Soils, a sink for N₂O? A review

Abstract Soils are the main sources of the greenhouse gas nitrous oxide (N 2 O). The N 2 O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on net N 2 O production. However, in the literature, there are numerous reports of net negative fluxes of N 2 O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise. Net N 2 O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N 2 O consumption. This fits in with denitrification as the responsible process, reducing N 2 O to N 2 . However, it has also been reported that nitrifiers consume N 2 O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N 2 O consumption, ranging from low to high temperatures, wet to dry soils, and fertilized to unfertilized plots. Generally, conditions interfering with N 2 O diffusion in the soil seem to enhance N 2 O consumption. However, the factors regulating N 2 O consumption are not yet well understood and merit further study. Frequent literature reports of net N 2 O consumption suggest that a soil sink could help account for the current imbalance in estimated global budgets of N 2 O. Therefore, a systematic investigation into N 2 O consumption is necessary. This should concentrate on the organisms, reactions, and environmental factors involved.