Unearthing Irrigation
How Irrigation in Controlled Environment Agriculture Is Different
While irrigation techniques refer to methods of delivering water to plants, watering crops in controlled environment agriculture (CEA) gives you a bit more to consider. This is because unlike irrigation in conventional agriculture, CEA irrigation requires not only water but also active consideration of nutrients, oxygen, and space to grow.
Put differently, in conventional agriculture you apply fertilizer and water separately; in CEA you apply them together by dissolving nutrients in water and feeding it to the plant roots, while making sure not to drown them. Plants in soil agriculture have their roots buried in soil, where they can draw both water and air from little pockets. In CEA, you can immerse roots in different kinds of media through which they are able to grow, or you can allow roots to hang in the air or float in water while the plant is supported from the base of its stem.
In conventional farming, natural water recycling processes occur outside of the farmers control, through evaporation and precipitation. In CEA, growers strive for a closed system where water is recycled and waste minimized. This gives growers control over their water- and nutrient-use efficiency but also adds to the complexity of the system.
Different Techniques for Different Crops
Farmers experiment with many different irrigation techniques to get the best results for their particular situations. We can’t explore every technique, so let’s take a closer look at some of the popular ones and why they work.
- Deep Water Culture (DWC) systems suspend a plant over a water basin. The plant roots grow into the basin, which is flooded with nutrient-rich water. Lettuce raft systems show how you could implement DWC commercially. In this system, you place lettuce crops on a raft, typically a foam board, that floats in a large basin of water. DWC offers a simple and elegant way to produce lettuce, but it doesn’t work with heavier crops such as tomatoes because they could tip the raft.
All roots require oxygen to grow, and more oxygen leads to better yields, so there is a balancing act. Lettuce roots are submerged in water in a raft system, but the water must be aerated so that oxygen gets dissolved in the water and the roots can breathe. Other systems might create space for the top of the roots to be above the water level or implement an ebb and flow system, where basin periodically drains out and refills. It’s up to the grower to choose which system works best for them.
2. Nutrient Film Technique (NFT) sets your crop atop a water channel that has a thin film of nutrient-rich water running through it. The roots touching the bottom of the channel absorb the water while leaving the upper section to absorb air. Leafy greens can succeed in this kind of system, as can some fruiting crops such as strawberries and cucumbers.
One concern with NFT is the lack of space for roots to grow. The roots must be touching the bottom of the channel from day one, so they can’t grow downwards. Instead, they grow sideways, which can interfere with neighboring root systems. Of course, you can place crops further apart, but producing fewer greens will also yield you fewer greenbacks!
3. Drip Irrigation buries the roots of a crop in media and allows water to drip in from the top and trickle down through it. Most people will recognize this as a common method for irrigation in conventional farming. In fields, the grow media is soil; but in CEA, other grow media, such as rockwool, are available.
One example, the dutch bucket system, gives each crop its own bucket to grow in. Nutrient-rich water is dripped into the bucket, trickles through the media, and drains out the bottom. Drip irrigation allows for a wide variety of crops to be grown as bucket size can be matched to crop size. This kind of system suits vining, fruiting crops such as tomatoes, cucurbits, and peppers.
4. Aeroponics suspends your crop over a water basin, similarly to DWC; but instead of flooding the basin, aeroponics deploys an array of nozzles to periodically spray the root system with a nutrient-rich mist. Suspended in air, they can breathe more easily whilst dining on the cool mists.
That’s a pretty good life for a plant, and this may explain why the technique is growing in popularity for its commercial potential. I say “potential” because the system can be both expensive and difficult to operate, thus limiting its use, at least for now, to plant physiology research. For example, NASA uses aeroponics in space to combat the failure of other systems to function in low-gravity environments. In the process, they’ve found it offers a ton of other benefits.
A Hotbed of Innovation
The biggest barriers to implementing irrigation systems commercially remain cost and complexity. The good news on this front is that researchers are continuing to create innovative systems with an eye to lowering costs and finding easier solutions. In the meantime, the benefits of CEA speak for themselves as growers are able to get increased yields and shorter grow cycles year-round with increasing reliability.
