Optimization of nitrogen rate and seed density for safflower (Carthamus tinctorius L.) production under low-input farming conditions in temperate climate

Field experiments under low-input farming conditions were conducted in South West Germany (lhinger Hof) and North Switzerland (Wil) in 2004 and 2005 aimed at optimizing nitrogen rate and seed density for the production of the newly introduced safflower (Carthamus tinctorius L.). The experiments were laid out in a four-replicated-split plot design with three nitrogen fertilizer rates (0, 40, 80 kg/ha) as main plots and cultivars (Sabina, Saffire, BS-62915) and seed densities (50, 100, 150 seeds/rn2) randomized in split plots. It was shown that many traits responded differentially across environments to rate of nitrogen and seed density. Application of 40 and 80 kg N/ha did not significantly affect most of the investigated traits. At Ihinger Hof, the total nitrogen fertilizer needed to maximize safflower yield was estimated to be 86 kg N/ha. At Wil, residual soil nitrogen alone resulted in satisfactory seed yield when safflower followed a crop fertilized at a commercial rate. The nitrogen rate × seed density interaction was only significant for seed yield and Alternaria leaf spot disease. Nitrogen rates provided significant increases in seed yield at high seed density compared to low seed density. Seed density did not reveal any significant variation in seed yield, oil content, and oil yield. On average, the low seed density produced substantially higher numbers of heads/plant and seeds/plant compared to medium and high densities. These results demonstrate the ability of safflower to use residual soil nitrogen efficiently and to compensate for low plant density.