Some 50 years ago, the standard method for producing vegetable seedlings for transplanting was to sow the seed in a nursery bed and then dig up the seedlings when they were large enough to be successfully transplanted.
The system was anything but fool-proof; in fact, it provided an ideal means of distributing soilborne pests and diseases (that were present in the seed bed) over a larger cropping area. This was overcome by many brassica seedling growers by fumigating the soil with a chloropicrin/methyl-bromide mixture some months prior to sowing the seed. This method also provided some weed control as a by-product.
In the 1970s, the use of cell trays for growing vegetable seedlings was developed. This provided a means of mass-producing seedlings for later planting in the field by supplying water and nutrients via overhead booms and having the roots air pruned. For the past 20 years, it has become a common practice for vegetable seedling producers to germinate the seeds—after sowing in cell trays—in special temperature-controlled rooms to ensure better and more even germination.
It is now timely to consider the potential for growing seedlings (until transplantation) in a totally environmentally controlled room—in which nutrition, water supply, temperature, day length, light intensity (and wavelength), humidity and levels of carbon dioxide are precisely controlled.
Using such technology, it should then be possible to produce perfect vegetable seedlings at any time of the year without reference to the outside conditions. It might also have the potential for a very fast throughput, as it might be possible to produce seedlings using a 24-hour day. Thus, producing quality seedlings would be greatly simplified.
Also, such a system would also reduce the amount of variation currently occurring in conventionally produced vegetables crops (if 50% of the plants life is spent in controlled climate conditions, then any variation in the weather in the field after planting will have a much reduced impact on time to maturity). Still, the shorter time the plants are exposed to variable weather conditions, the more precise you can time crop maturity. As such, a further advantage of plant factories would be the potential to hold plants if planting conditions in the field are not satisfactory.
This might involve no more than simply reducing the temperature (an action that is much harder hard to achieve in a greenhouse than in a plant factory because it is very difficult to reduce either light intensity or temperature in a greenhouse; thus, to hold young seedlings in a greenhouse, you have to ventilate, supply the seedlings with no fertilizer and keep the watering levels low—a sub-optimal solution).
An additional factor (following the necessary research) would be to develop a technology that would prepare the plants beyond standard hardening-off in order to assist the plant in rapid growth after transplanting. This might be a simple as feeding the plant with nutrients and dropping the temperature, but not the light intensity, so the plants become loaded up with carbohydrates and inorganic nutrients.
Grafting plants is becoming increasingly important for high-value crops, such as tomatoes and cucurbits, so the production of more even rootstocks and scions, and the ability to provide a very precise environment for the germination stage, the graft union process and for the growing on stage has real potential. The high value of these plants makes plant factory technology very relevant for the present, let alone for the future.
In September 2012, there was a major international workshop at the University of Maryland on the challenges in vertical farming. The motivation for this meeting was stated by the organizers as follows:
By the year 2050, we expect human population to increase to 9 billion and to be further concentrated in urban centers. An estimated billion hectares of new land will be needed to grow enough food to feed the earth. At present, however, over 80% of the land suitable for raising crops is already in use. Further, if trends in climate change persist, the amount of land available for farming will decrease. Since crops consume 87% of all water used globally, an increase in water usage is not possible.
Finally, while the need is for 50% higher yield by the year 2050 to maintain the status quo, we expect agricultural productivity to decline significantly across the world, especially in densely populated areas. There is an urgent need for high-yield agriculture that decreases the use of water and carbon based [sic] inputs per unit of product, while simultaneously reducing vulnerability of crops to natural environmental conditions.
Whether plant factories are a suitable vehicle for the complete cycle of crop production could be debated, but their potential for high-quality vegetable seedling production appears to be unlimited.
This article was previously published in Practical Hydroponics.