2.2.3 Determination of soil physical and chemical properties
We determined soil organic matter content using the potassium dichromate volumetric method, soil total N using the semi-micro Kjeldahl method, soil total phosphorus (P) using the sulfuric acid perchloric acid digestion molybdenum-antimony anti-colorimetric method, soil available P using the molybdenum-antimony anti-colorimetric method extracted by sodium bicarbonate, soil available potassium (K) using ammonium acetate flame spectrophotometry, and soil alkali-hydrolyzed N using the alkali-hydrolyzed diffusion method (Wei et al., 2014).