The current trend of indoor farming is catching up in the urban world, and for good, since it encourages safer & healthier eating and sustainability of the planet. It involves the application of both agriculture and technology at the same time to locally produce food while minimizing the use of resources such as water, soil and fuel. Recently, the industry is witnessing a rise in its stakeholders with more and more growers being from a non-farming background. However, such lack of scientific and industry background knowledge leads to total dependency on the available technology which might sometimes mislead the growers from their target harvest output in terms of quality, quantity and shelf life of the crop. For instance, despite of state-of-the-art infrastructure and high-quality inputs like soluble hydroponic nutrients, an improper lighting and environmental conditions maintained in such farms might render the final produce with compromised quality in terms of flavor, color or texture. A ‘perfect plant quality’ can be achieved via a ‘perfect plant recipe’. Let us peek through the 5 ingredients for a ‘perfect plant recipe’-
1. Light spectrum – all about the right colors
Light spectrum refers to the color wavelength(s) chosen to provide the plant through LEDs. It is important to know as each color wavelength is responsible for expressing specific morphological and/or physiological changes at each growth phase throughout the life cycle of plants right from germination to flowering and fruiting. These plant responses are governed by four major photoreceptors i.e. UVR8, phytochromes, cryptochromes and phototropins (and Zeitlupe family) which are sensitive to UV-B; red/far-red and UV-A/blue wavelengths respectively. For instance, phytochromes regulate germination, photomorphogenesis, shade avoidance and transition to flowering; phototropins direct the movement of plants towards light (phototropism) and cryptochromes work concurrently with the phytochromes to control photomorphogenesis and flowering of plants. Other wavelengths from the PAR spectrum (400 to 700 nm) like green have also been shown to cause significant changes in the morphology of plants when exposed to them. Thus, each color wavelength should be wisely chosen to trigger specific changes in the plant at the required growth stage to yield the desired response.
2. Light intensity – PPFD and not Lux
Plants see light differently than human eyes. Hence, ‘lux’, a unit of light intensity perceived by human eyes, is just so inaccurate and unfair for plants. Yet, the horticultural lighting market seem to ignore the crucial fact that, it is the photons (packets of light energy) of a wavelength or range of wavelengths i.e. the PAR (Photosynthetically Active Range) received per unit area per unit time, which makes more sense to the plants. Every light source produces these photons which can be quantified in terms of µmoles per meter square per second which is known as the PPFD (Photosynthetic Photon Flux Density) of the light source. The key lies in providing the adequate PPFD by using different light sources (fluorescents, metal halides, HPS, LEDs), their combination or as supplement lighting with sunlight (in greenhouses) to fulfill the Daily Light integral (DLI) requirements of a plant type or species. Think of it as our total calorie intake (DLI for plants) through an energy source i.e. food (light in case of plants) to sustain our metabolic processes per day.
3. Light Duration – it’s on the clock
The importance of time can never be overlooked, especially when it comes to a ‘perfect plant recipe’. Broadly, the number of hours/days for which plants are exposed to the light source will determine the expression of the desired response at the time of harvest. However, it may also last for few seconds to minutes depending on the wavelength used for specific purpose (yes, I mean UV treatment). Generally, the ‘photoperiod’ or the duration of light provided to plants is decided by the daily light integral (DLI) values for the crop. Based on the PPFD delivered by the different light sources – the sun, high pressure sodium (HPS) lamps, metal halides (MH), fluorescent lights or light emitting diodes (LEDs), one can easily calculate the number of hours for which that light source must be available to plants to fulfill the DLI requirements. This decision must be made by the grower at each growth stage of the plant right from the germination (sometimes even before) and becomes extremely crucial during the flowering period depending on the crop. For instance, the dark period must be increased by switching off the lights during the day (or daybreak) reducing the day-length for short day plants to flower. On the contrary, for the long day plants to flower, the night must be interrupted with occasional switching on the lights during the dark period inside the farm.
4. Environment – making sure the plants feel comfortable
This is one of the most essential aspects of indoor farming. It is complementary to the light (quality, quantity and duration) provided to the plants, to exert a positive effect on its yield, quality and shelf life. Although, it is pretty easy to find huge variety of various environmental sensors in the market, it is unfortunate that there is still a huge gap in their intercommunication skills and generation of meaningful insights. Instead, they tend to overload the grower with loads of data without any actionable guidelines. There is certainly more to than just maintaining the proper levels of these variables like temperature, humidity, vapor pressure deficit (VPD), pH, electrical conductivity (EC), carbon dioxide etc. It is vital to understand how they interact with and are influenced by the plants and the surrounding growing media (soil or water with nutrients), also when and how can they become a source of stress (abiotic or biotic) for the growing plant, if not optimized.
5. Crop stage – all it takes is the ‘right timing’
It closes the loop of the entire discussion on the ‘perfect plant recipe’. None of this would make sense to the plants (or the grower) if the timing of all input variables (light, environment, water, nutrients) is not correct. Plant is a biological entity meaning its development is decided by its physiological state. In order to move on to the next phase, it must achieve a specific amount of growth in terms of size or days (sometimes months or years too). The plant growth stage at which the light spectrum, intensity and duration must be changed or maintained to increase biomass, number of flowers/fruits, yield, nutrient content, color of plants or any other quality trait, should be essentially recognized beforehand considering the timing when receptivity of the plant towards a light regime would be maximum. Having said that, it is equally vital to understand the effects of different environmental variables on the plant at this point and how they can be modified to support or enhance the plant response towards a ‘perfect plant recipe’.