Impact of liming and maize residues on N2O and N2 fluxes in agricultural soils: an incubation study

Since it is known that nitrous oxide (N₂O) production and consumption pathways are affected by soil pH, optimising the pH of agricultural soils can be an important approach to reduce N₂O emissions. Because liming effects on N₂O reduction had not been studied under ambient atmosphere and typical bulk density of arable soils, we conducted mesoscale incubation experiments with soils from two liming trials to investigate the impact of long-term pH management and fresh liming on N transformations and N₂O production. Soils differed in texture and covered a range of pH levels (3.8–6.7), consisting of non-limed controls, long-term field-limed calcite and dolomite treatments, and freshly limed soils. Both soils were amended with ¹⁵N-labelled potassium nitrate (KNO₃) and incubated with and without incorporated maize litter. Packed soil mesocosms were cycled through four phases of alternating temperatures and soil moistures for at least 40 days. Emissions of N₂O and dinitrogen (N₂) as well as the product ratio of denitrification N₂O/(N₂O + N₂), referred to as N₂Oi were measured with the ¹⁵N gas flux method in N₂-reduced atmosphere. Emissions of N₂O increased in response to typical denitrifying conditions (high moisture and presence of litter). Increased temperature and soil moisture stimulated microbial activity and triggered denitrification as judged from ¹⁵NO₃⁻ pool derived N₂O + N₂ emissions. Fresh liming increased denitrification in the sandy soil up to 3-fold but reduced denitrification in the loamy soil by 80%. N₂Oi decreased throughout the incubation in response to fresh liming from 0.5–0.8 to 0.3–0.4, while field-limed soils had smaller N₂Oi (0.1–0.3) than unlimed controls (0.9) irrespective of incubation conditions. Our study shows that the denitrification response (i.e., N₂O + N₂ production) to liming is soil dependent, whereas liming effects on N₂Oi are consistent for both long- and short-term pH management. This extends previous results from anoxic slurry incubation studies by showing that soil pH management by liming has a good mitigation potential for agricultural N₂O emissions from denitrification under wet conditions outside of cropping season.