Table 2.
Soil organic carbon (% by mass), bulk density (g cm-3), and total C (Mg ha-1) in Fresno County and Napa County.
| Factors and treatment | Fresno County (Five points) | Napa County (Oakville) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Average SOC (% mass) | p-value a | Bulk density (g cm-3) | p-value | C (t ha-1) | p-value | Average SOC (% mass) | p-value | Bulk density (g cm-3) | p-value | C (t ha-1) | p-value | |
| Tillage system (T) | ||||||||||||
| NT | 0.70 | ns | 1.4 | ns | 14.68 | ns | 1.44 a | ** | 1.3 | ns | 28.15 a | ** |
| CT | 0.69 | 1.4 | 14.39 | 1.37 b | 1.3 | 26.62 b | ||||||
| Cover crop (CC) | ||||||||||||
| AG | 0.88 | ns | 1.4 | ns | 18.56 | ns | 1.47 | ns | 1.3 | ns | 28.67 | ns |
| RV | 0.90 | 1.4 | 18.93 | 1.45 | 1.3 | 28.33 | ||||||
| PG | 0.86 | 1.4 | 17.99 | 1.41 | 1.3 | 27.55 | ||||||
| Depth (D) | ||||||||||||
| 0–15 cm | 0.88 a | *** | 1.4 | ns | 18.50 a | *** | 1.45 a | ** | 1.3 | ns | 28.18 a | ** |
| 15–30 cm | 0.50 b | 1.4 | 10.57 b | 1.36 b | 1.3 | 26.59 b | ||||||
| Year (Y) | ||||||||||||
| 2020 | 0.64 | ns | 1.4 | ns | 13.42 | ns | 1.30 | ns | 1.3 | ns | 25.37 | ns |
| 2021 | 0.69 | 1.4 | 14.53 | 1.40 | 1.3 | 27.29 | ||||||
| CC × T | -- | ns | -- | ns | -- | ns | -- | ns | -- | ns | -- | ns |
| CC × T × D | -- | ns | -- | ns | -- | ns | -- | ns | -- | ns | -- | ns |
| CC × T × D × Y | -- | ns | -- | ns | -- | ns | -- | ns | -- | ns | -- | ns |
a ANOVA was used to compare data (p-value indicated). Letters within columns indicate significant mean separation according to Tukey's honestly significant difference (HSD) test (at p = 0.05), where *: p-value < 0.05; **: p-value < 0.001, and ***: p-value < 0.0001. b NT, no tillage; CT, conventional tillage; AG, annual grass; RV, residual vegetation; PG, perennial grass; SOC, soil organic carbon; ns, not significant; and --, not applicable.