Climate change, nitrogen and yield response of wheat crops

The response of crop growth and yield to enhanced CO2 in the biosphere is known to depend on climatic conditions and is difficult to quantify due to complexity of the physiological and environmental processes involved. In multi-site and -years wheat experiments average measured yield increase due to CO2-doubling was approx. 30% (SD 22%). Average yield increases by simulation models amounted to approx. 25 and 40%, respectively. The models predicted lower variation among sites and years than was measured. A considerable part of the variation in yield was not related to direct effects of light intensity, temperature, and CO2; it is supposed that specific interactions cause this residual variation. Higher temperatures during the vegetative phase enhance the effect of elevated CO2 levels; however, the duration of ear development is shortened and the number of grains reduced. Temperature stress during anthesis turned out to be another factor influencing the number of grains per ear, and therefore the sink capacity. It is hypothesized, that the additive effect of elevated CO2 concentrations and predicted temperature change will result in a 25 to 30% increase of the current potential yield level, if new genotypes of wheat become available that are better adapted to the warmer conditions; especially, higher temperatures should not shorten the duration of ear development and the duration of post-anthesis crop growth. Furthermore, the availability and utilization of nitrogen and other nutrients have to be improved to meet the demands of a high-yielding crop and quality standards.