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Nitrous oxide (N2O) is the contributor to agricultural greenhouse gas emissions with the highest warming global potential. It is widely recognised that traffic and animal-induced compaction can lead to an increased potential for N2O emissions by decreasing soil oxygen supply. The extent to which the spatial and temporal variability of N2O emissions can be explained by soil compaction is unclear. This review aims to comprehensively discuss soil compaction effects on N2O emissions, and to understand how compaction may promote N2O emission hotspots and hot moments. An impact factor of N2O emissions due to compaction was calculated for each selected study; compaction effects were evaluated separately for croplands, grasslands and forest lands. Topsoil compaction was found to increase N2O emissions by 1.3 to 42 times across sites and land uses. Large impact factors were especially reported for cropland and grassland soils when topsoil compaction—induced by field traffic and/or grazing—is combined with nitrogen input from fertiliser or urine. Little is known about the contribution of subsoil compaction to N2O emissions. Water-filled pore space is the most common water metric used to explain N2O emission variability, but gas diffusivity is a parameter with higher prediction potential. Microbial community composition may be less critical than the soil environment for N2O emissions, and there is a need for comprehensive studies on association between environmental drivers and soil compaction. Lack of knowledge about the interacting factors causing N2O accumulation in compacted soils, at different degrees of compactness and across different spatial scales, limits the identification of high-risk areas and development of efficient mitigation strategies. Soil compaction mitigation strategies that aim to loosen the soil and recover pore system functionality, in combination with other agricultural management practices to regulate N2O emission, should be evaluated for their effectiveness across different agro-climatic conditions and scales.

We compared the soil C input potential of a common catch-crop (fodder radish) established in 6-year-old direct-drilled (DD) plots with adjacent conventionally tilled (CT) plots on a Danish sandy loam soil by use of 14C-isotope labelling techniques. Intact monoliths of soil with actively growing fodder radish seedlings were extracted in Autumn of 2008 from DD and CT field plots and labelled with 14CO2 at different time intervals during fodder radish growth. Labelled monoliths were then sampled 6 and 100 days after termination of labelling by clipping above-ground biomass at soil level and separating below-ground components into macro-roots and macro-root-free soil at 0–10, 10–25 and 25–45 cm soil depth. Using fodder radish 14C data and the preceding spring barley biomass yield data we estimated C input from the spring barley-fodder radish cycle in addition to evaluating the effect of the removal of spring barley harvestable straw on soil C input. Potential soil C input under straw removal scenarios with and without an established fodder radish crop was also evaluated. Relative to other depths, over 70% of labelled below-ground C was found in the 0–10 cm soil depth in both DD and CT treatments for each of the two samplings. For both macro-root and macro-root-free soil and in both tillage treatments, labelled C decreased significantly with depth (P