Use of optimum plant spacing (planting density) is one of the important agronomic practices to maximize the productivity of lettuce. A field experiment was conducted to assess the responses of two lettuce varieties to different plant spacing at Debrezeit and Holeta Agricultural Research Centers representing two different agro-ecologies in Ethiopia. Nine treatment combinations of three levels of inter-row and three levels of intra-row spacing were studied on two types of lettuce varieties. The treatments were arranged in a randomized complete block design (RCBD) with three replications in a factorial experiment. The results revealed that marketable and total fresh leaf yield, and fresh leaf weight per plant were significantly affected by the main effect of plant spacing and variety as well as its interaction (p<0.05). Increasing planting density increased the total fresh leaf yield per unit area in both varieties, however reduced the fresh leaf weight per plant. The highest fresh leaf yield was obtained using 40 cm x 20 cm (125000 plants ha-1) planting density from variety Great Lakes, while variety Rsk-3 recorded its highest fresh leaf yield at the highest planting density of 30 cm x 20 cm (166667 plants ha-1). Great Lakes was superior over Rsk-3 in most yield parameters studied though Rsk-3 was better in leaf dry weight percent. Besides, both varieties responded differently in both sites while Great Lakes performed better at Debrezeit than at Holeta and Rsk-3 did well at Holeta than at Debrezeit. Hence, 40 cm x 20 cm and 30 cm x 20 cm could be used as the optimum plant spacing to grow Great Lakes and Rsk-3 respectively in the respective agro-ecologies.
Key words: Agronomic practices, planting density, inter-and intra-row spacing, competition.
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