Distribution of Organic Carbon, Nitrogen and Phosphorus in Water-Stable Aggregates of Onwu Floodplain Soils, Nigeria.

Soil pedons studied of Onwu floodplain in Cross River State, Nigeria for physic-chemical properties of whole-soil and water-stable aggregates 4.75 – 2.00, 2.00 – 1.00, 1.00 – 0.50, 0.50 – 0.25 and < 0.25 mm. Whole-soil and WSA relative distributions of organic carbon, total nitrogen and available phosphorus were evaluated under two tillage systems CT and NT. Nearness to the river affected the SOC distribution within the WSA with high values of SOC obtained from WSA 4.75 – 2.00 mm mostly in pedons nearest to river. SOC concentrations whole-soil and aggregate 4.75 – 2.00 mm of CT were ( p < 0.05 ) in pedon, horizon recorded ( p < 0.01 ) whole-soil and other aggregates sizes except aggregate 0.50 – 0.25 mm, interaction ( p < 0.05 ). Under NT whole-soil, 4.75 – 2.00 and 1.00 – 0.50 mm aggregates were ( p < 0.05 ) among pedons, while wholesoil and 4.75 – 2.00 mm aggregate were ( p < 0.01 ) among horizons, while other aggregates organic carbon were ( p < 0.05 ). Total nitrogen concentration of whole-soil was ( p < 0.05 ) among pedons while horizon whole-soil and other aggregates were ( p < 0.01 ), except < 0.25 mm aggregate with ( p < 0.05 ) of CT. Total nitrogen concentration in aggregates 4.75 – 2.00 and 0.50 – 0.25 mm were ( p < 0.05 ) of NT among pedons, horizons whole-soil and other aggregates were ( p < 0.01 ) except 0.50 – 0.25 mm aggregate, interaction( p < 0.05 ) for 4.75 – 2.00 and < 0.25 mm aggregates. Higher C/N ratio of whole-soils over the WSA classes implied active mineralization of soil organic matter in aggregates. Available Phosphorus content of both whole-soil and five WSA classes is low reflecting the low phosphorus contents of the parent materials, fixation and redistribution of phosphorus by erosion and flood.