engleski

The effect of nitrogen fertilization on nitrate accumulation, and the content of minerals and glucosinolates in broccoli cultivars

Variable content of bioactive compounds and minerals is the main problem in the production of vegetables as functional food, due to genetic, abiotic and agronomic factors (especially fertilization), which may affect the nutritional and medicinal value of vegetables. In order to achieve the higher yield, producers often apply large amounts of nitrogen fertilizer, which can result in the accumulation of nitrate, reducing the quality of broccoli. There are no results about the content of bioactive compounds and minerals in broccoli inflorescence grown on the principles of Good Agricultural Practices in Croatia. Therefore, the research has been set up to determine the effect of nitrogen fertilization on the content of glucosinolates, some minerals (potassium, calcium and nitrogen) and nitrate levels in the broccoli top inflorescence during different growing seasons. The two factorial field trials were conducted in spring/summer and summer/autumn growing seasons in 2009 according to a randomized complete block design with four replications. Two broccoli cultivars (Marathon and Parthenon) and four levels of nitrogen fertilization (0, 60, 120 and 240 kg/ha) were tested. There was a significant effect of cultivar and rate of nitrogen fertilization on the nutritional quality of broccoli top inflorescence in both growing seasons. The average values of total glucosinolates per g of dry mass (12.82 μmol) and calcium (1.12 %) in broccoli top inflorescence were significantly higher during the spring/summer growing season. The prevailing glucosinolates in that growing season were glucobrassicin and neoglucobrassicin. In the summer/autumn growing season, higher amounts of nitrate per kg of fresh mass (553 mg), nitrogen (5.40 %) and glucoraphanin per g of dry mass (5.4 μmol) were achieved and the dominant individual glucosinolates were glucoraphanin and glucobrassicin. Combination of Marathon with N 120 or 240 kg/ha, which resulted in the highest values of determined glucosinolates and some minerals, with nitrate content in the allowed range, could be recommended for conventional broccoli production under climate conditions of northwestern Croatia.

Brassica oleracea L. var. italica; growing season; glucoraphanin; neoglucobrassicin; potassium; calcium; nitrogen

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