Climate Change Doesn’t Pass the Hot Potato

Climate change is affecting the growth of potatoes, the world’s fourth largest food crop.

By: Grace Kennedy

It’s a clash of the scientists when it comes to the future of sweet potatoes in a carbon saturated world. From Hawaii to Peru to the Annapolis Valley, the importance of change in the developing world’s fourth largest food crop is of varying degrees.

Benjamin Czeck, a graduate student at the University of Hawaii, conducted a study in the fall of 2011 on the effects of CO₂ on sweet potatoes. He looked at four different concentrations of carbon dioxide, and found the sweet potato root could grow up to twice its normal size when there was nearly four times the current amount of carbon dioxide in the atmosphere.

Czeck also found decreases in several micro-minerals, such as iron, phosphorous, and manganese. Iron, which is beneficial for bones, blood, and protein fixation, decreased by as much as 45 per cent; phosphorous, important for energy, protein, and bones as well, by 25 per cent; and manganese, which is an anti-oxidant to help with tissue health, by 75 per cent.

In addition to these, the protein content in sweet potatoes also decreased by 32 to 43 per cent, while the increased carbohydrates by 4 to 4.7 per cent. Although sweet potatoes are not a significant source of protein – there are only about 1.37 grams of protein in 100 grams of an orange-fleshed sweet potato, or about one paper clip in half a cup of water – this is still a substantial change.

“Because we have high obesity rate and we’re not good at eating food with these sorts of minerals, eating vegetables and stuff like that, it’s a negative thing,” says Czeck on the nutrition changes.

“In the future, if this is a response – this decreased protein, increased carbohydrates and decreased minerals – the diet that we have is going to have to change even more to get what is essential for our bodies to be healthy.”

The nitrogen levels in the soil remained the same for each level of carbon dioxide, and this is where other scientists begin to have issues. Nitrogen helps to change the sugars created by photosynthesis into protein for the plant’s long-term use; if there is more carbon dioxide, there will be more sugar, and less nitrogen to change it into protein.

Czeck doesn’t think that the sweet potato would be able to take up more nitrogen from the soil than it already able to do, but others such as David Burton, an agriculturalist at Dalhousie University, and Viliam Zvalo, a horticulturalist with the company Perennia, think that it will.

If sweet potatoes can take up more nitrogen, then there is a possibility that the protein content would remain stable.

“It’s not an issue for us here, because sweet potato is such a minor part of our diet,” says Zvalo from his office in Kentville.

“It would not really impact human health in any way, if we had a decreased percentage of those elements. But in the developing world where people’s diets are based on sweet potatoes, that could be a different issue all together.”

For people like Wolfgang Gruneburg, a sweet potato breeder and geneticist in Peru, the problem with Czeck’s study was its academic nature, neglecting the importance of other factors in the growth and nutrition of sweet potatoes.

“This article that sweet potato was producing twice as much – interesting study, but it is not so much on the ground at the moment,” Gruneburg said in a skype interview from Lima.

“It’s a little bit more – I don’t want to say this was a wrong study or the data is not okay, this is exactly not. It can be absolutely true, but this situation will not come tomorrow, and most likely not in twenty years.”

Czeck agrees. The highest level of carbon dioxide in his study was almost four times as much CO₂ than is currently in the atmosphere, and he thinks this could be a reality in 200 years, not 20.

“I think in going forward with these sorts of experiments temperature, drought conditions, water supplies, those sort of questions need to be approached because those are going to be a lot of the problems that we’re going to be facing, especially in developing countries.

“If we’re going to relate this to agricultural production, we’re also going to have to understand other sort of hurdles we’re going to be facing which are going to be high, extreme temperatures and drought issues.”

Increasing concentrations of CO₂, according Burton, would bring mixed benefits to Nova Scotia’s fledgling sweet potato industry.

“In agriculture we have looked at some of the positive impacts of that,” Burton said about the increasing carbon dioxide from his office in Truro.

“In terms of regions like Nova Scotia, crops like sweet potatoes have been a challenge here because we don’t have a very warm or very long growing season. So there could be some positive impact in terms of the total number of heat units we’re exposed to and also the length of our growing season. But the potential for more extreme, intense weather events may offset that positive.

“So there’s concern that while we may have warmer, wetter future that would be more conducive to the production of crops like sweet potato in Nova Scotia, there’s equally a concern that this extreme weather may not allow us to realize that.”

The current production of sweet potatoes in Nova Scotia is a recent development spurred on by Zvalo.

“It started about 10 years ago when I went to a conference in New England, and realized they were growing sweet potatoes,” he said in a phone interview.

“That made me wonder – if they can do it in Maine, why can’t we do it here? So, I talked to Agriculture Canada … and we started a regional project that looked at 17 different varieties of sweet potatoes, and how they would be suitable to the region.”

Zvalo worked with Keddy Nursery, who is currently the only major producer of sweet potatoes in Nova Scotia. There are a number of smaller producers as well, but none of them are on the same scale as Keddy Nursery.

Exactly how Nova Scotia’s sweet potato industry will be expanding in the coming years is uncertain – Zvalo said that its growth would be tied to the ability to invest in processing and storage facilities.

Sweet potatoes need to be cured if they are to get their recognizable texture and taste – being saturated in heat and humidity for six to eight weeks helps increase their sugar content and reduce shrinkage in storage.

“Producing sweet potatoes is one thing, but storing, long-term storage is another thing all together,” Zvalo said.

“This one large producer [Keddy Nursery] has invested into a long-term storage last summer, so he’s involved and the quality of the product is excellent. But the future growth of the industry will depend on the ability of the growers to invest in storage. And that’s really hard to predict.

“We could grow the crop, there’s really no magic to it. There’s some expertise or knowledge, but that can all be learned. But the capital expenditure on the curing and storage facility is going to limit growth in the industry.”

But how will the results of Czeck’s study, if they do become reality in the next 200 years, affect the Nova Scotia sweet potato market?

“I think one of the big movements in agriculture is a desire to move to more local food sources, and I think agriculture needs to diversify and sell more directly to the consumer,” Burton said.

“So I think developing a greater diversity of products, like sweet potatoes, those sorts of things, are probably really key to agriculture’s sustainability.”

Sweet potatoes come in many different varieties, and since the vegetable makes six different copies of its DNA, instead of two like humans, there could be a greater potential for adaption in adverse climates.

Czeck thought of the market in global terms.

“Right now we consume a lot of wheat, corn, soybean, rice globally,” he said, “but a lot of these crops don’t respond to CO₂ ­in the same way that root crops do.

“Globally it could change the way we approach our agricultural practices, maybe convert to more root crop-type diets while also figuring a way to do this transition in a sustainable, societally accepted way. I think if you were to say: everyone has to start eating sweet potatoes or carrots or whatever it may be – it’s going to have to be a way to transition that works for all.”

Gruneburg, however, thinks this is thinking too far ahead.

“200 years, wow,” he paused and laughed. “Sorry, I’m laughing because I was thinking about one of my professors, when I had such a discussion with him, and he said ‘right well, if humans will still exist in 200 years is also another question.’

“What is in 200 years is very difficult to say … The animals we grow today are in a very protected environment, for chicken or for pigs it is a very industrial environment, but it is a very protected environment. There is no pig anymore which needs air to run around in the winter.

“In 200 years perhaps crops will be planted in factories in a nutrition solution without soil, I don’t know. But what is more important is what is in 20 years or 40 years or so.”

Or, as Zvalo put it more succinctly: “There’s so many things at play that I wouldn’t worry too much about that at this point.”

Feature image courtesy of Dave McLear
Banner image courtesy of iamrenny