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Planting wheat earlier in the spring to avoid crop damage from ever-hotter summers may not keep harvests on pace with current levels.

That's a key finding from new research at Washington State University challenging assumptions that earlier planting could offset the effects of a warming climate. Researchers used computer modeling to show that moving crop plantings earlier in the season brings about other plant growth issues that could hinder productivity.

The findings are in Communications Earth & Environment.

"Over the years, a lot of studies addressing climate change in agriculture have talked in positive terms about earlier planting as a fix for increased heat," said Kirti Rajagopalan, an assistant professor in WSU's Department of Biological Systems Engineering. "We wanted to look at that more critically because it seemed very simplified. We thought the reality could be more nuanced, and that is reflected in our findings."

Rajagopalan and her graduate student, Supriya Savalkar, are the lead authors on the paper. They studied spring wheat across much of the northern U.S., working with other scientists, including wheat breeders, to analyze planting windows and temperatures in the various regions. The team used high-performance computing power to run simulations in every region.

Their data clearly showed that spring wheat could have less productivity than current levels even if the crop is fully grown before the height of summer temperatures.

"Yes, earlier planting has some benefits," Rajagopalan said. "But we wanted to make sure we haven't overemphasized those benefits compared to potential trade-offs."

Early planting can still, despite a changing climate, expose crops to less than ideal temperatures in other growth stages, which could limit growth.

"We looked at how the crops experience temperature ranges," said Savalkar, who will defend her Ph.D. dissertation in November. "You can reduce heat stress in some stages, but at the cost of exposing it to elevated heat or cold stress in other growth stages."

Another impact of earlier planting is a reduction in the planting window. The USDA provides current planting windows for crops by region, and spring wheat currently has a window of around 11 weeks. Earlier planting may shrink that window down to one to seven weeks, Savalkar said.

"Shrinking the planting window is a nightmare for farmers," Rajagopalan said. "It's already challenging for them to get all their crop in the ground; having less time would be much harder."

The study could have an impact on other facets of the agriculture industry, including wheat breeding. Mike Pumphrey, WSU's O.A. Vogel, Chair of Spring Wheat Breeding and Genetics and a co-author on the paper, said it shows a need for wheat varieties that mature earlier while still producing high yields.

"We had no idea what the results of this study would be because nobody has really looked in depth at the impact of early planting," said Pumphrey, a professor in WSU's Department of Crop and Soil Sciences.

"Wheat has been produced from average conditions for over 100 years. Now, conditions are changing so significantly in such a short period of time that it's hard to adjust."

The paper only covered spring wheat generally and did not look at specific varieties. It did include one finding that may be helpful for growers in Washington. The only region that showed the potential for similar crop productivity between early planting and normal planting was the Pacific Northwest.

"Other spring wheat regions face more heat or cold stress," Rajagopalan said. "Plants have a range of temperatures that work well for them, and most parts of the country are on the edges of those ranges. The Pacific Northwest has more leeway on that."

The paper does not say early planting is all negative, it only points out some of the potential risks. Rajagopalan and Savalkar both hope to see more work done to help growers keep producing crops in a changing environment.

"Earlier planting is something that should and will be considered," Savalkar said. "But there's a lot of work to be done to make sure farmers can continue, or even increase, their production."