Comparative topsoil characterization of sawah rice fields in selected inland valleys around Bida, north-central Nigeria: textural, structural and hydrophysical properties

2011

English

Although the West African inland valleys arecharacteristically wet all-year-round, their hydrologicalconditions are known to be site-specific and may differmarkedly between the rainy and the dry seasons. Informa-tion on their physical properties would be useful for properwater management under the sawah rice culture and forplanning dry season cropping. Representative inland valleysat four locations (Gadza, Nasarafu, Shaba-Maliki and Ejeti)around Bida in the Guinea savanna zone of Nigeria wereselected for the study. Apart from Ejeti where the soil is clayloam, the predominant texture is sandy loam. The total andclassified water-stable aggregates (WSA) were lowest atEjeti, followed by Nasarafu. On the average, over 82% ofthe WSA were below 1.0 mm. Variations among thelocations progressively decreased from the largest to thesmallest aggregate-size class. Aggregate stability, asevaluated by both sand-corrected WSA and the meanweight diameter (MWD), followed similar trend as theWSA. Values were generally low for soil organic matter(SOM) (0.8–2.2%), but moderate for bulk density(0.98–1.55 Mg m-3) and total porosity (40.6–62.6%).Overall, Ejeti maintained the most favourable values ofthese three parameters, followed by Shaba-Maliki, Nasarafuand Gadza in the order listed. Micropores constituted over87% of the soils’ pore system. Saturated hydraulic con-ductivities were, however, highly variable; indicatinglowest rates at Ejeti. Clay fraction correlated positively withthe unstable (\0.25 mm) aggregates and porosity parame-ters, but negatively with other structural indices. The SOMcorrelated negatively and positively with MWD and totalporosity, respectively. Soil–water management implica-tions of these results are discusse.

Obalum, S. E.; Nwite, J. C.; Oppong, J.; Igwe, C. A.; Wakatsuki, T.