Influence of fertilizer practices on S-containing metabolites in garlic (Allium sativum L.) under field conditions.

Cysteine sulfoxides (e.g., alliin) are the characteristic sulfur-containing secondary compounds in garlic, which account for taste and pharmaceutical quality. It was the aim of the present study to investigate the influence of sulfur and nitrogen supply under field conditions on the alliin content and cysteine and glutathione as possible precursors. Sulfur and nitrogen were applied in four different rates, and five samplings were conducted. Sulfur fertilization significantly increased the cysteine, glutathione, and alliin contents of leaves and bulbs, while nitrogen fertilization had no significant influence. Cysteine increased by a factor of 1.3-1.5 in leaves and 1.0-2.0 in bulbs. Glutathione increased significantly in bulbs by a factor of 0.9-1.6 but only at main growth and not at maturity. The alliin concentration in bulbs increased with S fertilization significantly at all harvesting dates and at maturity from 5.1 to 11.2 mg g(-1) of dry weight. High sulfur application in combination with low nitrogen fertilization increased the alliin concentration in garlic significantly during main growth until the beginning of ripening. At the last harvest, 15 kg ha(-1) S resulted in high-quality garlic suitable for consumption and use in plant protection or pharmaceutical industries.