Restoring the Soil - Canadian Foodgrains Bank

70Green Manure/Cover Crop Systemsspaced anywhere from 8 m to 12 m square. Parallel rows of nyama would run underevery row or every other row of trees (i.e. every 12 to 24 m across the field). In driernorthern areas, where the nyama grows rather slowly, tephrosia (Tephrosia vogelii or T.candida) could be planted along with the nyama to provide plenty of organic matteruntil the nyama is large enough to do so.With sufficient rainfall, the mother of cacao trees will produce well within five toseven years, and the nyama would produce sometime before that. Within seven years,this system would produce enough gm/cc organic matter to maintain soil fertility. Byincluding the already traditional cowpeas, peanuts and Bambara groundnuts (whosenitrogen would be better-maintained because of the dispersed shade), I am sure thesystem would be capable of increasing soil fertility in the Sahel, without using anychemical fertilizer.42. Benin. Two plots on a research station showthe relative growth of speargrass with and withoutmucuna. (This is the only photo of green manuresused in this book that was not taken on the field ofa farmer who had already adopted the use of greenmanures.)BeninS59. All crops/mucuna. Mucuna is used inBenin to control imperata grass (Imperatacylindrica, generally called speargrass inWest Africa). Imperata grass is one ofthe world’s most noxious weeds (Photo42). With mucuna, imperata-dominatedwastelands are returned to cultivation.The specific techniques vary somewhat,depending on the level of infestation ofimperata grass. Usually the imperata grassmust be burned. Mucuna is then planted.The imperata grass may need to be cutonce more to let the mucuna developsufficiently to smother it. The imperata grass will die after being shaded four or fivemonths. Often the last 5% of the imperata grass must be eliminated by hand. Thelast I knew, 14,000 farmers were using this system, which was largely introduced byIITA (International Institute of Tropical Agriculture) in Nigeria. 25 Sometimes tithonia(Tithonia diversifolia) is used in a similar manner to control imperata grass. Leucaenaand mother of cacao can also be used, but these take three or four years to shade outthe weed.CameroonS60. Tephrosia fallow. Tephrosia vogelii is used as an improved fallow near the townof Bamenda. A year or two after the tephrosia is planted, it is cut down and croppingbegins again. The fertilizing effect of this one-year improved fallow equals the impactof between two and four years under a natural fallow (Photo 43). One farmer starteddoing this in the late 1990s; eight years later the practice had spread spontaneously25Okon, Paul B. and Uche C. Amalu, “Rehabilitation of Degraded Tropical Farms Using Weed to Fight Weed,” n.d.Unpublished.