By Kay Ledbetter
Texas A&M AgriLife
Cotton production in the Texas High Plains can survive expected climate changes, especially if water is available to compensate for higher temperatures, and increased atmospheric carbon dioxide concentrations can mitigate yield loss in dry years. That was the conclusion of a Texas A&M AgriLife Research study.
“We believe cotton production in the Texas High Plains can withstand the effects of future climate variability under moderate increases in carbon dioxide levels,” says Dr. Srinivasulu Ale, AgriLife Research geospatial hydrologist. “Our study shows that maintaining high yield levels will require greater than 80 percent of current irrigation levels, even when accounting for increased carbon dioxide levels.”
Joining Ale on the study were Dr. Pradip Adhikari, AgriLife Research post-doctoral research associate, and Jim Bordovsky, AgriLife Research senior research scientist and agricultural engineer, among others.
Dwindling groundwater resources in the underlying Ogallala Aquifer, future climate variability and frequent occurrences of droughts are major concerns for cotton production in this region, Ale said. Climate change can affect agriculture both positively and negatively. Increases in carbon dioxide concentration due to climate change are positive for plant growth. Previous research reported elevated carbon dioxide levels could enhance crop growth and yield by increasing photosynthesis and decreasing stomatal conductance. As a result, transpiration per unit leaf area is reduced and overall water-use efficiency is improved.
“This region is predicted to have warmer summers and reductions in annual precipitation in the future,” Ale says. “Such trends would necessitate larger groundwater withdrawals to meet higher evapotranspiration cotton needs and prevent yield loss.”
That is why it is important to begin assessing the impacts of climate change on cotton production now to enable the development and evaluation of irrigation strategies for efficient utilization of groundwater resources in this region in the future.
“Our study showed it may still be possible to produce cotton yields of 1,000 pounds of fiber per acre even under high-deficit – 60 percent – irrigation,” Ale says.
In this study, the CROPGRO-Cotton model was evaluated for the Texas High Plains region using 27 treatments of measured data from cotton water-use efficiency experiments conducted from 2010-2013.
The measured data came from Bordovsky’s work at the Texas A&M AgriLife Research Center at Halfway and the impacts of future climate variability and change on irrigated cotton yield were assessed at Halfway and four other locations. The future climate data used in this study was taken from research conducted by Dr. Naga Modala, also a co-author on the paper. The evaluated CROPGRO-Cotton module within the Cropping System Model was used to simulate the irrigated seed cotton yield under historic – 1971-2000, and future – 2041-2070 – climate scenarios projected by three climate models.
On average, when compared to historic yields, simulated future yields across the region decreased within a range of 4 to 17 percent due to the combined effect of the increase in temperature and decrease in rainfall when carbon dioxide concentration was assumed to remain at the current level of 380 parts per million under three climatic model scenarios.
When the carbon dioxide concentration was assumed to increase from 493 parts per million in year 2041 to 635 parts per million in 2070, the simulated irrigated yields increased within a range of 14 to 29 percent as compared to historic average yield. When irrigation was reduced by 40 percent, the average 2041-2070 yields under the constant carbon dioxide concentration and the increasing concentration scenario decreased by 37 percent and 39 percent, respectively.
In general, average seed cotton yields under changing carbon dioxide concentration were higher by 11 to 15 percent when compared to constant carbon dioxide concentration among different irrigation levels. This trend varied among wet, normal and dry years. The percentage change in average seed cotton yield due to changing carbon dioxide concentration ranged between -9 percent at a 60 percent irrigation level and 7 to 8 percent at 100 percent irrigation level for the wet and normal years. It changed 30 percent and 98 percent at the respective irrigation levels for the dry years.
“These results imply that cotton is sensitive to atmospheric carbon dioxide concentrations, especially in dry years,” Ale says.