Nitrogen dynamics during the seed-filling period in safflower under dryland Mediterranean conditions

Precise knowledge of safflower (Carthamus tinctorius L.) nitrogen (N) dynamics is essential to optimize crop nutrition and minimize environmental impacts of fertilizers. Two-year field experiments were conducted to evaluate the influence of N rates (0, 100 and 200 kg ha−1) and genotype (hybrids vs. open pollinated variety) on N uptake, distribution, remobilization and use, and to quantify the relative contribution of different plant organs as N-providers to seed in dryland Mediterranean safflower. The rate of 100 kg N ha−1 was adequate to maximize N content at anthesis and N use efficiency. Early N uptake was a key physiological process that largely determined the N dynamics during the achene-filling period. Enhanced N content at anthesis improved N remobilization from vegetative parts to achenes, with capitulum vegetative components (including bracts) contributing to N remobilization, on average, more (69%) than leaf plus stems (31%). The N remobilization efficiency ranged between 56 and 63%. High early N accumulation (> 158 kg N ha−1) and low sink N (< 113 kg N ha−1) resulted in N losses from plants during the post-anthesis period. Nitrogen application had no influence on the N harvest index or the efficiency of biomass production. Selection for improved N utilization efficiency would theoretically penalize achene protein content due to the negative correlation between these parameters. Safflower produced up to 32 kg achene yield per unit of N taken up. The inclusion of safflower in the rotation system of winter cereals in semiarid Mediterranean environments, apart from the diversification of cropping systems might keep the overall N utilization efficiency unchanged.