2.3 Soil basic physiochemical properties
The soil bulk density was calculated as the ratio of the oven-dried (105 °C) soil mass to the volume of the cylinder. The soil pH was determined in a soil-to-water mass ratio of 1:2.5, and particle size by the United States Department of Agriculture (USDA) were measured using the gravimetric method. The soil organic matter was analysed using the Walkley-Black potassium dichromate sulfuric acid oxidation method (Nelson and Sommers, 1982). The total N was measured using the semimicro-Kjeldahl method after complete digestion in CuSO4-K2SO4-Se (100:10:1) at 400 °C (Bremner and Mulvaney, 1982), and available N was determined using NaOH-hydrolysation reduction-diffusion (Lu, 2000). The total P and available P were measured using the colorimetric molybdenum blue method via HNO3-HClO4-HF digestion and 0.5 mol L−1 NaHCO3 (pH = 8.5) extraction, respectively (Murphy and Riley 1962; Olsen et al. 1954; Thomas et al. 1967). The basic soil physiochemical properties are listed in Table 3.