2.2 Soil physicochemical properties determination
Measurement of soil properties were carried out following the methods of
the soil agrichemical analysis (Lu, 2000). Soil pH was measured with a
METLER TOLEDO FE20 at a soil/water ratio (m/m) of 1:1. Soil moisture
content was determined after drying at 105°C for 12 h. Soil organic
matter was calculated with organic carbon determined with potassium
dichromate and sulfuric acid. Total carbon (TC) and total nitrogen (TN)
were measured by the elemental analyzer (Vario EL Ⅲ, Elementar).
Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) were
measured by TOC/TN analyzer (Multi N/C Model 3100, Analytic Jena,
Germany). Ammonium-N (NH4+-N) and
nitrate-N (NO3--N) were extracted from
6.0 g fresh soil with 1.0 mol L-1 KCl solution
(soil/extract ratio of 1:5) and shaken for 1 h at 180 rpm. The soil
extract was analyzed by continuous flow analyzer (AA3, SEAL, Germany).