Response of Japanese bunching onion (Allium fistulosum L.) to nitrogen fertilization

Abstract. New pseudostem cultivars of Japanese bunching onion may be a good alterna-tive to common bulb onion grown for bunches in early spring season. There is still limited knowledge upon the requirement of this vegetable species for nitrogen fertilization. In two factorial field experiment, calcium nitrate, ammonium nitrate and Entec 26 – nitrogen mineral fertilizer containing DMPP nitrification inhibitor used as the source of N and ap-plied at the rates of 75, 150 and 225 kg·ha-1 were compared. Seed propagated transplants produced in the greenhouse were planted in early April and harvested after 10 weeks of cultivation in the open field. The yield and nutritional value of edible parts expressed by the content of dry matter, vitamin C, total chlorophyll, carotenoids, volatile oils, total N, NO3 – N, P K Ca and Mg were estimated. Results of the study proved that all tested fertil-izers were equally valuable sources of nitrogen for Japanese bunching onion. The use of Entec 26 was associated with higher amounts of total chlorophyll and carotenoids in edi-ble part of plants if compared to commonly recommended ammonium nitrate and similar to calcium nitrate. The other important advantage of this fertilizer was a substantial de-cline of nitrates content. The increment of preplant nitrogen rate from 75 to 150 and 225 kg·ha-1 did not affect the crop yield and significantly enhanced the nitrates accumula-tion in plants at harvest. Key words: nitrogen form, N rate, yield, nutritional crop value