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 allevia te the persistent food shortage while also protecting and conserving the en vironment for sustainability, the general fertility status of hood plain so ils were assessed. The whole sub-region was found to be deficient in availa ble phosphorus. Available P (Bray No. 2) was deficient for both the humid E quatorial forest (EF) and sub-humid Guinea savanna (GS), as well as the dri er northern sector of Sudan savanna (SuS) and Sahel savanna (SaS) zones. Me an available P levels in the topsoil (0-15 cm) were 9.84, 8.01, 7.25, and 7 .31 mg kg(-1) for the EF, GS, SuS, and SaS zones respectively. Effective ca tion exchange capacity (eCEC) and levels of exchangeable K, Ca, and Mg were higher for the SaS and SuS than for the GS and EF zones. The level of exch angeable K was, however, very low within the EF zone. The soils were slight ly acidic to neutral but with isolated areas of high salinity. Mean topsoil (0-15 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 zo nes which showed respective topsoil means of 0.71 and 0.88 g kg(-1). Mean t opsoil level of total nitrogen for West Africa hood plains was 0.98 g kg(-1 ). C/N ratios ranged from 8-13 except for the EF which showed quite higher, 18-20, ratios.