2.3. Test soil
All tests were performed with natural soil. Surface (5–20 cm)
soil was collected from an agricultural field in Henan, China. For more than 5 years, wastewater or sewage sludge had not been applied
to the agricultural field. The main characteristics of the test
soil were: organic matter content of 23.19 ± 0.47 g kg1, pH of
8.05 ± 0.05, cation exchange capacity of 17.10 cmol kg1, 3.91%
clay, 32.04% silt, and 64.05% sand. Before the test, the soil was
air-dried and then passed through a 4-mm sieve.