Distribution of soil organic carbon and important soil nutrient ratios along toposequence in humid tropics of Nigeria

Abstract

Landscape attributes including soil-environmental factors are the dominant factors impacting soil organic carbon (SOC) and nutrient ratio distribution in areas with rolling terrain, homogeneous parent material, and uniform climate patterns. This study investigated the depth distribution of SOC, and nutrient ratios (C:N, C:P, and N:P ratios) in soil developed on coastal plain sand in Calabar. Soil samples were collected from nine identified profile pits, air-dried, crushed, sieved, and subjected to laboratory analysis. The results showed that the values of SOC and nutrient ratios (C:N, C:P, and N:P ratios) gradually decreased with soil depth along toposequence in each aspect position. In the north- and East-facing aspects, the depth distribution of SOC followed the order; upper slope > lower slope>middle slope. While, in the South-facing slope, the distribution was in the order of lower slope> middle slope >upper slope. The North-facing aspect contained maximum SOC ( 16.6 gkg^-1) than the East-facing ( 16.0 gkg^-1) and South-facing ( 13.2 gkg^-1) aspect. The mean C:N ratios were < 10 in all toposequence and aspect positions. C:N and N:P ratios significantly and positively influence topsoil SOC in the study area. C:N ratio was significantly and positively influenced by pH, clay ratio, SOC, clay, and Hillshade. C:P and N:P ratios were influenced by SOC and TN. SOC and nutrient ratios (C:N, C:P, and N:P) can be used as an indicator of soil fertility and productivity to advance an understanding of the aboveground plant community and below-ground soil nutrients at various depths along the toposequence.