A study of the components of growth of the spring-sown onion and their relationships with meteorological data

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Abstract
Accumulated dry weight data for onion leaf, sheath and whole plant were studied with the view to understanding the relationships between these components of growth and the environment. Logistic growth curves were found to give good representations of the development of both the whole plant dry weight and the bulb plus sheath dry weight from emergence to harvest in two spring-sown cultivars of bulb onion grown at three sites in two seasons. Logistic curves still gave good fits to these dry weight data when various meteorological variables were used in place of time. Accumulated day-degrees between limit temperatures of 6 and 20°C reduced, but did not eliminate, the inter-site and season differences in the pattern of growth. For the whole plant dry weight, accumulated sun-hours did not eliminate inter-site and season differences: however, the inter-site differences, within a season, were in good agreement with the observed density at harvest. The total leaf dry weight increased to a maximum before subsequently declining. A suitable curve was found to describe this behaviour and the use of meteorological scales again investigated. The accumulated day-degree scale fitted the relationships better than the time scale. The scale using accumulated sun-hours was only effective in describing the relationships in one of the two seasons.