2.3 Soil sampling
We collected soil samples from depths of 0–10 cm and 10–25 cm using a 10 cm diameter soil auger on 1 August 2019. The sampling date corresponded to the tasseling stage. The soil samples were stored in airtight polypropylene bags and placed in a cool box at 4°C during transportation to the laboratory. Litter, roots, and gravel in soil samples were removed and the soil was divided into several samples for further analyses.