Soil humus and aluminum—iron interactions enhance carbon sequestration and yield sustainability after long-term fertilization in three different soils

Conceptual model comparing key findings: soil humus and aluminum-iron interactions; soil pH levels, carbon sequestration rate, and sustainable yield index of broad bean and sweet potato in granite, purple sandy shale, and Quaternary red soils under long-term rice straw return and NPK fertilization. Sizes of the arrows and lines reflect magnitude of effects on specific variables. • Humus carbon fractions distinctly regulated aluminum and iron concentrations in the three soils. • Straw with NPK fertilizer and single straw return increased SOC sequestration and crop yield • Sustainable yield index of broad bean increased with carbon sequestration rate, whereas that of sweet potato decreased • Granite soil had the highest SOC sequestration, yield sustainability, and humus-mediated regulation of aluminum and iron