Mitigation of climate change through soil organic carbon sequestration in smallholder farming systems of Zimbabwe

Download Mitigation of climate change through soil organic carbon sequestration in smallholder farming systems of Zimbabwe

Post on 15-Jul-2015




1 download


  • Mitigation of climate change through soil organic carbon sequestration in smallholder

    farming systems of Zimbabwe Mujuru La, Mureva Aa, Velthorst Eb. and Hoosbeek Mb

    a Bindura University of Science Education, Department of Environmental Science, Private Bag 1020, Bindura, Zimbabwe; bDepartment of Soil Quality, Wageningen University, P. O Box 47, 6700AA, Wageningen, The Netherlands.

    ACKNOWLEDGMENTS We thank the Netherlands Fellowship Programme and the Climate Food and

    Farming Network (CLIFF). We are also grateful to CIMMYT Zimbabwe and farmers in Shamva and Bindura.

    INTRODUCTION Soil organic matter (SOM) represents a large, dynamic and complex

    terrestrial reservoir of carbon (C). Soil management strategies

    therefore become an important C mitigation approach through

    mitigation measures involving both CO2 emissions reduction and

    increasing C sinks (Food and Agriculture Organisation (FAO), 2010).

    Land use practices in agro ecosystems affect the storage of organic

    carbon in soils especially in sub- Saharan Africa, where crop farming is

    characterised by mono cropping, frequent soil tillage and removal of

    crop residues from fields through livestock grazing or burning

    (Chigonda 2008). Conservation farming practices such as minimum or

    no tillage minimise soil disturbance and utilises crop residues to retain

    moisture and enrich the soil among the smallholder communal farming

    systems. Addition of manure and other organic fertilisers improves

    nutrient efficiency and enhances biomass yields (Nyamangara et al.,

    2003). Increasing biomass can improve soil organic carbon (SOC)

    storage therefore becomes a major focal point for climate change

    mitigation through accumulation of significant quantities of organic C.

    This study evaluated the effects of tillage practices and fertility

    amendments on SOC storage in sandy and clayey soils of Zimbabwe.

    RESEARCH SITE AND METHODOLOGY Research was carried out in farmers fields in Bindura, Shamva and Murewa districts of Zimbabwe. Altitudinal ranges from 1000 to 1800

    m.a.s.l. with annual unimodal rainfall of 750-1000 mm. Soil samples

    were collected at 0-10 and 10-30 cm depths in three tillage systems;

    (conventional tillage (CT), Minimum tillage (MT) with a ripper, No

    tillage (NT) using a direct seeder in Haplic Arenosols (sandy) in

    Shamva and Rhodic Ferralsols (clayey) in Bindura. Minimum and no

    tillage treatments received 2.5-3.0 Mg ha-1 organic inputs and the

    three treatments received equal amounts of inorganic fertiliser. To

    assess effects of agricultural land use on SOC, irrespective of

    treatment, soil samples were also collected from adjacent natural

    forests. In another experiment cattle manure and nitrogen fertiliser

    were added to conventionally tilled soils and SOC was assessed.



    When conventional tillage is the only available option, application of nitrogen fertiliser can be more beneficial for increasing C stocks in sandy soils

    whereas application of organic fertiliser (cattle manure) has greater C benefits in clayey soils. Increased SOC improves crop production thus,

    ensuring climate change mitigation and food security. Residue retention strategies need to be developed to improve environmental and productive

    capacity of cropping systems in smallholder farming systems in arid and semi-arid areas where communal grazing rights are common.

    Carbon storage under fertility treatments in

    conventionally tilled soils Application of N fertiliser plus cattle manure significantly increased

    the SOC stocks in soil compared to application of N Fertiliser alone at

    all depths on clayey soils. On sandy soil, application of N Fertiliser

    resulted in greater SOC than N Fertiliser + manure and control at all

    depths except the 10-20 cm depth

    Figure 3: Carbon storage in three density fractions (a) free light

    fraction (fLF) (b) Occluded light fraction (oLF) (c) Mineral associated

    heavy fraction (MaHF).

    Figure 1: Carbon storage in bulk soils in three tillage systems and natural

    forests on two contrasting soil types

    Caborn storage in tillage systems On clayey soils, C storage was higher in minimum tillage (32 Mg ha-1)

    than no tillage and conventional tillage which had similar C stocks (31

    Mg ha-1) at 0-30 cm. There were no significant difference in SOC stocks

    among tillage systems in clayey soils. Sandy soils however, showed

    more C under no tillage (11 Mg ha-1) than minimum tillage (10 Mg ha-1)

    and conventional tillage (8 Mg ha-1). Lack of significantly different C

    gains under conservation tillage practices (MT and NT) could be

    attributed to limited residue cover which makes soils more vulnerable to

    agents such as wind erosion compared to conventionally ploughed soils,

    where the roughness created by tillage can reduce wind and water


    Figure 2

    CT NT MT

    Depth distribution of soil organic carbon in tillage treatments Depth distribution showed significantly higher (F= 22.98; p


View more >