Enhancing safflower traits: a comparative study of fertilizer treatments on growth, yield, and oil quality

Efficient nutrient management plays a key role in improving safflower (Carthamus tinctorius L.) yield and oil quality. This study examined the effects of conventional and integrated fertilization strategies on safflower growth, yield components, oil yield, and fatty acid composition over two growing seasons (2021–2023) in Tabriz, Iran. A randomized complete block design included six treatments: an unfertilized control, 100% urea (UR), foliar NPK, and the biofertilizer PhosphoBARVAR-2 (PSB) combined with 100% UR, 50% UR, or NPK. All fertilized treatments performed significantly better than the control in most parameters across both years. The chlorophyll index increased by up to 31.12% under PSB+100% UR in Year 2 and by 38.43% under NPK in Year 1, showing improved photosynthetic activity. Seed yield rose markedly, reaching 296.18 g/m2 with NPK in Year 1 and 290.78 g/m2 with PSB+NPK in Year 2. Oil yield also increased sharply by 66.2% with NPK in Year 1 and 58.87% with PSB+NPK in Year 2 compared to the control. The highest oil content (37.7%) was recorded with PSB+50% UR. Integrated nutrient management (INM) treatments, i.e., PSB+100% UR, PSB+50% UR, and PSB+NPK, proved highly effective. They often matched or exceeded the performance of full conventional fertilization, particularly PSB+50% UR. These treatments also enhanced oil composition. PSB+100% UR and PSB+50% UR produced the highest linoleic acid (C18:2) levels (up to 73.55%), while PSB+NPK maximized the amount of oleic acid (C18:1) to 16.05% and total unsaturated fatty acids to 83.57%. Cluster analysis clearly separated INM treatments, highlighting their distinct impact. Overall, integrating PSB with urea or NPK fertilizers, even at reduced rates, offers a promising and sustainable approach to improve both safflower yield and oil quality.