Changes in pungency of onions by soil type, sulphur nutrition and bulb maturity

'Texas Grano 1015Y' onions were grown in two commercial fields with clay or loam soil with or without an excess sulphur (22.4 kg S ha(-1)) treatment. Onion bulbs were harvested every one or two weeks from March until bulb maturity and enzymatically produced pyruvic acid, dry matter, total sulphur in bulbs and sugar content were measured. Additional sulphur nutrition had no significant effect on any of the parameters. Total sulphur content in the bulbs was not influenced by S nutrition or soil type. Onions grown in loam soil were slightly higher in sugar content. Pyruvic acid, dry matter content and sugar content all decreased at the second sampling date and gradually increased as bulbs matured. This study indicated that pungency and sugar content of onions cannot be significantly changed by choosing the field or applying extra sulphur nutrition in a commercial field containing sufficient levels of sulphur or irrigated with water of high sulphur content. (C) 1998 Elsevier Science B.V.