Purpose

The effects of soil pH manipulation and KCl addition on N₂O production in adjacent forest and grassland soils in central Alberta were studied in a 16-day laboratory incubation experiment.

Materials and methods

The soils were subjected to four pH and two salt treatments: CK (control)—no addition of acid or alkali solution (pH 4.50 and 4.48 for the forest and grassland soils respectively; same below); HCl—addition of HCl solution to lower soil pH (3.95 and 3.75); L-KOH and H-KOH—addition of 6 mL of 0.2 (5.36 and 5.57) and 0.4 (6.41 and 6.72) mol L⁻¹ KOH solution respectively to increase soil pH to two different levels. In order to differentiate between the effect of a change in pH and of changed salt concentrations on N₂O production 6 mL of 0.2 (L-KCl) (4.56 and 4.41) or 0.4 mol L⁻¹ (H-KCl) (4.59 and 4.42) KCl solutions were also applied as treatments to create two levels of salt application rates.

Results and discussion

Increasing pH promoted gross nitrification and cumulative N₂O production in both soils particularly in the forest soil. However cumulative N₂O production decreased in the forest soil but increased in the grassland soil when pH decreased. Cumulative N₂O production in the grassland soil was 36 times higher in the L-KCl treatment (1442 μg N kg⁻¹) than in the CK (40 μg N kg⁻¹) whereas the H-KCl treatment reduced cumulative N₂O production. In contrast in the forest soil both KCl treatments reduced cumulative N₂O production.

Conclusions

(1) The most important factor to increase N₂O production in this study was increasing soil pH suggesting that careful soil pH management could be used as a tool to control soil N₂O production; (2) salt effect was also involved in affecting N₂O production.