How necessary is the foundation zone atmosphere in managed atmosphere hydroponic manufacturing?

 

As the water strikes although a nutrient movie method (NFT) manufacturing system it’s close to saturation with oxygen due to mechanical aeration that’s occurring from the water recirculation. Photo courtesy of Hort Americas

The oxygen degree and temperature within the root zone can have a significant affect on charge of plant development and inhibiting root ailments.

When it involves hydroponic vegetable manufacturing the foundation zone atmosphere, together with oxygen ranges and root temperature, play a important position within the success of the crop.

“For true hydroponics, which would come with deep water tradition and nutrient movie method (NFT), each have completely different oxygen profiles,” mentioned Neil Mattson, greenhouse horticulture professor at Cornell University. “Typically with NFT, there may be close to saturation with oxygen due to mechanical aeration from the water recirculation that’s occurring. The water that’s pumped by means of an NFT system and is emitted by spaghetti tubing turns into primarily saturated with oxygen. This water is operating throughout the plant roots constantly.”

Deep water tradition, which often has a large water reservoir, has a big storage capability for dissolved oxygen.

“Deep water tradition techniques are much less vulnerable to temperature and pH swings,” Mattson mentioned. “Growers trying so as to add oxygen to a deep water tradition system need to actively add oxygen to ensure there’s a enough degree within the water.

“Typically growers do one among two issues so as to add oxygen. The first possibility is to put in a Venturi pump to bubble in outdoors air into the water reservoir after which distribute the oxygen all through the pond. Oxygen doesn’t diffuse effectively by means of water so a grower has to ensure to not place the pump in a single location and never distribute the oxygen all through the pond. A grower additionally has to put in tubing and a manifold system in order that the oxygen is distributed to quite a few factors all through the pond. Smaller growers have a tendency to make use of the Venturi system.”

In addition to effervescent or pumping in air, growers with deep water tradition techniques can inject liquid oxygen or incorporate a nanobubble oxygen technology system.

“The oxygen comes both from tanks of liquid oxygen or from an oxygen-generation system,” Mattson mentioned. “Growers who select these choices would nonetheless want a pond distribution system. But as an alternative of utilizing a variety of pumping capability to bubble within the air (about 21 % oxygen), the air could be circulated with a pump.”

Deep water tradition manufacturing techniques, which often have a large water reservoir, have a big storage capability for dissolved oxygen.
Photo courtesy of Hort Americas

Seasonal variations in oxygen ranges

Mattson mentioned growers utilizing deep water tradition want to observe the oxygen degree with a dissolved oxygen meter. The oxygen degree ought to be adjusted over time because the crop is rising.

“Factors that have an effect on the oxygen degree within the water embrace the absorption of oxygen by the plant roots,” he mentioned. “How rapidly the oxygen is depleted will depend on how rapidly the vegetation are rising and the water temperature.

“Other elements affecting the oxygen degree embrace microbes and algae within the water that is perhaps competing for the oxygen. There can also be diffusion of some oxygen off the floor of the pond. It is a dynamic system and there may be not a hard-and-fast rule for each sq. foot of pond water that a certain amount of oxygen must be added.”

Growers often need to pay nearer consideration to the oxygen degree in the course of the summer season as a result of hotter water temperatures maintain much less oxygen. During the winter if the air temperature is cooler, the pond water temperature goes to trace that method as effectively until a grower heats, cools or adjusts the pond water temperature.

“During the summer season when the water temperature is hotter, due to its bodily properties, water holds much less dissolved oxygen,” Mattson mentioned. “This can also be the time of yr when the vegetation are rising extra rapidly and the roots are breathing (consuming oxygen) extra rapidly.”

Mattson mentioned one other problem growers might face is the affect of water temperature on illness infestation.

“There are sure species of the foundation illness pathogen Pythium that proliferate extra rapidly beneath hotter temperatures,” he mentioned. “Typically growers are extra involved concerning the unfold of those pathogens in the course of the summer season with the hotter pond water temperatures. Chilling the pond water to maintain the temperature between 68ºF-72ºF may help to discourage these pathogens from proliferating rapidly.”

Paul Fisher, professor and extension specialist/ floriculture on the University of Florida, mentioned the goal oxygen degree ought to be at saturation within the root zone in all elements of a hydroponic rising system.

“A crop ought to be grown near saturation (8-9 elements per million at 68ºF-72 ºF water temperature),” Fisher mentioned. “As oxygen ranges drop, particularly all the way down to 2-3 ppm, that is the place Pythium an infection is favored. Even with high-wire tomato and cucumber crops the place the vegetation are being grown in rockwool or coir slabs, the substrate shouldn’t be allowed to grow to be waterlogged. Pythium and Phytophthora are water molds that may infect vegetation at any level of the crop cycle.

“Every hydroponic grower ought to have a dissolved oxygen meter. A tip for taking readings is to have the nutrient answer flowing over the meter to acquire an excellent steady studying.”

At 68ºF, which is a typical root zone temperature, strawberry requires practically double the quantity of oxygen content material as cucumber and about 40 % greater than the oxygen requirement of tomato. Photo courtesy of Chieri Kubota, Ohio St. Univ.

Oxygen necessities for various crops

Mattson mentioned though some hydroponically-grown crops seem like extra delicate to low oxygen within the root zone, there hasn’t been a variety of analysis to group vegetation in response to their root zone oxygen necessities.

“Strawberries and hashish appear to be comparatively delicate to root ailments if there’s a low oxygen degree within the root zone,” he mentioned. “This is in distinction to tomatoes, cucumbers and recent reduce roses, that are fairly tolerant of low root oxygen ranges.

“Future analysis to find out goal oxygen ranges would assist us perceive why some crops are extra delicate than others to low oxygen ranges and that might assist long-term breeding efforts. Plants could possibly be chosen by breeders for hydroponic manufacturing as a result of they’re extra tolerant of low root oxygen ranges and fewer prone to illness pathogens.”

Spinach varieties, specifically have been chosen for root-disease resistance. Bowery Farming Inc., a industrial vertical farming firm, has begun working with researchers on the Arkansas Agricultural Experiment Station to develop disease-resistant spinach for its proprietary indoor manufacturing techniques.

“Spinach is among the crops which might be very delicate to Pythium root rot,” Mattson mentioned. “By deciding on varieties which might be extra immune to Pythium, it is perhaps potential to develop the vegetation with decrease root oxygen ranges.”

Chieri Kubota, professor and director of Ohio Controlled Environment Agriculture Center (OHCEAC) at Ohio State University, is conducting in depth analysis research with hydroponically-grown strawberries.

“Strawberries require extra oxygen within the root atmosphere in comparison with different greenhouse vegetable crops,” Kubota mentioned. “Indoor strawberry growers must pay shut consideration to ensure the oxygen degree is just not depleted within the root zone.”

Based on a research carried out in Japan with strawberry, the oxygen requirement per grams of root mass is greater for strawberry than different meals crops. There is a big distinction within the oxygen requirement between hydroponic crops.

“Comparing strawberry with cucumber and tomato at completely different temperatures, the oxygen degree is crop particular,” Kubota mentioned. “At 20ºC (68ºF), which is a typical root zone temperature, strawberry requires practically double the quantity of oxygen content material than cucumber. It’s about 40 % greater than the oxygen requirement in comparison with tomato. More analysis must be carried out with regard to figuring out the goal root zone oxygen necessities of different hydroponic crops like lettuce and hashish.”

Mattson mentioned the oxygen necessities for a crop might change because the plant development stage adjustments.

“A extra mature plant that’s actively rising has an intensive root biomass that’s going to have a bigger oxygen requirement than a smaller youthful plant,” he mentioned. “With a deep water tradition lettuce crop there may be usually going to be all ranges of development phases with younger vegetation on one facet of the pond and extra mature vegetation on the opposite facet. In that case, there may be form of a longtime equilibrium regarding the vegetation’ common oxygen necessities. Regardless of the crop, if there’s a massive root system there may be probably extra biomass that’s going to be breathing at the next charge so the vegetation’ oxygen wants are going to be better.”

Maintaining goal temperatures

One of the advantages of deep water tradition techniques is the massive quantity of water that’s sluggish to vary with regard to water temperature, pH and dissolved oxygen ranges. If the water is at an optimum temperature, it’ll take lots to vary the temperature.

“In a NFT system there may be a variety of uncovered floor space due to the shallow channels or troughs and water is constantly recirculating on these channels,” Mattson mentioned. “There is a variety of floor space that isn’t effectively insulated in comparison with a deep water tradition system, which is insulated and has a big quantity of water. The deep water tradition vegetation are additionally often grown in a foam insulation board.”

Chilling the nutrient answer in hotter climates like Florida may help to cut back warmth stress and enhance the dissolved oxygen degree. Photo courtesy of Paul Fisher, Univ. of Fla.

With a NFT system the water temperature goes to carefully match the air temperature due to the uncovered floor space. During the winter if the air is being heated to the specified air temperature, the water temperature goes to be similar to the air temperature.

“Floriculture crop research in containers have proven if root-zone heating is used, a grower could possibly decrease the greenhouse air temperature with a view to preserve power,” Mattson mentioned. “Similarly growers who’re utilizing deep water tradition can warmth the water temperature to 72ºF after which keep a cooler air temperature as a result of the pond water is held on the desired temperature.”

During the summer season for deep water tradition techniques growers can use inline water chillers to decrease the water temperature. This allows the water to carry extra oxygen and cut back the probabilities of illness infestation.

“With a NFT system attempting to heat or cool the water temperature is just not as sensible,” Mattson mentioned. “The heated or chilled water is uncovered to a variety of floor space in a greenhouse. This goes to trigger the water to lose warmth comparatively rapidly in a chilly greenhouse in the course of the winter and heat up rapidly on a scorching summer season day.”

Fisher mentioned root zone chilling is essential for greenhouse growers attempting to make use of hydroponics in the summertime in Florida. Chilling the nutrient answer can decrease the temperature of the plant crown which may help to cut back warmth stress and enhance the dissolved oxygen degree. University of Florida horticulture professor Germán Sandoya is doing breeding work on heat-tolerant lettuce varieties for each greenhouse and subject manufacturing.

Kubota mentioned reducing the water temperature so the foundation zone temperature is round 20ºC (68ºF) helps when rising leafy greens.

“For spinach, the foundation zone temperature ought to be even decrease,” she mentioned. “From a pathogen administration standpoint, the advice is 15ºC (59ºF) for the foundation zone. But this might have a downside of lowering the general development of the vegetation.

“The root zone temperature is just like the typical 24-hour temperature. Growing at 18ºC (64.4ºF) at evening and 24ºC (75ºF) in the course of the day, the typical temperature is round 22ºC-23ºC (71.6ºF-73.4 ºF) for lengthy day circumstances. For fruiting greens, the aerial temperature for fruiting is extra necessary than the rising level temperature which is an extended distance away from the foundation zone. This might be why growers don’t attempt to management the foundation zone temperature with these crops.”

The root zone temperature has an affect on the oxygen degree. The oxygen saturation level declines with growing temperature.

“Water loses the capability to carry oxygen because the temperature will increase,” Kubota mentioned “It is an unfavorable situation when the temperature will increase as a result of the respiration requirement will increase additionally. The roots want extra oxygen at greater temperatures. However, water loses the capability to dissolve oxygen so it’s simple to suffocate the roots at excessive temperatures.”