A PHS-3C pH meter (Shanghai Lida Instrument Factory, Shanghai, China)
was used to measure the soil pH via the potentiometric method in a
soil-to-water ratio of 1:2.5 (w/v). The soil moisture was
gravimetrically measured. An elemental analyzer (2400 II CHNS/O,
Perkin-Elmer, Danbury, CT, USA) was used to measure the soil total
carbon (C) and total nitrogen (N) via dry combustion at a combustion
temperature of 950 °C. The soil inorganic C was volumetrically measured
using an inorganic C analyzer (Calcimeter 08.53, Eijkelkamp, Giesbeek,
Netherlands). The soil organic C content was indirectly determined as
the difference between the total C and inorganic C contents.
An
automated segmented flow analysis (SmartChem140, AMS Systea, Roma,
Italy) was used to colorimetrically measure the ammonium
(NH4+) and nitrate
(NO3-) contents in the soil via the
salicylate/dichloroiso-cyanuric acid
and
cadmium column/sulphanilamide reduction methods, respectively. The
available phosphorus (P) was extracted using 0.5 mol
L-1 NaHCO3 (pH 8.5) and measured by a
722s visible light spectrophotometer (Shanghai Precision and Scientific
Instrument Corporation, Shanghai, China).