Figure 1.
The pools and flows of carbon in the CENTURY model.
The diagram showed the major factors which control the flows [29].
Table 1.
Land management practices for the long-term experimental sites during the different blocks and periods used in the CENTURY model simulations.
Table 2.
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.
Table 3.
Soil classification and initial physical and chemical properties (0–20 cm) in 1989.
Figure 2.
Average monthly precipitation, maximum (Tmax) and minimum (Tmin) temperatures from 1990 to 2010 at (A) Changping, (B) Yangling, and (C) Qiyang.
Error bars are standard deviations for the mean values from 1990–2010.
Figure 3.
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.
Figure 4.
Simulated and measured soil organic carbon (SOC) stocks (0–20 cm) under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at Changping.
Figure 5.
Simulated and measured soil organic carbon (SOC) stocks (0–20 cm) under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at Yangling.
Figure 6.
Simulated and measured soil organic carbon (SOC) stocks (0–20 cm) under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at Qiyang.
Figure 7.
Correlation between simulated SOC and measured SOC under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.
Table 4.
Statistics comparing simulated and measured SOC stocks at the three long-term experimental sites.
Figure 8.
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.
Figure 9.
Proportion of changed SOC between the 1990 (initial) and 2010 in each soil organic matter pool under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.
Figure 10.
Soil organic carbon dynamics under the control, N, NP, NPK, NPKM, hNPKM and NPKS treatments at (A) Changping, (B) Yangling, and (C) Qiyang sites.
Table 5.
Estimated carbon sequestration potential (0–20 cm) under long-term hNPKM and NPKS fertilization treatments.