Changes of inorganic nitrogen in the leachates of urban forest soil and its soil nitrogen under the irrigation of different mass concentrations of ammonium nitrogen: taking Harbin City of northeastern China as an example

ObjectiveThis paper aims to ascertain the changes of soil nitrogen and ammonium nitrogen, nitrate nitrogen in the urban forest soil leachate irrigated with different mass concentrations of ammonium nitrogen.

MethodThis paper selects 3 typical forest types in the demonstration base of urban forest in Harbin City of northeastern China (Quercus mongolia plantation, Fraxinus mandshurica plantation, Phellodendron amurense plantation) as the object of this study. Bare ground without vegetative growth was used as control. Through the method of field collecting soil column and indoor soil column simulation, different mass concentrations of ammonium nitrogen solutions (100, 50, 25, 0 mg/L) were prepared by ammonium sulfate for indoor simulation irrigation, ammonium nitrogen and nitrate nitrogen in soil column leachate and soil nitrogen in column after treatment being measured and analyzed.

ResultThe effects of three forest types on the removal of ammonium nitrogen were significant, the removal rate was above 95%; there was no significant difference in the removal of ammonium nitrogen by different forest types under the load of different mass concentration of ammonium nitrogen; the mass concentrations of nitrate nitrogen in original soil column leachate for three forest types and a control was higher, it ranged from 4.41 to 5.53 mg/L; when the influent ammonium nitrogen mass concentration was 100 mg/L, except for control, the content of ammonium nitrogen in soil columns for the three forest types was increased; when it was lower than 100 mg/L, except for the Quercus mongolia plantation, the content of ammonium nitrogen in the soil columns for the other two forest types was reduced; the content of nitrate nitrogen in soil column for each forest type and the control was significantly increased, but the difference in total nitrogen content between them was not significant. After irrigation with different mass concentrations of ammonium nitrogen, the change of ammonium nitrogen in soil column leachate was not significantly affected by the forest type, influent water amount and their interaction. But their effects on nitrate nitrogen reached a significant level. The change of nitrogen in the soil column after irrigation was significantly influenced by the above three factors.

ConclusionFor the original soil column in three forest types and bare soil, ammonium nitrogen removal and nitrate nitrogen leaching loss in the soil in Quercus mongolia plantation were most significant, followed by the soil in Phellodendron amurense plantation, Fraxinus mandshurica plantation soil and bare soil.