Inclusion of legume species into grass leys reduces nitrogen (N) fertilizer need but increases the risk of freeze-thaw induced N₂O emissions. We investigated how liming and presence of clover affect N₂O accumulation under snowpack and its emission during freeze-thaw cycles in autumn and spring under sub-boreal conditions. A field experiment was performed in southern Norway in limed and control plots containing grasses only (fertilized with 270 kg N ha⁻¹ yr⁻¹), a grass-red clover mixture (fertilized with 140 kg N ha⁻¹ yr⁻¹) and unfertilized pure red clover. Soil air samples were collected at 8, 24, and 40 cm depths and analyzed for gas concentrations including N₂O, and N₂O fluxes measured by a fast-chamber robot. Red clover produced more N₂O than the grass-only plots during freeze-thaw cycles in autumn and spring and accumulated more N₂O under snow cover (emissions were not measured during this period). Contrary to expectations, limed red clover plots emitted more N₂O than control plots during freeze-thaw cycles. Liming reduced subnivean N₂O accumulation in grass-only but not in grass-clover or pure clover plots. After spring fertilization, grass-only plots had larger N₂O emissions than red clover plots. Our data suggest that winter-sensitive, N-rich clover biomass fuels decomposition and nitrification, thereby increasing NO₃ ^- and depleting O₂, resulting in increased N₂O emissions from denitrification. Although liming of pure clover leys exacerbated the risk of high N₂O emissions during freeze-thaw, this effect was not observed in grass-clover mixtures. Interestingly, grass-clover mixtures also emitted less N₂O than expected from their proportions and the emissions recorded in pure grass and clover stands. This warrants further studies into off-season functional diversity effects on N cycling and N₂O loss in temperate and boreal forage production.

在禾本科植物中加入豆科植物可减少氮 (N) 肥料的需求，但会增加冻融引起 N ₂ O 排放的风险。我们研究了石灰和三叶草的存在如何影响积雪下N ₂ O 的积累及其在亚北方条件下秋季和春季冻融循环期间的排放。在挪威南部进行了田间试验，在仅含草（用 270 kg N ha ^-1 yr ^-1施肥）、草-红三叶草混合物（用 140 kg N ha ^-1 yr ^-1施肥）和未受精的纯红三叶草。在 8、24 和 40 厘米深度收集土壤空气样本，并分析包括 N ₂在内的气体浓度O 和 N ₂ O 通量由快室机器人测量。在秋季和春季的冻融循环中，红三叶草产生的 N ₂ O 比仅有草的地块多，并且在积雪覆盖下积累了更多的 N ₂ O（在此期间未测量排放量）。与预期相反，在冻融循环期间，石灰红三叶草地块比对照地块排放出更多的 N ₂ O。石灰减少了纯草中亚天际 N ₂ O 的积累，但在草三叶草或纯三叶草地块中没有。春季施肥后，仅草的地块比红三叶地块的N ₂ O 排放量更大。我们的数据表明，冬季敏感、富含 N 的三叶草生物质能促进分解和硝化作用，从而增加 NO ₃ ^-并消耗O ₂，导致反硝化过程中N ₂ O 排放量增加。尽管对纯三叶草进行石灰处理会加剧冻融过程中高 N ₂ O 排放的风险，但在草-三叶草混合物中并未观察到这种影响。有趣的是，草-三叶草混合物排放的 N ₂ O也低于其比例和纯草和三叶草林中记录的排放量的预期。这需要进一步研究淡季功能多样性对温带和北方牧草生产中N 循环和 N ₂ O 损失的影响。