Formation of mineral‐associated organic matter (MAOM) supports the accumulation and stabilization of carbon (C) in soil, and thus, is a key factor in the global C cycle. Little is known about the interplay of mineral type, land use and management intensity in MAOM formation, especially on subdecadal time scales. We exposed mineral containers with goethite or illite, the most abundant iron oxide and phyllosilicate clay in temperate soils, for 5 years in topsoils of 150 forest and 150 grassland sites in three regions across Germany. Results show that irrespective of land use and management intensity, more C accumulated on goethite than illite (on average 0.23 ± 0.10 and 0.06 ± 0.03 mg m⁻² mineral surface respectively). Carbon accumulation across regions was consistently higher in coniferous forests than in deciduous forests and grasslands. Structural equation models further showed that thinning and harvesting reduced MAOM formation in forests. Formation of MAOM in grasslands was not affected by grazing. Fertilization had opposite effects on MAOM formation, with the positive effect being mediated by enhanced plant productivity and the negative effect by reduced plant species richness. This highlights the caveat of applying fertilizers as a strategy to increase soil C stocks in temperate grasslands. Overall, we demonstrate that the rate and amount of MAOM formation in soil is primarily driven by mineral type, and can be modulated by land use and management intensity even on subdecadal time scales. Our results suggest that temperate soils dominated by oxides have a higher capacity to accumulate and store C than those dominated by phyllosilicate clays, even under circumneutral pH conditions. Therefore, adopting land use and management practices that increase C inputs into oxide‐rich soils that are under their capacity to store C may offer great potential to enhance near‐term soil C sequestration.

Formation of mineral-associated organic matter (MAOM) is a key process in the global carbon cycle, stabilising organic carbon in soils. The relative importance of mineral composition and land use as potential controls of MAOM stability at regional scales and underlying microbial processes are still unresolved. Here, we assessed the stability of MAOM formed on goethite (iron oxide) and illite (phyllosilicate clay) exposed for five years in topsoils at 68 forest and grassland sites across Germany. We incubated the newly formed MAOM, determined its extractability, and analysed the composition and functioning of associated microbial communities. Decomposition of MAOM was always significantly lower for goethite than illite, highlighting that higher organic carbon accumulation on goethite was not exclusively due to its larger sorption capacity. Instead, reduced organic carbon extractability and higher phosphorus-acquiring enzyme activities indicated stronger substrate limitation of microbial growth on goethite than illite. Across the two minerals, MAOM decomposition was consistently lower for forests than grasslands, relating to greater nutrient constraints and a different microbial community composition in forests. Overall, mineral type and land use explained 34.6 and 23.2% of the variance in MAOM decomposition. The pronounced land use effect on MAOM stability underlines its potential responsiveness to environmental change.

Aglime (agricultural lime), commonly applied to acid soils to increase the soil pH and productivity, may lead to the release of CO₂ into the atmosphere or to carbon (C) sequestration, although the processes involved are not fully understood. As large acreages of arable land are limed annually, exploring soil management practices that reduce aglime-induced CO₂ emissions from acid soils while maintaining or improving the soil quality is paramount to mitigating the effects of global climate change. This study, therefore, assessed the effects of organic residues and ammonium on CO₂ emissions and soil quality indicators in two limed soils. Two contrasting acid soils (Nariva series, Mollic Fluvaquents and Piarco series, Typic Kanhaplaquults) were amended with varying combinations of aglime (0% and 0.2% w/w CaCO₃), organic residue (0% and 5% w/w biochar or poultry litter), and NH₄-N (0% and 0.02% w/w) and were incubated in 300 mL glass jars for 31 days. The sampling for CO₂ was performed on 11 occasions over the course of the incubation, while soil sampling was conducted at the end. The results indicate that aglime application significantly (p < 0.05) increased the cumulative CO₂ emissions in all cases except with the addition of poultry litter. Alternatively, ammonium did not regulate the effect of aglime on CO₂ emissions, which was likely because of the low rate at which it was applied in comparison to aglime. The results also showed that poultry litter significantly (p < 0.05) increased the soil electrical conductivity (EC), available nitrogen (N), and pH, especially in the Piarco soil, while the hardwood biochar had little to no effect on the soil properties. Our findings indicate the potential for utilizing poultry litter to reduce the impact of aglime on CO₂ emissions while improving the soil quality. Further studies utilizing ¹³C to trace aglime CO₂ emissions are, however, required to identify the mechanism(s) that contributed to this reduction in the emissions.