2.1 Site description
A two-year field experiment was conducted from 2018 to 2019 in Xun County (114°40′E, 34°40′N; 72.3 m above mean sea level), Henan Province, China. The study field is located in a warm, semi-humid region with a continental climate. The annual mean temperature in this region is 13.7 ℃, and the frost-free period lasts 220 days. The average annual rainfall is 647.8 mm, with above 60% of the local rainfall is concentrated in the summer, which can satisfy the water requirement for summer maize. The crop rotation in this region is winter wheat (Triticum aestivum L.) followed by summer maize (Zea mays L.) every year. The soil type is calcareous (Fluvo-Aquic soil) with pH of 7.88. It is a typical soil in the region with a profile of sandy loams with a texture of 65% sand, 25% silt, and 10% clay. The basic properties (0-20 cm depth) of soil are organic matter 15.0 g kg-1, total nitrogen 1.1 g kg-1, Olsen-P 30.5 mg kg-1 and NH4OAc-K 95.1 mg kg-1.