MODELING THE EFFECTS OF CLIMATIC-CHANGE AND GENETIC-MODIFICATION ON NITROGEN USE BY WHEAT

This paper considers how and the extent to which climate change and th e balance of nitrogen between crops and soils may interact and how the ability to modify genetically specific crop attributes might affect t he overall nitrogen balance of the crop-soil system. The possible effe cts of each change have been assessed using the AFRCWHEAT2 crop model for wheat. Model output pointed to a decrease in harvest index as a re sult of coincidental increases in CO2 level and temperature, and the i mportance of considering not only changes to average but also to the v ariability of environmental driving variables is illustrated. When mea n temperatures were raised the model predicted that more nitrate would be left in the soil at the end of the season but that raising CO2 lev el could counter this effect. Doubling the variability of temperature had a more complicated effect on the soil N balance with the mean amou nt of residual soil nitrate predicted to be at about the same level as for the baseline and with only a comparatively small change in its co efficient of variation. These results are interpreted in terms of a be ll-shaped response of mineralisation rate to temperature. Raising the value of the maximum N concentration (N-max) in the shoots increased t he amount of NO3-N extracted from the soil. However, the overall effec ts were not simply proportional to the increase in N-max because the c rop could also become limited by the supply of N from the soil.