The Brassica rapa var. japonica is a valuable plant, commonly cultivated in the Far East. It is still unknown vegetable crop in Poland. It is necessary to assess plant response to field conditions in Polish climatic zone before introducing this species to the large-scale production. The aim of the study was to evaluate the effect of growing date (transplants were planted out to the field in the middle and at the end of August – 1^st and 2^nd production term, respectively) and cultivar (Mibuna, Mizuna) on morphological parameters, yielding and chemical composition of the plants. Before planting out, transplants of Mibuna have been found to be larger than Mizuna, the differences in the contents of chemical components in these cultivars were statistically insignificant at this time (with the exception of dry matter). The transplants from a later production term were characterized by greater fresh weight and height, longer leaves, and lower content of dry matter, soluble sugars and carotenoids. Based on collected data regression equations were developed to predict the course of growth and development of Brassica rapa var. japonica during field vegetation with a precision of more than 94%. There were no statistical differences in yields among cultivars, while significant effect of growing date was observed. The total and commercial yield was higher by 3.34 and 3.77 t·ha^-1, respectively, in the 2^nd production term than in an earlier one. During harvests the content of chlorophylls, carotenoids and L-ascorbic acid was higher in the rosettes of Mibuna cultivar, while Mizuna had more dry matter and soluble sugars. Production of the plants from later plantings resulted in significantly increased soluble sugars content in the rosettes, but the reduction in dry matter and L-ascorbic acid was observed.

131-143