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

Pot experiment was conducted under semi-controlled screen house in Nepal in 2022 to evaluate the effects of nitrogen, potassium, and soil texture on potato yield and nutrient use efficiency. It followed three-factorial randomized complete block design with N rates (50, 100, 150, and 200 kg N ha⁻¹), K₂O rates (30, 60, 90, and 120 kg K₂O ha⁻¹), and soil textures (silt loam, sandy loam, and loamy sand), along with an N-omission treatment. Pots contained 21.2 kg soil. The highest tuber yield (568 g pot⁻¹) was obtained with 200 kg N ha⁻¹ + 120 kg K₂O ha⁻¹, followed by 150 kg N ha⁻¹ + 120 kg K₂O ha⁻¹ (521 g pot⁻¹). Agronomic N efficiency was highest (74.4 kg tuber kg⁻¹ N) at 50 kg N ha⁻¹ + 60 kg K₂O ha⁻¹. Soil × N × K interactions were nonsignificant, indicating consistent responses across soil textures. A two-year field experiment evaluated 25 N–K combinations in the same design. The combination of 200 kg N ha⁻¹ + 150 kg K₂O ha⁻¹ produced the highest yields (26.51 and 26.40 t ha⁻¹). Agronomic N efficiency (56.86 kg tuber kg⁻¹ N) and N recovery efficiency (51.99%) were greatest at 150 kg N ha⁻¹ + 150 kg K₂O ha⁻¹. The highest benefit–cost ratio (2.1) occurred at 150–150 and 200–150 kg ha⁻¹ N–K₂O. Overall, 150 kg N ha⁻¹ + 150 kg K₂O ha⁻¹ was identified as the optimal fertilizer rate to enhance potato yield, nutrient use efficiency, and profitability in mid-hill of Nepal.