Characteristics and agricultural potential of soils with plinthic materials in the savanna ecology of south western Nigeria

Plinthite occurs in most parts of savannah soil at varying depths, thus limiting the productivity of the soil for crop production. However, plinthic soils are not well defined in the USDA classification. Therefore, we surveyed nine plinthites bearing pedons, to characterize their suitability, quality and sustainability over the basement complex formation in southwestern Nigeria; and to suggest new classification based on USDA and FAO classification systems. In the entire land area, two types of hardened plinthites were identified: 41% with petroferric contact and 59% with petroplinthite. The percentage of aggregate soil quality indices of both petroferric contact and petroplinthite was low to moderate, ranging from 32% to 56%. Sustainability indices of the soils ranged from 20 to 37 with petroferric contact have the lowest index while soils with petroplinthite have the moderate index. Setting up an integrated conservation structure with soil amendments is essential for the sustainability of petroplinthite soils but petroferric contact, even with high inputs, cannot sustain intensive cropping, and therefore, recommended for pasture and forestry. The inclusion of hyperplinthic and orthoplinthic in USDA and FAO-WRSB classification systems as classes of petroplinthite is hereby suggested.