Although there is adequate information on the influence of plant population on root yield and size of carrot on flat and raised bed for rain fed production system, information on ridge-furrow bed preparation method is limited for irrigation production system. Therefore, in this study, field experiments were conducted for 2 years to determine the appropriate spacing of carrot on ridge-furrow carrot production practice under irrigation. Root yield increased significantly as the population increased. On the contrary, root size significantly decreased as population increased. The result of combined analysis over season and locations indicated that the narrowest spacing of 10 cm × 4 cm rows on the ridge and between plants, respectively, which accommodates 1,250,000 plants ha−1 gave significantly highest marketable carrot root yield of 26 t ha−1 followed by 22.6 t ha−1 with spacing of 20 cm × 4 cm which accommodates 1,000,000 plants ha−1, but it produced the smallest individual root weight of 83 g which is mostly preferred for household consumption unlike jumbo roots. Therefore, in terms of root sizes and marketable yield, the current study identified that spacing of 10 cm × 4 cm is optimum on ridge-furrow carrot production practices.

Plant population of 40,000 ha−1 with the respective inter- and intra-row spacing of 50 cm × 50 cm is the blanket recommendation for the production of head cabbage in Ethiopia. However, producers complain that this spacing produces too large head size, which is not the market's preference for household consumption instead for hotels and big institutions like universities. This two-season field experiment was conducted to optimize the head cabbage yield with appropriate head size by adjusting inter- and intra-row spacing. The result of the combined analysis over location and season revealed that all tested parameters were significantly (P < 0.05) influenced by the interaction effect of inter- and intra-row spacing. The combinations of 35 cm × 30 cm, 35 cm × 50 cm, and 50 cm × 30 cm inter- and intra-row spacing gave the highest head yield of 45, 43 significantly, and 42 t ha−1, respectively as compared to other treatment combinations. The interaction of the lowest inter- and intra-row spacing of 35 cm × 30 cm gave the lowest average head weight of 923 g of cabbage. The result showed that as intra-row spacing increased from 30 to 50 cm with all possible combinations of inter-row spacing, head-sized cabbage increased linearly. The current study identified that blanket recommendation of 50 cm × 50 cm inter-and intra-row spacing which assures a plant population of 40,000 ha−1 produced more than 1.4 kg individual head weight with a yield penalty of 10.70 t ha−1 compared to 50 cm × 30 cm inter- and intra-row spacing combination which assures a plant population of 66,667 ha−1. The current study confirmed that the earlier blanket recommendation of 40,000 plants ha−1 should be enhanced to a plant population of 66,667 ha−1 with a yield advantage of 131%. Concretely the manifested plant population difference gives an opportunity to producers to harvest a maximum yield with an acceptable head size of 1.2 kg. Therefore, it is concluded that the combination of 50 cm × 30 cm inter- and intra-row spacing assures that a plant population of 66,667 ha−1 is optimum for the production of head cabbage in the study and similar agro-ecologies.