Objective  Effects of planting density and nitrogen (N) application on the yield and agronomic efficiency on N (AE_N) of winter potato were studied to improve the crop cultivation practices.

  Method  Minshu 1 , a major winter potato cultivar, was used to determine the effects of planting density and N application rate on tuber yield, AE_N, and leaf photosynthesis of the plants in a split plot experimentation. Three planting densities at 47 600 plant·hm⁻² (D_4.76), 66 700 plant·hm⁻² (D_6.67), and 109 600 plant·hm⁻² (D_10.96) were implemented on a main plot, and 4 varied N inputs applied at the rates of 0 kg·hm⁻² (N₀), 75 kg·hm⁻² (N₇₅), 150 kg·hm⁻² (N₁₅₀), and 300 kg·hm⁻² (N₃₀₀) on a subplot.

  Result  Both planting density and N input significantly affected the tuber yield and AE_N of the potato plants. The two independent variables also significantly interacted to result in varied effects. Increasing the planting density improved the total yield and AE_N of the potato plants, as D_6.67 delivered the highest yield, while D_10.96 the highest AE_N, among all treatments. With N₃₀₀, the total potato yields under D_6.67 and D_10.96 were 21.3% and 21.2%, respectively, whereas, AE_N 20.5% and 49.2%, respectively, higher than those under D_4.76. N applications significantly affected the tuber production with the highest yield found with N₁₅₀. There was no significant difference on the yield between N₇₅ and N₁₅₀ under D_4.76 or D_6.67. But, as the planting became denser under D_10.96, the N₇₅ treatment produced significantly less potatoes than N₁₅₀. AE_N of the plants decreased with increasing N input. As compared to N₇₅, N₁₅₀ and N₃₀₀ showed significantly reduced AE_N by 41.2% and 75.2%, respectively. N application promoted the gas exchange parameters and SPAD on the leaves of the potato plants. High planting density was detrimental to photosynthetic efficiency, as shown by the leaf P_n of D_10.96 being lower than that of D_6.67. There was a significant correlation between the photosynthetic characteristics and potato yield of a plant.

  Conclusion  In the experimentation, the highest tuber yield of 32.2 t·hm⁻² was achieved when the potato were planted at 66 700 plant·hm⁻² and fertilized with 150 kg N·hm⁻². The greatest AE_N of 156.5 kg·kg⁻¹ was achieved with a planting density of 109 600 plant·hm⁻² and a N input of 75 kg·hm⁻². Thus, planting potato plants either at a high density with increased N application or at a low or medium density with reduced N input could improve the tuber yield and AE_N of the plants.