Safflower assimilate remobilization, yield, and oil content in response to nitrogen availability, sowing time, and genotype

In rainfed cropping systems, crops are typically subjected to terminal stresses, which diminish the assimilation process. Information regarding safflower (Carthamus tinctorius L.) dry matter dynamics during the seed-filling period and its association with yield-forming components is lacking. Field experiments over two years were conducted to assess the influence of nitrogen (N) fertilization levels (0, 100 and 200 kg ha-1), sowing time (autumn vs. spring) and genotype (two hybrids and an open-pollinated variety) on growth, assimilate remobilization, achene- and oil yield of safflower, and to identify early crop attributes as predictors of yield. Greater than 100 kg N ha-1 were required to optimize achene yield ( 4 Mg ha-1). On average, N promoted early growth and increased capitula and achenes per unit area compared with the non-fertilized control. The higher the availability of assimilates at the source, the greater their remobilization to sink (r = 0.823, P < 0.01), which was in turn associated with achene yield (r = 0.53, P < 0.05), provided that a critical sink size (number of achenes) had been established during flowering. Dry matter remobilization efficiency ranged between 29.5 % and 39.1 %. Under favorable conditions, hybrids exhibited higher achene- and oil yield than the variety. Oil yield was almost entirely (98 %) determined by achene yield. Autumn sowing increased the average achene yield (28 %) and oil production (20 %) compared with spring sowing. Harvest index (HI) ranged from 0.17 to 0.35 and was associated with achene yield (r = 0.703, P < 0.01). Achene yield could be predicted by measurements of dry matter at anthesis, while the estimation of biomass from plant height measurements was not applicable in safflower. Findings highlight the value of properly designed cropping systems for safflower production based on environmental variables and crop management practices, which can support high yields and improve N management.