April 2014
Preparing for the Future By Dave Wilkins, Spudman correspondent

Global warming may be the farthest thing from the minds of U.S. farmers after the arctic assault experienced by much of the country last winter.

One frigid year notwithstanding, scientists still take climate change pretty seriously. It might be worthwhile for potato growers to know what experts are saying about the potential impacts on spuds. Studies so far have painted a mixed picture.

Like other plants, potatoes take in carbon dioxide, the gas most often associated with the buildup of greenhouse gases. Scientists say CO2 has a fertilization effect and simulation models suggest that, for many crops, this may partially offset some negative effects from climate change.

David Fleisher, an agricultural engineer with the USDA’s Agricultural Research Service (ARS), wanted to find out how potatoes would respond to increased CO2 levels under drought conditions.

He and his colleagues at the ARS Crop Systems and Global Change Laboratory in Beltsville, Md., used outdoor growth chambers to conduct the study. They found that except for the most severe drought conditions, tuber yields under elevated CO2 levels actually exceeded tuber yields under current levels.

Averaged across all drought treatments, tuber yield from plants grown under elevated CO2 levels was as much as 60 percent greater than that from plants grown under current CO2 levels.

Experiments were conducted in 2011 using the Kennebec variety and in 2012 with Snowden and Harley Blackwell cultivars. Results were similar for all three varieties, Fleisher said.

Scientists have long known that most plants respond positively to elevated CO2 levels, often with higher photosynthetic rates and increased biomass.

But where do plants allocate the added biomass? This is what scientists have been trying to learn. Does it go toward vegetative growth or more toward the yield portion of the plant?

Fleisher’s study revealed some promising results for potatoes.

He found that potato plants tend to channel the added energy from elevated CO2 into tuber growth rather than vegetative growth, even when there’s a scarcity of water after tuber initiation.

That was pretty encouraging,” Fleisher said. “It’s a positive message that CO2 increases may be good for potato yields and for water use too.”

There is one caveat and it’s a big one: Fleisher’s study did not factor in temperature changes.

A significant change in temperature and/or precipitation could have a much greater influence on tuber growth than increased CO2 levels, he said.

“That can cancel out those positive effects,” he said. “Obviously, higher temperatures are not very good for potato.”

Most climate change projections factor in both increased temperatures and elevated CO2 levels.

How will that affect potatoes in the Pacific Northwest, the nation’s largest production area? Scientists have used computer modeling to get some idea.

An assessment of long-term climate change impacts in eastern Washington found that temperature increases would likely reduce yields of wheat, apples and potatoes moderately by the 2020s. Yields could be severely affected for all three crops by the 2080s, a team of Washington State University (WSU) scientists found. Their projections, made in 2010, assumed no change in available irrigation water in the coming decades.

Increased CO2 levels compensated significantly for increased temperatures for all three crops. But even with elevated CO2 levels, the model simulations suggest a 2 percent yield decline for Columbia Basin potatoes by 2020 and a 3 percent decline later in the century.

Project scientists factored in a shorter growing season of up to nine days for potatoes by the end of the century due to accelerated development and the earlier senescence that’s likely to come with warmer temperatures.

The study included some likely adaptive strategies too. After all, farmers aren’t going to just stand around while climate change destroys their crops, said Kristy Borrelli, University of Idaho (UI) Extension specialist for Regional Approaches to Climate Change (REACCH).

“Farmers are adaptable and they already manage risks and handle climate variations every year,” Borrelli said.

One possible adaptation would be to modify planting dates to reduce exposure to higher temperatures during tuber growth and extend leaf area duration. But project scientists saw no benefits when they ran simulations of two-week and four-week planting delays. They also simulated earlier planting without any benefit.

Scientists had better results when they anticipated the development of future apple and spud varieties that are able to maintain a green leaf area longer, thus taking advantage of longer growing seasons.

“When they looked at this adaptation, they actually found for apples and potatoes that the yield increased beyond current averages,” Borrelli said.

But no such varieties exist yet and any breeding efforts might take 10 to 30 years to develop, Borrelli said.

There are still plenty of skeptics out there, and climate scientists frequently hear from them.

The REACCH team, which includes scientists from ARS, UI, WSU and Oregon State, lays out the most current data available, including precipitation, temperature and greenhouse gas projections.

Borrelli said that skeptics remain unconvinced by the data.

“In which case I try to illustrate the point that even outside of the context of climate change itself, weather variations exist day to day, season to season and year to year, presenting risks as well as opportunities to them,” she said.

Farmers are not strangers to dealing with the risks and opportunities from uncertain conditions, and they adapt their systems accordingly all the time, she said.

“I try to highlight this point,” Borrelli said. “Therefore, even if they still don’t accept the idea of change, they can hopefully identify how our research can help them continue to be adaptable and resilient land managers in the face of any environmental disturbances.”

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