The test soil used was a sandy loam soil collected from the Ahn Mountain (Seoul, Korea). The soil was sieved (using a9-mm mesh) and dried for 24 h at an oven temperature of105⬚C. The soil pH was measured by shaking the air-dried soil in distilled water for 1 h and waiting for another hour prior to the pH assay using a digital pH meter (Model 420 A; ORION Research, Boston, MA, USA) [13]. The mean pH of the test soil was 4.7 (1:2 slurry). The soil texture was measured using a soil texture test kit (Model 1067; LaMotte, Chester town,MD, USA) that is based on the general method of mechanical analysis or soil separation [14]. The percentage of organic matter content of the test soil was measured using an organic matter soil test kit (Model ST-OR 5020; LaMotte). The aciddichromate soil solution was titrated with 0.4 N ferrous ammonium sulfate until its color changed from dark brown to a deep green endpoint. The mean of the three deter minations was 0.77% organic matter.