Rehabilitating degraded croplands for improved crop productivity and soil carbon sequestration on smallholder farms in Zimbabwe
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This presentation was presented during the 3 Parallel session on Theme 3.3, Managing SOC in: Dryland soils, of the Global Symposium on Soil Organic Carbon that took place in Rome 21-23 March 2017. The presentation was made by Mr. Hatirarami Nezomba, from Soil Fertility Consortium for Southern Africa - Zimbabwe, in FAO Hq, Rome
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Rehabilitating degraded croplands for improved crop productivity and soil carbon sequestration on smallholder farms in Zimbabwe
- 1. Rehabilitating degraded croplands for improved crop productivity and soil carbon sequestration on smallholder farms in Zimbabwe Hatirarami Nezomba (PhD) Soil Fertility Consortium for Southern Africa (SOFECSA) Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe GSOC 17-Global Symposium on Soil Organic Carbon 21-23 March 2017, FAO Headquarters, Rome, Italy
- 2. • 13 million people • Capital city is Harare • 70% of the population live in rural areas and derive livelihood from agriculture
- 3. Introduction • Most of the croplands in smallholder farming systems of Zimbabwe & other parts of Southern Africa are degraded – severe nutrient deficiencies, – critically low SOM levels and – a general low response to mineral fertilizer addition
- 4. Introduction • Against this background, the region is facing increased demands for food due to population rise, and unfavourable changes in climatic patterns Projected dry days . Pascale et al, 2015
- 5. Introduction • Rehabilitating the degraded croplands is therefore key not only to increasing farm-level crop production, but also for sequestering soil carbon to reduce greenhouse gas emissions.
- 6. Introduction • Restoring soil biochemical properties and increase responsiveness to mineral fertilizers are therefore key to 'kick- starting‘ productivity on these degraded croplands • Nitrogen-fixing indigenous herbaceous legumes mostly of the genera Crotalaria, Tephrosia, and Indigofera, commonly referred to as weeds by farmers, were found to establish well on degraded sandy soils on smallholder farms in Zimbabwe • We envisaged that the establishment of these legumes on degraded soils could enable crops to respond better to subsequent applications of the small amounts of organic and inorganic nutrient resources commonly available to farmers.
- 7. Diversity of indigenous legumes in Zimbabwe Crotalaria pallida Crotalaria laburnifolia Indigofera arrecta Crotalaria cylindrostachys
- 8. Alysicarpus ovalifolius (Schumach.) J. Le´onard Chamaecrista absus (L.) Irwin & Barneby Chamaecrista mimosoides (L.) Greene Crotalaria cylindrostachys Welw. ex Baker Crotalaria glauca Willd. Crotalaria laburnifolia (L.) Crotalaria microcarpa Hochst. ex Benth. Crotalaria ochroleuca G. Crotalaria pisicarpa Welw. ex Baker Crotalaria rhodesiae Baker f. Crotalaria sphaerocarpa Perr. ex DC. Desmodium tortuosum (Sw.) DC. Eriosema ellipticum Welw. ex Baker Eriosema nutans Schinz Indigofera antunesiana Harms Indigofera arrecta Hochst. ex A. Rich. Indigofera astragalina DC. Indigofera brachynema J.B. Gillett Indigofera demissa Taub. Indigofera flavicans Baker Indigofera nummulariifolia (L.) Livera ex Alston Indigofera praticola Baker f. Indigofera vicioides Jaub. & Spach var. rogersii (R.E.Fr.) J.B. Gillett Indigofera wildiana J.B. Gillett Macrotyloma daltonii (Webb) Verdc. Neonotonia wightii (Wight & Arn.) J.A. Lackey Rothia hirsuta (Guill. & Perr.) Baker Stylosanthes fruticosa (Retz.) Alston Tephrosia acaciifolia Welw. ex Baker Tephrosia longipes Meisn. subsp. longipes Tephrosia lurida Sond. var. lurida Tephrosia purpurea (L.) Pers. subsp. purpurea Tephrosia radicans Welw. ex Baker Tephrosia reptans Baker Teramnus repens (Taub.) Baker f. Vigna vexillata (L.) A. Rich. Zornia glochidiata C. Rchb. ex DC. Diversity of indigenous legume species in Zimbabwe (Mapfumo et al., 2005)
- 9. Indigenous legume fallows (indifallows) Over 36 species were identified across different agro-ecological zones of Zimbabwe (Mapfumo et al., 2005). The legumes exhibited effective root nodulation and substantial growth on nutrient- depleted soils (< 10% clay, < 5 ppm available P, < 0.4% organic C).
- 10. Objectives A 3-year study conducted to 1. Assess the effect of indigenous herbaceous legume fallows (indifallows) on above-ground C and N productivity on degraded soils, 2. Determine maize grain yield responses to mineral N fertilizer under indigenous legume-based ISFM sequences, 3. Determine the influence of indigenous legume-based ISFM sequences on soil carbon dynamics.
- 11. Study sites Wedza Makoni district •Rainfall: 650-750 mmyr-1 (November-March ) Soils: Granitic sands (Lixisols) Over 36 species were identified across different agro-ecological zones of Zimbabwe (Mapfumo et al., 2005). Most Hwedza district •Rainfall: >750 mm yr-1 •(November-March •Soils: Granitic sands (Lixisols) Makoni
- 12. Establishing indicators of soil degradation: A participatory approach Farmer mobilization FGDs, key informants, community meetings, transect walks Laboratory soil characterization & experimentation
- 14. Soil rehabilitation sequences Sequencing option Year 1 Year 2 Year 3 ‘Indifallow-start ’ Indifallow + P Maize + cattle manure + mineral fertilizer N and P Maize + mineral fertilizer N and P ‘Sunnhemp-start’ Sunnhemp fallow + P Maize + cattle manure + mineral fertilizer N and P Maize + mineral fertilizer N and P ‘Natural fallow-start ’ Natural fallow + P Maize + cattle manure + mineral fertilizer N and P Maize + mineral fertilizer N and P Continuous fertilized maize Continuous fertilized maize Continuous fertilized maize Continuous fertilized maize Mineral fertilizer rates = 26 kg P ha-1 and 120 kg N ha-1 Cattle manure = 7 t ha-1
- 15. C and N productivity on degraded soils •Indifallow and sunnhemp fallow generated more N and C than natural fallows
- 16. C and N productivity on degraded soils Indifallow Natural fallow Sunnhemp
- 17. Maize grain yield responses to N-Year 3
- 18. Soil microbial biomass C in Year 3 at 6 weeks after maize planting SoilmicrobialbiomassC(mgkg-1 ) 0 100 200 300 0-10 cm 10-20 cm 50 'Indifallow-start' 'Sunnhemp-start' 'Natural fallow-start' Continuous fertilized maize Continuous unfertilized maize •Higher MBC under herbaceous legume-based ISFM sequences……. more labile N and C to stimulate microbial activity
- 19. Soil microbial biomass N in Year 3 at 6 weeks after maize planting 0 SoilmicrobialbiomassN(mgkg-1) 0 10 20 30 40 50 0-10 cm 10-20 cm 'Indifallow-start' 'Sunnhemp-start' 'Natural fallow-start' Continuous fertilized maize Continuous unfertilized maize 'Indifallow-start' 'Sunnhemp-start' 'Natural fallow-start' Continuous fertilized maize Continuous unfertilized maize •Higher MBC under herbaceous legume-based ISFM sequences……. more labile N and C to stimulate microbial activity
- 20. Soil organic C in Year 3 at 6 weeks after maize planting •Slightly more soil organic sequestration under natural fallow-based ISFM sequences....but not enough to tilt the balance building SOC a major challenge on sandy soils in tropical environments Soilorganiccarbon(tha -1 ) 0 1 2 3 4 5 6 0-10 cm 10-20 cm 'Indifallow-start' 'Sunnhemp-start' 'Natural-fallow-start' Continuous fertilized maize Continuous unfertilzed maize
- 21. Key findings • Herbaceous N2-fixing legumes such as naturally-adapted indigenous legumes offer prospects for generating high initial biomass on degraded soils. • The predominantly legume biomass produced under indifallow and sunnhemp fallow in combination with cattle manure increased soil biological activity (microbial biomass) and the responsiveness of the degraded soils to mineral N fertilizer • Natural fallow-based ISFM sequences offer promise for increasing C sequestration on degraded sandy soils
- 22. References 1. Nezomba, H., Mtambanengwe, F., Tittonell, P. and Mapfumo, P. 2015b. Point of no return? Rehabilitating degraded soils for increased crop productivity on smallholder farms in eastern Zimbabwe. Geoderma 239-240: 143–155. 2. Nezomba H., Tauro T.P., Mtambanengwe, F., Mapfumo P., 2010. Indigenous legume fallows (indifallows) as an alternative soil fertility resource in smallholder maize cropping systems. Field Crops Research 115:149–157 3. Nezomba, H., Tauro, T.P., Mtambanengwe, F. and Mapfumo, P. 2009. Indigenous legumes biomass quality and influence on C and N mineralization under indigenous legume fallow systems. Symbiosis 48: 78–91. 4. Mapfumo P, Mtambanengwe F, Giller KE, Mpepereki S. 2005. Tapping indigenous herbaceous legumes for soil fertility management by resource poor farmers in Zimbabwe. Agriculture Ecosystems and Environment 109: 221-233
- 23. Acknowledgements • Funding for this work was provided by the European Union through the Agroecology-based Aggradation–Conservation Agriculture: Tailoring innovations to combat food insecurity in semiarid Africa (ABACO) project • Soil Fertility Consortium for Southern Africa
- 24. Thank you