Organic Carbon (OC) and total N content in soils were determined by the dry combustion method using a CHN elemental-analyzer (CHN NA 1500, Carlo Erba). The N-NH4+ and N-NO3− contents were determined using the Kjedhal method. Total K content was determined after extraction with H2SO4 (5 ml g−1) and HClO4 as catalyst (0.5 ml g−1) using a Flame photometer (code of method TCVN 4053-81). Total P content was determined using a spectrophotometer after similar extraction.