Soil organic carbon management for sustainable land use in Sudano-Sahelian West Africa

Judged by their negative nutrient balances, low soil cover and low productivity, the predominant agro-pastoral farming systems in the Sudano-Sahelian zone of West Africa are highly unsustainable for crop production intensification. With kaolinite as the main clay type, the cation exchange capacity of the soils in this region, often less than 1 cmolc kg−1soil, depends heavily on the organic carbon (Corg) content. However, due to low carbon sequestration and to the microbe, termite and temperature-induced rapid turnover rates of organic material in the present land-use systems, Corg contents of the topsoil are very low, ranging between 1 and 8 g kg−1 in most soils. For sustainable food production, the availability of phosphorus (P) and nitrogen (N) has to be increased considerably in combination with an improvement in soil physical properties. Therefore, the adoption of innovative management options that help to stop or even reverse the decline in Corg typically observed after cultivating bush or rangeland is of utmost importance. To maintain food production for a rapidly growing population, targeted applications of mineral fertilisers and the effective recycling of organic amendments as crop residues and manure are essential. Any increase in soil cover has large effects in reducing topsoil erosion by wind and water and favours the accumulation of wind-blown dust high in bases which in turn improves P availability. In the future decision support systems, based on GIS, modelling and simulation should be used to combine (i) available fertiliser response data from on-station and on-farm research, (ii) results on soil productivity restoration with the application of mineral and organic amendments and (iii) our present understanding of the cause-effect relationships governing the prevailing soil degradation processes. This will help to predict the effectiveness of regionally differentiated soil fertility management approaches to maintain or even increase soil Corg levels.

[1]  D. J. Greenland,et al.  INCREASES IN THE CARBON AND NITROGEN CONTENTS OF TROPICAL SOILS UNDER NATURAL FALLOWS , 1959 .

[2]  F.W.T. Penning de Vries,et al.  La productivite des paturages saheliens : une etude des sols, des vegetations et de l'exploitation de cette ressource naturelle , 1982 .

[3]  G. W. Padwick.  Fifty Years of Experimental Agriculture II. The Maintenance of Soil Fertility in Tropical Africa: A Review , 1983, Experimental Agriculture.

[4]  G. Mcclellan,et al.  Phosphate deposits of tropical sub-Saharan Africa , 1986 .

[5]  C. Pieri.  Fertilisation des cultures vivrières et fertilité des sols en agriculture paysanne subsaharienne , 1986 .

[6]  J. Powell,et al.  Nitrogen and phosphorus transfers in a crop-livestock system in West Africa , 1987 .

[7]  V. Hien,et al.  Le maintien de la fertilité des sols dans l'ouest du Burkina Faso et la nécessité de l'association agriculture-élevage , 1987 .

[8]  J. Stoorvogel,et al.  Assessment of soil nutrient depletion in sub-Saharan Africa: 1983-2000. , 1990 .

[9]  A. Mokwunye,et al.  Agronomic evaluation of two unacidulated and partially acidulated phosphate rocks indigenous to Niger. , 1990 .

[10]  H. Breman,et al.  Manual sur les pâturages des pays sahéliens. , 1991 .

[11]  A. Manu,et al.  FERTILITY STATUS OF SELECTED MILLET PRODUCING SOILS OF WEST AFRICA WITH EMPHASIS ON PHOSPHORUS , 1991 .

[12]  M. Amato,et al.  Decomposition of 14C-labelled glucose and legume material in soils: Properties influencing the accumulation of organic residue C and microbial biomass C , 1992 .

[13]  H. Marschner,et al.  Long‐term nitrogen balance for pearl millet (Pennisetum glaucum L.) in an acid sandy soil of Niger , 1993 .

[14]  J. Powell,et al.  Livestock and sustainable nutrient cycling in mixed farming systems of sub-Saharan Africa : proceedings of an international conference, International Livestock Centre for Africa (ILCA) Addis Ababa, Ethiopia, 22-26 November 1993 , 1994 .

[15]  H. Marschner,et al.  Short- and long-term effects of crop residues and of phosphorus fertilization on pearl millet yield on an acid sandy soil in Niger, West Africa , 1994 .

[16]  M. Sivakumar,et al.  Wind erosion control using crop residue II. Effects on millet establishment and yields , 1995 .

[17]  J. Baidu-Forson.  Determinants of the Availability of Adequate Millet Stover for Mulching in the Sahel , 1995 .

[18]  J. Powell,et al.  Manure utilisation, drought cycles and herd dynamics in the Sahel: implications for cropland productivity , 1995 .

[19]  A. Buerkert,et al.  Effects of Crop Residue and Phosphorus Application on the Spatial Variability of Non-destructively Measured Millet Growth in the Sahel , 1995, Experimental Agriculture.

[20]  A. Buerkert,et al.  Anti-erosive, Soil Physical, and Nutritional Effects of Crop Residues , 1996 .

[21]  B. Allison,et al.  Wind Erosion in Niger , 1996 .

[22]  E. Schlecht,et al.  Livestock-mediated nutrient transfers in Sahelian agro-ecosystems , 1997 .

[23]  S. Koala,et al.  Research on nutrient flows and balances in west Africa: state-of-the-art 1 Paper contributes to EC I , 1998 .

[24]  P. Hiernaux,et al.  Nutrients in the West African Sudano-Sahelian zone: Losses, transfers and role of external inputs , 1998 .

[25]  H. Young,et al.  1. Main report , 1998 .

[26]  J. Powell,et al.  URINE EFFECTS ON SOIL CHEMICAL PROPERTIES AND THE IMPACT OF URINE AND DUNG ON PEARL MILLET YIELD , 1998, Experimental Agriculture.

[27]  A. Buerkert,et al.  Mechanisms of residue mulch-induced cereal growth increases in West Africa. , 2000 .