Growth, productivity and profitability of potato (Solanum tuberosum L.) as influenced by nitrogen fertilizer and intra-row spacing in Ethiopia highlands

Nitrogen fertilizer and intra-row spacing are critical agronomic practices influencing potato (Solanum tuberosum L.) production. In Ethiopia, smallholder farmers often apply nitrogen and manage plant spacing without evidence-based guidelines, resulting in low productivity. A field experiment was conducted during the 2023 main rain fall season on a farmer's field in the Ethiopian highlands to assess the growth and seed tuber yield of the potato variety 'Belete' under different nitrogen rates and intra-row spacings. The study evaluated four nitrogen levels (0, 55, 110, and 165 kg N ha⁻¹) and three intra-row spacings (20, 30, and 40 cm) in a factorial randomized complete block design with three replications. Interaction effects of nitrogen and spacing significantly affected days to 50% flowering, stem number, yields of very small, small, and large-sized tubers, average tuber weight, marketable yield, and total tuber yield. The highest marketable tuber yield (41.38 t ha⁻¹) was recorded with 110 kg N ha⁻¹ and 20 cm spacing. However, partial budget analysis revealed that the combination of 110 kg N ha⁻¹ and 30 cm spacing provided the highest net benefit (236,614 ETB ha⁻¹) and marginal rate of return (12,692.11%). These results underscore the need to optimize nitrogen application and plant spacing for enhanced seed tuber productivity and economic returns. Therefore, applying 110 kg N ha⁻¹ with 30 cm intra-row spacing is recommended for profitable potato production, improving income and food security for smallholder farmers in the study area and similar agro-ecologies.