Characterization and classification of rice-growing soils on Imo clay shale residua in Eastern Nigeria and current suitability for rice production: I. Omasi-Agu and Omor agrarian communities
The soils on Imo clay shale residua at Omasi-Agu and Omor areas in Anambra State, Nigeria were sampled in order to characterize classify and evaluate their current suitability for rice production following standard scientific procedures. The soils generally belong to loamy textural classes or finer, especially in the subsoil layers. The morphological and physical properties of soils showed that the soils were poorly drained favouring high water retentivity due to low hydraulic conductivity and slow permeability. All these soil conditions support good rice performance. Though the soils at Omasi-Agu contained high levels of exchangeable bases, exchangeable acidity was equally high leading to low base saturation of < 35% but at Omor the base saturation was > 35%. Thus, the soils were, respectively, classified as Typic Kandiaquults (Soil Taxonomy) correlated with Gleyic Cambisols of the World Reference Base for Soil Resources (WRBSR) and Typic Kandiaqualfs (Soil Taxonomy) correlated with Gleyic Cambisols (WRBSR). Even though the soils of Omor appeared to be generally more fertile than Omasi-Agu soils, both have similar constraints to rice production, that is, insufficiency of nutrients (f) and possibility of erosion by flooding (e) in limited areas (< 25%). Therefore, the current suitability of the soils for rice production is suitability class 2 with fertility constraints (S2fe). For sustainable rice production, supplementary addition of nutrients especially P2O5 from triple superphosphate and some minor levelling and bunding are required to control erosion due to flooding in the limited areas.