Spear yield and quality of white asparagus as affected by soil temperature

In three consecutive years two asparagus cultivars (Gijnlim, Grolim) were cultivated at three different temperatures in the ridge surface ranging from 12 to 26 degrees C to assess (1) the onset of spear yield, (2) the mean daily yield increase per plant, and (3) the establishment of spear quality defects. The objective was to determine the temperature dependence of the spear growth and quality of white asparagus with respect to different cultivars and the harvest year. The mean time interval At from the beginning of the temperature treatment to harvest start was 16.5 d at the reference temperature of 20 degrees C. This time interval corresponded to a thermal time of 255 degrees C d at a base temperature of 4.4 degrees C. The mean yield increase Delta w per plant at the reference temperature was 17.4 g d(-1). The temperature dependence of Delta t and Delta w was expressed by the relative change of these quantities per I degrees C alteration, which were on average 0.08 and 0.14 degrees C-1, respectively. The frequency of quality defects (rusted spears, split spears, hollow/club-shaped spears, spears with open heads) and grade I quality depended significantly (P < 0.05) on the temperature, cultivar, and harvest year. Generally, 'Gijnlim' showed fewer quality defects than 'Grolim', whereas spears without defects were most frequent for those grown between 18 and 22 degrees C. With rising temperatures, the frequency of split or hollow/club-shaped spears and spears with open heads increased, while the frequency of rusted spears decreased. The derived functions of yield and quality parameters should improve the controlling of the yield and quality of white asparagus spears at varying temperatures in the ridge. (c) 2006 Elsevier B.V. All rights reserved.