Restoring the Soil - Canadian Foodgrains Bank

Green Manure/Cover Crop Systems69MaliS57. Millet/Faidherbia albida. Farmers in Mali, Burkina Faso and Niger purposelyleave existing Faidherbia albida (previously Acacia albida) trees in their fields. Thesetrees, different from all the other Sahelian trees, drop their leaves during the rainy season,therefore supplying a very beneficial 15 to 25% shade to the crops under them.This shade allows crops to keep on growing all day, instead of closing down duringthe excessive mid-day heat, thereby increasing productivity by up to 40%. The lowersoil surface temperature achieved by the shade also dramatically reduces evaporationand transpiration rates. As a result, soil moisture losses are reduced and the annualgrowing season is extended by a week or two. Farmers who practice this traditionalsystem probably number in the hundreds of thousands.S58. Millet/nyama-3. This is the only system in the decision tree that has never beenpracticed by any farmers exactly as described. But I believe it would be an ideal systemfor the African Sahel. I venture this bit of hubris for two reasons. First, the systemI am suggesting is basically a combination of two already-existing systems (S52 andS57). A fast-growing exotic tree and organized on a grid to make animal tractionplowing easier will reduce the labor requirement of the traditional systems.Second, the Sahel suffers from a lack of good gm/cc systems. This has happened inpart because of a widespread but mistaken belief that they will not work under semiaridconditions. It also has happened in part because the environment in the Sahelis definitely somewhat hostile to all living things, especially gm/cc species, with theirhigh nitrogen, and therefore high protein content.Yet even in the northern Sahel, two gm/cc systems are presently working very well.Farmer managed natural regeneration (FMNR) has populated some 5 million hectaresof Niger with trees, as well as another half million hectares in northern Mali. Sincea large number of these trees are leguminous, the soil in this system has gained bothan increase in organic matter and an increase in nitrogen. Millet yields have increasedsignificantly. Another system, developed by the Dogon around the town of Koro,involves leaving naturally occurring trees in the fields and protecting certain otherdesired species of trees (such as Faidherbia albida) that sprout naturally in their fields.These trees are all pruned in the shape of a funnel, which prevents the area under thetree from getting too much shade, yet shades all the field at some time during the dayas the sun moves across the sky. Under this dispersed shade, the Dogon farmers practicea rotation that includes such gm/ccs as peanuts, Bambara groundnuts and fonio.Just as with FMNR, yields have increased as the organic matter content of the soil hasalso increased. The last time I visited this area, the Dogon farmers using this systemwere collecting the largest harvest they had had in years, while everyone around themfor many miles was complaining that the drought had destroyed their crops.For the southern Sahel (from about 13 o N latitude towards the south), the gm/ccsystem that I would like to see tried more widely consists of dispersed shade providedby mother of cacao (Gliricidia sepium) and, if farmers wish, Faidherbia albida trees,