Soil organic matter control of water transmission properties of coarse-textured soils under contrasting land-use types in tropical rainforest
P. C. Oguike, Brown M. Onwuka, Sunday E. Obalum
Abstract
Infiltration rate (I) and saturated hydraulic conductivity (Ks) depend on soil organic matter (SOM) in a manner that is poorly known for genetically similar soils of the humid tropics. This study examined I and Ks dependence on SOM under continuous cultivation (CCT), bush fallow (BFL) and secondary forest (SFT) on deep coarse-textured Nigerian soils using linear regressions. Soil texture, SOM and Ks varied by both land use and depth zone, while I was lower under CCT (0.20 cm/h) than BFL/SFT (0.30 cm/h). For Ks, trends were CCT (0.72 cm/h) < BFL (0.82 cm/h) < SFT (1.02 cm/h), and topsoils > subsoils. The SOM was lower in CCT (19.65 g/kg) than BFL/SFT (35.60-39.70 g/kg). Topsoil SOM and subsoil SOM had similar influence on I (82-85%), while SOM influenced Ks less in topsoils (51%) than subsoils (81%). Clay correlated positively with SOM, I and Ks. Land-use practices that promote SOM accretion increase clay-SOM complexation into silt/sand-sized stable aggregates forming 'porous' granular structure in these soils, enhancing their permeability.