Soil Organic Carbon Stock Variations Across Depth and Land use Types in the Sudano-Sahelian Zone, Gashua, Nigeria

Abstract

This study assessed the differences in soil organic carbon (SOC) stocks across different land uses and depths in the Sudano-Sahelian area of Gashua, Yobe, Nigeria. Samples were collected from the depths of 0-15 cm and 15-30 cm under wetland, forested land, cultivated land, and grassland. Due to non-normal data (Shapiro-Wilk p < 0.05), Spearman's correlation analyzed SOC relationships with macronutrients, land use, and depth. Kruskal-Wallis tests assessed land use and depth effects on SOC distribution. "Wetlands and forested lands appear as the primary carbon sinks. Wetlands recorded the highest mean SOC stock of 8.45 Mg ha⁻¹ at the 15-30 cm depth, followed by forested land (8.28 Mg ha⁻¹), cultivated land (6.89 Mg ha⁻¹), and grassland (5.00 Mg ha⁻¹). The soil pH is slightly acidic to neutral (6.5-7.2); the bulk density is from 1.2 to 1.3 g cm⁻³; nitrogen ranges from 1.8 kg ha⁻¹ to 1.7 kg ha⁻¹; phosphorus recorded 1.20 kg ha⁻¹, and potassium recorded 1.08 kg ha⁻¹. Spearman's correlation showed strong positive SOC relationships with N (ρ=0.81, p<0.001) and P (ρ=0.81, p<0.001), and a moderate positive correlation with depth (ρ=0.66, p<0.01). Kruskal-Wallis tests revealed significant depth effects (H=5.14, p=0.023) but non-significant land use differences (H=3.71, p=0.16). "These findings highlight the need to protect wetland and forested land, alongside subsurface soil management, to enhance SOC sequestration in Northern Nigeria.