Land-use change is widely considered to be a major factor affecting soil carbon (C) sequestration (ΔC_s). This paper studied changes to soil C stocks (C_s) following the conversion of farmland to forest, shrub and grassland across the key area for implementing China's “Grain for Green” — the Loess Plateau. The results are based on a synthesis of 44 recent publications (including 424 observations at 70 sites) which has allowed us to further refine our understanding of the mechanisms driving the increase in C_s following farmland conversion. This synthesis suggests that the ΔC_s potential of the Loess Plateau could reach 0.59 Tg yr⁻¹ based on an estimated annual average ΔC_s rate of 0.29 Mg ha⁻¹ yr⁻¹. In the region's different rainfall zones both the main contributing factors and C_s dynamics varied. Across the entire Loess Plateau, C_s showed first an increasing (10 yr) yet again. In addition, the ΔC_s rates depended primarily on restoration age. This synthesis demonstrates that both the initial s C_s and the average annual temperature have a significant effect on ΔC_s while the effect of land-use conversion type, rainfall zone and average annual precipitation were minimal.

Natural vegetation restoration can enhance soil organic carbon (SOC) sequestration, but the mechanisms and control factors underlying SOC sequestration are still unknown. The objectives of the study are to quantify the temporal variation of soil and aggregate‐associated organic carbon (OC) and identify factors controlling the variation following natural vegetation restoration after farmland abandonment. We collected soils from sites having 5, 30, 60, 100, and 160 years of a natural vegetation restoration chronosequence after farmland abandonment in the Loess Plateau, China. The results showed that natural vegetation restoration increased macroaggregates (0.25–2 mm; 46.6% to 73.9%), SOC (2.27 to 9.81 g kg⁻¹), and aggregate OC (7.33 to 36.98 g kg⁻¹) in the top 20‐cm soil compared with abandoned farmland, and the increases mainly occurred in the early stage (<60 years). The increase of SOC was contributed by OC accumulated in macroaggregates (0.25–2 mm) rather than microaggregates (≤0.25 mm). Moreover, SOC sequestration in the topsoil (0–10 cm) was mainly determined by fine root biomass (FR), labile organic carbon (LOC), and microbial biomass carbon (MBC). And in the subsoil (10–20 cm), SOC sequestration was mainly determined by the proportion of macroaggregates. The results suggest that natural vegetation restoration increased SOC and aggregate OC, and FR, MBC, LOC, and the physical protection of aggregates played important roles in regulating SOC and aggregate OC.