Optimize Irrigation with Water Sensors

August 24, 2012 07:04 PM
Optimize Irrigation with Water Sensors

Remote water sensor technology saves water and money

Farmers understand how precious water is as a resource, but that point was driven home even further during the historical drought of 2012. Farmers such as Ryan Weeks and Leon Knirk have embraced a simple, yet effective, technology to help optimize their irrigation strategy—water sensors. Using these sensors creates an opportunity to change irrigation from a guessing game to a numbers game.

"You just use a soil probe to make a hole, and then stick the sensors in at 1', 2' and 3'," says Weeks, who farms corn and soybeans in Nebraska. "Then you use a monitor to measure the moisture of your soils at 1', 2' and 3'. The University of Nebraska has done a lot of research to determine when you need to start watering based on the sum of those three numbers."

Knirk, who farms in south-central Michigan, says he’s used his sensors for two years and is still fine-tuning his processes, but says that just gaining a baseline amount to work from has been valuable.

"I had something to look at," he says. "I had a number. I wasn’t just taking a shovel out and trying to turn over some soil and make a guess at it. I had some kind of tool that wasn’t just an estimation."

Soil moisture measurement is important in any year, but it’s especially critical in light of this summer’s drought-choked conditions.

What’s more, soil moisture is never steady. It is based on a number of obvious elements such as rainfall and temperature. Soil moisture is also influenced by less obvious factors, such as no-till practices, which help with water retention, and the planting of newer hybrids that are more efficient users of water.

To that end, Knirk says, it can matter greatly where the water sensors are placed in each field. Zone-mapping his fields helped him choose smart locations for his water sensors, he says.

"We tried to get them on zones that were relatively large in our field. I didn’t go to the absolute driest zone in the field, but I went into one of my drier zones that was a relatively large portion of the field. We used that for a measuring tool because I knew if my moisture levels had fallen there, I had a buffer for the rest of the field that had better water-holding capacity," Knirk says.

Weeks adds that his monitors have allowed him to map out a smarter irrigation schedule. Oftentimes, better monitoring means fewer pivot trips, he says.

"Most years, I think this has saved me at least two applications," he says. "We’re talking $750 to $1,000 per pivot, per circle. We have estimated that [has saved us a total of] 500 gal. of diesel, 145 hours of operation on the motor and 22.68 million gallons of water."

How it works. Using the water sensors and monitors is not a difficult process. Every time farmers take a reading from the water sensors, they get a readout from 1 to 200, says Tom Penning, president of Irrometer Company, Inc., which manufactures Watermark sensors and handheld meters. Other companies, such as Memsic and ETgage, offer similar products.

To imagine how soil water tension works, think about a sponge, Penning says. If you have a sponge that is completely saturated, it takes almost no effort to begin extracting water. But as water continues to leave the sponge, it becomes more and more difficult to squeeze out the remaining moisture.

Soil holds moisture in a similar manner, Penning says. A good rule of thumb is that the first 50% of available water moisture is relatively easy for the plant to extract. The plant has to work much harder for the remaining 50%, he says.

"You want to irrigate before you get to that point," he adds.

Farmers take multiple readings and graph out the results, which reveals a "comfort" range where plants in the field are optimizing water resources. The goal is then to time irrigation to keep the crop in the comfort range, which is slightly different in every field based on crop, soil type and additional factors, Penning says. He suggests fine-tuning the amount by personal trial and error or by working with your agronomist or Extension specialists.

p70 Sensing Savings 1
Texas farmer Mark Schlechte shows how easy it can be to install water sensors in the field.

That’s exactly what farmers such as Weeks have done.

"My agronomist has adjusted the way he ribbons the soil a little bit, and everybody has adapted as this has come to fruition," he says.

And while some setups allow instant readings to be beamed to a remote computer or smartphone, Knirk prefers the basic setup, even though it requires a reading to be taken directly from the meter itself.

"I thought it’d be better for me to get some transition into the field, look at that number, and look at the corn I’m standing in," he says.

State resources. As a Nebraskan, Weeks is fortunate to belong to a robust group of more than 700 farmers called the Nebraska Agricultural Water Management Network (NAWMN). Established in 2005, it helps farmers and advisers make better informed irrigation management decisions. Gary Zoubek, a University of Nebraska–Lincoln Extension educator, says one of the program’s benefits is the opportunity for collaboration.

"This is not a formal network, but we have held more than 200 meetings to connect area farmers," he says. "The meetings bring together the people who already have the technology with the people who want to learn more."

Surveys show that NAWMN is paying real dividends to its participants, who cited an average annual irrigation water savings of 2.4" for corn and 2.1" for soybeans in 2010, with a six-year average savings of 2" a year. That equals total energy savings of more than $3 million.

As the 2012 drought proved, water is an important resource to manage, no matter where you farm. Some parts of the country are even engaged in so-called "water wars," such as the heated tristate water dispute in Flor-ida, Alabama and Georgia that has raged for the past 20 years.

For Weeks, though, water sensor technology continues to be an easy, cost-effective way to make the most of a limited resource. 

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