Effects of planting density on potato growth, yield, and water use efficiency during years with variable rainfall on the Loess Plateau, China

A 3-yr field study was conducted in semiarid areas of the Loess Plateau to investigate the effects of different planting densities on the soil water, potato growth, yield, and WUE during the normal year (2015), relatively dry year (2016), and relatively wet year (2017). The five potato planting densities were 3.75 x 10(4) (A, traditional local planting density as a control), 4.50 x 10(4) (B), 5.25 x 10(4) (C), 6.00 x 10(4) (D), and 6.75 x 10(4) plants ha(-1) (E). During the three years, the differences in soil water storage among the five planting densities were significant in the early and middle potato growth stages, when the soil water storage levels in treatments B and C were 8.8 % and 10.8 % higher (P < 0.05) than those in A. Treatments B and C significantly (P < 0.05) increased the potato emergence rate by 12.5 % and 7.5 % to promote growth in the early and middle stages. The planting density had a decreasing parabolic relationship with the potato yield. After fitting a function to the three years of data, the highest tuber potato yield varied with the amount of rainfall and the optimum level was 5.12-5.58 x 10(4) plants ha(-1). The WUE and rainwater use efficiency (RWUE) were significantly higher under B and C compared with A in the normal and relatively dry years. WUE and RWUE were significantly higher in B, C, and D compared with A in the relatively wet year. The optimum planting density with treatments B and C obtained higher net profits. Thus, the recommended optimum planting density should be 4.50-5.12 x 10(4) plants ha(-1) in relatively dry years and 5.13-5.58 x 10(4) plants ha(-1) in normal and relatively wet years to increase dryland potato production and water use efficiency in the semiarid regions of the Loess Plateau, China.