Vertical nutrient and trace element migration in cambisols after application of residues from anaerobic digestion of manure
At an alpine grassland cambisol, one site had been intensely fertilized with urban sewage
sludge for 10 years of 7.5 tons/ha annually, whereas an adjacent site had been left untreated.
A model column experiment was set up to investigate changes of permeabilities and trace
element retentions at 0–20 cm and 20–60 cm layers thereof. The particular goal was to monitor
losses of nutrients to deeper soil layers or aquifers from biogas residues deposited on site.
Residual slurry after biogas production or equivalent amount of water were added on top of
the model columns, followed by gradual elution with de-ionized water at amounts of expected
rainfall at the sampling site (1000 mm). Long-term sludge treatment changed organic carbon,
soil nutrients as well as Ba, Cu, Pb, and Zn significantly, resulting in different vertical
migration and elution of applied substances. Differences between the mobilities of P, Fe, S,
Cu, B, as well as nitrate and ammonia losses were much more affected by the long-term
sludge pretreatment than by the characteristics of the biogas residue or just de-ionized water
applied on top of the columns. Largest differences between biogas residue addition and water
only were noticed for zinc and ammonia. The addition of iron salts in order to increase sulfide
precipitation, had measurable but low effects.