When To Water

Slideshow: When To Water

University of Georgia’s Marc van Iersel is focused on knowing when to water. For the last seven years he has been working with soil moisture sensors to improve irrigation and reduce leaching and runoff water– seeking total water-use efficiency. Simultaneously, colleagues at the University of Maryland and Carnegie Mellon University were developing equipment that could take soil moisture measurements and transmit them to a central computer. In addition, the University of Colorado team had been focused on technology that demanded real-time modeling of water use based on environmental conditions in the nursery.

“We had basically several projects that have been going off independently for the last seven years, and now we’re combining all of our efforts to develop a system that will be commercially available,” van Iersel says.

So what’s the key ingredient keeping these somewhat separate agendas together? A $5.16 million, five-year USDA Specialty Crops Research Initiative Sensor Networks grant. “The USDA thought this project wasn’t incremental, but completely transformative,” van Iersel says.
In total, because specialty crop grants from the USDA require a one-to-one match, more than $10 million is invested in water-use efficiency in four areas–field production, container nursery production, greenhouse production and green roofs.

Dollars At Work

“When you talk to growers, they can tell you the fertilizer, pesticide or growth regulator concentrations they need,” van Iersel says. “But, if you ask a grower how much water it takes to grow a certain plant, you’re not going to get a good answer.”

Van Iersel says in the past when he’s shown a picture of a plant to growers and asked them how much water it takes to grow it, the lowest estimates he hears are at least 10 times higher than the actual water requirements of that plant.

“This research will help us give growers tools to make better decisions when it comes irrigation and fertigation,” van Iersel says. According to its website, Smart-Farms.net, the project’s participants know from initial data that growers water too much (current estimates are between 5 and 20 times the actual plant water requirements).

Van Iersel is currently trialing four bedding plant species at substrate water levels that range from 5 to 40 percent. “We’re developing guidelines for these growers on how to make the most of the information provided by these sensors,” he says. At the same time, researchers are measuring how much water the plants are using on a daily basis, and how that is affected by light, temperature and humidity.

“The amount plants use is amazingly small,” van Iersel notes. “When you start with plugs, after the seedlings get established, these plants are only using a tablespoon of water a day.” However, he says it’s important to remember that they are not growing these plants with the smallest amount of water they can survive on. “What we do is give these plants every single drop of water they can use, but not a drop more.”

Data At A Snap

Charles Bauers of Maryland’s Flowers By Bauers Greenhouses is one of many industry and R&D partners involved in this five-year grant. Bauers grows high-quality cut-flower snapdragons. An integral part of this research, he has been able to work with the sensors and monitor the root environment. His brother developed a user-interface that takes 10,000 readings a day, which then allows the Bauers to crunch those numbers into meaningful data.

“I’ve been growing in hydroponics for 16 years, and before this system was in place, I thought I watered what the plants needed. Now I water to what I know the plant needs. It has increased our quality so much,” he says. “Water drives the quality of the snaps. Too much water and you get increased disease pressures. By managing less water, you manage fewer issues.”

When observing temperatures, humidity and vapor pressure deficit all in real-time, the Bauers like to monitor two positions within a given bench. “We pick what we consider to be stress areas that for whatever reason turn out the poorest quality snaps. Then we compare data with areas that always perform well.”

Dr. John Lea-Cox, a key player in the writing and development of the USDA grant, says without the intimate help of growers like Bauers, this project couldn’t be a success. Lea-Cox is an Extension specialist and associate professor at the University of Maryland. He and his colleagues are confident that through this research, growers will save 50 to 75 percent of the water they currently use.

Another end-goal for the researchers is the development of a software package. “We need the system we develop to be plug and play,” Lea-Cox says. With formalized existing models and newly created models that can be plugged into the userface, we can practice predictive water use and not be in a reactive mentality, he adds. Carnegie Mellon University, Decagon Devices and Antir Software are involved in this part of the project.

“Charles (Bauers) wants to know how to increase his percentage of No. 1 cut snapdragons and now he knows he needs to get smarter about irrigating. With what we’re developing, he can get a more precise reading. It’s not just knowing about the moisture in the bag, but also integrating temperature and relative humidty. We can’t just monitor. We have to monitor and control. It needs to be an automatic decision that’s based on set points.”

Lea-Cox knows when the research is done and systems have been developed, cost may be an issue for many growers. “It’s important these systems are scaleable,” he says. “Start off with two nodes and two sensors, the software and radio station. If you like it, you have a base, which you can grow over time.”

Growers know their problems areas, Lea-Cox says. They just don’t have many tools to make a better decision–yet.

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