EFFECT OF THE HEATING TECHNIQUE ON EARLINESS AND TOTAL YIELD OF THREE ASPARAGUS CULTIVARS GROWN IN A HIGH TUNNEL

The purpose of this study was to investigate the efficacy of different heating techniques applied to raised beds, where the asparagus spears were grown. A central heating system burning peach stones was used to provide heating to the raised beds of three hybrid cultivars, Dariana, Larac and Steline, in a greenhouse, considered as a high tunnel. The hot water was circulating in two pipes placed in three different positions in terms of the asparagus crowns as follows: Above the crowns (AC), a pipe at each side of the crown (SC), and under the crowns (UC). An unheated bed of each cultivar was used as control. Raised beds were covered with black plastic mulch to ensure white spears and weed control. The heating system was activated in mid January 1998 for the first harvest period and in mid December of the same year (1998) for the second harvest period. In both harvest periods mean early yield of asparagus spears in the UC treatment was significantly higher compared with the control and the AC and SC treatments, which were similar. In the first period, total yield of all cultivars was similar under any applied heating treatment but significantly higher compared to the control. In the second period, only the total yield of the AC and SC heating treatments were significantly higher compared to the control. In the first period, cvs Dariana and Steline produced significantly earlier yield than Larac and in the second, the range of cultivars in terms of early yield was Steline, Larac and Dariana, respectively. Concerning the total yield of cultivars in both periods, Dariana yielded significantly more than the other two cultivars.