Topography and Depth Influences on Soil Nitrogen and Carbon Sequestration

Topography is one of the important factors affecting soil carbon accumulation in a tropical ecosystem. Slope effects vary in magnitude in different agro-ecosystems. The study was conducted to evaluate the influence of topography on soil nitrogen and carbon equestration in Mbano Imo State, Nigeria. Three profile pits were dug along a landscape of approximately 200 meters, one on each topographic position. Each profile pit was demarcated into 4 equal depths of 30 cm apart and 3 replicated soil samples were collected from each of the depths for laboratory analyses. Analysis of variance and correlation analysis were used for data analysis. From the results, the average bulk densities and moisture content varied between 1.36-1.59 g cm-3 and 6.43-7.27% with the footslope (valley position) containing significantly (p=0.05) higher values. 0-30 cm depth had the least bulk density value compared to other depths. At 0-30, 30-60, 60-90 and 90-120 depths, carbon and nitrogen sequestration varied depending on the landscape position. At the depth of 0-30 cm in upslope (summit), mid-slope and footslope, organic carbon, total nitrogen, carbon and nitrogen sequestration were the highest (p=0.05). 30-60 cm depth of the footslope sequestered significantly higher carbon (520.30) than that of the summit (376.74 g cm-2) and mid slope (26.64) (p=0.05). Considering the three different topographic units, the footslope sequestered significantly (p=0.05) highest quantities of carbon (629.42 g cm-2) and nitrogen (33.18 g Nm-2) than the up slope (249.36 g cm-2, 23.39 g Nm-2) and mid slope (170.72 g cm-2, 14.80 g cm-2). Also, organic carbon and total nitrogen were highest in the foot slope compared to the mid and up slopes. Generally, ANOVA result revealed higher availability and sequestration of carbon and nitrogen at 0-30 cm depth and valley position.