Changes in nitrogen transformations in forest soil as a result of sprinkling infiltration
ABSTRACT Sprinkling infiltration through forest soil is a relatively new technique for generating artificial groundwater reserves to supplement urban water supplies in Finland. The aim of this study was to determine the effects of infiltration and surface runoff, resulting from sprinkling infiltration, on the acidity status and nitrogen transformations in forest soil and in percolation water. The amount of infiltrated water applied annually during the study period was more than 2000 times greater than natural annual recharge in the area. The study area is located on an esker in southern Finland (Ahvenisto, Hämeenlinna). The tree cover on the relatively fertile site consisted of Scots pine and Norway spruce. The results obtained during the first two years of the project indicated that the pH(H2O) of the organic layer of the soil had increased strongly due to sprinkling infiltration. The original pH of the organic layer was 4.7–5.1, and infiltration increased the pH to 6.5. The pH of percolation water collected below the organic layer increased strongly as a result of infiltration (>6.7 during infiltration). The pH of the infiltration water is about 7.0, which is higher than that of precipitation in the area (4.5). Sprinkling infiltration initiated net nitrification due to the elevated pH and increased ammonium availability. Infiltration increased emissions of N2O from the soil. During breaks in the infiltration treatment the leaching of NO3 from the topsoil was considerable compared to that on the control plots.
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ABSTRACT: In Ahvenisto esker, southern Finland, artificial recharging of groundwater has been done by sprinkling infiltration, i.e. by sprinkling lake water directly onto forest soil. Due to infiltration, the pH of the humus layer rose from about 5 to 6.5, nitrification was initiated and the fluxes of N2O and leaching of nitrate from the soil increased. Our aim was to study nitrogen transformations in different soil layers and to determine the response of nitrification to pH. Nitrification in ammonium-enriched soil suspensions was pH-dependant in a gradient from 4.7 to 6.7. In the soils subjected to infiltration, the production of (NO2+NO3)-N was inhibited by decreasing the pH to 5.3 or lower. Low pH also led to decreased numbers of nitrifiers. In the soils not subjected to infiltration (control soils), (NO2+NO3)-N production initiated at pH 6.7 and the numbers of nitrifiers increased. In incubation experiments, with no added ammonium, the adjustment of pH to 6.7 also initiated nitrification in the control soils. Thus, increase in soil pH was the main reason for initiation of nitrification at this site. During infiltration, N2O was produced mainly by denitrification and approximately 75% of the denitrification products was N2. In the samples from the humus layer, the concentrations of (NO2+NO3)-N, the net production of mineral N and net nitrification were in general less, whereas denitrification enzyme activity and denitrification potential were higher than in the samples from the mineral soil layer. The mineral soil may therefore contribute substantially to the leaching of nitrate.Soil Biology and Biochemistry 05/2000; 32(5):669-678. DOI:10.1016/S0038-0717(99)00194-7 · 4.41 Impact Factor