Application of organic and chemical fertilizers promoted the accumulation of soil organic carbon in farmland on the Loess Plateau

Aims Understanding the accumulation and mineralization of soil organic carbon (SOC) in aggregates under long-term fertilization conditions is of great significance in comprehending the dynamic changes in farmland C pools on the Loess Plateau. Methods The long-term field experiment has been established for 26 years and includes six fertilization treatments: no fertilization (CK), organic fertilizer (M), organic and nitrogen fertilizers (MN), organic and phosphorus fertilizers (MP), NP and MNP. We determined nutrient content, mineralization characteristics, temperature sensitivity (Q 10 ), and extracellular enzyme activities of soil aggregates (< 0.25 mm, 0.25–1 mm, 1–2 mm, > 2 mm). Results (1) M, MN, MP, and MNP significantly increased the SOC content of aggregates by 92.58%, 82.84%, 73.55% and 83.23% compared to NP. The SOC in < 0.25 mm aggregates was significantly highest than other particles. (2) Organic fertilizer treatments (M, MN, MP, and MNP) significantly increased the cumulative mineralization of different-sized aggregates by 97.10–178.75% compared to NP. The average mineralization rate and the cumulative mineralization of < 0.25 mm aggregates was the lowest. (3) The mineralization of aggregates is directly and significantly affected by the available soil nutrients and enzyme activities. (4) Fertilization and aggregate size had significant effects on Q 10 and the Q 10 of MNP was lower than that of M, MP, and MN. Conclusion < 0.25 mm aggregates had the strongest C sequestration effect. MNP reduced the amount of mineralization by regulating enzyme activities and promoted the accumulation of SOC in farmland on the Loess Plateau by increasing the percentage of < 0.25 mm aggregates.