2.1 Study site
The study site is located at Jingzhou Hill, Maoxian County, in the arid
valley of the Minjiang River, Sichuan, China (31°70′N, 103°87′E,
altitude 1637 m). The RFC ranges from 1% to 65% (g
g-1), and most rock fragments have a particle size
larger than 10 mm (Bao et al., 2012). These characteristics served as
the basis for the design of the RFC gradient and selection of particle
size. The mean annual precipitation at the nearest climate station
(Maoxian County Meteorological Station, 2 km from the study site) was
495 mm, with 83% of the precipitation occurring during the growing
season from May to October. The mean annual potential evaporation is
1332 mm, and the annual air temperature is 15.6 ℃. The site has
historically been cultivated for agricultural crops, with potatoes and
celery planted 2 years before the start of the present study. Typically,
cinnamon soil has a clay loam with coarse texture and low fertility (Bao
et al., 2012). The soil depth is typically 50–70 cm.