Nitrogen fertilization and sowing date as wheat climate change adaptation tools under Mediterranean conditions

In the current situation, climate change has substantially disturbed precipitation occurrence in the Mediterranean region, by increasing its variability and decreasing the total annual amount, which both negatively affect rainfed crop productivity. We hypothesize that a simple cost-effective method for enhancing crop adaptation to new climate conditions would consist of modifying the crop sowing date. Traditional nitrogen (N) fertilization rates could also be adjusted to the current situation given the interdependent water/N relation in plant nutrition. Based on this hypothesis, during a 4-year field experiment with bread wheat (Triticum aestivum L., var. Pistolo), the effects of three sowing dates (October, November, February) and three N fertilization rates (54 kg N ha⁻¹, 27 kg N ha⁻¹, 0 kg N ha⁻¹) on crop development, yield, grain quality, soil N content and N use efficiency were analyzed. The results showed that water scarcity was the predominant limiting factor, because it outweighed N deficiency with half-fertilized crops being as productive as fully fertilized treatments. Nevertheless, sowing date was the most influential factor, with up to a 30 % yield increase noted for the November-sown wheat compared to that sown in October, while delaying wheat sowing to February decreased crop yields. Grain protein content remained the same between the November- and October-sown crops, but increased in the February one crops. Optical sensor measurements showed that an optimal assessment of the current water/N nutritional status of crops can be achieved with these tools.