ABSTRACT Field experiments were carried out on Kohlrabi (Brassica oleracea var. gongylodes) ‘Purple Vienna cv.’ at the Experimental Farm of the Faculty of Agriculture, Moshtohor, Benha University, Egypt, during the winter seasons of 2009 and 2010 under drip irrigation system. This study aimed to investigate the effect of organic manure and/or mineral N-fertilizer with or without biofertilizer inoculation on growth, yield and quality of kohlrabi knobs. Results show that using 50% mineral-N + 50% organic-N combined with biofertilizer, improved plant growth, yield and knob quality compared to other N-fertilizer systems. Inoculation of kohlrabi transplants with biofertilizer gave good results in this respect. Therefore, this treatment gave the best growth and increased total yield with the best knob quality as compared with uninoculated one. The highest content of nitrate in knobs (803.84 mg kg-1 DW) was recorded by using 100% mineral-N treatment (average in both seasons). Whereas, adding 100% organic-N recorded the lowest content of nitrate in knobs (387.75 mg kg-1 DW) average of both seasons. It is worthy to mention that nitrate concentration in tested kohlrabi knobs is still in the safe border for human consumption. Finally, kohlrabi plant contains good amounts of antioxidants substances positioned to be at the forefront of salad plants.