If global warming continues as predicted, the next 50 years could see the best growing conditions for corn and soybeans shift from Iowa and Illinois to Minnesota, the Dakotas and Canada.
Researchers at Pennsylvania State University looked at more than three decades of crop-yield data from the U.S. Department of Agriculture’s National Agricultural Statistics Service across 18 top-producing states. They concluded that ideal growing conditions for corn and soybeans were moving north.
“In general for corn and soybean and if precipitation does not change, the southern edge of the production area may see worsening growing conditions and the northern edge toward Canada will get a boost from moderate warming,” said Armen Kemanian, associate professor of production systems and modelling at the university’s College of Agricultural Sciences. “But precipitation must come timely. So, I will say the potential yield increases are conditional on precipitation.
“What seems more certain is that uncertainty will increase.”
Kemanian and his team evaluated crop yields and weather data and the study analyzed relationships between climate and corn, sorghum and soybean yields from 1980 to 2016. They used a data search system known as Random Forest, a form of machine learning that takes a dataset with thousands of observations and variables that document yields, temperatures in a growing season, precipitation, and other factors.
“In the analysis, we used air or atmospheric information, temperature, rainfall, humidity, and solar radiation,” he said. “We also separated the days that were too hot (extreme temperatures) as a separate variable. No soil information was used. The patterns of drought or other stresses are embedded in the analysis because we summarized the data for different phases of crop growth, such as near flowering, flowering, and grain filling.”
The coming changes will likely be gradually, allowing farmers to adapt and consider producing two crops in a year or a different mix of crops.
The study showed that yields have steadily increased, but there were threshold responses to high temperatures. Yields dropped sharply when maximum temperatures exceeded 29 C and 30 C for corn and soybeans, but showed a higher temperature tolerance for sorghum, whose yield decreased gradually as maximum temperatures exceeded 32.5 C.
“Corn yield maximizes roughly when it gets above 18 to 24 inches (457 to 609 millimetres) of precipitation,” said Kemanian. “Corn also showed a plateau response to temperature (and outstanding adaptation to relatively cool temperatures). An interesting result was the sharp sensitivity during flowering to dryness of the air.”
He said this means even if soils held enough water, corn reacted negatively to dryness in the air.
Sorghum, however, was not sensitive to dry air during flowering, likely because it is mostly closed pollinated. Sorghum also showed its well-known tolerance to high temperatures, and sensitivity to cooler conditions.
Soybeans appeared to benefit from warmer nights to some extent, but Kemanian said more research was necessary.
“The corn response to air humidity during flowering is worth a separate chapter in research,” said Kemanian. “In this work, we mapped out a potential migration of the ideal conditions for corn growth. But what about expected yields, with or without further technical advances? And what about soybean and sorghum?”
As to short term concerns, he said researchers hope to learn more about temperature swings and combined temperature and flooding stress.
“We already know what drought does to crops,” he said. “But swings in temperature are becoming more common.”
The team is also looking at whether there has been a shift in the number of crops a farmer can expect in a growing season. Kemanian said that, while the southern edge of Iowa may become less suitable for corn, it may be able to accommodate two crops per year in the future.
As prime corn and soybean production areas shift, there will be winners and losers.
“A lesser talked-about benefit that I think has already accrued is the increase in atmospheric carbon dioxide somewhat folded within technological improvements,” he said. “But from now on, increases in carbon dioxide will have decreasing benefits in terms of crop growth and the spikes in warming or swings in precipitation may take control (with) swings of warm and cold that on average trend upward.”
He said management will be more important than ever for farmers to adapt to changing conditions in their regions.