In June of each year, soil samples were collected from the 0 to 30 cm depth for NO3--N analysis. Six samples were taken in each plot with a 2.5-cm hand probe, composited, and air-dried
at 30°C. Nitrate-N was extracted from 10 g soil samples with 100 mL of 2M KCl and determined using the cadmium reduction method [28].