Long-term manure fertilization enhances red soil organic carbon storage

Enhancing soil organic carbon (SOC) in farmland is essential for maintaining soil fertility and mitigating climate change. Yet, soil chemical and biological drivers of SOC storage under organic and mineral fertilization strategies remain unresolved, especially across multi-decadal time scales. To investigate how microbial communities, dissolved organic matter (DOM) dynamics, and soil physicochemical properties influence SOC storage, we used Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and high-throughput sequencing to analyze soil samples from a 31-year field experiment with five fertilization regimes (non-fertilization, CK; mineral fertilization, NPK; NPK with stover return, NPKS; NPK with manure, NPKM; and manure alone, M). Results revealed that mineral fertilization, stover return, and manure application all enhanced SOC content; however, the magnitude of and mechanisms underlying these increases varied significantly among treatments. Compared to CK treatment, NPK and NPKS treatments increased SOC content by 38%–45%. These increases were associated with a significant decrease in soil pH and the relative abundance of bacterial copiotrophs, but increases in soil Olsen-P (51–53 times) and nitrate content (43%–109%). The portion of tannin and condensed aromatic compounds in NPK and NPKS treatments significantly increased by 240%–540% compared to CK treatment. Manure amendments resulted in a significantly higher increase in SOC content by 93%–116% compared to CK treatment. This was associated with a rise in soil pH, and a higher increase in Olsen-P (138–157 times), nitrate content (227%–281%), and the relative abundance of bacterial copiotrophs (43%–51%). Manure inputs further promoted the formation of tannin and condensed aromatic compounds by 56%–65% and 103%–165%, respectively, compared to NPK and NPKS treatments. A higher increase in the chemical diversity, aromaticity, and transformation potential of DOM after manure input may contribute to the enhanced SOC accumulation. These findings highlight the potential of manure amendments to enhance SOC storage through changing the microbial communities and chemical properties of DOM in red soils. This can provide valuable insights for sustainable agricultural practices in soil carbon management. • SOC was associated with soil pH, nutrients, copiotroph: oligotroph ratios, and recalcitrant DOM indicators. • Manure input had the highest SOC in a multi-decadal annual cropping system trial. • Manure application increased the copiotroph: oligotroph ratios. • Manure input increased recalcitrant DOM portion compared to chemical fertilization. • Manure inputs exhibited higher diversity, stability, and transformation potential of DOM.