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Title: MODELLING CO2 EFFECTS ON WHEAT WITH VARYING NITROGEN SUPPLIES

Author
item JAMIESON, P - N.Z. INST FOR CROP & FOOD
item BERNTSEN, J - DANISH INST OF AGR SCI
item EWERT, F - DEPT OF AGR SCI DENMARK
item Kimball, Bruce
item OLESEN, J - DANISH INST OF AGRI SCI
item Pinter Jr, Paul
item PORTER, J - DEPT OF AGRI SCI DENMARK
item SEMENOV, M - DEPT OF AGR SCI UK

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2000
Publication Date: 11/15/2000
Citation: Jamieson, P.D., Berntsen, J., Ewert, F., Kimball, B.A., Olesen, J.E., Pinter Jr, P.J., Porter, J.R., Semenov, M.A. 2000. Modelling co2 effects on wheat with varying nitrogen supplies. Agriculture Ecosystems and the Environment. 82:27-34

Interpretive Summary: The CO2 concentration in the atmosphere is increasing and expected to double near the end of the next century. The elevated levels of CO2 affect plant photosynthesis and also cause a partial closure of the stomata in plant leaves through which the plant exchanges CO2 and water vapor with the atmosphere. The magnitude of both effects and the extent to which they change growth, yield, and water requirements of crops is likely to be influenced by other environmental factors such as soil nitrogen supply. In order to predict the effect of elevated CO2 on future crop production and to aid in developing improved management strategies, crop growth simulation models are being developed. This paper reports a successful test of three such models (called Sirius 99, AFRCWHEAT2, and FASSET), comparing model predictions against the results of an experiment in which open-field-grown wheat was exposed to elevated levels of CO2 using free-air CO2-enrichment (FACE) technology at ample and limited levels of soil nitrogen. Most model results were acceptably close to observed values, predicting for example, that at CO2 concentrations of about 550 ppm, such as expected near the middle of the next century, should cause wheat grain yield to increase about 18% at ample nitrogen but only 11% at low soil fertility. This work will benefit both future growers and consumers of wheat and wheat products.

Technical Abstract: The predictions of three one-day-time-step wheat simulation models were tested against data from experiments in which the amount of applied N and the atmospheric CO2 concentration were both varied. All three models predicted, both in absolute terms and in the magnitude of responses, very similar effects of the variations on green area index (GAI), shoot and grain biomass accumulations, and shoot and grain biomass yield. Analysis with the models showed that CO2 effects were expressed through effects at the level of light use efficiency (LUE) at the unit green area level, whereas N effects were expressed at the level of the canopy by causing variations in GAI.