There was a great variety in nitrogen during the incubation experiments. The Css had a low C/N ratio suggesting a rapid release of N. No3—increase sharply, with no significant differences among the soil samples amended with different CSS dose. Content of NH4+-N and organic nitrogen decreased while contents of NO3-increase, showing mineralization and nitrification simultaneously occurred. The maximum concentration of NH4+-N in soil tolerated by nitrifying organism is between 400 and 800 mg/kg. S3 and S4 treatments were beyond this range, indicating the nitrification ratio was slow.
Fig.3 Evolution of organic (a), ammonium (b), and nitrate (c), nitrogen in soil