Effects of substitution of chemical fertilizer by Chinese milk vetch on distribution and composition of aggregates-associated organic carbon fractions in paddy soils

Green manure plays a key role in reducing chemical fertilizer applications and increasing soil organic carbon (SOC) stock. The effects of substitution by Chinese milk vetch (MV) on the distribution composition fractions macroaggregates microaggregates SOC stability mechanism were investigated paddy soils southern China. A 10-year (2008–2018) field experiment was conducted, including no (CK), 100% NPK (F100), MV with different percentages (MV + F100, F80, F60 F40). separated into distinct using aggregate density fractionation structure analyzed fourier-transform infrared nuclear magnetic resonance. Chemical increased contents bulk 9.1% F80), 5.8% F60), 17.9% F40) compared to F100. Organic fraction mainly existed mineral associated (mSOC), accounting for 70.3–83.7% 69.4–84.0% relative mass microaggregates, respectively. Compared aromatic C 11.6% 29.1% under within mSOC microaggregates. Within macroaggregates, CK, F80 promoted proportion alkyl 9.6% 6.7%, decreased content O-alkyl 14.1% 11.0%, respectively, which correspondingly C/O-alkyl ratio. Substitution (especially F60) improved via recalcitrant mSOC, conducive sequestration soils.