2.3 | Analysis of soil physicochemical properties
The soil pH was measured using a pH meter in a soil: water suspension
(1:5 w/v), after being shaken for 30 min. The soil organic carbon (SOC)
and soil organic matter (SOM) were determined using the
K2Cr2O7-H2SO4oxidation–reduction colorimetric method (Schulz, 2002). The soil total
nitrogen (TN) was measured using the Kjeldahl digestion method
(Krishnamoorthy et al., 1982). The total organic carbon (TOC) was
measured using a TOC analyzer (Elementar GmbH, Langenselbold, Germany).
The humus content (HC), TN, total carbon (TC), nitrate nitrogen
(NO3–N), nitrite nitrogen (NO2–N), and
ammonium nitrogen (NH4–N) levels were determined using
colorimetry (Wang et al., 2011). Measurements of available phosphorus
(AP) and available potassium (AK) were performed using the methods
described by Mitchell et al. (2010). Soil available nitrogen (AN) was
determined using a diffusion method (Khan et al., 1997).