Impacts of Acid Atmospheric Deposition on Woodland Soils in the Netherlands: II. Nitrogen Transformations1
- N. van Breemen,
- J. Mulder and
- J. J. M. van Grinsven2
Inorganic N budgets were estimated for four oak-birch (Quercus robur L.-Betula pendula L.) woodland soils in the Netherlands, that receive high inputs (40–60 kg ha−1 yr−1) of atmospheric N, mainly as (NH4)2SO4-. Budgets were based on measured inputs in through-fall water, measured soil solution concentrations, and simulated soil-water fluxes. Substantial nitrification occurred in both highly acidic (pH 3–4) and calcareous (pH 6.5–7.5) soils. The acidity formed during N transformations (3–9 kmolc ha−1 yr−1) accounted for a major part of all soil acidification taking place. Extreme soil acidification due to nitrification (4–14 kmolc ha−1 yr−1) in the 10-cm surface soil in three of the four plots was partly alleviated at greater depth by removal of NO-3. Presumably, most of this NO-3 was removed by plants and microorganisms and, perhaps, in part by denitrification. In two of the four soils, leaching of inorganic NO-3 exceeded atmospheric throughfall input. This trend indicates that N inputs were still higher, e.g., due to direct assimilation of atmospheric NH3 by tree leaves, or that the pool of soil N decreased by mineralization in excess of uptake. In one of the four soils, most of the atmospheric N2 was assimilated and soil acidification due to N transformations was relatively small. The differences in N budgets and associated soil acidification may be related to (i) consistent differences in N input over many years, and (ii) differences in accumulation of N in biomass. Variation in these two factors may be responsible for differences in the degree to which the ecosystems are now “saturated” with N.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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