September 23, 2011

Corn (i.e., CO2RN) v. Drought

Filed under: Adaptation, Plants

Let’s think about the future of corn in the United States; no one would ever doubt the importance of this major agricultural crop throughout the world. Corn is used for everything from a food staple for humans and animals to a substitute for fossil-fuel based energy (well, not a very good substitute as things have worked out). The global warming crusade insists that droughts in the future will become more frequent and/or more severe thereby crushing corn production in the central United States. They eagerly point to reports from the Intergovernmental Panel on Climate Change (IPCC) where they conclude that “areas affected by droughts” have increased and will increase and that it is “likely” that there has been a human contribution to the observed pattern. We have covered this topic repeatedly here at World Climate Report, and we certainly encourage you to explore what we found on this highly controversial subject.

A recent article in Agricultural and Forest Meteorology gives us a clearer picture of the nature of drought in the corn belt of the United States. The article was produced by six scientists with tree-ring labs at the University of Missouri, the University of Arizona, and the Lamont-Doherty Earth Observatory in New York. The Stambaugh et al. team acknowledges that “This research was supported by a grant from the National Science Foundation. Previous support was received from the University of Missouri Center for Agroforestry and the USDA Forest Service, Northern Research Station.” The goal of the team was to create a record of drought for the corn belt extending back 1,000+ years nearly doubling the length of record currently available.

The group collected tree-ring data from live and subfossil oak trees from northern Missouri and southern Iowa. As is the custom in this type of research, they related the tree rings to climate variables over the period of historical climate records (starting in 1895). They found that the trees grew large rings in periods with cool and wet summers and small rings with conditions were warm and dry. They were able to relatively accurately reconstruct the Palmer Hydrological Drought Index from 1895 to near present for their study area (Figure 1).


Figure 1. Time series of actual (bold black line) and reconstructed (thin grey and black lines) summer season (JJA) Palmer Hydrologic Drought Index (PHDI), 1895–2004 for the region of northwest Missouri and southwest Iowa. The calibration period is shown with grey background (from Stambaugh et al., 2011).

The climate records do not go back before 1895, but the tree rings extend back to AD 912. With some statistical wizardry, Stambaugh et al. were able to generate a time series of drought for over 1,000 years (Figure 2).


Figure 2. Low frequency reconstructions of Palmer Hydrologic Drought Index (PHDI) for the period 993–2004. Annual reconstructed PHDI (grey) and a 15-yr weighted moving average are shown (from Stambaugh et al., 2011).

In describing their fundamental results, the authors state “Separate reconstructions tailored to emphasize high-frequency and low-frequency variations indicate that drought conditions over the period of instrumental records (since 1895) do not exhibit the full range of variability, severity, or duration of droughts during the last millennium. For example, three years in the last millennium were drier than 1934, a classic Dust-Bowl year and the driest year of the instrumental period. Thirteen decadal to multidecadal droughts (i.e., ≥10 years) occurred during the last millennium – the longest lasting sixty-one years and centered on the late twelfth century.” We also note that no trend exists toward increasing drought during the most recent century when greenhouse gas concentrations increased substantially!

So from this study we definitely learn that droughts in the region naturally occur with relative frequency, and undoubtedly will continue to do so in the future—no need to invoke large-scale human alteration to the atmospheric composition.

In the same volume of Agricultural and Forest Meteorology, a second article appears with fabulous news for corn growers the world over. The article was written by five scientists with the US Department of Agriculture and the University of Maryland. The Chun et al. team notes early in the piece that “There have been many studies on the interaction of CO2 and water on plant growth. Under elevated CO2, less water is used to produce each unit of dry matter by reducing stomatal conductance.” Under elevated CO2 conditions, plants will simply use and need much less water to achieve the same outcome – yet another benefit of increased CO2 concentrations.

But what about corn? To find out, Chun et al. grew corn in chambers with CO2 concentrations at either 400 ppm or 800 ppm, and they varied the amount of water the plants would receive. At the end of the experiment, they concluded “Approximately 13–20% and 35% less water was used under the elevated CO2 conditions than under the ambient CO2 conditions, for the water stressed conditions and for the well-watered conditions, respectively. These results suggest that under increased CO2 concentrations as generally predicted in the future, less water will be required for corn plants than at present.” Their final two sentences are priceless as they tell us that the higher water use efficiency in the elevated CO2 chambers “indicates that less water was used under the elevated CO2 condition to produce similar biomass as that in the ambient CO2 treatment. This study suggests that less water will be required under high-CO2 environment in the future than at present.”

We realize that our future will see droughts in the corn belt – whether these future droughts are related to human activities can be debated forever. The good news is that elevated CO2 will give corn in the future a defense against any droughts that occur – corn will simply require much less water given the biological benefits associated with extra levels of CO2. The goodness will be felt the world over, not just in America’s corn belt.

References:

Chun, J.A., Q. Wang, D. Timlin, D. Fleisher, and V.R. Reddy. 2011. Effect of elevated carbon dioxide and water stress on gas exchange and water use efficiency in corn. Agricultural and Forest Meteorology, 151, 378–384.

Stambaugh, M.C., R.P. Guyette, E.R. McMurry, E.R. Cook, D.M. Meko, and A.R. Lupo. 2011. Drought duration and frequency in the U.S. Corn Belt during the last millennium (AD 992–2004). Agricultural and Forest Meteorology, 151, 154–162.




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