Low soil organic matter is a prevalent problem in soils with semi-desert climates, which seems to have effects on the efficiency of the utilized chemical fertilizers. The purpose of this experiment was to evaluate the interaction between farmyard manure (FYM0=0, FYM10=10, and FYM20=20 t ha-1) and nitrogen fertilizer (N0=0, N40= 40 and N80=80 kg ha-1) on growth ad seed production of safflower in the west of Iran. Results showed that the application of nitrogen at all levels of animal manure increased the height of the plant. The effect of using small amounts of nitrogen (40) was more evident in the conditions of application of animal manure. The application of FYM10+N80 increased the number of lateral branches by about 56%. With the increase in nitrogen consumption, the chlorophyll content in the leaves increased linearly. The increasing effect of applying FYM20 on chlorophyll content was similar to the application of 40 kg of nitrogen and improved the chlorophyll content by about 26%. Canopy width increased by 80% with the utilization of FYM20+N80 compared to the control condition (FYM0+N0). Application of FYM10 and FYM20 increased capitulum diameter by canopy by 40% and 54%, respectively. Altogether, the best safflower performance was achieved under the conditions of using FYM20+N80, which improved the yield by 439 kg ha-1 over control. The use of FYM increased the positive effect of nitrogen on leaf chlorophyll, canopy width, and capitulum number and ultimately improved seed yield. Improving soil organic matter is one of the necessities to increase the efficiency of nitrogenous fertilizers in semi-arid areas.
