Table 3.
Average soil respiration (Rs) (t C ha-1 year-1) analyzed over the 2-year study across five (Fresno) and six (Napa) timepoints as measured in each cover crop and tillage treatment combination and under vine (bare soil).
| Fresno County (Five points) | ||||||||
|---|---|---|---|---|---|---|---|---|
| Tillage system (T) | Cover crop (CC) | |||||||
| NT | CT | p-valuea | AG | RV | PG | Under vine | p-value | |
| 2020 | ||||||||
| 3-Feb | 3.45 | 2.12 | ns | 2.15 | 3.43 | 2.78 | 1.03 | ns |
| 25-Mar | 4.27 | 5.13 | ns | 4.26 | 5.43 | 4.41 | 1.23 | ns |
| 16-Apr | 4.34 | 3.60 | ns | 2.85 | 3.99 | 5.07 | 2.04 | ns |
| 17-Apr | 3.80 | 4.63 | ns | 4.14 | 4.20 | 4.32 | 2.42 | ns |
| 12-Jun | 2.10 | 2.11 | ns | 2.12 | 2.15 | 2.04 | 2.46 | ns |
| Season-long Average Rs | 3.59 | 3.52 | ns | 3.10 | 3.84 | 3.72 | 1.84 | ns |
| 2021 | ||||||||
| 14-Feb | 2.41 | 3.24 | ns | 3.42 a | 2.20 b | 2.86 b | 1.92 c | * |
| 24-Mar | 3.35 | 5.35 | ns | 4.02 b | 4.02 b | 5.01 a | 1.38 c | * |
| 28-Apr | 4.99 | 4.32 | ns | 5.10 | 4.12 | 4.74 | 1.85 | ns |
| 29-Apr | 4.29 | 7.52 | ns | 6.48 | 5.39 | 5.84 | 3.34 | ns |
| 1-Jul | 3.66 | 4.32 | ns | 4.79 | 3.76 | 3.42 | 6.30 | ns |
| Season-long Average Rs | 3.74 | 4.95 | ns | 4.76 | 3.90 | 4.37 | 2.96 | ns |
| CC × T | -- | -- | ns | -- | -- | -- | -- | ns |
| Year (Y) | -- | -- | ns | -- | -- | -- | -- | ns |
| CC × T × Y | -- | -- | ns | -- | -- | -- | -- | ns |
| Napa County (Oakville) | ||||||||
| Tillage system (T) | Cover crop (CC) | |||||||
| NT | CT | p-valuea | AG | RV | PG | Under vine | p-value | |
| 2020 | ||||||||
| 24 January | 7.14 b | 8.52 a | * | 10.02a | 6.19 b | 7.29 b | 5.29 c | * |
| 13 April | 6.70 b | 9.61 a | * | 8.30 | 7.02 | 9.14 | 8.13 | ns |
| 21 April | 6.78 | 6.90 | ns | 8.21 | 6.75 | 5.56 | 2.82 | ns |
| 23 April | 5.52 | 5.43 | ns | 5.09 | 5.15 | 6.19 | 2.05 | ns |
| 22 May | 0.91 | 1.60 | ns | 0.67 | 1.02 | 2.08 | 1.36 | ns |
| 19 June | 5.30 | 4.27 | ns | 4.93 | 4.56 | 4.86 | 2.64 | ns |
| Seasonal Average Rs | 5.39 b | 6.06 a | ** | 6.20 | 5.12 | 5.85 | 3.71 | ns |
| 2021 | ||||||||
| 29 January | 14.78b | 15.87a | * | 15.60 b | 10.06c | 20.32a | 12.48b | * |
| 14 April | 7.14 | 5.42 | ns | 5.89 | 6.19 | 6.76 | 5.29 | ns |
| 16 April | 5.72 | 8.50 | ns | 8.74 | 7.14 | 5.45 | 2.40 | ns |
| 14 May | 6.78 | 6.90 | ns | 8.21 | 6.75 | 5.56 | 2.82 | ns |
| 15 June | 7.26 | 5.43 | ns | 5.09 | 7.76 | 6.19 | 2.05 | ns |
| 9 July | 0.91 | 1.60 | ns | 0.67 | 1.02 | 2.08 | 1.36 | ns |
| Seasonal Average Rs | 7.10 b | 7.29 a | * | 7.36 | 6.49 | 7.73 | 4.40 | ns |
| CC × T | -- | -- | ns | -- | -- | -- | -- | ns |
| Year (Y) | -- | -- | ns | -- | -- | -- | -- | ns |
| CC × T × Y | -- | -- | 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; ns, not significant; and --, not applicable.