Management Effects on Yam Production in Benin Republic

Abstract

Declining productivity in the Republic of Benin (West Africa) highlighted the need for a study to determine both the effect of fertilization on yam (Dioscorea spp.) yield and biomass production, as well as the best agronomic management options available for stabilizing yam productivity, via the modeling of yam growth and development. This study addressed the above issues by conducting plot experiments in the Benin Republic, which analyzed the effect of mineral fertilizer, manure and crop residue application on total biomass production, tuber yield and dry matter partitioning pattern, in two species of yam (Dioscorea alata var. Florido and Dioscorea rotundata var. Kokoro). Significant positive effects of mineral fertilizer were observed on yam total biomass production and tuber yield, but the magnitude of its effect were dependent on the species of yam. Crops receiving crop residues and manure also registered increases in yield, but were not significantly different from the yield under unfertilized conditions. Regarding partitioning pattern of dry matter to different plant organs, no significant difference was observed between control and fertilized treatments. An attempt has been made to simulate the effect of fertilization and fallow availability on yam (Dioscorea alata var. Florido) production by using the Environmental Policy Integrated Climate (EPIC) model. A new crop parameter file for Dioscorea alata was developed. The model accurately simulated the effect of fertilizer on the yam yield as indicated by a relatively low mean relative error (MR) ranging from 4.3 to 9.7 %. Different scenarios of fallow availability (Scenario S1 [100 % of the bush savannah is available as fallow land], Scenario S2 [50% of the bush savannah is available as fallow land] and Scenario S3 [25% of the bush savannah is available as fallow land]) were explored in the Upper Ouémé basin of Benin Republic (West Africa) by incorporating the EPIC model into the spatial decision support system (SDSS) PEDRO (Protection du sol Et Durabilité des Ressources agricoles dans le bassin versant de l'Ouémé). The best agreement between simulated and observed crop yields was found under the assumption that 50% of the bush savannah is available as fallow land under the prevailing cropping patterns. The results show the capacity of the EPIC model in connection with the SDSS PEDRO to capture both the biomass production and sensitivity of regional yields of yam to fallowing. They further reveal how a crop model can be used to analyze fallow practices at the regional scale. However, the models accuracy is most likely to be improved by a more detailed modeling of the phenological development of yam. In order to increase yam productivity and maintain soil fertility in the Upper Ouémé basin, fallowing the crop land is not a viable option due to increased demographic pressures. Mineral fertilizer application appears to be essential, but its high cost and accessibility restraints, limit its use by the farmers. The solution lies in providing mineral fertilizers to the farmers at subsidized rates. Additionally, nitrogen fixing crops could partially provide the N inputs needed, if included within crop rotations.