Denitrification in Low pH Spodosols and Peats Determined with the Acetylene Inhibition Method

Potential denitrification rates were determined for predominantly acid (pH ≥ 3.6) horizons of forestal, miry, and agricultural soils from 22 locations in southern Finland. The acetylene inhibition method was used with nitrate-amended water-logged soils incubated in an N₂ atmosphere containing 2.5 or 5% C₂H₂. Complete inhibition of the reduction of N₂O to N₂ was observed in 99.3% of the samples. The denitrification rates varied from 0.12 to 53.8 μg of N·cm^-3·day^-1. Correlation between denitrification rate and soil pH was highly significant: r = 0.84 on a volume basis, and r = 0.44 on a weight basis. Vegetation type and amount of soil organic matter had a minor or no effect, respectively. In spodosolized soils the rates were significantly higher for B horizons than for A horizons. These results show that denitrification can occur in acid soils.