The vertical movement of the D₂O-tagged soil water, ¹⁵NH₄⁺-N and major ions in topsoil of secondary forests

The vertical movement of soil water and major ions in topsoil of secondary forests were investgated by using D₂O and ¹⁵NH₄Cl as tracers of water and nutrient elements, respectively. Undisturbed soil columns were collected with cylinders made of vinyl chloride pipe in different stands. The rain solution was dropped uniformly on the column by using the artificial rainfall equipment in twice. The artificial rainfall was continued for 10 h at constant intensity of 4 mm/h. At the second time of rainfall, the tracer solution labeled with D₂O and ¹⁵NH₄Cl applied on the column. The concentrations of Cl^-, Mg²⁺, and Ca²⁺ increased with the D₂O discharge and only small quantity of ¹⁵NH₄⁺-N moved to the lower horizon on the Brown forest soil columns. The downward velocity of the D₂O-tagged water agreed approximately with that of Mg²⁺ and Ca²⁺. But large amount of the ¹⁵NH₄⁺-N was discharged with the D₂0-tagged water on the column that was collected in the forest floor removal stand. In spit of heavy water discharging, the concentration of Cl^- in discharged soil solution did not increase obviously in Andosol column because of the effect of anion absorption into the soil.