Optimization of pig slurry application to heavy metal polluted soils
monitoring nitrification processes
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Nitrification is often negatively affected by heavy metal pollution in soils, this limiting land revegetation.
Thus, the potential use of pig slurry as a nitrogen-rich organic amendment in different heavy metal contaminated
soils has been evaluated; this also being a way of recycling this waste. In order to identify the
factors affecting nitrification processes in heavy metal polluted soils (soil pH, heavy metal solubility and
the N source), incubation experiments were run using two polluted soils with different pH values (5.0 and
7.1) and a non-contaminated soil (pH 8.2). Ammonium was added as pig slurry or as ammonium sulphate
for comparison (both added at 150 mg NHþ4
-N kg1 of soil). Pig slurry provoked higher nitrification rates
and N-immobilisation than ammonium sulphate, especially in the neutral-polluted soil, reflecting an
improvement of the microbial activity in the soil. The microbial immobilisation of N led to an inverse
relationship between the amount of N added and nitrate conversion in the neutral-polluted soil and in
the non-contaminated soil amended with different pig slurry dosages (75, 150 and 225 mg NHþ4
-N kg1
of soil). Low rates of nitrification and N-immobilisation were found in the acidic soil. Pig slurry addition
to metal polluted soils enhanced soil nitrification, especially when metals were in low-solubility forms