Interaction of nitrogen and potassium influences potato yields and nutrient use efficiency across mid-hill soils of Nepal

Optimizing nitrogen (N) and potassium (K) across soil textures is critical for improving potato yield, nutrient-use efficiency, and farm profitability; however, such evidence is limited in Nepal’s mid-hills. This study comprised a pot experiment (2022) and a two-year field experiment (2024–2025) to identify optimal N–K rates. The pot experiment, in a semi-controlled screen house, used a three-factor factorial randomized complete block design with four N rates (50– 200 kg N ha⁻¹), four K rates (30–120 kg K₂O ha⁻¹), three soil textures (silt loam, sandy loam, and loamy sand), and an N-omission treatment. Tuber yield increased with N and K, with the highest tuber weight (568 g pot⁻¹) and agronomic N use efficiency (50 kg tuber kg⁻¹ N) at 200 kg N ha⁻¹ + 120 kg K₂O ha⁻¹. Soil × N × K interactions were non-significant, indicating consistent responses across soil textures. Based on pot results, 25 N–K combinations were evaluated in the field. Maximum tuber yield (26.51 t ha⁻¹) occurred at 200 kg N ha⁻¹ + 150 kg K₂O ha⁻¹, statistically similar to 150 kg N ha⁻¹ + 150 kg K₂O ha⁻¹ (26.40 t ha⁻¹). However, agronomic N efficiency (56.86 kg tuber kg⁻¹ N), N recovery efficiency (52%) and benefit-cost ratio (2.1) were highest at 150 kg N ha⁻¹ + 150 kg K₂O ha⁻¹. Overall, 150 kg N ha⁻¹ combined with 150 kg K₂O ha⁻¹ is recommended as the optimal fertilizer strategy for improving potato yield, nutrient-use efficiency, and economic returns in mid-hill Nepal.