This study was carried out during the winter seasons of 2014-15 and 2015-16 at the Experimental Farm of Environmental Agricultural Sciences Faculty, Arish University, North Sinai Governorate, Egypt. The main effects and their interactions of four different nitrogen levels (0, 50, 75 and or Kg/fed) and four foliar application rates of potassium silicate spray (0, 4, 6 or 8 cm³/L) on growth, yield component and chemical content of seeds (nitrogen, phosphorus, and potassium), and fresh leaves content of chlorophyll a and b as well as seed content of fixed oil of black cumin (Nigella sativa) were investigated under sandy soil conditions. A split plot design was used where nitrogen levels were randomly arranged in main plots and the potassium silicate spray rates were randomly distributed in the sub plots, Drip irrigation was used. Distance between lines was 50 cm and between plants in the same row was 30 cm (28000 plant per fed). The obtained results obviously showed that the highest value of plant height, number of branches/plant, fresh and dry weights of herb, number of capsules for each plant, number of seeds/capsule, seed yield, weight of 1000 seeds, seed content of N, P, K, leaves chlorophyll content (a and b) and seed fixed oil percentage were increased as N application level increased up to 100 kg N/fed alone or 8 ml/L potassium silicate spray alone. The interaction results indicated that the highest value of all previous traits was recorded with plants fertilized with 100 kg N/fedwith 8 ml/L potassium silicate as foliar spray.