Restoring the Soil - Canadian Foodgrains Bank

44Decision Tree Guidegrow well and effectively control weedsgiven the local conditions of altitude andweed pressure. The three varieties/speciesare bushy-type jackbean, climbing jackbeanor swordbean and tephrosia (eitherTephrosia vogelii or T. candida). A week ortwo before the beginning of the first rainyseason in the fallow period, broadcast theseed of both varieties of jackbean and thetephrosia. The jackbean seed (Photo 20)should be sown at a rate of about threeseeds per square metre and the tephrosiaabout one to two seeds per square metre.The jackbean (Canavalia ensiformis - whiteseed) and its close relative, the swordbean(Canavalia gladiatus - red seed), are by far22. Honduras. Tephrosia is most widely used as the most drought resistant gm/cc speciesa temporary shade for coffee, but has tremendous used, even when just a week or two oldpotential as a smallholder gm/cc crop where (Photo 21). They are also the most resistantto poor soils, and grow well in moder-uncontrolled grazing is practiced. Being poisonous,animals will not bother it.ate shade. The jackbean can fix up to 240kg N/ha each year, so where nitrogen isthe limiting factor, soil fertility will increase rapidly in one year. Furthermore, likethe tephrosia, jackbean can grow through much or all of the dry season, greatlyreducing the nitrogen loss problem.Both species of tephrosia are woody-stemmed bushes that will reach three orfour metres in height under good growing conditions. The tephrosias are verydrought-resistant, but usually don’t grow well below 300 to 400 m of elevation.Because they are poisonous, animals will not eat them except under conditionsof serious drought (Photo 22). 14 Tephrosia plants will die after about four years,but the soil is generally fertile before then. African farmers who use either of thetephrosias as an improved fallow usually cut it down and kill it after only one ortwo years, because the soil is ready for cropping by that time. Weed control isusually very good if it is sown thickly, as mentioned above. Tephrosia can be usedto make an insecticide. If tephrosia is the best fit, see S60, then go to #5.30. Are animals let loose during the off season? Are the domestic animals (cattle,sheep or goats) let loose when crops are not in the fields? If so, go to #31. If not,or if there are no grazing animals in the villages, go to #32.31. Improved fallows where the animals are loose. Here the best species are thetwo tephrosia species and the jackbean. As with the tephrosias, the jackbean maybe attacked by animals if they are very hungry, but this rarely occurs in areas with14See, for instance, Cherry, Stefan, “Tephrosia fallow management in Cameroon,” in ECHO Development Notes, Issue #65,1999.