Restoring the Soil - Canadian Foodgrains Bank

50Decision Tree Guideeties should not be intercropped with sorghum or millet, because the sorghumand millet stalks will not support the weight of the intercropped beans.Vigna species fix much more nitrogen than do the common beans (Phaseolusvulgaris). They can fix approximately 80 kg N/ha as opposed to about 30 kg N/ha for Phaseolus beans, so just switching from Phaseolus beans to a Vigna speciesas an intercrop can make a major difference in the maintenance of soil fertility(assuming all the nitrogen is not being burned off during the dry season).In general, among the Vignas, cowpeas and rice beans are more drought-resistant,while mungbeans require more soil moisture. For the driest situations, especiallyat the end of the wet season when soil moisture can be expected to graduallydecrease, short-cycle (60- to 70-day) cowpeas are probably the best option.In places like the Sahel, the introduction of short-cycle cowpeas can improvesoil fertility, because the crops with which they are intercropped usually last atleast a month longer. This fact means that the cowpea residues—at least thatpart of them that is not carried off to sell or store for forage—will die and beincorporated into the soil by termites before the millet or sorghum is harvested.In this way, the organic matter is protected from the heat and from other farmers’grazing animals, which are not allowed to roam free until the millet or sorghumis harvested.If you are working with cowpeas, select S22, S68, S70, S73, S74 or S80, and thengo to #5. If you are working with rice beans, select S9, S69 or S78 and then go to#5. If working with mungbeans, select S79 or S85, and then go to #5. Hedgerowscan also be used with these systems, and are advisable especially under 800m in elevation. See #45.39. Pigeon peas. Pigeon peas can be used as a gm/cc in many different ways.a) Pigeon peas can be a very good temporary, dispersed shade (up to four years)for vegetables or other low-stature crops. They allow flexibility in complicatedand changing farming systems because they can be taken out or replanted at anytime. They also provide a high-protein food and fertilize the soil very well. See#26.b) Pigeon peas can be used as an improved fallow. See #26.c) If you want to try a system in which pigeon peas are intercropped with maize,go to S30 and then go to #5. For upland rice, go to S72 and then #5. Pigeon peascan also be grown together with many other crops, often benefiting them becauseof the shade while producing additional food and organic matter for the soil.40. Peanuts and bambara groundnuts. Peanuts and bambara groundnuts are oftenplanted together with maize, sorghum, millet and even cassava. They are usuallyplanted at the same time as the basic grains with which they are being intercropped.Both species can also be intercropped with cassava (see S43, and then#5, if you and the farmers wish).I did not describe these systems below. They do not fertilize the soil well because