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Testing CERES-Wheat with Free-Air Carbon Dioxide Enrichment (FACE) Experiment Data: CO₂ and Water Interactions

Columbia Univ. Ctr. for Climate Systems Research and NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025

Bruce A. Kimball, Paul J. Pinter, Jr., Gerald W. Wall, Douglas J. Hunsaker, Robert L. LaMorte and Richard L. Garcia

USDA-ARS, U.S. Water Conservation Lab., 4331 E. Broadway Rd., Phoenix, AZ 85040

^* Corresponding author (franci{at}giss.nasa.gov).

Dynamic crop-growth models are used to project the effects of rising atmospheric CO₂ concentration and associated climate change on crop yields. Such model predictions are largely untested in the field, for lack of experimental data. We tested the CERES-Wheat model, modified to include leaf-level photosynthesis response to elevated CO₂, using field data from 2 yr of Free-Air Carbon Dioxide Enrichment (FACE) experiments with spring wheat (Triticum aestivum L. cv. Yecora Rojo) in Maricopa, AZ. Two irrigation treatments (well-watered, WW; water-deficit stressed, WS) and two atmospheric CO₂ concentrations (ambient, 350 (µmol mol^–1; elevated, 550 (µmol mol^–1) were simulated. The model was evaluated using measurements of crop phenology, aboveground dry matter (DM) production, grain yield, and evapotranspiration (ET). Model calculations of crop phenology were within 2 to 3 d of observed values under WW, ambient CO₂ conditions in both years. The model did not simulate the accelerated crop phenology (5-8 d at physiological maturity) observed in the WW and elevated CO₂ treatments, indicating the need to include effects of increased stomatal resistance on canopy temperature. Simulations of DM and grain yield were within 10% of measured values, except for a tendency to overcalculate DM response to CO₂ by 10 to 15% in Year 1 for WS treatments. The model undercalculated cumulative ET under WW conditions by 15%; model sensitivity analyses suggest that simulation of potential evapotranspiration (PET) was too low for this arid site. The model reproduced measured dynamics of CO₂-water interactions. Simulated reductions in water loss due to elevated CO₂ were about 4%, in agreement with measurements. The model simulated larger increases in DM production and yield due to elevated CO₂ under WS than under WW conditions. In Year 1, simulated crop response to CO₂ was 2% larger (measured: 3%) under WS than under WW conditions; in Year 2, it was 11% larger (measured: 9%). The ability to simulate CO₂-water interactions, though it needs to be further evaluated with additional experimental datasets, is an important attribute of models used to project crop yields under elevated CO₂ and climate change.

Received for publication October 16, 1997.

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