Climate change impact on crops

For far longer than the current hoorah about global warming, climate change, and cap and trade, scientists have been studying the potential impact of the various scenarios on agriculture — particularly as related to increased concentrations of carbon dioxide (CO₂).

As research and data have multiplied, researchers are getting a clearer picture of how increases in CO₂ have already affected plants and what may occur as those levels see potentially more dramatic increases over the next 40 years.

It has long been known that soybeans, wheat, and other crops grow more when CO₂ levels are elevated. But the plants can also be damaged and stunted by higher concentrations of ground-level ozone from vehicles and industrial pollutants.

Levels of both gases are increasing; the Intergovermental Panel on Climate Change has estimated that current CO₂ levels of 380 parts per million could increase 1.5 times by 2050 and that the present 50-55 parts per billion of daytime summer-level ozone could rise 20 percent during the period.

Agricultural Research Service scientists at Raleigh, N.C., and Urbana, Ill., are studying how these increases will affect two of the world’s most widely-planted crops, wheat and soybeans, and are conducting a five-year project to determine whether no-till cropping will improve soil quality and sequester carbon when levels of these gases rise.

In open-top chambers that can be flooded with high levels of CO₂ or ozone, or a combination, and to which post-harvest residues are added, the Raleigh researchers can mimic conditions of no-till systems. Specific isotope markers in the CO₂ allow them to track it through the plant cycle and into the soil.

After three years, preliminary results show a trend for higher levels of soil carbon in the chambers with elevated CO₂, but not in chambers with elevated ozone. Higher CO₂ levels have reduced protein levels in wheat flour by 7 percent to 11 percent, but have had no effect on soybean seed protein.

The Urbana researchers, using a Soybean Free Air Concentration Enrichment system to measure effects of increased CO₂ and ozone under open field conditions, have found that CO₂ levels predicted for 2050 could increase soybean yields by about 12 percent — about half of what earlier studies had estimated.

But, the predicted 2050 levels of ozone were “quite harmful,” causing yield reductions of up to 20 percent. That impact was partially reduced by the higher CO₂ levels. The study indicated, however, that present-day ozone levels are already suppressing soybean yields as much as 15 percent.

These testing methods, according to USDA’s Agricultural Research magazine, give greater confidence in scientists’ understanding of how plants respond in the real world, and the impact of these gases on crop yields.

Further studies will look at how drought, higher temperatures, soil microbes, carbon storage, and other factors can affect plant growth and yield under higher concentrations of CO₂ and ozone.

e-mail: hbrandon@farmpress.com