The speakers and topics are:

Dr. Jim Owen, USDA-ARS, Water in Ohio – nursery use and return including reservoirs

Dr. Sarah White, Clemson, Reservoir water quality and management

Dr. Jeb Fields, LSU, Substrates and water management

Dr. Jake Shreckhise, USDA-ARS, Irrigation frequency and container color affect substrate temperature and controlled-release fertilizer longevity

Dr. Garrett Owen, OSU, Basics of substrate pH and soluble salts sampling and monitoring

Dr. Raul Cabrera, Texas A&M, Managing soluble salts in nursery and greenhouse production

Dr. Amy Fulcher, UT-Knoxville, TBD

Click here to enroll: https://cfaesosu.catalog.instructure.com/courses/water-management-and-quality-for-greenhouse-and-nursery-crop-production

Carson, CA — NovaCropControl, an industry-leading research and testing centre based in the Netherlands, has completed its independent study evaluating the impact of chemical-free nanobubble enriched irrigation water on tomato fruit growth, pathogen control, and nutrient uptake.

In a side-by-side study, NovaCropControl irrigated plants with technology provided by Moleaer, the global leader in nanobubble technology. Plants irrigated with Moleaer’s nanobubbles had:

• More efficient nutrient uptake and water usage
• Improved capillary root development
• Increased resilience to high heat
• Reduced Pythium levels of up to 80%

The study also showed plants irrigated with Moleaer nanobubble enriched water produced a 9% increase in fruit weight without sacrificing nutrient content or BRIX value (grams of sucrose). 

Tomatoes provide a rich source of vitamins A, C, K, and minerals, including iron and phosphorus, making them one of the most popular and valuable crops grown in greenhouses. 

Moleaer’s patented nanobubble technology is installed at over 200 horticulture facilities, enabling growers to enhance existing irrigation water, promote beneficial bacteria, suppress pathogens and diseases, and increase nutrient uptake.

Moleaer delivers these results by providing a consistent flow of nanobubbles to the plant’s roots to maintain high oxygen levels in irrigation water and deep water culture (DWC) systems. Increased root zone oxygenation through nanobubbles increases plant nutrient uptake. The outcome is healthier, more resilient plants, increased crop yields, and decreased time to cultivation.

“We know that improving water quality through increasing sufficient oxygen levels are important for plant health and crop resilience. Our trial confirmed that Moleaer’s oxygen-filled nanobubbles are a very efficient method of delivery,” said Koen van Kempen, Consultant, NovaCropControl Research Center.

“Nanobubbles are a complex science, but this latest third-party research demonstrates in the simplest of terms the value nanobubbles provide to our food supply by enhancing water quality, without using chemicals, to improve plant health and resilience to environmental stress, which ultimately leads to increased crop yields,” said Nicholas Dyner, CEO of Moleaer.

For more information, please visit moleaer.com.

About NovaCropControl

NovaCropControl is a research and test centre specializing in plant sap analysis. NovaCropControl aims to provide insight into the plant‘s nutrient uptake with a fast and accurate service based on low cost. To reach that goal, NovaCropControl uses plant sap analyses and, if necessary, in combination with (ISO-17025) accredited drip, drain or substrate water analyses. To learn more, visit: www.novacropcontrol.nl/en/method

About Moleaer

Moleaer^TM is an American-based nanobubble technology company with a mission to unlock nanobubbles’ full potential to enhance and protect water, food, and natural resources. Moleaer has established the nanobubble industry in the U.S. by developing the first nanobubble generator that can perform cost-effectively at municipal and industrial scale. Moleaer’s patented nanobubble technology provides the highest proven oxygen transfer rate in the aeration and gas infusion industry, with an efficiency of over 85 percent per foot of water (Michael Stenstrom, UCLA, 2017). Through partnerships with universities, Moleaer has proven that nanobubbles are a chemical-free and cost-effective solution to increasing sustainable food production, restoring aquatic ecosystems, and improving natural resource recovery. Moleaer has deployed more than 700 nanobubble generators worldwide since 2016. To learn more, visit: www.Moleaer.com 

About nanobubbles

Nanobubbles are tiny bubbles, invisible to the naked eye and 2500 times smaller than a single grain of table salt. Bubbles at this scale remain suspended in water for long periods, enabling highly efficient oxygen transfer and supersaturation of dissolved gas in liquids. Nanobubbles also treat and eliminate pathogens and contaminants of emerging concern as well as scour surfaces to break apart biofilm matrices, creating a powerful, sustainable, and chemical-free disinfectant (Shiroodi, S., Schwarz, M.H., Nitin, N. et al., Food Bioprocess Technol, 2021). 

The video is hosted by Dr. Paul Fisher of University of Florida IFAS Extension for the Five Tips for Horticulture series on the UF/IFAS Greenhouse Training Online channel (tinyurl.com/ufgto). The series highlights technical topics from university and industry experts. The channel is sponsored by the Floriculture Research Alliance (floriculturealliance.org).

For related training on this topic, see our Greenhouse Training Online certificate courses for growers at https://hort.ifas.ufl.edu/training, including the Irrigation Water Quality and Treatment course that will be offered in 2021.

The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries, and all Florida residents. ifas.ufl.edu | @UF_IFAS

It is said that managing irrigation is a bit like being married. No matter how hard you try, you never do it right. But it is because we try that we succeed in having a happy marriage.

Plants need water and fertilizer to grow. In the hi-tech glasshouse industry, we apply both at the same time. A fertilizer injection system provides the fertilizer, and the drip irrigation system distributes the water evenly to the plants. How hard can it be? When I was a student studying Chemistry, I was never interested in Agriculture. You plant a seed, add water, fertilizer, sunshine, and a little while later, you harvest. How hard can this be? A lot harder than I could have ever imagined.

We base irrigation strategies on the measurements from the day before. Then we look at today’s weather and try to adapt the irrigation strategy to suit. As a result, we are always one step behind. It is why it is so hard to get the irrigation right every day. 

The Tools We Need

There are some basic tools that we need to collect the right information. A scale or moisture content sensor is important. If they are not available, a manual drain station such as pictured below is a must. Even if a scale or moisture sensor is available, a manual drain station is still recommended. Use at least one slab and collect all the days drain water in a bottle or bucket. Be sure also to measure the volume irrigated per dripper. It is a good check to know if the volume of irrigation water calculated by the climate computer is the same as the measured dripper volume.

The key components we want to measure are the %dry-down, the EC in the drain, and the timing of the first drain. The dry-down is the loss of moisture from maximum saturation during the day to a minimum just before the first irrigation in the morning. The dry-down tells us if we are steering the plant into a vegetative or generative direction. The EC of the drain indicates whether we give the right amount of water. The timing of the first drain tells us if we have the growing medium hydrated enough so the plant can transpire at a maximum rate.

Now that we have the right tools in place let’s look at what are the most important rules in irrigation. 

1. A healthy, mature tomato plant uses approximately 1.7 ml/Joule/M². 

Light determines about 80-90% of the water uptake. Therefore, triggering irrigation based on light sum deserves preference. The Humidity Deficit of the glasshouse air determines the remaining 10-20%of the water uptake. Many growers open the vents in the spring so that plants get used to low humidity. It is a fallacy because a plant that can handle a high light intensity does not need to take up much more water to deal with low humidity. A healthy root system is the most important.

2. The drain percentage emerges from the desire to maintain a certain EC.

I get often asked how much drain should be achieved. It is an irrelevant question. The desired drain EC is the key parameter; the percentage drain is how the EC is controlled. If the desired drain EC is 4.5 and it reaches 5.0, the best way to lower the EC is through irrigating more. The best time to irrigate more is through the middle of the day. If the EC in the drain is too high, increase the frequency of the irrigation between 11 am and 2 pm. If the drain EC is too low, decrease the frequency of the irrigation between 11 am and 2 pm. Some growers use light intensity to decrease the Drip EC during the middle of the day. I’m not a great fan of this, as I don’t think it helps the plants transpire more easily, and it creates imbalances in the nutrient concentrations, especially when recirculating. 

The following guidelines can be used to generate a drain that maintains a steady EC, based on a drip EC of 3.0 and a drain target EC of 4.5.

              Less than 500 Joules;       0-10% drain

              500-1000 Joules;              10-20% drain

              1000-1500 Joules;            20-30% drain

              More than 1500 Joules;   30-40% drain

The important message here is that the drain percentage itself is not what should be         targeted. The EC in the drain is the best indication of whether the plant gets enough water. The values in the table above change considerably if the grower targets a higher drain EC. 

Decreasing the EC by irrigating more on a dark day is not a good strategy. On a dark day, we must reduce the amount of water significantly. The trigger for irrigation should still be light. It keeps the growing media dry, and the roots are encouraged to “find” water elsewhere.

3. The desired dry-down determines the timing of the last irrigation.

Generally, a dry-down of 10-15% is recommended. A 10% dry-down is a vegetative action, whereas a 15% dry-down is a generative action.  If the desired dry down is 10% and the sensors show 9%, the timing of the last irrigation needs to be earlier and vice versa. I prefer to be careful with the last irrigation. If the weather becomes cloudy during the late afternoon, the desired dry-down cannot be achieved. As it is impossible to take one irrigation away, it is better to be careful, and if it the dry-down is looking like it becomes too large, night irrigations are always an option.

In days where the light sum is only a couple of hundred Joules, there is no need to achieve drain. If we consider a day of 300 Joules, then the amount of water the plant uses is 300 Joules x 1.7ml/Joule/M²= 510 ml/M². Most standard slabs contain 10-15 liters of water, so there is no danger of the plant running out of water. If we irrigate twice at 0.25 liters/M2, the slab is saturated. It means that we have driven most of the oxygen out of the slab, which creates an ideal environment for soil diseases. One or no irrigation is a better option. It also means that during dark days, the saturation point on the moisture content meter is never achieved. As a result, the difference between the maximum and minimum moisture content is less. On these days, the dry down should be measured as the difference between the minimum moisture content of that day and the maximum saturation point of previous days. 

Roots are like muscles; if you don’t use them, you lose them. Three days of less than 500 Joules per day results in dying off of the root system. It is important to keep the above calculation in mind. Saturating the growing medium on these dark days results in Pythium and root dieback. In the graph below, you can see the irrigation strategy of a sunny day followed by a cloudy day. In this case, a scale was used. The maximum weight was 36.6 Kg (dark blue line). The minimum weight the next morning was 33.0 kg. The dry-down was (36.6-33.0)/36.6 = 9.8%. The next days’ light sum was 432 Joules. The maximum weight increased to 35.4 Kg, so the saturation point was not achieved. No drain was achieved, which allowed for oxygen to remain in the root zone. The last irrigation was at 3 pm, and the weight decreased to 33.14 Kg by the next morning. It means that the timing of the last irrigation was perfect. It is a good way to manage the irrigation on a cloudy day. Also, note that the EC (light blue line) is rising. It means that during the next sunny day, the irrigation frequency has to be increased during the middle of the day to decrease the EC.

4. The first drain should be achieved at 500 watts or 1.2-1.8 ltr/M2

During periods of high transpiration, we want to make it easy for the plant to take up water. The growing media should be saturated, and the EC becomes lower as the drain increases. Therefore, it is important to have the first drain at 500 watts. This rule of thumb can be applied regardless of where in the world you are. The second rule that can be applied is that the first drain should be achieved at 1.2-1.8 ltr/M2. This value depends on the desired dry down. If a dry down of 10% is required, the drain should come at 1.25 liters per square meter. At a dry down of 15%, the first drain should come at 1.8 liters per square meter. If the drain starts before that, the frequency in the morning is too fast.

During low or no radiation, we want to make it more difficult for the plant to take up water, so the roots are encouraged to spread through the growing media, looking for moisture. It is why we want to achieve a minimum dry down. In general, the plant sends assimilates to the warmest part of the plant. During the late afternoon, the growing media often is the warmest part. Having enough air in the growing medium at a time when the assimilates are directed to the roots results in optimum root growth.

The above strategies help implement the four key parameters for irrigation; a start time, drain time, the total amount of irrigation water, and stop time. By following these rules of thumb, the grower creates an environment for the roots where they are kept healthy and aerated so that they can perform at maximum transpiration when required.

Figure 2 shows a typical rootzone temperature, moisture content, and EC graph. In the morning, the moisture content is quickly brought up to the saturation level, and the drain starts at the 8^th irrigation (cycle size 0.2 ltr/m2). The EC decreases quickly during the day and starts rising again after the last irrigation. At the same time, the moisture level decreases, meaning air is entering the root zone. Moisture measurement within the slab has greatly enhanced the understanding of the irrigation requirements of plants. It is important to remember that the measurement needs to be representative of the whole irrigation zone. One measurement per hectare doesn’t seem enough to represent one hectare. However, using one measurement for multiple irrigation zones in the same glasshouse for the same variety gives a better statistical average. It is especially true if the electronic data is backed up by a manual drain station. It is recommended to perform manual EC measurements of the surrounding growing media to verify that the single points of measurement are valid representations of the irrigation zone. It is also important to make sure that the slabs of growing media contain a representative number of plants. When the planting density is increased, it can happen that the measured slab does not have the right amount of plants. Equally important is that any equipment that is used is maintained to a proper standard. It includes the EC and pH meter.

While manufacturers of moisture meters claim that their meters are compensated for temperature, the reality is often different. In the graph above, it appears that the moisture content is increasing. That is not true. The increase in water content is caused by an increase in temperature and EC over the three days of measurement. It complicates the interpretation of the data. However, the most important information from the moisture content meter is the difference between minimum and maximum. This difference is less prone to fluctuations. 

If no moisture content measurement is available, we can still get the dry-down information from manual drain stations. By physically checking the manual drain stations for the first drain every day, we can backward calculate the dry-down. For instance, if we know at which irrigation cycle the first drain arrived, we know the volume of water added to the slab at that time. If we know the saturation weight of the slab, we can calculate the dry down that was achieved. For instance, if the drain arrived at the 5^th cycle and we give 100 ml per cycle, there are four drippers per slab, and the slab saturation volume is 15 Liters, we can calculate that it took 5 x 4 x 100 = 2,000 milliliters to re-saturate the growing medium. We should allow for the water uptake for the plant during that time as well. If the first drain came after 200 Joules, then we can calculate the water uptake from the plant as 200 x 1.7 ml/Joule/M2 = 340 ml/M2. If the dripper density is 2,5 plants/M², the four plants on one slab have taken up 340 x 4/2.5 = 544 ml per slab. The real dry down is (2,000-544)/15000 = 9.7%. It seems like a lengthy calculation, but the only variables are the number of irrigations before the first drain, and how many joules have passed at the first drain. If the grower in the above example wants to maintain a 10% dry-down, he only has to make sure that the first drain comes at the 5^th irrigation at 200 joules light sum. If he wants to increase dry down to 15%, the first drain must arrive at the 7^th irrigation at 200 joules.

Different Strategies for Different Stages of the Crop

A tomato crop has 5 distinct periods that require a different approach to irrigation. I discuss the best strategies for each period, for a crop of tomatoes grown in a high light climate.

Propagation

In high light climates, young plants tend to grow vegetative. The block can be dried down to 40-50% of the saturation weight when the roots emerge from the bottom. Usually, a 10 x 10 x 7.5 cm block weighs about 500 grams when it is saturated. It means that the block can be dried down to 250-300 grams. The irrigation must be given in the morning so that the blocks are not too wet at night. When the plants suck water out of the blocks, air replaces it, providing the roots with necessary oxygen. The EC in the block can run up to 12 applying this practice, which makes the plant more generative and encourages the roots to fill the block. It also prevents the long, stringy roots that form when too much water is applied, and puddles form on the surface.

Planting to Flower

Most growers in warm climates do not have access to nurseries that can deliver a plant at flowering stage. When the plants arrive from the propagator and the plants are still small, the grower needs to complete the propagation cycle. When there are conditions of high light and low humidity, it causes the plant to make large leaves to cool itself. There are no fruits on the plant that function as a sink for assimilates. If allowed to grow without intervention, this plant grows very vegetative. The grower must give generative impulses that force the plant to flower and fruit. One well-known aspect of fruiting plant species is that threatening environmental conditions causes the plant to act reproductively. Most growers make use of this fact by not allowing the roots of the plant to grow into the growing media. An example of this is shown in Figure 8.10 and 8.11. The green sheet prevents the roots from going from the block into the slab with more volume.

By doing this, the volume of the growing media is restricted. Even a little plant can suck the moisture out of the block, which gives the grower control over moisture and salt content of the root zone. Drying down the weight of the block to 50% of its saturation weight is a generative impulse through which the plant starts producing hormones that steer it towards reproduction. 

The irrigation must be carefully controlled. Weighing the blocks multiple times per day allows the grower to dry the blocks down to 50% of their saturation weight. The plants should not go into the night with a wet growing medium. If the plants need irrigation, irrigate in the morning when the temperature is still cold. Check those areas of the glasshouse that are warmer or receive more light (wall or gable rows) are not drying out (and wilting) sooner. It is preferred to have the irrigation hoses under the gutter so that the sun does not have a chance to heat the irrigation water.

The EC in the drip should be 4.0. When the blocks are irrigated, the water system can be stopped when the first drain is visible. If it is evident that there is too much variance in EC between blocks, more drain needs to be realized. The EC in the block can rise to EC = 10-16. It creates a generative impulse.

The trend is to use less nitrogen in the fertilizer formula at this time to stop encouraging the plant to become vegetative. It seems low nitrogen also helps in increasing Brix of the fruit.

Flower to Harvest

Once the flowers on the first truss are open, the plastic sheet is removed, allowing the roots to grow into the larger volume of root space. The longer this action can be postponed, the better it is for the generativity of the plant. However, not allowing the plants to root into the slab makes them unstable, and they might fall over, even when tied up to the string. By the time the roots are allowed into the slab, the EC in the block is 10-16. The slab must be filled with EC=4 irrigation water. This difference in EC forces the roots to go into the slab very quickly. A nice truss such as shown in Figure 8.9 is a sign that the plants are generative. Notice the extreme curl in this cherry truss. If the irrigation is given too late in the afternoon, or the growing media is kept too wet, the trusses become more elongated and stick up, as shown in figure 4.

Now the plants have access to the almost unlimited water supply in the bag. It is a dangerous situation as the availability of so much water creates a vegetative impulse. To reduce this effect, apply the following rule of thumb; restrict the irrigation after planting and reduce the moisture content in the slab by 1-2% per day. It means that after 10 days, the water uptake of the plants creates a dry down of 15%. The decrease in water content must be realized with zero drain. After two to three weeks, the drain starts, and the EC in the drain from the slab is at 6-10. From this time on, reduce the drain EC by 0.5-1.0 EC unit per week. The EC should be at EC=4.5 by the time harvesting commences. Bring the drip EC down gradually to EC = 3.0.

Three weeks after allowing the roots into the slab, the dry down is 20%, and it should remain above 20% until one week before harvesting or earlier if the plants show a more generative appearance. Achieve this by stopping early with the irrigation and giving more water during the day between start and stop times to control the EC. Late irrigations have an extraordinarily strong vegetative impulse, causing trusses to stick up straight (see figure 5) instead of the nice curl shown in figure 4. If it seems the dry-down is too much overnight, night irrigations are a better choice. But in most cases, it is better to stop early. You can always give extra irrigations, but you cannot take one away after its given. The grower has an essential input in irrigation management. The weather is different every day, and the stop time of the irrigation varies as a result.

Harvest and Beyond

If everything went right, we should have a well-balanced plant, loaded with fruit, ready for harvest. The highest fruit load on the plant takes place approximately one month after harvesting begins. At maximum load, the plants required nurturing. The grower must make it as easy as possible for the plant to grow. The majority of the assimilates that the plant makes are used for fruit production. Nurturing the plants helps stimulate vegetative growth and guarantee a future harvest. Now is the time to switch from generative to vegetative actions. The focus switches from the plant making fruits, to making leaves.

Irrigation

The dry-down of the slab must quickly decrease to 10% or less. It means irrigating later into the day. By now, the EC in the drain should be 4.5, while the drip should be at EC = 3.0. With less light, the plants require less irrigation. The following rule of thumb can be applied;

The last irrigation should come at 200 joules before sunset. If the dry down is too high, night irrigation can be given between 9 and 11 pm. It is important to remember that the guidelines above emerge from a desire to maintain the correct EC. In other words, keeping the right EC is the prime directive. The drain percentage is a means to achieve this. If the EC is too high, Some companies put a high priority on Brix and believe that they can achieve a higher Brix by maintaining a higher EC. 

Topping

About 6 weeks before the end of the crop, the growing point is removed. The remaining seven to eight trusses ripen one by one over the next 6 weeks until the plant is empty. Removing the growing point results in the plant needing less assimilates for growth, making leaves and roots. The majority of assimilates that the plant creates are used for fruit growth. Due to the decreasing fruit load, the plant has a smaller buffer to direct water to the fruits when root pressure is high. Therefore root pressure must be reduced. We do this by increasing the EC and dry-down. The dry down can be increased slowly from 10% at topping to 25% at last harvest. The EC can be increased to 8. Due to the reduced fruit load, there are more assimilates available for the last couple of trusses. Even with a high EC, the fruit size up properly. 

Irrigation is a very important tool in the arsenal of a grower. 

If you like to be copied in on future articles or would like to know more and have questions, follow me on LinkedIn, Godfried Dol, or email Godfrey@glasshouse-consultancy.com or go to my website; http://www.glasshouse-consultancy.com. You can also download previous posts from this website.

This comprehensive summary is an essential information for indoor farming! February Indoor Ag Sci Café focused on water quality and biofilm for indoor production.

Dr. Fisher discussed characteristics of different source water and their potential issues (alkalinity, chlorine, salinity, and pathogens) as well as mitigation measures. Key steps of biofilm management was introduced and efficacy of different commercial products was discussed.

Indoor Ag Science Café is an outreach program of our project OptimIA, funded by USDA SCRI grant program (http://www.scri-optimia.org). The café forums are designed to serve as precompetitive communication platform among scientists and indoor farming professionals.

The Café presentations are available from the YouTube channel. Contact Chieri Kubota at the Ohio State University (Kubota.10@osu.edu) to be a Café member to participate.

University of Florida Greenhouse Training Online courses 

Our last Greenhouse Training Online courses for 2019!

Weed Management

Earn CEUs

An intermediate level course that teaches all aspects of weed management in nurseries and greenhouses, including weed identification, developing herbicide programs, and the latest non-chemical methods of weed control that work.

Irrigation Water Quality & Treatment

An advanced level course that helps interpret water quality tests for irrigation of greenhouse and nursery crops, select appropriate water treatment technologies, and design a water treatment and monitoring system.

Both courses run from November 4 to December 6, 2019, are offered in English and Spanish, and include a personalized certificate of completion. Weed Management has been approved for CEUs in several States. Each course has a cost of $US199 per participant, with discounts if you register 5 or more. The last day to register is November 11, 2019. Over 4 weeks, there are streaming video lessons, readings and assignments, which can be accessed at any time of day. Click here to register (http://hort.ifas.ufl.edu/training/).

For more information, including discounts for registering multiple staff, email us at greenhousetraining@ifas.ufl.edu, or visit http://hort.ifas.ufl.edu/training/.

If you are growing crops hydroponically in deep-flow or raft systems, one of the last things you want to see is an unusually low or empty tank. It is not uncommon for nutrient solution levels to be reduced by evaporation and transpiration, but when levels decrease rapidly, there may be a larger issue.

A common issue in nutrient film technique (NFT) or with drip systems is a leak from the tube delivering the nutrient solution. Another possibility is a crack in a tank or tube. However, what could be the cause if you do not see a leak? A less-intuitive issue that may occur is siphoning.

Watch out for siphoning if you are using air stones or tubes for oxygenation in deep-flow or raft systems or reservoir tanks. Siphoning may happen if the air pump is not supplying air flow due to a broken tube or the power going out. If the nutrient solution is siphoned into the pump, damage to the pump may occur. Siphoning may also be a result of air stone tubes breaking or coming loose from the air pump.

To prevent this issue, position air pumps higher than the nutrient solution reservoir. This will stop siphoning from a pump or power failure. However, if the tubing becomes loose, cracks, and falls outside of the tank beneath the water level siphoning may still occur. If feasible, consider installing in-line back flow prevention valves. Be aware this may be a problem and, if the nutrient solution is suspiciously low, check for siphoning.

About the Author:
Kellie Walters and Roberto Lopez Assistant Professor and Floriculture/Controlled Environment Extension Specialist(Michigan State University), and PhD candidate (Michigan State University), Roberto G. Lopez is an Assistant Professor and Floriculture/Controlled Environment Extension Specialist at Michigan State University. He has an appointment in research, teaching and extension. His area of expertise is; controlled environment specialty crop production; Lighting applications for greenhouses and indoor vertical production; light-emitting diodes; young plant propagation.

Nursery and greenhouse growers comprise an important sector of United States agriculture that is uniquely situated to conserve water while growing plants that provide many social and environmental benefits. In order for Extension professionals to effectively help growers use water conservation technologies, it is important to understand the knowledge level and adoption rates growers have surrounding different water conservation techniques. It is also important to understand how grower perceptions of water conservation strategies relate to their adoption. In this publication, we present results of a study designed to understand the knowledge level, adoption rate, and levels of continuance associated with eight water conservation technologies among nursery and greenhouse growers. We also examined whether five characteristics of these technologies (trialability, complexity, compatibility, relative advantage, and observability) predicted grower adoption.

Click here to read the publication: https://www.cleanwater3.org/research.asp

This is taught at an advanced level, designed for an experienced grower or technical manager. Lessons are offered in English and Spanish, and are taught by professors from six universities in the United States.

The course runs from November 5 to December 7, 2018. It costs $US 199 per participant, and includes a personalized certificate of completion. Over 4 weeks (no classes over Thanksgiving week), there are streaming video lessons, readings and assignments. The 3 to 4 hours of lessons and activities each week can be accessed at any time of day. Bilingual PhD instructors are available via discussion features. Click here to register (http://hort.ifas.ufl.edu/training/).

For more information, go to http://hort.ifas.ufl.edu/training/, or contact Greenhouse Training, Environmental Horticulture Dept., University of Florida, USA, by emailing greenhousetraining@ifas.ufl.edu.

This course is supported by the Specialty Crop Research Initiative project ‘‘Clean WateR3 – Reduce, Remediate, Recycle’’, #2014-51181-22372, from the USDA National Institute of Food and Agriculture. Spanish translation is supported by a grant from the American Floral Endowment.

Irrigation Water Quality PDF Flyer

This tool interprets the quality of a water source to irrigate plants in greenhouses and nurseries, and is available in English and Spanish.

Link to the WaterQual Tool

Clean WateR3 is a federally funded Specialty Crops Research Initiative grant focused on research and outreach to help growers Reduce, Remediate and Recycle irrigation water. The grant team is managed by Dr. Sarah White at Clemson University and includes many research collaborators.

Clean WateR3 – Reduce, Remediate, Recycle

Our projects focus on developing sustainable remediation technologies to encourage use of alternative water resources, especially recycled irrigation runoff, to decrease dependence on potable water, and enhance long-term economic viability. This is possible thanks to an award from the National Institute of Food and Agriculture Specialty Crop Research Initiative, and the involvement of 22 researchers in 9 universities. The objectives of this project are to:

• Reduce contaminant loading into recycled water sources via treatment technologies and improved water management strategies.
• Evaluate treatment technologies (physical and biological) to Remediate pathogen, pesticide, and nutrient contaminants.
• Provide online and published information to help growers successfully Recycle water.

Know your goals before investing in a water treatment system.

A water treatment system is not going to add value to your product. It’s all about reducing the risk of crop losses.

One of the advantages that ornamental plant growers have over growers of hydroponic edible crops is that ornamental crops are usually produced with some kind of root substrate.

“Most ornamental plant growers are not purely hydroponic,” said Paul Fisher, who is University of Florida professor and floriculture extension specialist. “That means ornamental growers have more options they can use for water treatment compared with a hydroponic system where the roots are bathed in the recirculating solution. For instance, with hydroponics, a grower needs to be especially sensitive to the accumulation of chloride from chlorination or copper from copper ionization in the recirculating nutrient solution.”

Know your water concerns first

Fisher said one of the challenges that growers face with water treatment is the tendency to choose a solution without first finding out what the problem is.

“There are many different potential water quality problems that growers can have,” he said. “These can be broken down into microbial problems (plant pathogens or biofilm), chemical problems (salts, alkalinity and occasionally pesticide residues) and particle (filtration) problems. Growers should think in terms of these three different types of potential problems.

“They should test their water and only then decide on the appropriate solution. No single technology is a silver bullet. In some instances, water treatment companies are aggressively pushing one particular technology that they sell, which may be a good solution for one problem, but not others.”

Fisher said before growers make any decision about water treatment, they need to define what issues of water quality they want to address.

“When a grower sends a water sample to an analytical testing lab, the most common water test is to measure the concentration of dissolved ions,” he said. “These tests could include alkalinity, sodium and chloride, electrical conductivity (EC), hardness (calcium and magnesium) and other ions such as iron or boron in the water.

“A complete lab analysis will help growers select the best fertilizer recipe, because the nutrient solution is a combination of the water source and added fertilizers. For example, if growers have enough calcium and magnesium in their irrigation water, then they may not need to add these nutrients in the fertilizer. Chemical water analysis also helps decide if additional treatment is necessary, such as acidification if water alkalinity is high or reverse osmosis if the EC is high.”

Common, uncommon water issues

Fisher said if growers are using well water or a municipal water source, the most likely problems to treat for are alkalinity or high salts, depending on where a grower is located.

“High alkalinity is a very common water treatment issue in our industry,” he said. “Irrigating with highly alkaline water is like adding lime to a crop with each watering. The pH climbs over time leading to iron deficiency. Injecting an acid such as sulfuric, nitric, or phosphoric acid may be needed.”

Fisher said another common issue with water is high EC. Typically the most common cause for this is sodium chloride. He said reverse osmosis is one of the treatment options for high EC where ions are removed when water is passed at high pressure through a membrane.

“One of the biggest differences from one hydroponic location to another is the incoming water quality,” he said. “For example, in the Midwest if there is a limestone aquafer and growers are using well water, there may be enough calcium and magnesium that these nutrients don’t need to be in the fertilizer solution. In contrast, in parts of the Northeast and North Carolina where the water has a low EC, growers must choose a fertilizer that is going to contribute most of the nutrients.

Fisher said another challenge with EC management that is important for hydroponic growers is to know what is making up the EC in their recirculating solution.

“For example, nutrient levels drop over time because of uptake by plant roots, but the water source contains a significant amount of dissolved ions,” he said. “Then much of the EC may be coming from sodium and chloride rather than nutrients such as nitrogen, phosphorus and potassium. These growers will have to do a certain amount of replacement of their nutrient solution. For example, they may have to dump a certain amount of their nutrient solution every two weeks to prevent the sodium chloride from accumulating. This can be an environmental hazard (encouraging eutrophication of water supplies) and also increases fertilizer costs.”

Fisher said once growers deal with common water quality issues they may face issues that are unique to different parts of the country.

“I am working with a grower in Indiana and another grower in Florida who have high iron in their water,” he said. “The iron is clogging filters either directly because of rust particles or because of bacteria growing on the iron. There can be a mix of iron that is already a solid particle, which is rust, and there is also dissolved iron.

“The process of removing iron is to oxidize it and turn it into rust. This can be done using chlorine or potassium permanganate or some other oxidant. Ozone could also be used. Once the iron is turned into rust the water can be run through a sand filter. The filter will trap the iron particles. The filter will have to be washed out periodically to remove the particles. These are examples of why it is important to test the irrigation water first, identify the issues, and choose appropriate solutions.”

Biological issues

Fisher said if growers are using well water or municipal water it is very unlikely that the water is going to be the source of a plant pathogen. These water sources may be helping to distribute a pathogen if growers are recirculating the water, but the incoming water is likely to be very clean. He said when the water source is surface water, from a pond, or from a recirculation tank, it’s more likely that the water could be a significant source of pathogen inoculum.

Fisher said one of things that can happen with any of these water sources is that there are three types of biological problems:

1. Plant pathogens

2. Biofilm

3. Human safety bacteria (i.e. E. coli)

“The most common pathogens that would be favored in irrigation water are the oomycetes of Phytophthora and Pythium,” Fisher said. “If growers have root disease problems and suspect that their irrigation water may be a part of the disease distribution, they can send a water sample to a university extension lab for testing. However, it can be hit-or-miss as to whether or not a pathogen is going to be present in a particular water sample. Routine sampling of irrigation water for disease detection is not something that most growers normally do because of the time and cost.”

Fisher said many of the state extension plant diagnostic testing labs are able to run samples for plant pathogens.

“The labs typically plate organisms out to the genus level of the organism, identifying whether it is Pythium or Phytophthora,” he said. “It really matters a lot what the species is, which many labs are able to analyze, although this may take longer and cost more. Pythium can be quite ubiquitous. Phytophthora tends to be more aggressive than Pythium.

“The University of Guelph diagnostic lab will check the DNA fingerprint of what’s in the water. The lab can compare a sample with a data base of other plant pathogens.”

Dealing with biofilm

Fisher said when growers contact him with a biofilm problem, he asks them to send samples to a water testing lab to measure the aerobic bacteria count from different sampling points in their irrigation system. Usually, but not always, he said, well water has a low bacteria count.

“If growers are using pond water, it is very likely that there is going to be a high bacteria count,” he said. “These high bacteria counts occur because of the presence of microbes including cyanobacteria and other algae. When there are very high bacteria counts, growers usually have to treat for microbes if they use mist nozzles or drippers. The microbes may not be plant pathogens that cause disease, but they may clog irrigation emitters and filters.”

Fisher said if growers have a biofilm problem, they need to determine where the bacteria are coming from.

“Growers would collect water samples from the water source, after the water is chlorinated, after the fertilizer is added to the water, and out in the greenhouse,” he said. “By testing samples from these different locations will identify where the bacteria are growing in the irrigation water and where the water treatment needs to occur. It will also tell growers, whether the treatment systems they are using, for example, chlorine, chlorine dioxide or ozone, are effectively controlling the microbes.”

Particle issues

Fisher said particles in the water could include algae from pond water or sediment (clay, silt or sand). These particles can clog up filters and water emitters.

“Water testing labs should be able to provide a measurement of turbidity, which is the clarity of the water, and also the amount of total suspended solids (TSS),” he said. “A lab will take a specific water sample volume, filter it through a very fine filter and then dry it down and weigh it. This will determine the TSS in terms of milligrams (weight) of particles in a liter of water.

“From experiences with growers, if there is more than 5 milligrams of suspended solids per liter of water, it is quite likely that there are enough particles in the water to cause some issues in the irrigation lines.”

Fisher said growers who are using municipal water typically use screen filters.

“It is unlikely that a high concentration of suspended particles will come from a municipal water source,” he said. “For risk management purposes, however, growers usually install one or more screen filters with enough filtration to remove any suspended particles that are large enough to clog up the finest irrigation emitters in the system.”

In the case of well water, Fisher said growers occasionally may pull up some suspended particles like silt that may require they install some additional filtration.

He said there are two kinds of recirculated water. Pond water usually comes from the water that is drained off outdoor areas or as runoff from a greenhouse. The other source of recirculated water drains off from ebb-and-flow concrete floors or troughs/benches in a greenhouse and is stored in concrete tanks. Water from these sources has similar needs in regards to filtration.

“Pond water will contain algae and other bacteria,” Fisher said. “With ebb-and-flood systems there can be root substrate and plant debris. With pond water there are usually pumps that are pumping water through a filter and then the water, which is under pressure, goes all the way to the greenhouse. There is usually a series of filters for organic materials, including disc filters, sand filters and sometimes screen filters.

“The greenhouse that is being filled with water and then drained back is filtered and stored in another supply tank. This is typically where paper filters, vibrating screen filters and rotating drum filters are used. This is usually a gravity-fed system.”

Agrichemical residues

Fisher said if growers suspect they are having a problem with their crops that is not related to nutrition or disease, it may be an agrichemical issue.

“Growers may suspect there is something toxic in their water that might be herbicide runoff from a neighboring farm or it may be growth regulator residues from past applications,” he said. “There are special labs that are able to test for these chemicals. But growers need to know what chemicals to specifically ask a lab to test for.

“In my research program we are doing a lot of work on removing paclobutrazol residues from irrigation water using carbon filtration. Paclobutrazol has a half-life of about six months in irrigation water. It is normally applied in the parts per million range. But the chemical has activity in the parts per billion range, even as low as 5 parts per billion, on sensitive crops like begonia. There can be some leachate from the spraying or drenching of paclobutrazol that gets into recirculated irrigation water that can then impact untreated plants.”

Keep the system clean

Fisher said growers should try to keep their irrigation systems clean, but they don’t have to sterilize them.

“Cleaning out the recirculating tanks, greenhouse surfaces and irrigation lines several times a year is good idea,” he said. “Although most of the microbes in a recirculation system are likely to be beneficial or benign, the equipment can start to clog. There is going to be algae growth and there is the possibility of pathogen spores getting embedded in biofilm. The goal is to keep the system clean, but there is no need to continually kill all of the organisms in the system.

“Growers who are not using fine drippers or mist nozzles are less likely to have a problem with clogging from biofilm.”

Fisher said after power washing the water storage tanks growers can apply an agricultural cleaning product, such as Strip-It, which is widely used. This helps to remove biofilm.

“This treatment may keep the system clean enough that it is not necessary to continually inject some type of sanitizing agent,” he said.

Maintaining dissolved oxygen levels

Fisher said dissolved oxygen is mainly an issue for hydroponic growers because roots are bathed in the nutrient solution. In contrast, when growing in a root substrate with a high level of air porosity (from large particles in the substrate), the roots will receive adequate oxygen so long as the plants are not overwatered.

“If growers are using a nutrient film technique (NFT) system, then the movement of the water helps oxygenate the nutrient solution,” he said. “Aeration of the nutrient supply tank may still be required.

“With floating pond systems, low oxygen conditions are likely to occur. If the water temperature is warm, there is going to be a lot of biological activity occurring and respiration by the microbes. Warm water also holds less oxygen than cool water. It is a good idea to install some type of bubbler. A bubbler creates small bubbles that add oxygen to the water and raise the dissolved oxygen level. If the oxygen level becomes low in a hydroponic solution then it can favor pathogenic organisms such as Pythium. The water should contain at least 5 parts per million of dissolved oxygen.”

Investing in a treatment system

Fisher said growers should place their emphasis first on ensuring their plants are healthy and growing well. Their incoming water should be from a high quality well or municipal source and there should be a high level of overall sanitation. With this foundation in place, he said, an expensive water treatment system may not be needed.

Fisher said growers need to think in terms of profitability of their business when considering water treatments.

“Margins are tight for most growers so they need to think about how they are going to generate a positive return on their investment,” he said. “If there is an existing chemical, biological or physical water quality problem that has been clearly identified (including lab testing), then investing in a targeted water treatment solution to that problem will rapidly be paid back.

“However, if growers are spending money on a water treatment system that they don’t need, then they don’t have that capital available to spend on an alternative investment such as supplemental lighting that could increase their yields.”

Fisher said a water treatment system is not going to add value to growers’ products.

“No one is going to pay growers more for their product just because they have installed a water treatment system,” he said. “It’s really about crop losses and reducing the risk. When growers have a root rot problem caused by a water-borne pathogen, then they can very quickly pay back the benefits of a water treatment system.”

For more: Paul Fisher, University of Florida, Institute of Food and Agricultural Sciences Extension.

David Kuack is a freelance technical writer in Fort Worth, Texas; dkuack@gmail.com.

An increasing number of ornamental plant growers are looking to take advantage of the growing interest in local food sales by expanding their production with seasonal crops of lettuce, leafy greens and herbs. Unlike ornamental plants, growers of edible crops have the added concerns of food safety.

“If growers are using municipal water for growing ornamental crops and then add lettuces and leafy greens, there should be no concerns related to water quality from the standpoint of human pathogens that might be associated with surface water,” said horticulture professor Sarah White at Clemson University. “There are pH issues associated with municipal water because most municipal water is neutral or alkaline to prevent the corrosion of pipes. Ornamental growers would likely need to acidify their water if the pH is above 7.5, especially for leafy greens and lettuces. These growers may already be acidifying their water for the ornamental plants they are producing.

“For new growers who are planning on using municipal water, they need to know what the water pH is. Because the pH is likely to shift during the year, growers need to be cognizant of the shifting pH and how injecting acid needs to be responsive to these changes. Some bedding plant crops may require more or less acid injection than lettuces and leafy greens.”

White said most municipal water sources are drawn from surface water reservoirs, which can cause some seasonal variation in water pH.

“Usually during the winter the water source quality is consistent,” she said. “If growers are producing during the winter and carrying production into spring there might be some changes in the water source that can affect the pH.

“Regardless of whether growers are producing lettuce and leafy greens in nutrient film technique (NFT) or deep water raft systems, they need to actively monitor pH year round. There are Bluetooth pH meters that can be stuck into a water source that will log pH. It’s easy to do. Growers should monitor and track their pH and know what they have to do to adjust it.”

White said for ornamental growers looking to add lettuces and leafy greens, it isn’t going to matter what type of acid is used to lower the water pH.

“Growers should be able to use the same acid for both ornamental and edible crops,” she said. “Usually they pick an acid based on the cost. If they are going to adjust the water pH they should inject fertilizers after the water pH has been adjusted.”

White said municipal water usually has a pH of 7.5 to 8. Most plants grow best at a pH of 6 to 6.5.

“Nutrient availability changes with different pH,” she said. “That is why the pH needs to be adjusted in order for the nutrients in the water to be available to the plants.”

White recommends if growers have never produced lettuces and leafy greens that they monitor the water pH more often.

“If growers don’t know how sensitive these new crops are to pH, they might try doing some trials with lettuces, leafy greens or herbs,” she said. “This will enable growers to determine the best pH for producing these new crops before they invest in filling a whole greenhouse.”

Adjusting water alkalinity

White said depending on where growing operations are located in the country, municipal water sources can have different alkalinities.

“In some western states and coastal regions of the United States, alkalinity issues are more likely,” she said. “In locations with higher alkalinity, more acid is required to get the water pH to the desired range for crop production. A lot of plants don’t do well with high alkalinity vs. low alkalinity. If the pH is being adjusted by injecting acid this coincidentally manages the alkalinity level as well. It typically requires more acid to accomplish the same pH change in water with higher alkalinity. Water that has high alkalinity will also have a high pH.

“If growers have a water source that is highly alkaline in a certain region of the country, chances are it won’t matter what source growers pull from because there are going to be alkalinity issues. The only thing they could do differently is if they capture rain water, filter it, and then blend it with their other water source.”

Well water

White said well water is the most common water source used by growers.

“We have done two surveys in the last 10 years and about 65 percent of all growers indicated they use well water,” she said. “The reason is because it is a clean water source and there are not usually any issues with plant diseases. The contaminants that most growers might encounter are salinity and iron. If growers have a lot of salts in their water, how it is managed becomes very critical. Many Southwestern growers deal with this issue.”

White said water with a high salt level can be caused by a mix of elements and it is regionally specific.

“Sodium, chloride, calcium and magnesium are the biggest contributors to high salinity water sources,” she said. “If growers are having high salt issues, it’s probably caused by chlorine or sodium. Growers can manage fertilizers to help balance the high salts.”

White said the other contaminant growers might find in well water is iron depending on the region of the country where they are located.

“There are typically problems with iron and iron-oxidizing bacteria associated with well water use. If there is iron in the water, growers should aerate it before they use it. Aerating the water oxidizes the iron so that it precipitates out. The aeration should be done before the water goes into the fertilizer tank and before growers start adding salts. Once fertilizers begin to be added it might be more difficult to remove the iron.”

White said the pH for well water is usually in a good range for growing plants. She said growers should still test the pH of their water.

“If growers are drawing from a salty water source, chances are they are going to have alkalinity and pH issues. If growers are using salty water sources on ornamental plants and decide to try growing lettuces, leafy greens and herbs, whether they can use that water and how it is being treated will depend on the type of ornamental plants being grown. Some ornamental plants tolerate salts more than others. Growers may not have to do much to bring the salts to an acceptable level for lettuces, leafy greens and herbs.”

White said most growers won’t put in a reverse osmosis system to remove high salts because of the high cost associated with the equipment and having to manage it along with the waste water it produces.

“Growers are more likely to manage high salts by blending water sources, by heavily irrigating the crops or by their choice of which plants to grow,” she said. “Growers may want to use a municipal water source to blend with well water so that salts are at a manageable level for the plants. I highly recommend that growers get water quality analyses done periodically. They should also have an inline monitoring system if they chemically treat the water so that they know the real-time pH and salinity (electric conductivity is a proxy) levels of their water.”

Water filtration

White said there really isn’t a need to filter municipal or well water unless growers are recirculating the water.

“A rapid sand filter, which is cheap and fast, will remove organic matter and other debris that might get into the water,” she said. “This filter might remove some disease organisms, but it’s not 100 percent. If growers are concerned with plant diseases, they are going to need to add a sanitizer like chlorine, ultraviolet light or ozone. A rapid sand filter is easy to pair with a chlorination system like Accu-Tab.

“Growers could also use a slow sand filter. This is a biologically-based system, but it just takes longer to filter the water. The slow sand filter removes both particulate and plant disease propagules. Depending on what a grower’s goal is, a slow sand filter would accomplish the same thing as a sanitizer.”

White said a lot of ornamental plant growers who use well water route it into an open containment pond.

“Most growers have a pond that they pump the well water into before irrigating their crops,” she said. “These growers might have an issue with using that water to irrigate edible crops. They would need to use a sanitizer, which would take care of plant pathogens as well as potential human pathogens such as Salmonella and E. coli. Those are the main pathogens growers would have to be worried about.”

For more: Sarah White, Clemson University, Plant and Environmental Sciences Department, (864) 656-7433; swhite4@clemson.edu; http://www.clemson.edu/cafls/faculty_staff/profiles/swhite4; http://cleanwater3.org.

David Kuack is a freelance technical writer in Fort Worth, Texas; dkuack@gmail.com.

Growers who are doing hydroponic production in nutrient film technique (NFT) or deep water raft systems should be monitoring pH and soluble salts content (electrical conductivity) more often than growers using container substrates.

“With hydroponics, especially with NFT production systems, the root zone conditions can change very quickly,” said Neil Mattson, associate horticulture professor at Cornell University. “The pH can change very rapidly because the water doesn’t have a lot of buffering capacity.

“With deep water culture (DWC) where there is typically a larger volume of water used, things like water temperature, pH, fertilizer strength and the overall concentration of the nutrients, are relatively stable over time as compared to NFT systems. In DWC, these parameters don’t change that much hour to hour. There may be slight changes from day to day and more changes from week to week. Deep water raft systems don’t generally take quite the degree of management that NFT systems do in terms of constant or continuous monitoring.”

Mattson said it would be good for growers using deep water raft systems to monitor soluble salts and pH every day.

“In terms of taking action with deep water raft systems such as adjusting the fertilizer strength that can be done on a weekly basis,” he said. “Adjusting the pH can be done daily or every two to three days. But that is better than with NFT systems that need continuous monitoring. Sometimes for nutrient management in NFT systems there is a need to do pH management every day if not several times a day. Some people have automated inline pH and EC sensors with peristaltic pumps that turn on automatically to add acid to the water reservoir or add fertilizer solution. Typically with NFT systems there is a much smaller water reservoir in relationship to the plant surface area that is growing.”

Mattson said monitoring whether growing in a deep water or NFT system is especially important in the early stages of growth.

“The young plants are the most valuable because they are initially at a high density,” he said. “The young plants need to get off to a good start because growers will never be able to recover that growth,” he said. “If growers start with poor plants, they are never going to achieve the optimum plants they are trying to harvest. Growers should focus on their crops more closely when they are younger.”

Mattson said lettuces, leafy greens and herbs are the most common crops grown in deep water systems.

“I have also seen growers grow microgreens with raft systems,” he said. “The microgreens are seeded onto substrate mats on top of the rafts. The growers add some weight to the rafts so the microgreens sit lower and are in constant contact with the water. This method has worked well for microgreen growers using pond systems.”

Maintaining water quality

Mattson said deep water raft systems typically don’t require as elaborate a water treatment system as NFT systems.

“There could be a benefit for water disinfestation for the raft systems, but growers in practice aren’t really using that for a couple of reasons,” he said. “A grower can’t easily sanitize a whole pond at one time. All the grower can do is pump out water and run it through a disinfestation system and then pump it back in. A grower is never completely getting rid of all of the disease organisms.

“Some of the water is being taken out, treating it and putting the water back in and then taking up more of the pond water. A grower never fully gets rid of the disease organisms. More commonly with DWC, growers will periodically pump water out and sanitize a whole pond before refilling with a nutrient solution and transplanting.”

Mattson said growers using hydroponic systems often have algae problems because algae will also access the water and nutrients.

“Algae make their own food,” he said. “They photosynthesize and use light to make their own energy. Algae will grow and become established naturally wherever there is light, moisture and a source of nutrients. If light can be excluded from a surface this can help to deter algae formation. When sunlight hits uncovered pond water there is a food source for algae. This can occur whether a grower is using conventional or organic fertilizers. This can also occur with NFT systems if the channels aren’t covered. If the channels are exposed to light where water and the fertilizer solution trickle down, algae starts growing very quickly.

“If light can be excluded from a surface this can help to deter algae formation. If a grower is using a pond system he doesn’t want to leave the pond water exposed to light. The water is covered with dummy rafts until that space is used again.”

Mattson said growers who keep reusing the same pond water have found they don’t normally run into problems with root diseases if temperature and dissolved oxygen are at optimal levels.

“There are communities of beneficial microorganisms that become established in the pond water that naturally suppress root diseases,” he said. “Even with the establishment of the beneficial microbes, growers need to maintain the dissolved oxygen level to near saturation (about 8 parts per million O₂ at room temperature) in the pond water to keep the plant roots and beneficial microbes actively growing.

“Growers can bubble in air or can inject pure oxygen into the water. It is also important to circulate the pond water so there is a uniform gradient related to temperature, pH, fertilizer and oxygen.”

Mattson said the Cornell University Controlled Environment Agriculture group found good plant performance in a 1,500-square-foot pond where water was recirculated and distributed through manifolds in the pond. Pumping capacity achieved a complete water recirculation exchange every 12 hours.

Monitoring water temperature

Water temperature can also be an issue with lettuces and leafy greens grown in warmer climates.

“The best water temperature is around 68ºF so even if the air temperature increases it helps to delay bolting of lettuce and helps to reduce disease organisms,” Mattson said. “Water heats up much more quickly in a NFT system than in a deep pond system. The NFT channels are not insulated. The NFT water is in contact with a large surface area so it starts heating up quickly if the air temperature in the greenhouse is warm.

“A pond is usually well insulated. Often the outer edge and the floor of the pond will be insulated. There are also the polystyrene rafts that float on top of the pond so the pond does not heat up very quickly.”

Despite having a beneficial microbial community in the water, Mattson said every once in while root disease can develop in the pond. Pythium is the major root disease.

“Usually it’s because of warm water temperatures that occur under summer conditions,” he said. “This can be a major issue for the grower who has to drain the pond, scrub and remove any debris, use a disinfesting agent and then refill the pond. The whole time the pond is being cleaned it can’t be used for growing a crop.”

Mattson said with NFT systems it is imperative to have a backup electrical source and pump backup because if there is an electrical outage or a water pump breaks then the plants can dry out within hours.

“In a pond if the power goes out, there is a concern about controlling the greenhouse temperature, but the plants are sitting in water and have access to plenty of nutrients,” he said. “The supply of dissolved oxygen could become depleted or run out, but that would take days if not weeks for that to happen. It is a much more robust system in that way.”

Fertilizer considerations

Mattson said growers who are considering using organic fertilizers with either NFT or deep water raft systems need to be aware of issues inherent with the source of the nutrients.

“I have tried organic fertilizers in a pond system and found that biofilm grows very quickly,” he said. “Organic fertilizers are byproducts of plants and animals. The biofilm microbes use the carbon in the organic fertilizers as a food source and use up a lot of the oxygen in the pond water. The microbes are respiring so it is difficult to maintain a good dissolved oxygen level in the water.

“The biofilm also quickly coats the plant roots making it more difficult for the plant roots to access oxygen and nutrients. They are not disease organisms, but the root system becomes coated with biofilm and the plants can’t grow. The biofilm is starving the plants for oxygen and nutrients. In a pond, the biofilm, which is floating in the water, will also coat all of the surfaces in the pond including the walls and the rafts.”

Mattson said another benefit of a NFT system in reducing biofilm buildup is the continual flow of water.

“There could still be biofilm and some coating, but the water in a NFT system is saturated with dissolved oxygen that is continually moving though the root zone,” he said. “That helps to deliver oxygen to the roots. There still may be some biofilm formation in the channels, but not nearly as much as in a pond.

“Growers who are using a NFT system and organic fertilizer are more used to starting a new crop over and over again. It’s up to the growers whether they want to start fresh with each crop cycle. Draining the reservoir after each crop cycle, cleaning the channels and the reservoir and sanitizing fits better with NFT systems. Growers using pond systems are not going to want to drain and clean the pond every crop cycle. That is very wasteful in terms of water and fertilizer and is labor intensive.”

For more: Neil Mattson, Cornell University, School of Integrative Plant Science, Horticulture Section, 49D Plant Science, Ithaca, NY 14853; (607) 255-0621; nsm47@cornell.edu; https://hort.cals.cornell.edu/people/neil-mattson; http://www.cornellcea.com; http://www.greenhouse.cornell.edu.

David Kuack is a freelance technical writer in Fort Worth, Texas; dkuack@gmail.com.