EFFECT OF DIFFERENT NITROGEN FERTILIZERS ON YIELD, PUNGENCY AND NITRATE ACCUMULATION IN GARLIC (ALLIUM SATIVUM L.)

Nitrogen plays an important role in growth, yield and quality of crops. Excessive application of nitrogen fertilizers causes nitrate accumulation in many plants. Garlic (Allium sativum L.) is an important vegetable in Iran and all over the world. Pungency, as an important character in garlic, is due to sulfur compounds like Alliine. In this study, the effect of two fertilizers (urea and ammonium sulfate) in five levels of Nitrogen (100, 150, 200, 250 and 300 kg N ha -1 ) was studied on yield, Pungency and Nitrate accumulation of garlic cv. Hamedani. Increasing the fertilizing level the leaf number and leaf length increased and the highest values were obtained with 300 kg N ha -1 . No growth differences were observed among various nitrogen fertilizers. The highest yield (16620 kg ha -1 ) and lowest yield (11530 kg ha -1 ) were observed with 200 and 300 kg N ha -1 , respectively. Using higher amounts of Nitrogen, pyruvic acid content (as an index to evaluate pungency) and nitrate accumulation were increased. The largest amount of nitrate accumulation (641 mg/g of dry weight) and pyruvic acid content (52.3 μmol/g of fresh weight) were obtained with 300 kg N ha -1 . There was no significant interaction between source and amount of nitrogen on yield; however, urea and ammonium sulfate were more effective on nitrate accumulation and pungency, respectively. According to the results obtained ammonium sulfate in 200 kg N ha -1 level was the best treatment to access high yield with good pungency.