Distribution of organic carbon and total nitrogen in aggregate size fractions in a southern Nigeria Ultisol under different agricultural land use

We studied the effect of different land uses on organic carbon and total nitrogen content in soil and soil size fractions. A range of land uses was selected, that included tree plantings, pasture and soil tilled at different intensity. Soil organic carbon and total N were significantly higher under forest and tree crops in comparison to pasture, no tilled and tilled plots. Converting conventional tillage to no tillage lead to significant increase of the soil organic matter content. Organic carbon and total nitrogen contents generally decreased with increasing size of soil aggregates, whilst the C:N ratio was directly related to the aggregate size. The presence of higher amounts of organic C associated with lower C:N ratio in the finer fractions suggests that these aggregate size classes protect the soil organic matter and make it inaccessible to degrading agents.