Impact of Soil Amendments on Organosulfur Compounds in Onion

Onion is most widely cultivated species of the genus Allium. Onion is valued as food and medicine primarily for the flavor and medicinal properties of its organic sulfur compounds. A field study was conducted at Kentucky State University (KSU) Research and Demonstration Farm. The soil in five plots was mixed with sewage sludge, five plots were mixed with yard-waste compost, five plots were mixed with laying hen manure each at 15t acre^-1, and five unamended plots were used for comparison purposes. Plots were planted with onion, Allium cepa L. var. Super Star-F1. The objectives of this investigation were to: i) determine the concentrations of organosulfur compounds (dipropyl disulfide and dipropyl trisulfide) in onion bulbs and ii) investigate the effect of soil amendments (sewage sludge, yard-waste, and chicken manure) on the concentration of sulfur compounds in onion bulbs. Gas chromatographic/mass spectrometric (GC/MS) analyses of onion oil in chloroform extracts revealed the presence of two major fragment ions that correspond to dipropyl disulfide and -trisulfide. Concentration of these two organic sulfur compounds was greatest (1.5 and 0.8 mg 100 g^-1 fresh weight, respectively) in onion bulbs of plants grown in chicken manure and lowest (0.4 and 0.07 mg 100 g^-1 fresh weight, respectively) in onion bulbs of plants grown in yard-waste compost treatments. We concluded that chicken manure could be favorably utilized in growing onions with health-promoting properties.