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Title: Are we approaching a water ceiling to maize yields in the United States?

item DELUCIA, EVAN - University Of Illinois
item CHEN, SHILIU - University Of Illinois
item GUAN, KAIYU - University Of Illinois
item PENG, BIN - University Of Illinois
item LI, YAN - University Of Illinois
item GOMEZ-CASNOVAS, NURIA - University Of Illinois
item KANTOLA, ILSA - University Of Illinois
item Bernacchi, Carl
item LONG, STEPHEN - University Of Illinois
item ORT, DONALD - University Of Illinois

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2019
Publication Date: 6/18/2019
Citation: DeLucia, E., Chen, S., Guan, K., Peng, B., Li, Y., Gomez-Casnovas, N., Kantola, I.B., Bernacchi, C.J., Long, S.P., Ort, D.R. 2019. Are we approaching a water ceiling to maize yields in the United States?. Ecosphere. 10(6):e02773.

Interpretive Summary: The amount of water vapor in the atmosphere relative to maximum amount that it can hold at any given temperature (vapor pressure deficit; VPD) determines the rate of water loss by plants and soil (evapotranspiration; ET). As the atmosphere continues to warm, VPD will go up driving greater rates of water loss, even as the amount of rainfall remains constant. We estimate that because of higher ET in the future, maintaining current yields of maize will require a dramatic increase in irrigation, an increase in irrigation that will need to be even greater to meet the increasing demand for grain to produce food and fuel.

Technical Abstract: While annual precipitation in much of the US Corn Belt is likely to remain constant, atmospheric vapor pressure deficit (VPD), the driver of crop water loss (evapotranspiration; ET), is predicted to increase by 20% by mid-century as temperature increases. Without irrigation, it has been hypothesized that the increase in VPD will create a ceiling to future increases in yield. We calculated current and future growing season ET based on biomass, water use efficiency, and the amount of yield these levels of ET would support for maize production in the Midwest US. We assume that the production of more grain will necessitate a proportional increase in the production of biomass, with a corresponding increase in ET. Here we show that as VPD increases, maintaining current maize yields will require a large expansion of irrigation (367%) in areas currently supported by rain. The average yield for the region of 236 bushels / acre projected for 2050, assuming yield increases observed for the past 55 years continue, will not be possible with predicted increases in VPD, creating a water ceiling to yields. Substantial increases in maize yields and the production of high yielding grasses for bioenergy will require developing cultivars with greater water use efficiency, a trait that has not been a priority for breeders in the past.