Soil organic carbon saturation deficit under primary agricultural managements across major croplands in China

<p><b>Introduction:</b> To generate information for the effective management of soil organic carbon (SOC) sequestration in Chinese croplands, we compared the additional organic carbon (C) that can be stabilized by fine soil particles (<20 μm) with typical fertilization practices across soil types and climate zones. Using data from 30 long-term experimental study sites across the major agricultural zones in China, we estimated stable SOC saturation deficit (SOC_deficit) under no fertilization (CK), chemical fertilization (CF), straw plus CF (S + CF), and manure plus CF (M + CF). Stable SOC_deficit was defined as the difference between potential and current SOC stabilized by fine soil particles. <b>Outcomes:</b> Stable SOC_deficit values varied from 51% to 82%. Soils dominated by 2:1 clay minerals showed larger stable SOC_deficit than soils dominated by 1:1 clay minerals under each treatment. For soils dominated by 2:1 clay minerals, stable SOC_deficit was significantly lower under M + CF (69%) than under CK, CF, and S + CF (78–82%) treatments, and it increased with increasing mean annual temperature (<10°C). In soils dominated by 1:1 clay minerals, stable SOC_deficit was considerably lower in paddy and paddy-upland than in upland soils, suggesting that paddies effectively stabilize C inputs. <b>Discussion:</b> Agricultural soils in China have considerable C sequestration potential, despite decades of fertilization practices. To manage soil C sequestration and model soil C dynamics effectively, factors such as soil mineral types, fertilization, and cropland use should be considered. <b>Conclusion:</b> Our results demonstrated that manure addition was the best fertilization method for improving soil fertility, whereas straw return in Chinese croplands should take into account climate mitigation in future.</p

Estimated carbon sequestration potential (0–20 cm) under long-term hNPKM and NPKS fertilization treatments.

<p>Estimated carbon sequestration potential (0–20 cm) under long-term hNPKM and NPKS fertilization treatments.</p

Soil organic carbon in the (1) active, (2) slow, and (3) passive pool under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.

<p>Soil organic carbon in the (1) active, (2) slow, and (3) passive pool under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.</p

Simulated and measured soil organic carbon (SOC) stocks (0–20 cm) under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at Yangling.

<p>Simulated and measured soil organic carbon (SOC) stocks (0–20 cm) under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at Yangling.</p

The Olsen P concentrations in the black soils under long-term fertilization.

<p>The Olsen P concentrations in the black soils under long-term fertilization.</p

Carbon input (kg ha⁻¹yr⁻¹) from manure and straw residue in each period used in the CENTURY model at Changping, Yangling, and Qiyang sites.

<p>Carbon input (kg ha⁻¹yr⁻¹) from manure and straw residue in each period used in the CENTURY model at Changping, Yangling, and Qiyang sites.</p

Soil organic carbon dynamics under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.

<p>Soil organic carbon dynamics under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.</p

Correlationship between simulated and observed crop (i.e.,□wheat and ▪corn) grain yield data under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.

<p>Correlationship between simulated and observed crop (i.e.,□wheat and ▪corn) grain yield data under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.</p

Relationships between the of PAC, soil organic matter and changes in the soil Olsen P in black soils under long-term fertilization.

<p>Note: To distinguish the no P and P addition treatments, the changes in soil Olsen P by each 100 kg ha^-1 P balance of no P treatments (CK, N and NK) were defined to the negative values in this figure.</p

Changes in the pH of the black soils under long-term fertilization at Gongzhuling and Harbin.

<p>Changes in the pH of the black soils under long-term fertilization at Gongzhuling and Harbin.</p