Interactions between liming and availability of C and P regulate nitrogen transformations and denitrifying potential in an acidic arable soil

Liming to increase pH of acidic soils is a common agricultural practice to optimize crop yields, which also modulates greenhouse gas emissions from soils. In particular, soil pH has been identified as a primary regulator of denitrification pathways with enhanced ratio of nitrous oxide (N₂O) to dinitrogen (N₂) emissions (i.e., enhanced N₂O/N₂ ratio) at lower soil pH. Therefore liming could represent a potential management option to mitigate soil N₂O emissions. However, changes in soil pH have pervasive effects on general microbial activity and on soil properties, including transformations of carbon (C) and bioavailability of phosphorus (P), with a feedback on microbial processes. Thus, the eventual net effects of liming on microbially derived N₂O emissions may be complex. The aim of this study was to discern the interaction between liming (soil pH), and availability of C and P in regulating N₂O emissions from acidic fertilized agroecosystems. Using coarse sandy soils from a long-term liming field experiment, N₂O/N₂ ratios from denitrifying enzyme activity was shown to be strongly affected by liming, i.e., with gradually decreasing ratios at increasing soil pH. Although liming acidic soil (pH, 3.6) to almost neutral (pH, 6.4) favored the reduction of N₂O to N₂, it also enhanced the overall denitrification rate, which eventually resulted in the highest N₂O emission from moderately limed treatments (pH, 4.7). Interactions between P availability and denitrification (and N₂O emission) occurred, where P addition generally increased cumulative N₂O emissions with strongest effect at the moderately limed soil. Mechanistic hypotheses for this effect are discussed. Overall, our results suggest that a critical liming rate should be pursued which may lead to substantial mitigation of N₂O emissions from acidic arable soil.