Soil moisture and temperature regulation of thaw-driven N2O emissions, kinetics, and thermodynamics with urea and SuperU in a Gleyed Humic Vertisol
Year: 2026
Type: article
Abstract: In the Canadian Prairies, freeze-thaw cycles can account for a large share of annual agricultural N₂O emissions. Among the factors controlling these thaw-driven emissions, soil moisture is a major driver, while thawing temperature and fertilizer source may further modify these emissions; their interactions and the processes underlying thaw-induced N₂O productions remain poorly understood. This study evaluated the effects of freezing (-20 °C), thawing temperature (4, 8, 12, and 16°C), soil moisture (32, 50, 75, and 100% water-filled pore space [WFPS]), and fertilizer source (control, urea, and SuperU) on N₂O emissions from a Gleyed Humic Vertisol from southern Manitoba, Canada. Laboratory incubation experiments were conducted following a simulated freeze-thaw event using a freeze-thaw chamber and incubators over a 60-hour thawing period. Results showed that soil moisture was the main factor controlling thaw-induced N₂O emissions. Increasing soil moisture increased mean N₂O flux from 0.14 to 1.19 μg N₂O–N kg⁻¹ h⁻¹, about 8.5 times higher, while cumulative emissions increased from 6.26 to 82.83 μg N₂O–N kg⁻¹, about 13 times higher, across 32% to 100% WFPS. The increase under wetter thaw conditions is associated with higher denitrification rates and greater N₂O production. Soil moisture also affected residual nitrate, whereas residual ammonium was influenced by thawing temperature and fertilizer type. There was no significant difference in N₂O emissions between SuperU and conventional urea. Soil moisture also controlled the kinetics and thermodynamics of thaw-induced N₂O emission. As WFPS increased, the first-order rate constant (k) declined from 0.03 to 0.02h-1, while half-life (t₁/₂) increased from 24.65 to 34.73 h, indicating slower but more prolonged N₂O accumulation. Activation energy declined from 38.1 kJ mol⁻¹ to near zero, while Gibbs free energy increased, enthalpy shifted from positive to negative, and entropy became more negative with increasing moisture. Thawing temperature mainly affected the kinetics of N₂O emission when combined with soil moisture, and fertilizer source had little impact on these kinetic or thermodynamic parameters. These results suggest that fall-applied nitrogen fertilizer is prone to thaw-induced N₂O emissions in poorly drained clay soils and that avoiding fall N application under these conditions may reduce emissions on the Canadian Prairies.
Source: Mspace (University of Manitoba)
Author: Amoah, Kingsford
Institution: University of Manitoba
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDGs: Climate action, Zero hunger
Open Access status: green
OpenAlex ID: W7208802405