Merbold, Lutz

Pellikka, P.

Rinne, J.

Räsänen, M.

Vesala, T.

Wachiye, S.

CGSpace

AFRICAKENYAQuantification of Annual Soil Greenhouse Gas Emissions under Different Land Use System  in Southern KenyaSheila Wachiye1,2,5, Lutz Merbold3, Timo Vesala2, Janne Rinne4, Matti Räsänen2, Petri Pellikka 1,2HELSINGIN YLIOPISTOHELSINGFORS UNIVERSITETUNIVERSITY OF HELSINKIMATEMAATTIS-LUONNONTIETEELLINEN TIEDEKUNTAMATEMATISK-NATURVETENSKAPLIGA FAKULTETENFACULTY OF SCIENCEIntroductionAgriculture is key land use in Kenya with both food and feed crops grown forsubsistence and commercial production. Agriculture is also reported to be thelargest source of GHG emissions, accounting for one-third of the total emissions inKenya (GOK 2010). Another key land uses are bushland, conservation and grazingland which are diverse savannah landscape types. Despite its extensive coverageand high diversity in Africa, GHG emissions from savannah soils are not wellunderstood. We quantified soil GHG fluxes from these four dominant land usetypes in the savannah landscape in Taita Taveta County in Southern.Site Characteristics1. Farmland - Maize, beans and cassava as main crops2. Bushland – Acacia spp, Commiphora spp trees, with shrubs and grasses3. grasses and Conservation area - grassland savannah protected for wildlife conservation.4. Grazing land - grassland with scattered Acacia spp trees as grazing area for livestock and wildlifeFig. 2: Main land use types, farmland, bushland, conservation and grazing in southern Kenya duringwet (left) and dry (right) season.  Materials and MethodsStatic chamber technique (Collier et al. 2014) was applied. Eight seasonalcampaigns were carried out between 29th November 2017 to 5th October 2018.Three clusters were randomly selected in each land use. In gas pooling method(Arias-Navarro et al. 2013) four 20ml gas samples were collected at 0, 10, 20, 30minutes (Rochette 2011). Gas samples were analysed by a gas chromatographysystem at ILRI in Nairobi. GHG fluxes were calculated from rate of change in gasconcentration in the chamber headspace over time.Results and Discussion1) Soil GHG and Land Use TypesMean CO2, fluxes were higher in the conservation area (75 ± 6 mg CO2 m-2 h-1) andgrazing land (50 ± 5 mg CO2 m-2 h-1) compared to farmland (47 ± 3 mg CO2 m-2 h-1) andbushland (45 ± 4 mg CO2 m-2 h-1). Likely explanation is the slight difference in soil Ccontent. N2O and CH4 were not significantly different between the land use sites. MostCH4 fluxes were below the detection level.Fig. 3: Mean CO2, N2O and CH4 flux comparison between from all the land use2) Soil GHG and Seasonal VariationFig. 4: Seasonal variation of  (a) CO2(b) N2O (c) CH4SeasonsTSW-SD:  Transition from short wet to short dry seasonSD: Short dryTSD-LW: Transition from short dry to long WetLW: Long wetTLW-LD: Transition from long wet to long dryLD: Long dry TLD-SW: Transition from long dry to short wetSW: Short wet  High mean CO2 fluxes were observed in the wetter than the dry season (Fig. 4). Soilmoisture evidently provided soluble substrates and oxygen needed by soil microbes,which was coupled with the growth of dense and fibrous grass roots thus increasing rootrespiration. N2O fluxes were very low during both wet and dry seasons in all the sitesranging from -0.09 to 6 µg N m-2 h-1. This can be attributed low N soil content (about0.07 %) recorded.3) Soil GHG and Environmental FactorsSoil moisture content was higher (14 to 25% ) in the wet season than in dry season (6 to9% ) in all sites. CO2 showed a significant positive relationship with soil moisture. Anincrease in moisture at the onset of rain increased CO2 fluxes in the sites. Nonetheless,N2O did not show a significant relationship with soil moisture although fluxes slightlyincreased with at the onset of the wet season but then dropped. Soil temperature didnot show a significant relationship with both CO2 and N2O fluxes.Fig. 5: Impact of soil moisture and soil temperature  on (a) CO2, (b) N2O, (c) CH4.ConclusionSoil moisture is the main driver of soil CO2 emission in the study area. Soil CO2emissions were higher in the wet season than in dry season from all the land use apartfrom the conservation area. Soil temperature on the other hand did not show a clearcorrelation. N2O fluxes were very low in all the sites both in wet and dry season. LowN2O from can be attributed to the low content of N observed. In farmland, this couldalso be due to low use organic and inorganic fertilizer as farmer only used smallquantities of manure from their livestock throughout their planting season.However, there might be episodes of the emission that we missed, but which needs tobe observed. There is a need for more continuous studies to cover spatial and temporalvariations in soil emissions from diverse savannah landscape and land uses acrossseasonal and management gradients.ReferencesArias-Navarro et al. (2013). Soil Biology and Biochemistry 67: 20–23. https://doi.org/10.1016/j.soilbio.2013.08.011.Collier et al. (2014). J. Vis. Exp. (90), e52110, doi:10.3791/52110.GOK (2010). National Climate Change Action Plan 2011-2012. Ministry of Environment and Mineral Resources, Nairobi, Kenya, Government of Kenya.Rochette, P. 2011. Animal Feed Science and Technology.https://doi.org/10.1016/j.anifeedsci.2011.04.063.Set up Gas pooling Samples Gas chromatography1) Department of Geosciences and Geography, University of Helsinki, Finland2) Institute for Atmosphere and Earth System Research, University of Helsinki, Finland 3) Mazingira Centre, International Livestock Research Institute (ILRI), Nairobi, Kenya4) Department of Physical Geography and Ecosystem Science, Lund University, Sweden5) School of Natural Resource and Environmental Management, University of Kabianga, Kericho, KenyaFunded by:E-mail: sheila.wachiye@helsinki.fi, petri.pellikka@helsinki.fiEmail: sheila.wachiye@helsinki.fiFig. 1: Study area in the lowlands of Taita Taveta County in southern Kenya.1234Wet DryFig 5: Soil moisture across eight campaigns in all the sites.abc

Quantification of annual soil greenhouse gas emissions under different land use system in southern Kenya

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Quantification of annual soil greenhouse gas emissions under different land use system in southern Kenya

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