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Abstract. Globally, tropical forest soils represent the second largest source of N 2 O and NO. However, there is still considerable uncertainty on the spatial variability and soil properties controlling N trace gas emission. Therefore, we carried out an incubation experiment with soils from 31 locations in the Nyungwe tropical mountain forest in southwestern Rwanda. All soils were incubated at three different moisture levels (50, 70 and 90 % water filled pore space (WFPS)) at 17 • C. Nitrous oxide emission varied between 4.5 and 400 µg N m −2 h −1 , while NO emission varied from 6.6 to 265 µg N m −2 h −1 . Mean N 2 O emission at different moisture levels was 46.5 ± 11.1 (50 %WFPS), 71.7 ± 11.5 (70 %WFPS) and 98.8 ± 16.4 (90 %WFPS) µg N m −2 h −1 , while mean NO emission was 69.3 ± 9.3 (50 %WFPS), 47.1 ± 5.8 (70 %WFPS) and 36.1 ± 4.2 (90 %WFPS) µg N m −2 h −1 . The latter suggests that climate (i.e. dry vs. wet season) controls N 2 O and NO emissions. Positive correlations with soil carbon and nitrogen indicate a biological control over N 2 O and NO production. But interestingly N 2 O and NO emissions also showed a positive correlation with free iron and a negative correlation with soil pH (only N 2 O). The latter suggest that chemodenitrification might, at least for N 2 O, be an important production pathway. In conclusion improved understanding and process based modeling of N trace gas emission from tropical forests will benefit from spatially explicit trace gas emission estimates linked to basic soil property data and differentiating between biological and chemical pathways for N trace gas formation.

Wind erosion mostly occurs in flat, bare areas, with dry, fine sandy to coarse silty soil or where the soil is loose and degraded. Soil degradation, including decline in soil quality caused by its improper use or poor management and soil erosion, has been considered as a major environmental issue in arid and semi-arid areas (Cornelis, 2006; Stroosnijder, 2007; Youssef et al., 2012). In arid areas, wind erosion is the main cause of erosion that leads to desertification. The extent of wind erosion, however, varies in different soils. Soil properties such as soil texture, structure, wetness, organic matter and aggregate stability affect the displacement of particles by wind. Long-term cultivation and intensive grazing decreases soil organic carbon and soil aggregate stability and increases its erosion potential (Obia, Mulder, Martinsen, Cornelissen, & Børresen, 2016). Various methods exist to stabilize soils, including biological, chemical, physical and mechanical stabilization methods. The effective addition of materials to degraded soils can

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