No‐Tillage Enhances Macroaggregate Stability and Carbon‐Nitrogen Storage but Drives Aggregate‐Size‐Dependent Phosphorus and Base Cation Distribution in Highly Weathered Tropical Soils of Central Africa

ABSTRACT The dynamics of soil aggregate stability and the associated organic carbon and nutrient pools under contrasting tillage practices remain underexplored in the humid tropics of Central Africa, where rapid organic matter decomposition due to high temperatures and microbial activity challenges soil health. This study fills this gap by investigating how long‐term conventional tillage and no‐tillage systems influence water‐stable aggregate distribution and stability, the partitioning of SOC, nitrogen, phosphorus, and exchangeable cations within aggregate fractions, and the mechanisms governing carbon‐nutrient protection in a highly weathered tropical Oxisol at 0–20 cm depths. The experiment consisted of four long‐term field plots (two conventional tillage and two no‐tillage), from which soil was sampled at two depths (0–10 cm and 10–20 cm) using seven replicated subplots per plot, yielding 56 composite samples for aggregate and nutrient analyses. Aggregates were fractionated into macroaggregates (> 250 μm), microaggregates (53–250 μm), and fine microaggregates (< 53 μm). The results indicated that NT significantly enhanced macroaggregate formation by reducing mechanical disruption, thereby preserving soil structure and increasing mean weight diameter (MWD) and stability in the surface horizons. This process minimized SOC exposure to decomposers through physical occlusion within aggregates, leading to higher SOC and TN stocks (28%–40%) via stabilization mechanisms such as organo‐mineral binding. Conversely, CT fragmented aggregates, accelerating SOC mineralization and shifting nutrients toward finer fractions. While NT promoted carbon‐nitrogen storage, it altered phosphorus and base cation (K + , Mg 2+ , Ca 2+ ) dynamics through nutrient stratification, with AP and cations enriched in microaggregates due to organo‐mineral associations and fixation to Fe/Al oxides in these acidic, low‐CEC soils, potentially reducing short‐term bioavailability. Strong correlations between SOC, TN ( r = 0.97), and aggregate stability highlight organic matter's role in aggregation potentially via microbial glues and mineral bridging. These mechanisms suggest NT fosters resilient soil structure and carbon retention but require integrated amendments to mitigate nutrient immobilization in tropical smallholder systems, balancing ecological benefits with productivity.