Precise Irrigation Reduce Nitrates

Getting Water to Crops When They're Thirstiest Pays Off

Wade Salo trudged through a muddy soybean field one day last month, mosquitos attacking his face and neck, carrying a soil sampler that resembled a silver pogo stick. He stopped at a metal pole bearing two pink flags atop a plastic water gauge. Sometimes, when the corn or wheat is high, he has to get on top of the old, aqua-blue pickup he drives to see the gauges he's looking for.

With a jab of his foot, Salo drove the pogo stick into the ground between the rows of loaded soybean plants and pulled up a long, narrow soil sample. He squeezed the plug of dirt in his hand to estimate its moisture content. "It's saturated," he said with the cadence of a young Paul Harvey. It wasn't surprising, given the heavy rainstorm the night before. "See, my hand is getting muddy."

Salo is an irrigation technician for the Wadena Soil and Water Conservation District. He's part of a growing program in central Minnesota that measures rates of "evapotranspiration," or loss of water in fields, using a complex formula involving solar radiation, wind speed, air temperature and other factors.

The goal is to keep track of soil moisture levels, by the week and on a micro level, so farmers can irrigate their crops more effectively, applying the right amount of water when plants are most likely to use it.

Traditionally, farmers say they irrigate when their neighbors do or when their crops look stressed. But that can be too early or too late and result in too much or too little water. More precise irrigation saves money and grows healthier corn, soybeans and potatoes, but it also helps keep nutrients like nitrate out of drinking water aquifers, a prominent issue in this sandy part of the state where runoff--from irrigation or rain--percolates down quickly.

Called irrigation scheduling, this method of targeted watering took hold in Minnesota in the 1990s in Otter Tail County and expanded exponentially after 2005, when Darren Newville took over as district manager of the East Otter Tail Soil and Water Conservation District.

He holds the same position with the Wadena district. At that time, there were 60 or 70 fields in the program, Newville said, compared to nearly 140 in a multi-county area today. "It's a spreading idea," he said. "From Benton County over into Hubbard, Todd and Wadena counties, it's catching on a bit." He also urges farmers to switch to low-flow sprinkler heads.

This type of scheduling is more heavily used in states like Kansas and Nebraska, where water is scarcer, but its rise here shows that a growing number of people are taking steps to protect and conserve groundwater.

In the Otter Tail County area, as in other parts of the state, the presence of nitrates in drinking water--which can cause oxygen depletion and a condition called "blue baby syndrome"--is of growing concern. In recent years, the city of Perham, where Newville keeps one of his offices, had to dig a new drinking water well, and nearby Park Rapidsspent millions building a new water treatment plantto deal with high nitrate levels.

It's impossible to ignore the link between nitrates and farm irrigation. "There are about 10,000 irrigation permits in the whole state," Newville said, noting the area's sandy, highly permeable and often-dry soil. "Otter Tail County has about 10 percent of that, or 1,000 permits. Todd, Wadena and Hubbard counties have another 800. Twenty percent of the state's irrigation is in these four counties."

So, it makes sense that some farmers in this part of the state would embrace irrigation scheduling, said Newville. "They want to make sure they are not over-applying water to lose nitrates into the ground water," he said. "If they can prevent having to turn (their system) on, that saves them money. And if they turn it on when their crop really needs it, that helps with production. It's a win/win situation."

Salo left the soybean field and walked up onto the nearby gravel road, grabbing his laptop, which he placed on the open tailgate of Newville's cranberry red Ford F-350. He pulled up a spreadsheet loaded with data related to this 200-acre farm, much of it gathered from a custom weather station. He punched in some soil moisture information and saved the file, which he would email to farmer Andy Dombeck later in the day.

Dombeck had no need to turn on his irrigation system, by Salo's calculation. It had been a rainy summer overall, aside from a dry patch in late July and early August, and it was nearing the end of the growing season, when crops tend to use less water. "A lot of farmers are tapering off," said Salo, who has been working on this program for three years, and as a staffer since early 2013. "He's good for the rest of the season. He's done."

This is Dombeck's first year with the scheduling program, which costs farmers around $200 per year and is partly paid for by state Clean Water Fund dollars. "It's helpful," Dombeck said by phone. "It's another reference point. I can see where things are at and print out the graphs. I like data and numbers," Dombeck said. "I like to go by that instead of guessing."

The bulk of the data used to calculate evapotranspiration--evaporation plus plant transpiration, the basis for estimating soil moisture levels--comes from a series of tall, custom-built weather stations.

There are four in Otter Tail County and an additional handful that are either online or soon to be in Becker, Hubbard, Pope, Todd and Wadena counties. Precision requires multiple stations since weather can be extremely local.

Newville paid a visit to one near the Wadena airport, pointing out the various rods, canisters and whirligigs that measure temperature, solar radiation, wind speed and direction, humidity and rain. And then he opened the station's brain box, which contains a cellular modem that transmits information to his offices, where it's plugged into spreadsheets and individual farm reports.

Source: MPR News

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