Agronomy Journal • Volume 111, Issue 2 • 2019 1 M ost of oilseed production worldwide is dominated by soybean ( Glycine max L. [Merr.]), rapeseed (Brassica napus L.), sunfower (Helianthus annuus L.) and cotton ( Gossypium hirsutum L.). Tese major crops are sensitive to climate and soil conditions and some require large amounts of fertilizers to produce acceptable yields. Relying on few crops also contributes to less diversifcation of agricultural land use. Te use of more sustainable oil crops that require less inputs, ofers environmental and agronomic benefts to ensure product stability in terms of climate change with respect to bio- diversity and efcient use of agricultural lands but also may have lower oil yield potential (Elfadl et al., 2009). Recently, research on new oilseed species such as Crambe abyssinica (Zanetti et al., 2013), niger ( Guizotia abyssinica Cass.) (Solomon and Zewdu, 2008), cuphea ( Cuphea viscosissima Jacq. × C. lanceolata W.T. Aiton, PSR23) (Berti et al., 2008) calendula ( Calendula ofci- nalis L.) (Johnson and Gesch, 2013) and camelina (Mohammed et al., 2017) as potential sources of oil crops has increased. Blessed thistle is an annual plant belonging to the Asteraceae family and is widely spread from Asia Minor to Caucasus, includ- ing Iran, Afghanistan, Syria and Mediterranean Europe, and appears promising as an oil crop for cultivation in arid and warm climate regions (Horn et al., 2015). It is tolerant to poor nutrient soils and dryland areas, as it is typically found in marginal lands that are not suited for other crops. Approximately 3 to 6 Mg ha –1 of dried aerial biomass and 300 to 600 kg ha –1 seed yield can be expected in sunny and warm locations that have calcareous loamy sand soils with sufcient water supply (Horn et al., 2015). However, higher seed yields of 1.3 Mg ha –1 (Von Regel, 1940) and 2 Mg ha –1 were recorded for blessed thistle grown under medium quality soils, that is, diluvial and loess sites (soil value index around 50) in Germany (Horn et al., 2015). Blessed thistle seeds contain 240 to 280 g kg –1 oil, which are primarily unsatu- rated linoleic and oleic fatty acids like those of sunfower and saf- fower ( Carthamus tinctorius L.) oils (Roth and Kormann, 2000). According to Horn et al. (2015), blessed thistle can be cultivated as an oil crop in low input farming production systems, due to its desirable characteristics of oil and grain yield. Tus, blessed thistle has a potential to be a promising industrial crop in low yielding soils and low input conditions. In addition, the oilcake obtained Seed and Biomass Yield Responses of Blessed Thistle to Nitrogen and Density M. Ghiasy-Oskoee, M. AghaAlikhani,* A. Mokhtassi-Bidgoli, F. Sefdkon, and M. Ayyari, Published in Agron. J. 111:1–11 (2019) doi:10.2134/agronj2018.05.0323 Copyright © 2019 by the American Society of Agronomy 5585 Guilford Road, Madison, WI 53711 USA All rights reserved ABSTRACT Developing alternative oilseed crops with acceptable seed yield and biomass production in low-yielding environments could be a part of sustainable agriculture management strategies. Field experiments were conducted in a semiarid region of Iran in 2013 and 2014 to determine the efects of N fertilizer rates and plant densities on growth, seed yield and quality of blessed thistle ( Cnicus benedictus L.) under low yielding conditions. Randomized complete-block design with factorial arrangement of treatments was used in three replicates. Treatments consisted of four N rates (0, 50, 100, and 150 kg N ha –1 ) combined with fve plant densities (5, 10, 15, 20, and 25 plants m –2 ). According to quadratic functions, the maximum seed yield (913 kg ha –1 ) was achieved with 122 kg N ha –1 and 16 plants m –2 . Although the seed oil content decreased with increasing N rates, increased seed yield partially compensated for the reduction in oil con- tent. Higher seed protein was obtained from low plant densities (5–10 plants m –2 ) and high N rates (100–150 kg N ha –1 ). Nitro- gen harvest index (NHI) decreased by 30 to 40% as a result of increased plant density across all N rates. Plant density and N did not afect seed fatty acid profles, even though N rate by year interaction afected the profle. Linoleic acid was the predomi- nant fatty acid comprising 62.5 to 66.2% of the total fatty acids. Te study demonstrates that blessed thistle could be a promis- ing oil crop for cultivation in low yielding soils, although breed- ing work is needed to enhance its prospects as a viable oil crop. M. Ghiasy-Oskoee, M. AghaAlikhani, and A. Mokhtassi-Bidgoli, Dep. of Agronomy, Faculty of Agriculture, Tarbiat Modares Univ., PO Box 14115-336, Tehran, Iran; F. Sefdkon, Research Institute of Forests and Rangelands, PO Box 13185-116, Tehran, Iran; M. Ayyari, Dep. of Horticultural Science, Tarbiat Modares Univ., PO Box 14115-336, Tehran, Iran. Received 14 May 2018. Accepted 12 Sept. 2018. *Corresponding author (maghaalikhani@modares.ac.ir). Abbreviation: NHI, nitrogen harvest index. Core Ideas • Tis is the frst report of blessed thistle response to nitrogen and plant density. • Optimizing nitrogen and density improved quality and quantity of blessed thistle seed. • Under low yielding conditions, the actual yield of blessed thistle is ac- ceptable. • Blessed thistle is rich in polyunsaturated fatty acids such as linoleic acid. CRop ECology And phySIology Published online January 4, 2019