Organic carbon pools and soil health indicators along a decadal mulching chronosequence in a tropical banana system: implications for land management

Understanding soil organic carbon (SOC) pools under prolonged organic residue management in tropical perennial systems provides insights into how organic matter is distributed, transformed, and retained in highly weathered soils. This study evaluated associations among mulching duration, SOC fractions, nitrogen pools, and multiple soil health indicators in a fully mulched banana plantation in southwestern Nigeria using a decadal chronosequence. Soil samples were collected at two depths (0–5 and 5–10 cm) across sites representing six mulching durations (1, 2, 4, 5, 7 and 10 years). Analyses included total organic carbon, total nitrogen, particulate and mineral-associated carbon fractions, carbon and nitrogen stocks, and key physical and chemical soil health indicators. Results are limited to the 0–10 cm soil layer. Sites representing longer mulching duration were associated with higher SOC and nitrogen pools, particularly in the surface layer. Particulate organic carbon fractions (coarse and fine) increased substantially in the topsoil, while mineral-associated carbon also showed consistent enrichment along the chronosequence. Soil C/N ratios declined with increasing mulching duration, suggesting progressive organic matter transformation and potential shifts in nutrient cycling dynamics. Improvements were also observed in several soil physical indicators, including lower bulk density, higher aggregate stability, greater available water holding capacity, and higher saturated hydraulic conductivity. Rooting depth increased and leaching potential decreased at sites with longer mulch histories. In addition, soil chemical properties, including pH, electrical conductivity, available phosphorus, and cation exchange capacity, generally showed higher values across sites with longer mulching duration. Collectively, these patterns indicate that sustained residue retention in tropical perennial banana systems is associated with the accumulation of both labile and stabilized SOC fractions and concurrent improvements in multiple soil health indicators. The study provides rare long-term evidence from a tropical perennial cropping system and highlights the value of integrating SOC fractionation with soil health metrics to evaluate the potential implications of residue-based management for soil functioning and sustainable agroecosystem management.