When a `natural' landscape is transformed into a `cultural' landscape, the carbon stored in biomass (POC) decreases and this is followed by a decrease in the soil organic carbon (SOC). The lower POC and SOC affect the field water balance: runoff and evaporation increase, while infiltration and transpiration decrease. This has a direct effect (more water erosion) and an indirect effect (a lower rainwater use efficiency or GWUE). Soil and water conservation (SWC) practices reduce erosion, improve soil qualities and increase GWUE. SWC in Burkina Faso can easily save 8 t ha4 y' in erosion, which is equivalent to 16-40 kg C ha"' y''. An increase in GWUE provides the water for the 'regreening' of land use systems. Seven SWC practices are described that have successfully contributed to higher POC and SOC in semi-arid Africa. In Burkina Faso, indigenous agronomic SWC practices have increased crop productivity by 2-3 % y'' over a period of 40 years (1960-2000) and improved SOC in compounds and village fields. With 10 t manure ha' applied during 10 years SOC increases from 4 to 5.8 gC kg" soil, an increase of 0.18 gC kg'' y'. The runoff from mulched plots (6000 kg ha'') was 35 % of that from non-mulched plots, while runoff threshold values decreased from 6.4 to 5,0 mm. Termite `management' reduces runoff significantly. When semi-permeable barriers (stone rows or grass strips) are used for water conservation and combined with composting the synergetic effect is a tripled grain yield. In Ethiopia, Eucalyptus planted along field boundaries produce 170 - 2900 kg wood ha' y" from stands 4 - 12 years old. In Zambia, C sequestration rates of 0.3 - 3.0 t C ha4 y' ' can be obtained with conservation tillage. It is concluded that SWC can stop the current decrease in SOC provided that land use systems are regreened. It is regrettable that the many requirements for CDM (Kyoto) are frustrating local initiatives. What we need is immediate and long-lasting action, not more research!
|Journal||Bulletin Réseau Erosion|
|Publication status||Published - 2004|