INFLUENCE OF INCREASING NITROGEN AND SULPHUR NUTRITION ON THE SULPHUR COMPOUNDS AND DRY MATTER CONTENT OF ONION

O. Huchette1, C. Bellamy1, J. Auger2, I. Arnault2, W.M. Randle3

1. DIJON CEREALES / COOPD’OR, R&D Department, INRA, BV 86510, 21065 Dijon Cedex, France
2. IRBI, Université François Rabelais, Avenue Monge, 37200 Tours, France
3. Department of Horticulture, University of Georgia, Athens, GA 30606, USA

Following a program which was aimed at improving the quality of garlic bulbs related to their health-value, experiments were conducted on yellow onion varieties with high dry-matter content to compare the results previously obtained under different fertilization regimes with garlic. Two varieties (Stuttgarter and KR41) were studied under 3 different mineral nutrition regimes varying in sulfur and nitrogen in a greenhouse experiment. Nitrogen was increased 2 fold and tested as combined to sulfur increased 4 fold. The growth of the plants was regularly observed. The bulbs were weighted at harvest, dried at ambient temperatures and analyzed for the dry-matter content, the soluble solids and different flavor attributes. Increasing both nitrogen and sulfur strongly affected growth of both varieties and accelerated maturity. The effect of increasing nitrogen alone could not be noticed during the growing period and did not improve the weight of the bulbs, especially for KR41, which produced significantly bigger bulbs under normal fertility conditions. As a consequence, bulbs grown under combined high levels of sulfur and nitrogen were significantly smaller. However, the dry matter content and soluble solids were only slightly affected. Concerning the bulb sulfur content, the response to the addition of high levels of nitrogen and sulfur was cultivar specific. This trend could also be confirmed on some flavor attributes. Results showed that garlic was much more responsive to increasing nitrogen and nitrogen and sulfur together when compared to onion.

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