Vertical farming: A potential farming practice for lettuce production

Land for agriculture is becoming limited in urban areas and the concept of vertical farming could help increase land productivity. Therefore, this study was conducted to investigate the potential of vertical farming on sunlight availability for lettuce (Lactuca sativa L.) production in the greenhouse system. The experimental design was completely randomized design with two different farming systems: Horizontal and vertical farming systems. Ten planting shelves including five horizontal shelves (HS) and five vertical shelves (VS) with three vertical levels as upper (VS_U), middle (VS_M) and lower (VS_L) were constructed. Two lettuce varieties, ‘Green Oak’ (L. sativa var. crispa) and ‘Green Cos’ (L. sativa var. longifolia), were selected for comparative measurement. Lettuce was planted in both HS and VS systems. Photosynthetically photon flux density (PPFD) was continuously monitored throughout lettuce growing period. Lettuce height and canopy width were measured weekly. Leaf fresh weight (FW) and dry weight (DW) were also evaluated. The averaged PPFD values were 245, 217, 158 and 147 μmol m-2 s-1 for HS, VS_U, VS_M and VS_L, respectively. Higher values of height and canopy width were observed on HS in comparison to VS. Values of FW and DW on HS were significantly higher as compared to VS. In addition, higher plant growth occurred from upper to lower levels on VS while lower FW and DW were observed from top to bottom. Plant densities of VS (24 plant m-2) were 1.5 times higher than HS (16 plant m-2). Light use efficiency was also pointed out that VS (0.46 g mol-1) tended to have better values in comparison to HS (0.28 g mol-1).