2.1. Study site
A field experiment was conducted in 2015-2018 at Yichang Irrigation
station (41°07′N, 108°00′E, 1 022 m ASL), in Wuyuan County, Inner
Mongolia, China. This region has a semi-arid climate, with annual active
accumulated temperature (≥ 10 ℃) of 3 100 °C. The average annual
precipitation is ~200 mm, whereas potential evaporation
is approximately 2 200 mm, indicating severe water deficit for crop
production (Zhang et al., 2019). Precipitation mainly occurs in summer
and autumn. Monthly precipitation and potential evaporation during the
growing season (i.e., May-October) of the experimental years are shown
in Figure 1. The soil is classified as chloride-sulfate saline soil with
silty loam. Basic properties in 0-20 cm layer were as below: soil
organic matter 11.3 g kg-1, total nitrogen 0.6 g
kg-1, total phosphorus 0.7 g kg-1,
alkaline hydrolyzed nitrogen 57.3 mg kg-1, available
phosphorus 10.2 mg kg-1, and available potassium 139
mg kg-1. Soil nutrient contents in deeper soil layers
(20-100 cm) are showed in Table 1. More information of the study site
was descripted in Huo et al. (2017).