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Field measurement data on greenhouse gas (GHG) emissions are still scarce for many land-use types in Africa, causing a high level of uncertainty in GHG budgets. To address this gap, we present in situ measurements of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions from the lowlands of southern Kenya. We conducted eight chamber measurement campaigns on gas exchange from four dominant land-use types (LUTs) comprising (1) cropland, (2) bushland, (3) grazing land, and (4) conservation land between 29 November 2017 and 3 November 2018, accounting for regional seasonality (wet and dry seasons and transitions periods). Mean CO2 emissions for the whole observation period were the highest by a significant margin (p value < 0.05) in the conservation land (75±6 mg CO2 -C m -2 h -1) compared to the three other sites, which ranged from 45±4 mg CO2 -C m -2 h -1 (bushland) to 50±5 mg CO2 -C m -2 h -1 (grazing land). Furthermore, CO2 emissions varied between seasons, with significantly higher emissions in the wet season than the dry season. Mean N2O emissions were highest in cropland (2.7±0.6 µ g N2O -N m -2 h -1) and lowest in bushland (1.2±0.4 µ g N2O -N m -2 h -1) but did not vary with season. In fact, N2O emissions were very low both in the wet and dry seasons, with slightly elevated values during the early days of the wet seasons in all LUTs. On the other hand, CH4 emissions did not show any significant differences across LUTs and seasons. Most CH4 fluxes were below the limit of detection (LOD, ±0.03 mg CH4 -C m -2 h -1). We attributed the difference in soil CO2 emissions between the four sites to soil C content, which differed between the sites and was highest in the conservation land. In addition, CO2 and N2O emissions positively correlated with soil moisture, thus an increase in soil moisture led to an increase in emissions. Furthermore, vegetation cover explained the seasonal variation in soil CO2 emissions as depicted by a strong positive correlation between the normalized difference vegetation index (NDVI) and CO2 emissions, most likely because, with more green (active) vegetation cover, higher CO2 emissions occur due to enhanced root respiration compared to drier periods. Soil temperature did not show a clear correlation with either CO2 or N2O emissions, which is likely due to the low variability in soil temperature between seasons and sites. Based on our results, soil C, active vegetation cover, and soil moisture are key drivers of soil GHG emissions in all the tested LUTs in southern Kenya. Our results are within the range of previous GHG flux measurements from soils from various LUTs in other parts of Kenya and contribute to more accurate baseline GHG emission estimates from Africa, which are key to reducing uncertainties in global GHG budgets as well as for informing policymakers when discussing low-emission development strategies. [ABSTRACT FROM AUTHOR]

For effective climate change mitigation strategies, adequate data on greenhouse gas (GHG) emissions from a wide range of land-use and land cover types area prerequisite. However, GHG field measurement data are still scarce for many land-use types in Africa, causing a high uncertainty in GHG budgets. To address this knowledge gap, we present in situ measurements of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions in the lowland part of southern Kenya. We conducted chamber measurements on gas exchange from four dominant land-use types (LUTs) and included (1) cropland, (2) grazed savanna, (3) bushland, and (4) conservation land. Between 29 November 2017 to 3 November 2018, eight measurement campaigns were conducted accounting for regional seasonality (including wet and dry seasons and transitions periods) in each LUT. Mean CO2 emissions for the whole observation period were significantly higher (p-value < 0.05) in the conservation land (75 ± 6 mg CO2-C m-2 h-1) compared to the three other sites, which ranged from 45 ± 4 mg CO2-C m-2 h-1 (bushland) to 50 ± 5 mg CO2-C m-2 h-1 (grazing land). Furthermore, CO2 emissions varied between seasons, with significantly higher emissions during the wet season than the dry season. In contrast, mean N2O emissions were not different between the four sites, ranging from 1.2 ± 0.4 µg N2O-N m-2 h-1 (in bushland) to 2.7 ± 0.6 µg N2O-N m-2 h-1 (in cropland). However, N2O emissions were slightly elevated during the early days of the wet season. CH4 emissions did not show any significant differences between LUTs and seasons, and most values were below the limit of detection (LOD, 0.03 mg CH4-C m-2 h-1). We attributed the difference in soil CO2 emissions between the four sites to soil C content, which differed between the sites and was highest in the conservation land. CO2 and N2O emissions positively correlated to soil moisture, thus an increase in soil moisture led to an increase in emissions. Soil temperature did not show a clear correlation with either, most likely due to the low annual variation in soil temperature. We found a strong positive correlation between soil CO2 and the normalized difference vegetation index (NDVI), but we observed no correlation with soil N2O emissions. We conclude that soil moisture is a key factor in soil GHG emissions in these tropical savanna LUTs. In addition, including vegetation indices in the model greatly improved the results, thus showing the importance of vegetation cover in predicting soil emissions. Our results are within the range of previous GHG flux measurements from soils from various land-use types in other parts of Kenya and contribute to more accurate baseline GHG emission estimates from Africa, which are key for informing policymakers when discussing low-emission development strategies. [ABSTRACT FROM AUTHOR]

Although grazing is the primary land use in the savanna lowland of southern Kenya, the effects of grazing on soil carbon dioxide flux (R S) remain unclear. A 12-month study was conducted from January to December 2020 on the effects of six grazing intensities sites (overgrazed (OG), heavily grazed (HG), moderately grazed (MG), moderately to lightly grazed (M-LG), lightly grazed (LG) and no grazing (NG)) on R S on. A camera trap was used to monitor the total number of animals at each site, indicating the grazing intensity. Weekly measurements of R S were taken using static greenhouse gas chambers along with simultaneous measurements of soil temperature (T S) and volumetric soil water content (W S) (depth of 5 cm). Mean R S at HG, MG, M-LG and LG sites was approximately 15–25% higher than at NG and OG sites (p < 0.001). Mean W S increased with decrease in grazing especially in the dry season, while T S increased with increase in grazing. We observed bimodal temporal variation in R S and W S due to two wet seasons in the year. Thus, variation in R S across the study period followed the changes in W S rather than those in T S. Mean values of R S in the wet seasons were significantly higher (> 45%) than those in the dry seasons, and W S accounted for 71% of the temporal variability in R S (p < 0.05). In addition, the enhanced vegetation index (EVI, interpreted as a proxy for vegetation cover) explained 60% of the variance of R S , and W S and EVI together explained 75%. EVI showed a negative relationship (p < 0.05) with animal intensity, indicating that more grazing reduced vegetation cover and, consequently, soil organic carbon and biomass. Soil bulk density was lower at less grazed sites. While R S variability was unaffected by total nitrogen content, pH, and texture, correspondence analysis demonstrated that the main factors influencing R S dynamics across the year under different grazing intensities were W S and vegetation cover. Our results contribute to closing the existing knowledge gap regarding the effects of grazing intensity on R S in East Africa savannas. Therefore, this information is of great importance in understanding carbon cycling in savanna grassland, as well as the identification of the potential consequences of increasing land pressure caused by rising livestock numbers, and will assist in the development of climate-smart livestock management in East Africa. • Soil CO 2 fluxes decreased with an increase in grazing. • Grazing reduced the vegetation cover, herbaceous aboveground biomass, and increased bulk density. • Enclosure no grazing had lower soil CO 2 fluxes due to lower soil temperturestemperatures and understorey. • Volumetric soil water content and vegetation cover explained the temporal variation in soil CO 2 fluxes. • Results are important in developing climate-smart pastoralism transformation in East Africa. [ABSTRACT FROM AUTHOR]

• Soil CO 2 fluxes varied with stand age with older stands emitting more CO 2 fluxes than the young stands. • Soil moisture and vegetation status are important drivers of CO 2 fluxes in the tropics. • Contribution of soil N 2 O and CH 4 to GHG emissions at site scale are negligible. • Sisal plantations are a minor contributor of agricultural GHG emissions in Kenya. Sisal (Agave sisalana) is a climate-resilient crop grown on large-scale farms in semi-arid areas. However, no studies have investigated soil greenhouse gas (GHGs: CO 2 , N 2 O and CH 4) fluxes from these plantations and how they relate to other land cover types. We examined GHG fluxes (Fs) in a sisal chronosequence at Teita Sisal Estate in southern Kenya. The effects of stand age on Fs were examined using static GHG chambers and gas chromatography for a period of one year in seven stands: young stands aged 1–3 years, mature stands aged 7–8 years, and old stands aged 13–14 years. Adjacent bushland served as a control site representing the surrounding land use type. Mean CO₂ fluxes were highest in the oldest stand (56 ± 3 mg C m-2 h-1) and lowest in the 8-year old stand (38 ± 3 mg C m-2 h-1), which we attribute to difference in root respiration between the stand. All stands had 13–28% higher CO₂ fluxes than bushland (32 ± 3 mg C m-2 h-1). CO 2 fluxes in the wet season were about 70% higher than dry season across all sites. They were influenced by soil water content (W S) and vegetation phenology. Mean N 2 O fluxes were very low (<5 µg N m-2 h-1) in all sites due to low soil nitrogen (N) content. About 89% of CH 4 fluxes were below the detection limit (LOD ± 0.02 mg C m-2 h-1). Our results imply that sisal plantations have higher soil CO 2 emissions than the surrounding land use type, and the seasonal emissions were largely driven by W S and the vegetation status. Methane and nitrous oxide are of minor importance. Thus, soil GHG fluxes from sisal plantations are a minor contributor to agricultural GHG emissions in Kenya. [ABSTRACT FROM AUTHOR]

AbstractFor effective adaptation and mitigation strategies of climate change, adequate data on greenhouse gases (GHGs) emissions from a wide range of land use and land cover types is a prerequisite. Such data is limited in Africa and especially in areas that face diverse land use changes because of human activities. In this study, we measured carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) fluxes in the lowland part of South-Eastern Kenya, using the static chamber method and gas chromatography. Gas samples were collected from four dominant land uses: farmland, bushland, conservation area, and grazing land. Eight individual gas sampling campaigns were conducted targeting wet and dry season and transition periods in between covering a total of 12 months. Data on soil moisture and soil temperature were also collected to better understand the flux patterns. Conservation area recorded the highest average CO2 fluxes (74.2mg CO2 m-2 h-1) followed by bushland (46.2mg CO2 m-2 h-1), grazing land (45.6mg CO2 m-2 h-1) and lastly farmland (39.5mg CO2 m-2 h-1). CO2 fluxes across land use were found to vary significantly (p-value<0.001). Those in the conservation area were higher than the other land use by about 37%-47% on average. CO2 fluxes also varied significantly across seasons with highest fluxes recorded during the transition period from wet to dry season. N2O, on the other hand, was highest in the grazing land (1.2ug N2O m-2 h-1), followed by farmland (1.14 ug N2O m-2 h-1), conservation area (1.13ug N2O m-2 h-1) and lastly bushland (0.91ug N2O m-2 h-1). The differences between the land uses were not found to be significant. Most CH4 fluxes across all land use were below the detection limit ranging on average from -0.011mg CH4 m-2 h-1, -0.018mg CH4 m-2 h-1, -0.024mg CH4 m-2 h-1, -0.025mg CH4 m-2 h-1 for in the grazing area, bushland, conservation area, and farmland respectively. For N2O and CH4, there were no significant differences in fluxes across seasons. Our results showed a non-linear relationship of CO2, N2O and CH4 fluxes with increasing temperature. For soil moisture, the rate of CO2 emission increased with increasing soil moisture contents especially after a period of dry season. In the conservation area and grazing area, higher CO2 and N2O fluxes can be attributed to high carbon (C) and nitrogen (N) contents, a dense root network and high C input from grass decay.KEYWORDS: Static Chamber, Seasonal Variability, Climate Change, Bushland, Conservation, Grazing land, Farmland. [ABSTRACT FROM AUTHOR]