Incorporating air or oxygen into irrigation water using nanobubbles can improve crop yields and reduce susceptibility to disease pathogens.
What started out as a way of making wastewater treatment systems more efficient with oxygen enrichment has expanded to how nanobubble aeration technology can improve production of agricultural crops. Moleaer Inc. in Torrance, Calif., filed a patent on nanobubble aeration technology in 2016 with the intention of using it as a way to deliver gas in a number of different applications.
Increasing the oxygen level in the root zone can ensure healthy root growth and can impact crop yields.
Low oxygen levels in the growing substrate can play havoc with the health of both vegetable and ornamental plants. Shalin Khosla, greenhouse vegetable specialist at Ontario Ministry of Agriculture, Food and Rural Affairs in Harrow, Ontario, said a substrate oxygen level below 5 parts per million can have a negative effect on plant growth.
Hort Americas is excited to announce that it has been appointed the exclusive distributor of the Moleaer Inc. nanoBoost Nanobubble Generator. The generator delivers a supplementary source of dissolved oxygen that can significantly increase plant growth, improve size uniformity, reduce stress and prevent root diseases under extreme production conditions. It is ideally suited for horticultural applications including hydroponics, greenhouse irrigation and pond management.
Hort Americas installed the 50-gallons-per-minute (GPM) nanoBoost in in its hydroponics demonstration greenhouse in Dallas, Texas, to improve the production of leafy greens and culinary herbs during the summer months when warm summer temperatures make production more difficult.
“Our thought was that if we enhance and maintain higher dissolved oxygen levels, we should be able to improve crop health and ultimately improve yield,” said Chris Higgins, general manager at Hort Americas. “We observed dissolved oxygen levels of 29 parts per million in water temperatures of roughly 90ºF. Not only did we achieve our highest level of dissolved oxygen, but our crop yields increased between 20 and 50 percent.”
Improving nutrient uptake and plant transpiration
The self-cleaning nanoBoost Nanobubble generator, which has no moving parts, produces oxygen-enriched nanobubbles that efficiently oxygenate an entire body of water and provides a reserve of oxygen encapsulated within the bubbles.
The generator delivers billions of nanobubbles with 200-times the inter-facial surface area when compared to micro bubbles, making them far superior in transporting valuable oxygen to the plants’ root system. The surface of the nanobubbles is negatively charged, attracting nutrient salts and enhancing nutrient uptake. Nanobubbles also increase the mobility of water molecules, potentially improving plant transpiration.
The generator is available in various flow rates and is fully encased in a durable, NEMA4-rated weather-tolerant PVC shell. The unit is self-cleaning and features plug-and-play installation with no moving parts, thus ensuring long-lasting durability with minimal maintenance. The generator can be configured with an integrated pump or retrofitted with a customer’s existing pump to maximize energy efficiency.
Moleaer announces commercial partnership with Hort Americas
PRESS RELEASE – LOS ANGELES
Moleaer Inc., the leading manufacturer of industrial scale nanobubble generators, expands its innovative product line with the new nanoBoost Nanobubble Generator, ideally suited for applications such as hydroponics, pond management, and irrigation.
Growers have affordable options for ensuring plants receive sufficient oxygen in hydroponic production systems to maximize growth and to reduce the chances of disease.
Oxygen is critical in the development and growth of edible crops grown in hydroponic systems such as nutrient film technique (NFT) and deep water raft culture. Tyler Baras, special projects manager at Hort Americas, is studying methods of adding oxygen to both conventional and organic hydroponic production systems in the company’s 12,000-square-foot research and demonstration greenhouse in Dallas, Texas.
“One of the big differences is how growers add oxygen,” Baras said. “A lot of times in conventional hydroponics, growers use air pumps and air stones to add oxygen. In organic systems these tend to be hot spots for biofilm development. We have removed all air pumps and air stones from the organic systems we are trialing.
In the conventional production systems Baras is studying he has installed water pumps with a Venturi attachment to add oxygen to the nutrient solution reservoir.
“The pumps aren’t injecting air into the irrigation lines, but simply into the reservoir to circulate the water and to create a circular flow within the fertilizer reservoir,” he said. “As the pumps operate they draw in air through a ¼-inch emitter. There is the benefit of moving around the solution and the air being drawn in increases the level of dissolved oxygen.”
A method that organic growers use to increase oxygen levels is cascading the water when it returns to the reservoir. As water returns it is allowed to fall and break the surface of the reservoir so that the water can pull in oxygen.
“This can also be done in vertical farms where the water will fall down large return pipes to the reservoir,” Baras said. “This can happen in multiple stages where the water will drop several times. This is an effective method for increasing dissolved oxygen.
“For NFT, it appears more oxygen can be delivered to plant roots when the flow rate is increased per channel. As the flow rate increases, more oxygen is delivered to the roots so water isn’t sitting in the channel as long. This allows freshly oxygenated water to be delivered quickly to the roots. In conventional hydroponic NFT systems the flow rate is about ½ liter per minute. In our hydroponic NFT system I have been aiming for about 1-2 liters per minute.”
Adequate oxygen levels
Baras said oxygen is necessary for plant roots to perform metabolic processes.
“Most of the water uptake in plants is passive,” he said. “But there is a stage where the plants use energy to actively pull up water through the roots. This requires oxygen. If there isn’t any oxygen in the root zone no water will make it up through the roots to the top of the plant. Low oxygen in the root zone can appear as wilting at the top of the plants. This can seem counterintuitive in a hydroponic system because the roots are sitting in water, but the tops of the plants look like their wilting if there isn’t any oxygen in that water.”
Baras said the need for oxygen in an organic hydroponic system is even more important because of the presence of living microbes in the fertilizer solution reservoir.
“These microbes also require oxygen,” he said. “The oxygen demand is often higher in organic systems than conventional systems because not only do the plant roots need oxygen, but the microbes need oxygen as well. In an organic hydroponic system one of the best ways of keeping biofilm in check is to keep the beneficial microbes happy.”
Baras said most of the oxygen measurements he has been taking in his research have been showing very similar oxygen levels for both conventional and organic production systems when the crops are performing well.
“I have been aiming for a level of 7-12 parts per million (ppm) dissolved oxygen, but generally the readings fall between 7-9 ppm,” he said. “I’m using a ProODO meter from YSI that is a very sensitive piece of equipment that accurately measures dissolved oxygen.”
Although most hydroponic growers are concerned with maintaining adequate oxygen levels, Baras said if too much oxygen is added to the solution it can cause root stunting.
“I haven’t reached that threshold yet in my trials,” he said. “It’s crop dependent on what that level is. When there is too much oxygen the roots have less motivation to grow larger because they are getting everything they need with a smaller surface area. That can then translate to the plants producing less biomass resulting in less leaf tissue. So at some point too much oxygen can actually cause less growth. For crops like tomatoes, peppers and cucumbers the whole plant would be stunted.
“The only way growers could reach excessive oxygen levels that damage the plants are when liquid oxygen or possibly ozone is used. Using air pumps or air stones to add oxygen, the levels won’t be high enough to stunt plant growth. To reach higher oxygen levels of 15-16 ppm, a grower would have to use other methods like liquid oxygen and ozone. It’s very difficult to reach high oxygen levels above 10 ppm unless an alternative method is used beyond air pumps, Venturis and cascades. I haven’t seen any growers go much higher than 8-9 ppm using the conventional methods.”
Baras said growers using a deep water raft system could try increasing turbulence in the pond to increase oxygen level. However, too much turbulence can sometimes cause damage to the roots.
“The roots in the turbulent areas are the ones that often times grow poorly,” he said. “The plants that are near the irrigation outlets where the currents are stronger, they have the poorest root growth. Sometimes growers will use air pumps in their ponds and those plants directly above where the air stones are located grow poorly.”
For more: Hort Americas, (469) 532-2383; https://hortamericas.com.
David Kuack is a freelance technical writer in Fort Worth, Texas; email@example.com.
While providing the proper soluble salts and pH levels are important in hydroponic systems, don’t overlook the significance of maintaining the optimum temperature, oxygen concentration and microbe level in the nutrient solution.
Maintaining the proper soluble salts (electrical conductivity) level and pH are critical in hydroponic systems like nutrient film technique and floating rafts. While monitoring these properties are important, growers should not overlook the importance that temperature, oxygen level and microbial activity play in the growth of plants in these production systems.
“It’s not as much about maintaining root health as it is about managing the conditions in the rhizosphere, which is the region around the plant roots,” said Rosa Raudales, assistant professor of horticulture and greenhouse extension specialist at the University of Connecticut. “The area around the roots undergoes a lot of biological and chemical activity. Microorganisms in the rhizosphere feed on the exudate of the roots. Managing the rhizosphere and the conditions in the nutrient solution are critical to maintaining plant health.”
Maintain optimum root temperatures
While providing the proper air temperature in a greenhouse or controlled environment agriculture system is important, maintaining the optimum root temperature can have a bigger impact on the health and production time of a crop.
“If higher temperatures are maintained in the root zone then the plants are going to lose a lot of energy,” Raudales said. “Temperatures above the optimum in the root zone affect the cell membrane integrity of the roots. A disruption of the cell membranes affects the function of the roots resulting in less nutrient uptake, which affects crop cycles and yields.
“If plants are grown at root temperatures lower than the optimum, the plants grow slower because their metabolism is slower. In the worst case scenario, if freezing temperatures occur then ice crystals could form in the cells resulting in cell leakage and cell disruption.”
Cornell University researchers have conducted studies (http://www.cornellcea.com/attachments/Cornell%20CEA%20Lettuce%20Handbook%20.pdf) to identify the specific temperatures that are ideal for hydroponically-grown vegetables.
“Cornell researchers found the temperature of the nutrient solution had a greater effect than the air temperature,” Raudales said. “Lettuce plants exposed to air temperatures ranging between17ºC (62.6ºF) and 31ºC (87.8ºF) had consistent yields as long as the nutrient solution had a consistent temperature of 24ºC (75.2ºF). This research was done in the 1990s, but it still has application today.
“Cornell researchers did a similar study with spinach and they found the optimum root temperature was 22ºC (72ºF). They tested air temperatures ranging from 16ºC to 33ºC (60.8ºF-91.4ºF) and they found as long as the root temperature was 22ºC, the air temperature could be in that range and plants still produced optimum yields. For tomatoes the optimum root temperature is 25ºC (77ºF).”
Raudales said growers who are producing hydroponic leafy greens like lettuce and spinach have the option of installing a water heater to maintain the optimum root temperatures.
“It is easier and less expensive to heat the nutrient solution than to keep the whole greenhouse warm,” she said. “Heating the greenhouse does not make economic sense, when the research indicates that the temperature of the nutrient solution is a more important factor. If a grower is producing lettuce and spinach, which can tolerate lower air temperatures, it makes sense to run the greenhouses cooler and to install a water heater to adjust the nutrient solution temperature.”
Maintain adequate oxygen levels
Raudales said the dissolved oxygen level in a hydroponic solution needs to be maintained so respiration can occur in the roots.
“When oxygen levels are low in the root zone, the roots do not take up the nutrients required for growth,” she said. “Low oxygen levels cause increased ethylene production in the roots. If there are higher ethylene levels in the roots then the roots start to mature and die. The more oxygen present, the better the nutrient uptake and the better the root system.”
Raudales said there is also an inverse relationship between the oxygen level and solution temperature.
“If the root zone temperature is high, then the oxygen level is going to go down,” she said. “This is another reason why the root zone temperature is so important. The optimum oxygen level should be greater or equal to 6 parts per million of dissolved oxygen in the root zone. Plants should be able to handle 6-10 ppm without any problems.”
Raudales said growers who are using nutrient film technique systems typically don’t need to do any type of aeration. The movement caused by the flow of the water is usually enough to keep the oxygen level high enough in the solution.
Raudales said growers who are using floating rafts usually incorporate some type of oxygen-generating system.
“There are different ways of oxygenating the water,” she said. “One is aerating the water where air is being pumped into the water. Air is not pure oxygen, but it contains enough oxygen for what is needed in the hydroponic solution.”
Raudales said another reason for maintaining a high oxygen level in the hydroponic solution is the effect it can have on pathogenic fungal zoospores.
“If there is more oxygen, then zoospores don’t survive as well,” she said. “Zoospores don’t want completely anaerobic conditions, but they do better in conditions where there is less oxygen.
Pathogens of concern include Phytophthora, Pythium, Thielaviopsis basicola and Xanthomonas.
“Growers should try to keep the oxygen level high. If there are warmer temperatures, then there are lower oxygen levels. When there are lower oxygen levels the plants are not as healthy and more zoospores tend to survive. This is one of the reasons why there tends to be more disease issues during the summer than during the winter.”
Raudales said growers who are using floating rafts should be measuring the oxygen level regularly. Meters for measuring dissolved oxygen look like pH meters and are simple to operate.
Maintain beneficial microbes
Raudales said beneficial microbes are present naturally in water. Commercial products with beneficial microbes can also be incorporated into the hydroponic solution.
“Growers who are using the floating rafts tend to treat the nutrient solution like gold,” she said.
“They don’t want to replace it because they have a solution which is very high in beneficial microbes. Growers can inoculate the nutrient solution with a commercial biocontrol product or they can allow the good microbes to build up with time.
“As long as growers maintain the other parameters at optimum levels, including root temperature, pH, nutrients and oxygen levels, there typically isn’t a problem with diseases. This is very comparable to what happens with plants grown in substrates. The microbes build up naturally in the water just like in a substrate. These microbes feed on the exudates of the roots.
They need carbon sources that they wouldn’t get just from the nutrient solution. The system has to be clean, but it doesn’t have to be clean to the point of having to start with a fresh solution every time a new crop is planted.”
For more: Rosa Raudales, University of Connecticut, Department of Plant Science and Landscape Architecture; (860) 486-6043; firstname.lastname@example.org; http://www.greenhouse.uconn.edu.
David Kuack is a freelance technical writer in Fort Worth, Texas; email@example.com.