Plant-Based Water Monitoring

Dan Crummett, Contributor

Like most irrigators, Ryan Speer has a long-standing desire to water his crops only when needed and avoid overwatering when he does start the sprinklers. He's used soil-moisture monitors and studied irrigation scheduling based on evapotranspiration models, but recently, he's been consulting the crop plants themselves and is being rewarded for his efforts.

Speer is a co-owner of the 125-year-old Jacob Farms, a 6,000-acre operation in south-central Kansas, near Wichita. With half the farm watered with 20 center-pivot sprinklers fed by the shallow groundwater of the Equus Beds Aquifer and the other in dryland production, the no-till farm typically is in a four-year rotation of corn, soybeans, winter wheat, grain sorghum and cotton.

For the past three years, Speer and his business partner, Steve Jacob, have set aside a 133-acre circle as the "Jacob Water Technology Farm" in cooperation with the Kansas Water Office (KWO), the state agency charged with developing water conservation through better farming management practices. The agency can showcase the latest in irrigation management technology as part of a network of 17 demonstration farms across Kansas.

"We'd been active in water conservation for years, even before hosting the technology farm," Speer explains. "The Equus Beds Aquifer has plentiful water reserves compared with other parts of the High Plains Aquifer, farther west in our state, but because of naturally occurring salts in the area associated with the nearby Arkansas River and salt deposits northwest of us, it's a highly saline water source."

WATCH SALT BUILDUP

"We need the water but want to limit how much we use because of the chlorides it contains," he says. "Because of that, we're trying to reduce irrigation use like our counterparts out west, but in our situation, it is to prevent salt buildup in the soil, not to work around depleting the aquifer."

To keep tabs on the soil chemistry, along with nutrient levels and organic matter content, grid soil samples are taken on 25% of the farm every year on a rotation basis, Speer explains.

He says they've had good results conserving water for years by adopting low-pressure sprinklers equipped with wobbler nozzles to increase water droplet size (for resistance to wind-caused evaporation and plant-damaging salt deposits on crop leaves) and LDN (low-drift nozzle) drops that placed the nozzles within 2 feet of the field surface. Soil-moisture probes have also played a part in the farm's overall water-use efficiency.

MANAGEMENT CHANGE

"Despite our successes with the drops, nozzles and moisture probes, about five years ago, we introduced Phytech direct-plant sensors to the farm, and they changed the way we irrigate," Speer says.

Phytech's system features a clamp-on sensor around the stalk of the crop to measure shrink and swell of the tissue, which correlates to the plant's stress levels and water demand.

"It just makes a lot of sense to consult the plant," he adds. "You may have water in the soil, but the plant still may be stressed. It's much better to listen to the plant than rely solely on monitoring soil water levels."

Speer recalls the early experience with the monitors that convinced him of their worth.

"It was hot weather in June, and we were busy trying to keep the corn watered on one circle by making a .90-inch pass with our 700-gallon-per-minute application rate," he says. "The monitors showed us we still had stress on the corn.

"We sped up the pivot and put on half-inch passes so the pivot would get back and cool the crop, thereby reducing the stress we were seeing with the shrink and swell of the corn stalks," Speer continues. "You would have never picked up that stress with a soil-moisture probe. The plant monitor registered the stress long before it was visible, and if it's visible, you're already losing yield."

Another experience with double-crop soybeans came in a year with generous rainfall.

"The beans were flowering and setting pods, and we knew there was not a moisture problem in the fields; but the plant monitors were registering crop stress," he explains. "When I inspected the area around the sensors, I found woolly bear caterpillars defoliating the canopy. The insects were causing the stress, and the swell and shrink measurements were catching it."

Speer says at first the watering recommendations from the plant-based sensors and their computer's algorithms frequently went against his better judgment, but they ultimately won him over.

"Typically, we would water corn up to pollination to meet the plant's highest water-consumption period," he explains. "We'd try to get ample moisture in the soil and hold it at that level."

The first year the monitors were in use, Speer says he compared a direct-plant-monitored circle with an adjacent circle of similar soils and identical hybrids, and planting dates managed conventionally with .90-inch watering passes.

"I was uncomfortable throughout the season because the monitors were calling for less water than I thought was needed," he explains. The technology vindicated itself, however, when Speer tallied up an 18-bushel-per-acre yield increase in the monitored circle, along with a water reduction of 4 to 5 inches for the season.

WATER TOO LATE

"The differences in pumping costs were not significant, but we did use less water. So, with increased yields and less pumping, I became a believer," Speer says.

"The monitors also taught us we were watering corn too late into the season," he adds.

In 2018, the first year Jacob Farms hosted the KWO test site, the plant-based monitors were an important part of the demonstration.

"At our July 24 through 25 field day, the plant-based monitors said no more water was needed, so we stopped irrigating," Speer recalls. "People were freaking out that we'd quit watering, and many growers in our area watered two to three times after that date. On our farm, the system showed us the corn was happy, so we were able to successfully end our watering season early."

Because of heavy flooding and numerous replanting operations, Speer says 2019's results were inconclusive.

In 2020, however, he was using the monitors on soybeans and says they may have called for one more irrigation than he would have made normally. However, he was pleased with the 86-bushel-per-acre yield.

"I'm going to follow the system's lead on soybeans even though it seems to be a little bit more sensitive on beans than with corn," Speer explains. "Sometimes, it calls for less water than I think is necessary, and sometimes it calls for more.

"I'm very comfortable with the Phytech system on corn, but I'm still working on my comfort level with it in soybeans," he adds.

PRECISION COSTS:

Ryan Speer says with volume discounts, the plant-based sensors, related computer hardware and reporting service cost about $950 per circle in his area compared with up to $2,000 for some competing soil-moisture monitoring probes.

"The service provider installs the system each season, usually placing monitors on six plants per circle and installing the system's computer at the pivot point," he explains. "Each system is calibrated to the farm's soil types and usually receives several software updates over a season." Visit www.phytech.com for more information.

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