2.4 Soil property analysis
Soil NH4+-N and NO3–N were extracted with a 2 M KCl solution at a soil/water ratio of 1:5 at 25 ℃ and measured using a SmartChem140 Automatic Chemistry Analyzer. Soil organic carbon (SOC) was determined by the potassium dichromate digest method. Total soil nitrogen (TN) was measured by the micro-Kjeldahl method. Soil pH was determined by pHS-3C acidity meter.