Table 2.
Summary of curvature-SOC function evaluation indices derived from commonly sampled depths and from the entire soil profile.
| Interval Depth (m) | Curvature-SOC Model Validation | Catchment | ||||||
|---|---|---|---|---|---|---|---|---|
| R2 | RMSE (kg C m−2) | MPE (kg C m−2) | SDPE (kg C m−2) | Average SOC (kg C m−2) | Total SOC Stock (Mg C) | Total SOC Stock Range (Mg C) | Relative SOC Stock (%) | |
| 0–0.05 | 0.28 | 1.22 | 0.51 | 1.45 | 1.4 | 1,777.50 | 2,722–903 | 11.2 |
| 0–0.1 | 0.24 | 1.48 | 0.57 | 1.81 | 2.6 | 3,280.90 | 4,866–1,801 | 20.8 |
| 0–0.2 | 0.36 | 1.98 | 1.02 | 1.7 | 4.6 | 5,863.50 | 8,379–3,466 | 37 |
| 0–0.3 | 0.38 | 2.97 | 1.19 | 2.4 | 6 | 7,654.10 | 11,133–4,459 | 48.4 |
| 0–0.5 | 0.57 | 3.22 | 1.45 | 2.87 | 8.1 | 10,425.40 | 14,599–6,644 | 66 |
| 0–1.0 | 0.88 | 3.27 | 1.59 | 2.85 | 11.2 | 14,355.00 | 18,601–10,603 | 90.8 |
| Entire Profile | 0.93 | 3.43 | 1.23 | 3.21 | 12.3 | 15,806.80 | 20,173–12,060 | 100 |
Indices include the coefficient of determination (R2), root mean squared error (RMSE), mean prediction error (MPE), and standard deviation of prediction error (SDPE). The average, total, and relative SOC inventories within the granitic portions of Johnston Draw are also reported for each depth. Relative SOC inventory is compared to the modeled total SOC inventory for the entire profile at the catchment scale. The strength of the curvature-SOC relationship increases with depth, and the typical shallow (<0.3 m) focus for assessment of SOC stocks may explain why curvature has been overlooked in previous studies.