Castor bean has a significant ability to regulate its yield components in response to the alteration in the plant population. The enhanced production of castor bean is possible mainly through maintaining optimum plant spacing and nitrogen (N) application. A two factor experiment, which included plant spacing (50, 75, 100 and 125 cm) and N levels (0, 60, 90 and 120 kg ha^-1) was conducted in Peshawar. Maximum plant height (194 cm), capsule plant^-1 (139), grain yield (1518 kg ha^-1), biological yield (9222 kg ha^-1), oil yield (701 kg ha^-1), nitrogen use efficiency (21.1 kg kg^-1) and agronomic efficiency (16.2 kg kg^-1) were obtained at plant spacing of 50 cm, while maximum branches plant^-1 (9), thousand grain weight (254 g) and capsule plant^-1 (58) were recorded in wider plant spacing of 125 cm. In case of nitrogen levels, 120 kg N ha^-1 resulted in taller plants (192 cm), higher number of branches plant^-1 (10), capsule plant^-1 (222), thousand grain weight (254 g) and biological yield (8753 kg ha^-1) of castor bean but application of 90 kg N ha^-1 resulted in maximum grain yield (1568 kg ha^-1), harvest index (20%), oil content (48.8%) and oil yield (766 kg ha^-1), while at 60 kg N ha^-1, the maximum nitrogen use efficiency (22.4) and agronomic efficiency (12.6) were recorded. Thus, plant spacing of 50 cm produced maximum seed and oil yields, nitrogen use efficiency and agronomic efficiency and application of nitrogen at the rate of 90 kg ha^-1 resulted in higher seed and oil yields.

Keywords: Plant spacing; Nitrogen levels; Yield; Oil content; AUE; NUE