With climate change expected to only worsen, might there be some way rice farmers can take advantage?
During a recent University of Arkansas-sponsored webinar (http://bit.ly/2OQd2yg), Lewis Ziska said it’s time for researchers to answer that question. A plant physiologist with the USDA’s Agricultural Research Service in Beltsville, Md., Ziska carries an impressive list of credentials. His most recent book is “Agriculture, Climate Change and Food Security in the 21st Century: Our Daily Bread.”
First, the bad news.
- Rising temperatures can increase floral sterility, and high nighttime temperatures may increase respiration. Can that be exacerbated by more CO2? “Potentially, but the overall bottom line is it’s going to negatively impact rice yields.”
- Water is essential to rice. Too little and too much may become the norm in the (coming extremes). “Energy use in terms of either pumping water up or how you’re going to get the water is going to have an impact.”
- Warmer temperatures can affect chalkiness and export quality. That comes at a cost.
- Recent and projected levels of CO2 are likely to reduce or alter nutritional rice quality. “What does that mean in terms of impacts on markets and health? Those are question we’re still trying to address.”
Potential good news?
So what’s the potential good news? First, Ziska said to look at opportunity.
“CO2 is a resource. So, can it be exploited as a means to increase yield?
“The first response I always get is ‘Wait, breeders are already doing this.’ No, they’re not. We can’t find any active breeding program that’s trying to actively select for CO2-responsive lines of rice — or, for that matter, CO2-responsive lines of wheat, barley, oats or anything. You can’t assume that just by happenstance you’re going to be selecting for lines that are CO2-responsive.”
Ziska and colleagues looked at oat cultivars and release dates — from the 1920s (when CO2 concentration was about 300 parts per million) and the 1990s (CO2 concentration of about 380) — at seven locations around the world.
“If breeders were, sort of de facto, selecting for the most CO2-responsive cultivars, those released in the 1990s should show a much stronger response to the change in CO2. What we found was that when you go to 300 to 400 parts per million, or 300 to 500 (the near-term future changes), none of the new cultivars did much. It was only the older cultivars that showed a stronger response.
“One of the things we found, which was quite interesting, is when you look at variables — it doesn’t matter what the variable is — and the equality of variance, there’s much more genetic and phenotypic diversity in the old cultivars.”
The new cultivars are essentially the same, said Ziska, “and I understand that: you want less variation as you go to more and more mechanized farming. But that variation, that genetic difference, I think, will be key in being able to respond to the rise in CO2.
“We have all of this genetic diversity ‘lying around.’ Can we exploit it? Use it to optimize this additional resource being added to the atmosphere as we speak? I think the answer is yes.”
Ziska asked Dr. Bobby Coats, University of Arkansas Professor, Department of Agricultural Economics and Agribusiness, to Google “CO2 and marijuana” and to read the first link provided. Sure enough, Coats read “How to use CO2 to increase cannabis yields.”
It turns out, said Ziska, “I can go to the internet to find out where to get the CO2, how to apply it, what temperature to apply it, how much more yield I can get, what varieties respond to it, what the THC content is going to be. Now, I have to figure if a stoner can do this why can’t a rice grower? Why can’t we exploit this CO2 as a means to increase rice yields given that it’s already gone up by 30 percent and it’ll double by the end of the century?”
Management and ratoon rice
What about management?
Ziska focused not only on planting dates but ratoon rice. “This is a kind of management used in rice and sugarcane — a way to cut the plant, add a fertilizer and get a second crop. Sometimes it takes minimal preparation and the yield can be up to 50 percent of the main crop.”
But there’s a catch as growers need a longer growing season — at least 75 days after the main crop is harvested, plus warm temperatures.
“Is there an opportunity here? We analyzed five locations: Cameron Parish and Avoyelles Parish in Louisiana; Desha County and Mississippi County in Arkansas; and Cape Girardeau in Missouri. In Cameron Parish, it’s warm enough and the season is long enough that ratooning is constantly practiced there.”
But, Ziska pointed out, the variation between water vapor and CO2 means “as you move towards the poles, as you go up in latitude, the effect of climate change will be greater. … Can we practice ratoon now? If not now, how about in the future?”
When looking at the five locations from 1976 to 2016 and the length of a ratooning season, “it isn’t changing much in Cameron Parish, but the farther north I go, the growing season is getting longer. In fact, right now, it looks like the growing season is long enough in Mississippi County and Cape Girardeau.”
Looking at a chart showing DD50 data, in 1976, “in Avoyelles Parish it wasn’t warm enough to ratoon but now it is. In fact, it’s warm enough and the growing season is long enough that if I were an Extension agent I’d go to those growing rice in the parish and say, ‘Yeah, maybe you should think about ratooning.’”
Desha and Mississippi counties “aren’t quite there yet. … But in Desha County, ratooning is something you could probably do routinely by the middle of the current century. And by the end of the century, depending on how quickly the climate warms, you might even be able to do it in Cape Girardeau.”
There are caveats, of course.
“Among them: high nighttime temperatures will still be important; the response of ratooning will also depend on cultivars; and water and energy (fertilizer) will still be key.”