In the glasshouse experiment outlined here, seedlings of 'Valcatorce INTA', a Spanish-type, and 'Dorada VGJ 1161', an early-bulbing type, were transplanted to containers of soil in a glasshouse.
The treatments consisted of maintaining the soil at 100 per cent, 80 per cent or 60 per cent of field capacity and the plants in each plot were harvested when the tops of at least 50 per cent of the bulbs had toppled over. Later, the bulbs were weighed individually and placed on perforated trays in a ventilated store at 14.4 degsC (63 per cent to 72 per cent RH). Each bulb was re-weighed every 14 days and those that had become soft or had sprouted were discarded.
In a separate field experiment, seed only of 'Valcatorce INTA' was sown 12mm deep in double rows spaced 12cm apart and the plots were either irrigated or not during bulb filling. The bulbs were harvested and stored as before.
In both experiments, treatments that restricted water availability during bulb filling delayed bulbing and produced lighter bulbs that lost weight more rapidly in store and sprouted earlier. Although controlled-deficit treatments have been recommended for onions, there is a risk that they may cause greater losses during bulb storage.
Dr Ken Cockshull, Associate Fellow, Warwick Crop Centre, University of Warwick
Accelerated Storage Losses in Onion Subjected to Water Deficit During Bulb Filling by Rattin, Assuero, Sasso and Tognetti (2011).
Scientia Horticulturae 130 (1): 25-31. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at www.elsevier.com/locate/scihorti.