Aggregate Size Mediates Carbon and Nitrogen Mineralization Responses to Lime, Gypsum, and Nitrogen Fertilization in a Tropical No-till Oxisol

This study evaluated how aggregate size mediates carbon (C) and nitrogen (N) mineralization responses to lime, gypsum, and nitrogen fertilization in a tropical no-till Oxisol under a soybean–maize–Guinea grass rotation. A laboratory incubation experiment was conducted after six years of field treatments combining lime, lime+gypsum, and two nitrogen rates. Soil was separated into water-stable aggregate classes (> 2, 1–2, 0.5–1, 0.25–0.5, and 0.106–0.25 mm), and C and N mineralization were quantified over 24 days. Statistical analyses included ANOVA and principal component analysis. Carbon mineralization was strongly dependent on aggregate size. Lime and lime+gypsum reduced cumulative C mineralization in large aggregates (> 2 mm), while nitrogen fertilization decreased C mineralization in intermediate fractions (0.5–1 and 0.25–0.5 mm). Smaller aggregates (0.106–0.25 mm) showed greater biological activity under improved chemical conditions. Net N mineralization exhibited significant interactions between soil amendments and N fertilization, particularly in large aggregates, indicating contrasting regulation of N turnover across structural domains. Aggregate size governs contrasting C and N mineralization dynamics under soil acidity alleviation in tropical no-till systems. Considering soil structural heterogeneity is essential for designing management strategies that balance carbon retention and nitrogen cycling in highly weathered tropical soils. Aggregate size regulates contrasting C and N mineralization responses to acidity alleviation and N fertilization. Lime and gypsum reduced C mineralization primarily in large (> 2 mm) aggregates. Nitrogen effects on C and N turnover varied across structural fractions. Large aggregates were associated with greater N retention, whereas smaller fractions showed higher biological activity. Aggregate-scale assessment improves understanding of amendment strategies in tropical no-till soils.