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Farming and ranching in a changing climate

The changing climate will have a direct impact on agriculture around the world, and according to a North Dakota geologist, farmers and ranchers in the Northern Plains will be among the first in the United States who will need to consider that imp...

The changing climate will have a direct impact on agriculture around the world, and according to a North Dakota geologist, farmers and ranchers in the Northern Plains will be among the first in the United States who will need to consider that impact on their operations.

Geologist Will Gosnold is a professor and chairman of the geology and geological engineering department at the University of North Dakota in Grand Forks. He has won awards for excellence in research and has authored or co-authored nearly 30 scientific publications related to climate change.

For more than two decades now, he and his students have been collecting subsurface temperature data from boreholes originally drilled for core samples by the U.S. Department of Energy in the late 1970s and early 1980s. Some of them are nearly a half-mile deep.

"We were really only interested in heat flowing from the earth's interior out," he says. "That's where the data gathering came from originally, and that is what I still do."

Those boreholes allow Gosnold to collect something akin to a fossil record of temperatures reaching back hundreds of years and draw some conclusions about U.S. temperature trends.

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"What we're able to do is look several hundred meters into the ground, where we get below this annual temperature change," he says. "The deeper you go, the farther back in time you can look."

Results

His data show an overall increase in the warming rate over the past decade, on the order of about two-tenths of a degree, but he's discovered that the farther north you go, the quicker the temperature changes are occurring. Since the late 1800s, he says, North American temperatures have been increasing at a higher rate across the northern ranges.

"Most of the temperature change we see in northern North Dakota is around 5 degrees Fahrenheit," he says. "As you go towards the south, toward South Dakota, the temperature change drops down to around 3.5 degrees."

In Nebraska, the change is down to a degree or a half-degree, he says, and farther south it's less until it gets into negative values at the equator.

"That was one of the predictions of the General Circulation Models on climate change that we should see what we call polar amplification of the signal," Gosnold says. "I'm pleased to see the close connection between our observations and the climate record on this because the goal of our just-completed project was to test whether the borehole data actually matched the climate data."

Heat flow,

subsoil temperaturesWhile meteorologists and climatologists have to rely on a weather record that becomes increasingly unreliable as you go back in time, Gosnold thinks his temperature data, which stretches back some 500 years, is highly stable.

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"It is so stable that I have been going back to boreholes that I logged in 1979, and I get the same measurements, at the depth that I got then, within a few hundredths of a degree," he says.

The device used to measure the soil temperature is called a thermistor. It is a temperature-sensitive resistor with measuring accuracy to within a thousandth of a degree, though for Gosnold's work, they use it for a hundredth of a degree. They lower this into the borehole and take readings at a number of pre-determined depths, each of which relate to a period of time in the past.

The heat from the earth's core flows out toward the surface at a known rate, once allowances are made for the different types of subsurface material like rock, shale, clay and soil. The deeper you drill, the warmer it gets.

If there were no changing conditions such as weather or the seasonal climates on the surface, the rate of change in temperatures from warmer to cooler, as you near the surface, would be steady.

But surface changes do occur, affecting this rate of cooling nearer the surface. Since Gosnold knows what the rate should be, he can deduce the past surface temperatures from the altered temperature changes he finds as he goes deeper.

More insect pestsAll of this adds up to changes for agriculture in the Northern Plains, sooner than in the South. According to Janet Knodel, North Dakota State University Extension Service entomologist in Fargo and co-editor of the NDSU Crop and Pest Report, some problems already are cropping up.

"What we're seeing in general is an increase in problems," she says. "Insects are coming out earlier because there are more heat units available."

Insect body temperature is regulated by outside temperatures, she says.

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"The warmer it is, the more active they become and faster they can reproduce."

They're also hanging around longer as the fall months warm up, creating added stored grain pest problems, she says. Small grain pests such as red and confused flour beetles, seed weevils, lesser grain borers and Indian meal moths may all be tougher to control. Knodel also expects insect problems in the fields to last longer and be more intense.

"Grasshoppers would be a good example," she says. "The warmer weather gives them a longer season to develop, and quicker, so they can do more injury to the crops."

The longer warm season gives the adults a longer egg-laying period.

"It's usually from late summer through fall, say, August through freeze," Knodel says. "Now we're seeing them in July. This varies, though, with the species of grasshopper."

She says the pest status of soybean aphids last year could have been rougher on producers without the late frost in May. "We would have had an earlier and larger infestation," she says.

The added temperatures also will allow insects that traditionally have been found only in the South to migrate north.

"This past year, we had problems with the sunflower head moth, particularly in western North Dakota," she says.

The moths, which feed on the nectar and pollen of blooming sunflowers, had been coming north only every five to seven years, depending on the wind and temperatures.

"Now we're thinking about organizing a multistate trapping network, from Texas up to here as a pest alert system."

The good news is that higher midsummer temperatures should slow insects down.

Generally, "at about 85 degrees or 90 degrees and above, most insects slow their reproduction and then seek shaded areas," Knodel says. "So they do have an upper-temperature threshold."

However, the overall picture still is one of increased insect pests.

"I think we are going to see more insect pest problems with the climate warming and probably a shift in geographic ranges of insects," she says.

Cattle pests, tooInsects also affect the cattle industry, and depending on the kind of pest, similar behavior as predicted by Knodel can be expected.

"I am confident that if it warms up, we will see more flies more of the year," says Roger Moon, professor of veterinary entomology for the University of Minnesota at St. Paul.

"For cattle, there are flies on rangeland and feedlots that, if it warms up and gets wetter, we can expect our fly problems to worsen," he says. "On the other hand, some of the precipitation models are calling for drier climates, and that will work against the flies."

He points out the connection between climate and survivability.

"It appears that moisture affects survival, from egg to adult," he says. "The same goes for temperature. For 100 mothers out there, we have more daughters when it's warmer than when it's cooler."

But there are preventive measures that can be taken, beginning right now.

"We would like to see producers do things differently, regardless of climate change," Moon says. "The most serious pest right now is the stable fly, which is a blood-feeder that impacts the cattle's average daily gain. They get a real boost in the spring if the producers leave feed waste on the ground."

Feed waste is created when loose hay mixes with manure and urine, creating a pack. Coming out of winter, "it may be the only place these flies reproduce we're not sure yet," he says. "So producers should move every new bale a couple hundred feet. Be nomads out there."

Over-wintering plant diseasesAdded insect activity can lead to added disease problems, according to University of Minnesota small grains plant pathologist Dr. Char Hollingsworth, who notes that plant diseases often are spread by insects.

"It's called vectoring," she says. "I think the warming temperatures and a changing environment will influence insects, and that might change not only historical distribution patterns of some diseases but will affect when crops are infected."

She cites wheat streak mosaic, a viral disease that has the potential to cause serious crop loss in both winter and spring wheats.

"The disease depends on the wheat curl mite for spread," she says. "As the temperatures gets warmer and drier, we may see more wheat streak mosaic because that is a great environment for the vector. The mite reproduces best between 75 Fahrenheit and 85 Fahrenheit, so increasing populations of the vector may increase disease."

Hollingsworth also sees winter survival of diseases as a potential issue.

"If it doesn't get as cold here, or if we have shorter winters, that may allow more disease to over-winter."

As a general rule, younger plants are more susceptible to disease, she says. Northern states benefit somewhat because plants escape infection early on since pathogens haven't yet arrived from southern states.

"An example would be rust on wheat," she says. "We have examples of rust in Nebraska that have over-wintered. It has been detected, though rarely, in Minnesota after surviving the winter, but maybe this will be something that won't be as rare anymore."

According to researchers, pathogen spores arriving from southern U.S. states often are transported on high-level winds. They sometimes cause disease but other times arrive too late and develop too slowly to cause problems.

"For example, when sunflower rust establishes late enough, not only is disease management not necessary, the disease helps to dry the crop down for harvest," she says.

There is a possible upside to the plant disease question.

"I've heard some trends that say we're going to get drier as well as warmer," Hollingsworth says. "The good news is less moisture means less disease. There's a fine line between too dry for disease and too dry for plants. I remain optimistic about ag production in Minnesota, North Dakota and South Dakota in a changing environment."

Resilient weedsWeed infestation may become the toughest challenge if the climate continues to warm. By sheer number of species and a stubborn resistance to eradication, weeds continue to turn up each year despite widespread spraying with modern chemicals. Lengthening growing seasons could lead to even tougher weed challenges.

"Weeds are very resilient, and Mother Nature always wins," says Richard Zollinger, a weed specialist with the NDSU Extension Service in Fargo.

In 1978, NDSU undertook a statewide survey of weeds by county and created a list of the top 10 weeds, based on distribution, population and overall nuisance value. Zollinger led an effort to repeat that survey in 2000 and was able to draw some surprising conclusions.

"We did the survey in the same manner, and the same top 10 weeds that we were battling in 1978 and 1979 were still the same, though the ranking was not in exactly the same order."

Zollinger's data indicate that weeds may be losing the battles each year, but they're still in the war.

In a 22-year period, the industry "has come up with some very superior herbicides," he says. "They are extremely effective, but we still didn't make much of a dent in the severity of the weeds."

The upside of the weed war?

"The good news is if we were to give a weed a nuisance rating, for the most part, the weeds are still here, but the populations are a lot less," Zollinger says. "There are exceptions like Canada thistle, which increased, but the annual weed populations decreased."

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