Distribution of Total Nitrogen in Soils of the Tropical Highlands of Cameroon

Understanding the factors controlling soil total N (TN) is helpful in simulating N cycling at local and regional scales. This study was conducted with the aim to; (i) understand the distribution of TN in specific soil horizons (A and B horizons) of three reference soil groups: Acrisols, Cambisols and Ferralsols, common in humid tropical environments, and (ii) to identify factors controlling TN variations among the various soil groups. Twenty-eight Acrisols, 21 Cambisols and 8 Ferralsols profiles spanning a wide range of precipitation gradients, vegetation type/land use and parent materials, from the Northwestern Highlands (NWH) of Cameroon were considered. Soil properties were analyzed following standard procedures. TN had very high coefficients of variation (>35%) in all the reference soil groups (RSGs), with highest mean TN (0.31 ± 0.03%) observed in the A horizons of Acrisols and the lowest (0.05 ± 0.01%) in B horizons of Ferralsols. Variations in TN content were significantly (p < 0.05) influenced by parent material, land use type, precipitation and slope gradient. In surface (A) horizons of all the RSGs, TN correlated positively and significantly with clay (p < 0.05), silt (p < 0.01) and soil organic carbon (SOC) (p < 0.01), and negatively with sand (p < 0.01). This observation was slightly different in subsurface (B) horizons. This study provides data which contributes to a better understanding of soil fertility in tropical highlands.