1. Soil organic carbon dynamics, functions and management in West African agro-ecosystems Bationo A., Vanlauwe B., Kihara J. and Kimetu J.

2. Outline Introduction Variability of soil organic carbon content at agro- ecosystem and farm level. Effect of soil and crop management on soil organic carbon Role of organic amendments on land productivity Future research challenge with emphasis on organic matter quantity and quality Conclusion

3. Lack of Resources Lack of Knowledge Land Degradation Improved Knowledge Improved Soil Management Improved Livelihoods Virtuous cycle Vicious cycle The Vicious and Virtuous cycle

4. The growth rate for cereals grain yield is about 1% while population growth is about 3%. During the last 35 years, cereals production per capita has decreased from 150 to 130 kg/person, whereas in Asia and Latin America an increase from about 200 to 250 kg/person have been observed. Both labor and land productivity are among the lowest of the world. Per Capita food production declined by about 30% and cereal self-sufficiency from 85 to 65% Introduction…

5.  Annual cereal deficit in sub-Saharan Africa amounts to 100 million tons  Food imports increased by about 185% between 1974 and 1990, food aid by 295%  The food gap (requirements minus production) is widening  The average African consumes only about 87% of the calories needed for a healthy and productive life

6. Introduction … ¨16% of Africa’s current arable land base is so eroded that it cannot be useful any longer agriculturally ¨70% of deforestation is caused by farmers who in their quest for food have no incentive to ponder long- term environmental consequences ¨Increase in area under food crop in sub-Saharan Africa was mainly due to use of marginal lands hence further environmental degradation through soil erosion and nutrient mining

7. Increase in yield has been more due to land expansion than to crop improvement potential CropsAreaYieldProduction Cassava2.60.73.3 Maize0.80.21.0 Yam7.20.47.6 Cowpea7.6-1.16.5 Soybean-0.14.84.7 Plantain1.90.02.0 Based on three-year average for 1988-1990 and 1998-2000. FAO database.

8. Growth rate of millet 1979-1994 CountryArea (%)/year Yield (%)/ year Production (%)/year Production/ hbt (%)/year WA4.7- 0.44.21.2 Mali5.1- 1.04.02.3 Niger3.9- 1.02.8- 1.3 Nigeria7.7- 2.35.22.2 B.F3.82.05.93.0

9. Percentage chances in soil fertility parameters in farmers’ fields as a result of 50 years of cultivation in the Savannah zones Source: Balasubramanian et al. 1984 ZonesExchangeable cations CaMgKpH Sudan2132254.0 N. Guinea1927333.8 S. Guinea46515010.0

10. Macronutrient loss versus consumption in Africa

11. Biophysical and economic parameters related to household resource endowment (Shepherd & Soule, 1998)

12. Effect of depth of soil mechanical de-surfacing at Mbissiri, Cameroon

13. Influence of mulch cover on erosion

14. Influence of cumulated erosion for a three year banana mulch on grain yield of next maize crop

15. Variability of soil organic carbon content at agro-ecosystem and farm level

16. 0 20 40 60 80 100 120 Total System C (t ha -1 ) Senegal River Valley Sahelian Shrubby Grassland (Sylvo-pastoral Zone) Sahalian-Sudanese Transition Drier Sudanese Woodland (Old Groundnut Basin) Wetter Sudanese Woodland (New Groundnut Basin) Sudanese-Guinean Transition (Casamance) forest cultivatedgrazed cultivateddegraded grazed parkland cultivated fallow woodlandgrazed cultivated forest parklandfallowcultivated Vegetation and Land Use 16.5 o N13.1 o N16.1 o N15.2 o N14.8 o N14.1 o N Source: Woomer 2003

17. Carbon stocks and other fertility indicators of granitic soils in different agro-ecological zones in West Africa Source:WindmeijerandAdriesse1993

18. Carbon stocks of different subsystems in a typical upland farm in the Sudan-savanna zone 4.0-2420-2200.9-1.811-226.7-8.3Home garden 0.6-15-160.2-0.52-55.7-6.2Bush field 4.0-1113-160.5-0.95-105.7-7.0Village field Exchangeable K (mmol/kg) Available P mg/kg Total N g/kg OC g/kg pH H 2 O AEZ Source: Prudencio et al

19. Use of organic resources within a farm for various farmer typologies

20. Correlation (r) between selected soil (0-20 cm) fertility parameters and average annual rainfall ** and *** indicate statistical significance at the 0.05 and 0.001 level, respectively. Source: Manu et al., 1991 Soil organic carbon losses are more related to clay and slit contents than rainfall

21. Effect of soil and crop management on soil organic carbon

22. Carbon losses (kg ha-1 yr-1) by erosion, runoff and leaching in the topsoil (30cm) in runoff plots (Adopted from Roose E and Barthes B, 2001)

23. Annual loss rates of soil organic carbon measured at farm level in WASAT SiteClay + silt (%) Annual losses (K) (%) Bambay37 Saria (non eroded)122 Saria eroded196

24. 2:1 clays 1:1 clays Forest Grassland Cultivated Source: Six et al., 2002 Relationship between silt+clay content and silt+clay associated carbon for different systems

25. Organic carbon changes under continuous cropping and under fallow in an ultisol Adapted from Kang 1993

26. Evolution of carbon content in the 0-10cm horizon, as affected by time and treatment in runoff plots of Mbissiri station, Cameroon

28. Kg P/ha

29. Sorghum-groundnut rotation in Burkina Faso shows good crop as opposed to Continuous Sorghum crop (inset)

31. Role of organic amendments on land productivity

33. Phosphorus use efficiency (kg grain/kg P) in village (non degraded) and bush (degraded) fields for pearl millet production, Niger

35. Effect of cattle dung and urine on millet grain and total above ground bio-mass, Sadore Niger ManureDung+ Urine- Urine ApplicationGrainBiomassGrainBiomass Kg/ha Cattle0--80940 299058041703202170 6080115070304703850 7360171092905603770 s.e.m175812109496 Adapted from Powell et al., 1998

36. Effect of fertilizer application and crop residue on maize grain yield Adapted from Kang 1993

37. Pearl millet total dry matter yield as affected by long-term application of crop residue and fertilizer Source: Bationo et al, 1998.

38. Incremental millet grain and stover yield due to fertilization in sadore, Niger Source: Bationo et al., 1995 GrainStover 1985CR-- Fertiliser67188 CR + Fertiliser137427 1986CR-- Fertiliser57184 CR + Fertiliser112359 YearTreatmentFertiliser effect ----- kg per kg P applied ----

39. ORGANIC INPUTS FOR N MANAGEMENT Decision Guide

40. FEs for Different Organic Materials

42. Base saturation and pH (water) for soil experiments in Saria, Burkina Faso TreatmentBase saturation pH Control0.635.2 Chemical fertilizer0.374.6 Crop residues 5t ha -1 0.75.2 (Source: Pichot et al 1981)

43. Soil pH as affected by soil depth and management practices. Sadoré, Niger, rainy season, 1996

44. Maximum phosphorus sorbed as affected by soil depth and management practices, Sadoré, Niger, 1999

45. Availability of crop residue Optimum rate : 2 t ha -1 Farmers field : 200kg ha -1 Farmers’ doses combined with the use of small quantities of P fertilizers can boost crop biomass. Limitations

46. Utilisation de micro-dose de P (4kg/ha) - P + P

47. Limitations – Manure use is part of internal flow and does not add always nutrients from outside the farm –Limited quantities, low nutrient content and often high labor demands for processing and application –Potential livestock transfer of nutrients in W. Africa is 2.5 kg N and 0.6 kg P per hectare of cropland

48. –5-20 tons recommended but less than 700kg is available in semi- arid W. Africa –Can only increase yield by 2% per year –Need between 10-40 ha of grazing land to maintain yield on 1 ha of cropland Limitations

49. Future research challenge with emphasis on organic matter quantity and quality

50. Future research challenges Focus more on whether the organic resource quality concept is also useful for predicting different degrees of stabilization of applied organic C in one or more of the organic matter pools Increasing the dual purpose grain legume component for improvement of soil organic carbon and for a better integration of crop-livestock production systems Improvement of nutrient use efficiency in order to offer cost- effective mineral fertilizer recommendations to the small-scale farmers Use of decision support systems, modelling, and GIS for the extrapolation of research findings