Shrinking to Multiply?
Height, light, and vertical farming production
In its simplest sense, controlled environment agriculture (CEA) is in every amateur grower’s knowhow. From burlap to row tunnels, protecting plants to promote crop yield is time-honored practice, with scope for environmental manipulation increasing in step with ag tech. Vertical farming (VF) has taken CEA sky-high, bringing multi-storied crop beds into previously ground-level play. Still, in warehouse settings, the ceiling remains the limit. Short of raising the roof, how can we boost capacity?
Tentative answers lie in plant morphology. Reducing crop height can make room for additional vertical layers. Leafy greens are a case in point, to which myriad shrinkage methods apply. Traditional techniques include pruning and cultivar selection, while varying diurnal and nocturnal temperatures has recently yielded results. Light intensity and quality are equally vital factors with repercussions not only for produce height but also for quality and nutritional value. Investigations into the impacts of light treatment thus merit nuanced attention.
A 2008 study found lettuce stem and leaf length to be significantly shorter under white-blue light (Figure 1). What’s more, white-blue light correlated with increased carotenoids and flavonoids (Figure 2), which — along with essential oils — constitute key building blocks of fragrance, taste, and nutrition. Shifting into a ‘bluer’ spectrum, while keeping light intensity constant, both reduce lettuce height and amps up quality.
A subsequent paper holds the lateral shoot leaf weight to be greatest under blue light (Figure 3). Blue-spectrum basil’s essential oil content also surpassed that of its white-spectrum counterpart in four out of seven cases. In total, exposure to blue-spectrum light more than doubled basil plants’ essential oil content (Figure 4), packing a significantly more nutritional punch.
Blue LED light similarly spurred height reduction in three different species of mint (Figure 5). These varieties showed no statistical height difference under 100% blue treatment, but each grew to a distinctly shorter height than its white-light equivalent. Though blue-spectrum light shortened all three species, essential oil content only increased in two, namely mentha spicata and mentha piperita (Figure 6). It would seem some effects of light treatment hinge on species.
Though divergent conditions preclude a direct comparison of the above-mentioned studies, much can be gleaned from their collective findings. Light intensity and spectra evidently affect plant height, quality and taste, but optimum conditions are species-specific. If we are to use light treatment to shrink produce and ultimately increase output, much fine-tuning is required. Where is the equilibrium between nutrition, flavor and productivity?
