Soils of flood plains of West Africa: General fertility status

As a part of efforts to effectively utilize the wetlands of the West Africa sub-region for the production of rice and other crops, in order to alleviate the persistent food shortage while also protecting and conserving the environment for sustainability, the general fertility status of flood plain soils were assessed. The whole sub-region was found to be deficient in available phosphorus. Available P (Bray No. 2) was deficient for both the humid Equatorial forest (EF) and sub-humid Guinea savanna (GS), as well as the drier northern sector of Sudan savanna (SuS) and Sahel savanna (SaS) zones. Mean available P levels in the topsoil (0(-1)5 cm) were 9.84, 8.01, 7.25, and 7.31mg kg(-1) for the EF, GS, SuS, and SaS zones respectively. Effective cation exchange capacity (eCEC) and levels of exchangeable K, Ca, and Mg were higher for the SaS and SuS than forthe GS and EF zones. The level of exchangeable K was, however, very low within the EF zone. The soils were slightly acidic to neutral but with isolated areas of high salinity. Mean topsoil (0(-1)5 cm) pH for West Africa was 5.4. Mean soil pH varied from 5.7 in the drier SaS, through 5.4 for the SuS and GS zones to 5.2 in the EF zone. Mean topsoil levels of total carbon for the EF (humid) and GS (sub-humid) zones were 14.4 and 16.3 g kg(-1) while the dry SuS and SaS zones showed topsoil means of 8.3 and 6.2 g kg(-1) respectively. Total nitrogen levels, however, were low throughout the sub-region particularly within the SaS and SuS zones which showed respective topsoil means of 0.71 and 0.88 g kg(-1). Mean topsoil level of total nitrogen for West Africa flood plains was 0.98 g kg(-1). C/N ratios ranged from 8(-1)3 except for the EF which showed quite higher, 18-20, ratios