 15 x 24 cm (28 plants/m2) were applied. The results showed that as the within-row spacing of lettuce plants increased, shoot fresh (FW) and dry weights (DW) per plant increased until they reached an upper limit of FW and DW, whereas the yield of lettuce per area declined. The relationship between fresh and dry weights of the shoot was linear. A quadratic equation was used to characterize crop growth rate (CGR), relative growth rate (RGR), and loss time (tb). Planting density showed a strong correlation with CGR, RGR, and tb. The development of PGH charts for lettuce provides valuable insights into crop growth, yield estimation and offers practical guidance for designing efficient plant production systems, which may be an useful resource for facilitating informed decision-making in agricultural settings.