Influence of added ammonium sulphate on the leaching of aluminium, nitrate and sulphate - A laboratory experiment

Relationships between the concentrations of sulphate, nitrate and Al were studied in leachates from reconstructed soil profiles of a previously N fertilized Haplic Podzol. Half of the profiles were covered with the grass Deschampsia flexuosa (Trin.), and the other half were not. The soil profiles were subjected to different N loads, in the form of ammonium sulphate. The doses were 0.5 mmol ammonium-N during the first part of the experiment and 1.0 mmol ammonium-N during the later part. Uptake of N by the vegetation almost completely eliminated the effects of added ammonium, even when the soil profile was strongly nitrifying. Fertilizer treatment caused nitrate to leach from the non-covered soil profiles, although there was a net retention of N. The concentration of Al in leachates was positively correlated with nitrate. Fertilizer treatment increased the proportion of inorganic monomeric Al in leachates. Most sulphate retention seemed to take place in the O horizon. In the presence of vegetation sulphate concentration was enhanced to a greater degree than could be explained from differences in evapotranspiration estimated from the Cl-/SO42- ratio in the leachates. Soil N dynamics on a forest clear-cutting are discussed with reference to the present findings.