Irrigating Crops On Demand

Cleome watered by hand on the left and watered with a tensiometer on the right. Orange flags in pots can give a sense of height differences.

Automating greenhouse irrigation can be a huge labor saver, which is imperative for a modern greenhouse to be competitive. Irrigation controllers make it possible to automate greenhouse irrigation, but one usually programs the system to come on for a set time on a set schedule. Environmental conditions change such that a set program may be wrong more often than it is right. Sensing devices can be employed to aid a greenhouse operator making decisions about when to water, or one can take this a step further and let the substrate itself decide when it needs to be watered.

Comparing On-Demand To Automated Irrigation
Rather than have a set schedule programmed into a controller, it is possible to wire a moisture-sensing device, such as a tensiometer, between an electric valve and a source of electricity (transformer). When the moisture level in the substrate falls below a set-point, a switch on the tensiometer closes, allowing electricity to flow from the transformer to the electric valve, thereby irrigating the crop. As the substrate moisture increases, the tensiometer switch opens, stopping the flow of electricity, and the valve automatically closes.

Because the irrigation system is being turned on whenever the substrate reaches a certain set-point, we refer to this as on-demand irrigation rather than automated irrigation. If the crop calls for water three times in one day, the crop gets watered three times that day.

At Oklahoma State University, we have been using this system of on-demand irrigation to grow annuals and perennials for the department’s spring plant sale for the past three years. Students are responsible for checking the greenhouse daily, if not twice daily, but they have to do little to no hand-watering. The greenhouse is watered on-demand by a number of tensiometers wired between transformers and their associated electric valves. We feel we are able to grow higher-quality crops in a shorter period of time by using this on-demand system. To investigate it further, we conducted an experiment this spring comparing hand-watering to a tensiometer based, on-demand system of irrigation.

Comparing Hand-Watering To On-Demand Watering
Ipomoea ‘Margarita’ and Cleome ‘Seniorita Rosalita’ were chosen for the study. Two greenhouse benches of each were grown from plugs in the spring of 2013 in 6-inch plastic containers. All plants were grown in Metro-mix 902 (manufactured by Sun Gro Horticulture), to which was added 1.5 grams/liter of Everris Nursery Mix (19-3-10).

One bench of each species was watered by hand by our greenhouse manager and one bench of each was watered using drip irrigation controlled by a tensiometer, model MLT (manufactured by the Irrometer Company).

The tensiometer was placed in a sweet potato plant along the edge of the bench near the greenhouse heat source. In other words, the tensiometer was placed in the pot we assumed would dry out first and utilize the greatest amount of water. Both the sweet potato and cleome crops were controlled by one tensiometer. It was set to turn the water on when the substrate reached a moisture tension of 4.5 kPa.

The water was delivered by a drip system using Netafim polyethylene distribution tubing, into which was inserted a Netafim 2 gallon/hour emitter. The water from each emitter was split to eight pots for an effective rate of approximately 0.25 gallons per hour.

There were 80 plants per bench on the hand-watered benches and 79 plants per bench on the tensiometer controlled benches. Our greenhouse manager has more than 25 years of growing experience and we asked him to hand-water the crop as he saw fit. We wanted to compare hand-watering by an experienced grower using his experience and judgment to determine when the crop should be watered, to on-demand irrigation controlled by a tensiometer.

We kept track of how many times a day the crops were watered and estimated the volume of water used. Water from one drip emitter on each bench was collected and measured to estimate total water use for the tensiometer-controlled system.

For the plants that were hand-watered, the time it took to irrigate the crops at a known flow rate was recorded to estimate the total volume used by the hand-watering system. At the end of the study, we measured lateral growth on the sweet potato, and height and number of flower stalks on the cleome.

Crops Demanded More Water Than They Typically Get
The most surprising result of this study was how often the crops were watered. In a 20-day period, the hand-watered crops were irrigated nine times while the tensiometer called for water a total of 31 times, twice watering three times in one day (Figure 1). There were 11 days when the greenhouse manager chose not to water, while there was only one day when the tensiometer did not call for water.

Although the tensiometer-controlled crops were watered more than three times more frequently, the hand-watering method used approximately 10 percent more water than the on-demand system with drip. Hand-watering used approximately 168 gallons while the on-demand method used approximately 152 gallons during the 20 days of the study.

Cleome watered by hand grew to an average height of 16.6 inches while the cleome watered by the on-demand system had an average height of 22.9 inches. There were on average 2.6 flower stalks per plant on the hand-watered cleome and an average of 4.1 flower stalks on the on-demand cleome.

The length of sweet potato stems averaged 12.4 inches when hand-watered, while the on-demand sweet potato plants grew more than twice as much to an average of 30.5 inches.

On-Demand Irrigation Offers Taller, More Vigorous Plants
With on-demand irrigation controlled by a tensiometer and delivered by drip, we were able to grow taller cleome with more flowers and sweet potato vines with more than twice the growth than those watered by hand. We were able to do this using less water and saved a tremendous amount of labor by letting the tensiometer water the crops. Labor savings, greater growth, and less water use suggest that on-demand irrigation controlled by a tensiometer could have financial and environmental benefits for greenhouse growers.

With this study, it is not possible to tease apart the contribution by each of the variables but we speculate that the greater growth was caused by a more even moisture regime in the on-demand irrigation system. There was almost no leachate from the on-demand system suggesting that the pots were irrigated to less than field capacity, perhaps maintaining a higher level of oxygen in the root zone, and the crop was watered whenever the moisture tension reached 4.5 kPa.

With hand-watering, the pots were filled to field capacity and were allowed to dry down between waterings. It would be interesting to know how dry the substrate got between waterings in comparison to the 4.5 kPa.

Tensiometers Are Valuable Tools For Controlled And On-Demand Irrigation
Even if a grower wanted to maintain more control over their irrigation timing than using the simple on-demand system outlined here, a tensiometer can be a valuable tool for measuring substrate moisture. It is not affected by fertilizer or salt buildup in the substrate. It can be used as a monitoring device to decide when to water and it can be used in conjunction with an irrigation controller, allowing the crop to be watered when the substrate is dry but preventing irrigation when the substrate is moist.

If the tensiometer is wired between the controller and the valve on the common wire, it can act as a common wire interrupt preventing the valve from turning on even though the controller is scheduled to water. An irrigation controller can be programmed to water three times a day but the crop will only be watered if it actually needs it.

If using a tensiometer as part of an irrigation system, there are certain precautions that should be taken. First of all, the crop must still be monitored. Although we believe the tensiometer is better at making watering decisions than perhaps even the most experienced grower, it is not a substitute for good oversight of the crop.

Like any automated system, problems can arise. For example, with the on-demand system outlined here, if the tensiometer or the drip tube were to fall out of the pot, there would be no way for the tensiometer to read the substrate moisture level and the irrigation would remain on until manually turned off or until the problem were fixed.

We have found the tensiometer to be a very valuable greenhouse tool that has saved tremendous amounts of labor, allowed us to cut back our crop time and helped us grow better crops.

We zone our greenhouse so that crops of similar age, pot size and water use requirements are controlled by their own tensiometer but we were pleasantly surprised by how many different crops we were able to manage on the same zone. We place the tensiometer in the crop that we think will require the most amount of water and make sure to use a well-draining greenhouse mix, so even if other crops are being watered more than they need, the substrate drains quickly.   GG


Leave a Reply

One comment on “Irrigating Crops On Demand

More From Equipment...
Great Lakes Expo

November 30, 2015

6 Reasons You Should Attend The Michigan Greenhouse Growers Expo

The Michigan Greenhouse Growers Expo, held Dec. 8-10 in conjunction with the Great Lakes Fruit, Vegetable and Farm Market Expo, will feature an expansive trade show and several educational sessions aimed at greenhouse growers.

Read More
Colorado State University 2015 Container Field Trials

November 29, 2015

2015 Colorado State University (Fort Collins, Colo.) Field Trials Results

See the 2015 field trials results (includes photo gallery) for Colorado State University in Fort Collins, Colo.

Read More
Coleus 'Colorblaze Velveteen' (2015 University of Tennessee Field Trials)

November 28, 2015

2015 University of Tennessee Gardens (Knoxville and Jackson, Tenn.) Field Trials Results

See the 2015 field trials results (includes photo gallery) for University of Tennessee Gardens in Knoxville and Jackson, Tenn.

Read More
Latest Stories
Feature Image Cob 700 (NewLux)

November 28, 2015

16 LED Lighting Solutions For Your Greenhouse

Narrowing in on the right LED lighting product often comes down to considering your specific crop needs and growing requirements to see what works best for your application. Here are 15 LED products to take into account when choosing the right fit for your greenhouse.

Read More

October 27, 2015

How Dallas Johnson Greenhouses Is Simplifying Shipping

Two years ago, Dallas Johnson Greenhouses, a 61-acre operation in Council Bluffs, Iowa, and No. 21 of Greenhouse Grower’s Top 100 Growers, was struggling to get its orders out. With its range of potted annuals, there were so many skus that it was impossible to get enough carts into the shipping greenhouse, and the crew couldn’t get orders processed fast enough. As a result, the operation was consistently pulling orders until midnight every night during the busy shipping season, says President and CEO Todd Johnson. So Johnson got together with Arie Van Wingerden at Cherry Creek Systems to discuss his problem, and what they came up with has changed everything, Johnson says. Inside one of Dallas Johnson Greenhouses’ existing structures, the team installed a shipping system made with Echo-Veyors, the popular cable conveyor system designed by Cherry Creek Systems. The system was placed right in the front of the greenhouse, […]

Read More
Tidal Creek Growers

October 24, 2015

Five Tips For Successful Use Of Boom Irrigation Lightin…

Michigan State University Extension shares five tips to help growers use boom irrigation lighting more effectively to accelerate flowering of long-day ornamental crops.

Read More

October 8, 2015

Industry Standards For Greenhouse Lighting On The Horiz…

As the use of LEDs has risen among greenhouse growers, so have concerns about the best way to measure and compare the many LED light products across the market. As a result, the lighting industry is responding to a call for greater transparency and the development of standardized measuring and testing methods.

Read More

September 28, 2015

11 Products For Precision Greenhouse Growing

These new options in equipment, automation, structures, lighting and software are designed to help growers run their operations with efficiency and accuracy and at a lower cost.

Read More
Laura Drotleff

September 25, 2015

Growers Solve Problems With Precision Horticulture

My dad’s hands are covered with sores, nicks, scratches and bruises. It’s the ongoing reward — or drawback — of his ingenuity, as he’s constantly wrenching on equipment or constructing new innovations that will help him get work done more efficiently on the farm. As a kid, I would always marvel at his toughness, and how he would barely notice a new wound, shrugging it off as he kept working, driven to complete his work and bring his idea to fruition. He’s still at it today, and his hands tell the story of the many projects he’s completed over the years. I’m guessing many of you can relate, and your hands look similar to my dad’s. After all, ingenuity is the name of the game in this business, where creative thinking to solve problems often leads to revolutionary solutions that automate production, save labor and cut costs. That’s easy to […]

Read More

September 24, 2015

AgriNomix Helps Keepsake Plants Cut Labor Costs With Au…

Keepsake Plants reduced labor for trimming Hydrangeas from 60 people to 28 by automating the process with AgriNomix Venti Trimmers.

Read More

September 24, 2015

4 Dramm Products That Put The Precision Into Growing

When accuracy counts, the right tool makes all the difference. New products from Dramm put tools in growers hands to get the job done efficiently.

Read More
The single cells move forward, still grouped with their pack, until the pack is positioned in front of an arm that can pick up several individual plants at a time

September 24, 2015

How Spring Meadow Nursery’s Custom Sorting Machine Kee…

The Michigan-based nursery uses automation to cut apart trays of immature plants and regroups them into new trays of similar-sized plants.

Read More
Figure 3. Sole-source lighting in a multi-layer vertical growing system utilizing hydroponics for vegetable production.

September 23, 2015

MSU Offers New Greenhouse Lighting Online Course For Gr…

  Michigan State University Extension is now offering a non-credit, pre-recorded online course on greenhouse and horticultural lighting. The lighting course is intended for greenhouse and ornamental plant growers and others interested learning about the fundamental concepts about how plants respond to light quality, quantity and in duration. It provides introductory to moderately-challenging content primarily based on experiments performed at Michigan State and Purdue Universities. This is the second course in the College of Knowledge Online series offered on the national Extension website. The first course was Floriculture Root Zone Management, also available online. What Growers Will Learn From Taking This Course The 3-hours of pre-recorded lecture and video demonstrations are divided into seven units. The first and second units cover the properties of light and its importance for plant growth and development. The third unit discusses how light quality influences stem extension and flowering. The fourth unit of the course teaches […]

Read More
ArmstrongGrowers Hanging Basket Area

September 22, 2015

Sole-Source Lighting In Horticulture: Bedding Plant Plu…

Researchers determine how sole-source LED lighting can be used effectively for the production of bedding plant seedlings.

Read More

September 18, 2015

Visser North America To Provide Mayer Potting Machines …

Visser North America (NA) will now be the official North American supplier for sales, service and parts provider of Mayer potting machines and equipment. The Mayer premium line of potting machines is the latest addition to the Visser NA lineup, including the NewLux, Logitec Plus and Visser product lines. “Much like our current product lines, Mayer is a leading provider of potting machines and further horticultural equipment worldwide and its brand represents quality in our industry,” says Kevin Vander Ploeg, president of Visser NA. “We believe in providing our customers with the best solution for their operation with ongoing support and service excellence. Naturally, we are pleased to add Mayer to our product line up.” Mayer, a German company manufacturing in Europe and with a global presence, has been designing and manufacturing potting machines since 1967. The Mayer product range includes solutions for the entire process chain from soil preparation to filling of pots/trays […]

Read More
Costa Farms’ new solar panels will offset 493,487 pounds of carbon dioxide annually

September 15, 2015

Costa Farms Ramps Up Sustainability Efforts With Solar …

Costa Farms is seeking to make sustainability a top priority at its headquarters and two other buildings in Miami with the recent construction of new solar panels, which will replace 25 percent of the company's power usage with solar energy.

Read More
Trays move on an overhead conveyor to the end of the production line, where workers carefully pack the cleaned, sized, graded, counted and sorted Calla tubers

September 14, 2015

Golden State Bulb Growers Increases Efficiency With New…

Necessity is the mother of invention, and that’s certainly true for Golden State Bulb Growers. The Moss Landing, Calif., operation, which supplies its Callafornia Calla Lily bulbs to wholesale markets around the world, was in need of a more streamlined and less labor-intensive solution to grade and sort bulbs. So Golden State’s management team got creative and started talking with MAF Industries, part of the MAF-RODA Group that specializes in the design and manufacture of grading, packing, palletizing and handling fresh fruit and vegetable systems. The manufacturer was willing to work with Golden State on the Calla Lily bulb grading and sorting machine design process. This resulted in Golden State Bulb Growers investing $700,000 to purchase the new grading system to better serve the needs of its customers, increasing uniformity and productivity in its Callafornia Callas bulb processing. Investing in the new system has also allowed Golden State Bulb Growers […]

Read More
Figure 1. Mustard microgreens grown under sole-source (SS) lighting using light-emitting diode (LED) arrays.

August 21, 2015

Sole-Source LED Lighting In Horticulture: Microgreens P…

In Part 3 of a four-part lighting series highlighting the multiple uses of light-emitting diodes (LEDs), researchers examine the effects of sole-source LED lighting on microgreen production to achieve the highest quality crop possible in an energy efficient manner.

Read More
Lighting 2015 August Feature Image

August 14, 2015

Customizing Crop Foliage Color With LEDs: Ornamental Cr…

Do you find that your purple fountain grass (Pennisetum setaceum ‘Rubrum’) crop is often green to light purple? What if we told you there is a quick solution to enhance and darken the foliage of purple fountain grass or other floriculture crops? In this second article of a four-part series highlighting the multiple uses of high-intensity light-emitting diodes (LEDs), we will discuss our research methodology and findings for enhancing the foliage color of ornamental crops with end-of-production (EOP) supplemental lighting (SL) in the greenhouse. Many ornamental crops that greenhouse and nursery growers produce vary in size, shape and color. These variables are often influenced by the growing environment. For example, leaf color (intensity, distribution or both) of ornamental crops such as purple fountain grass is a key component that often influences the consumer’s perception and ultimately an impulse purchase. The red or purple pigmentation of purple fountain grass leaves is […]

Read More
WaterPulse retail mats can help cut water use in retail settings

August 10, 2015

Technology Provides Solutions For Growing In Drought

In April, California Gov. Jerry Brown directed the State Water Resources Control Board to institute reductions in cities and towns across the state with the goal of reducing water usage by 25 percent. The announcement comes following the lowest snowpack ever recorded in the High Sierra. It was the first time in state history that action was taken to implement mandatory water restrictions. In May, the farmers in California’s Sacramento-San Joaquin River Delta agreed to reduce their water use by 25 percent in exchange for assurance that they will not face further curtailment during the June to September growing season. Their proposal was approved by the State Water Resources Control Board. Growers who participate in the program could opt to either reduce water diversions under their riparian rights by 25 percent, or fallow 25 percent of their land. Given these conditions, growers and retailers are in need of methods and […]

Read More
Heating Roundup Feature Image

August 1, 2015

5 New Heating Options For The Greenhouse

Five heating systems manufacturers share their latest and greatest products. Tubing And Aluminum Heat Pipes (BioTherm) From Megatube and MicroClimate tubing to DuoFin and StarFin aluminum heat pipe, BioTherm is dedicated to providing heat solutions that can withstand the toughest greenhouse environments. The MegaTube and MicroClimate tubing options are easy to install and ideal for bench or floor heating. The tubing has a conductive heating surface that allows for maximum root-zone heating. The DuoFin and StarFin aluminum pipe options are great for perimeter heating and melting snow trapped in the greenhouse gutter. It can also be useful for bench heating. Both pipe options provide gentle, radiant heat for plants and don’t require welding. Infinite Energy 2 Condensing Boiler (Delta T Solutions) With up to 98 percent efficiency, the IE2 condensing boiler boasts a stainless steel heat exchanger with larger waterways to ensure maximum heat transfer. The product’s design ensures flexibility while […]

Read More
[gravityform id="35" title="false" description="false"]