Soil Carbon–Nitrogen Pools and Soil Health Across Contrasting Land Uses and a No‐Till Conservation Chronosequence in a Tropical Guinea Savanna Agroecosystem

ABSTRACT Soil carbon–nitrogen pools are central to soil health, yet their responses to conservation‐oriented management remain insufficiently quantified in tropical agroecosystems. This study evaluated soil carbon–nitrogen pools, stocks and soil health indicators across conventionally managed arable land (CMA), no‐till‐based conservation systems with 2, 4, 7 and 10 years of establishment (NT2, NT4, NT7 and NT10), and natural forest land (NFL) in a tropical Guinea Savanna Ferric Luvisol in southwestern Nigeria. Soil samples were collected at 0–5 and 5–10 cm depths and analyzed for carbon and nitrogen fractions, stocks, physical properties, water‐regulation indicators and chemical fertility attributes. Total organic carbon ranged from 4.7 to 11.2 g kg −1 , while total nitrogen ranged from 0.3 to 3.7 g kg −1 across land‐use systems and depths. Within the NT2–NT10 chronosequence, total nitrogen increased by 0.24 and 0.38 g kg −1 year −1 in the 0–5 and 5–10 cm layers, respectively, while nitrogen stock increased by 0.09 and 0.17 Mg ha −1 yr −1 . Surface carbon stock also increased with no‐till duration by 0.21 Mg ha −1 year −1 . Longer no‐till duration was associated with higher aggregate stability, increasing by 0.68 and 0.83 percentage units year −1 in the 0–5 and 5–10 cm layers, respectively. Soil pH increased by 0.15 and 0.13 units year −1 , while cation exchange capacity increased by approximately 0.46 cmolc kg −1 year −1 in both depths. In contrast, leaching potential declined by 0.98 and 1.29 percentage units year −1 in the 0–5 and 5–10 cm layers, respectively. The integrated soil health score increased from 19.6 under NT2 to 82.6 under NT10 in the surface layer, and NT10 also had the highest score in the 5–10 cm layer. These findings indicate that sustained no‐till‐based conservation management can improve soil carbon–nitrogen status, nutrient retention, water regulation and overall soil health. However, the observed responses reflect the combined effects of reduced disturbance, organic inputs, mulching, perennial crop cover and irrigation rather than no‐till alone.