Improving the agronomic performances and nitrogen use efficiency of carrot ( Daucus carota L.) variety, spacing, and nitrogen fertilization

Abstract

Carrot ( Daucus carota L.) is a nutritionally vital root vegetable, yet productivity in Ethiopia's Sankura District remains constrained by suboptimal agronomic practices. This study evaluated the interactive effects of variety, plant spacing, and nitrogen (N) fertilization on carrot growth, yield, and nitrogen use efficiency (NUE) components: partial factor productivity (PFP), agronomic efficiency (AE), physiological efficiency, and recovery efficiency. A 2 × 4 × 3 factorial randomized complete block design with three replications tested two varieties (Nantes and Nantes‐Improved), four intra‐row spacings (4, 6, 8, and 10 cm), and three N rates (0, 69, and 138 kg N ha ^{− 1} ) across two cropping years (2023 and 2024). Nantes‐Improved consistently outperformed Nantes in yield and NUE parameters. The combination of 6 cm spacing with 69 kg N ha ^{− 1} produced the highest marketable yield (23.7 t ha ^{− 1} ) and net economic benefit (292,411 ETB [Ethiopian Birr] ha ^{− 1} ), while the interaction between narrow spacing (4 cm) and high N (138 kg N ha ^{− 1} ) increased unmarketable yields due to competition‐induced deformities. Tissue N (nitrogen concentration) content and AE peaked at 69 kg N ha ^{− 1} , beyond which diminishing returns occurred. PFP was highest (38.1 kg kg ^{− 1} N) at the moderate N rate, indicating optimal N utilization. Correlation analysis revealed a trade‐off between shoot vigor and root development, with plant height positively correlating with yield but negatively affecting root dimensions. This study provides the first comprehensive assessment of variety × spacing × N interactions for carrots in Ethiopian highland conditions, demonstrating that adopting Nantes‐Improved at 6 cm spacing with 69 kg N ha ^{− 1} optimizes productivity, quality, and profitability while improving NUE. These findings offer actionable recommendations for smallholder farmers and extension services to enhance sustainable carrot production.