Edited by: Ravi Gupta, Kookmin University, South Korea
Reviewed by: Georgios Koubouris, Hellenic Agricultural Organization DEMETER, Greece; Maria Martínez-Mena, Center for Edaphology and Applied Biology of Segura (CSIC), Spain
*Correspondence: Sahap Kaan Kurtural,
†Present address: Runze Yu, Department of Viticulture and Enology California State University Fresno, California State University, Fresno, CA United States; Nazareth Torres, Department of Agronomy, Biotechnology and Food, Public University of Navarra, Pamplona, Spain
This article was submitted to Crop and Product Physiology, a section of the journal Frontiers in Plant Science
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Globally, wine grape vineyards cover approximately 7.4 M ha. The potential for carbon (C) storage in vineyards is of great interest to offset greenhouse gas emissions and mitigate the effects of climate change. Sustainable soil management practices such as cover crop adoption and reduced tillage may contribute to soil organic carbon (SOC) sequestration. However, site-specific factors such as soil texture, other soil physicochemical properties, and climate largely influence the range and rate to which SOC may be stored. To measure the potential for C storage in vineyards under varying sustainable soil management practices, we calculated the net ecosystem carbon balance (NECB) of three cover crops [perennial grass (
As temperatures rise and rain events become more unpredictable due to the changing climate, soils are under threat of loss of soil organic matter (SOM), soil nutrient imbalances, loss of soil biodiversity, contamination, and compaction (
Traditionally, the interrows of vineyards were kept free of vegetation with the use of herbicides and tillage. However, it has been shown that both practices may have detrimental effects on soil quality and the surrounding ecosystem (
Framework for increasing soil organic carbon (SOC) conversion effiency in vineyards by increasing inputs of cover crops, compost, and perennializaiton and decreasing outputs from tillage and erosion avoidance.
Previous studies have indeed identified vineyards as C sinks. However, the management practices largely influenced the storage potential of the vineyard systems (
One source of limitation in quantifying C sequestration in previous literature may be the presence or absence of measurement of CO2 efflux from assessing soil respiration (Rs). Soil CO2 efflux results from the combination of biological and physical processes, both of which are sensitive to edaphic factors and highly variable in space and time (
Thus, a net ecosystem carbon balance (NECB) is needed to elucidate C inputs and outputs in commercial production settings at vineyard scale. One method of estimating net C storage within a system is through the net ecosystem production (NEP) methodology (
Thus, the objective of this study was to investigate the synergic effects of the implementation of cover crops and NT practices by quantifying C inputs and losses at the vineyard scale through the NECB determination in two different wine production regions and to investigate the contributions of specific site characteristics toward these vineyard floor management practices in two hyperarid seasons in California. We hypothesized that the vineyard agroecosystem can serve as a C storage pool, and the effectiveness of the ecological functioning of NT and cover crops will be determined by site characteristics, including climate and soil texture.
Field experiments were conducted at two sites for two consecutive growing seasons (2019–2020 and 2020–2021). The first site was located in Five Points, Fresno County, CA, USA (36.671514, -119.925823), in a Ruby Cabernet/Freedom (27%
At both sites, experiments were arranged in a split-plot 3 × 2 factorial design (three different cover crops subjected to two tillage managements) with four (Napa) and three replications (Fresno). At both vineyards, each treatment replicate consisted of 15 grapevines. Three vines in the middle of each replicate were used for on-site measurements, including the parameters from both grapevines and soils under grapevines, while the distal vines on either end were treated as border plants. Cover crop treatments included 1) perennial grass (PG) (
The site conditions in both Fresno County and Napa County vineyards are presented in
Site conditions at two commercial vineyards in Fresno County and Napa County from experimental years (2019–2021) and long-term mean values (2011–2021).
Year | Air temperature (°C) | Soil temperature (°C) | Precipitation (mm)b | GDD (°C) | ||||
---|---|---|---|---|---|---|---|---|
Daily max | Daily min | Daily average | Daily max | Daily min | Daily average | |||
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Mean | 25.6 | 9.1 | 17.3 | 25.7 | 10.7 | 22.6 | 199 | 2,358 |
Annual maxa | 35.8 | 18 | 27.3 | -- | -- | -- | -- | -- |
Annual mina | 15.6 | 0.6 | 7.6 | -- | -- | -- | -- | -- |
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Mean | 25.8 | 9.2 | 17.6 | 26.6 | 10.4 | 22.8 | 152.5 | 2,488 |
Annual max | 37.8 | 18.7 | 28.5 | -- | -- | -- | -- | -- |
Annual min | 12.5 | 3.1 | 7.7 | -- | -- | -- | -- | -- |
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Mean | 25.4 | 9.4 | 17.2 | 25.6 | 10.1 | 22.3 | 209.6 | 2,259 |
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Mean | 24.4 | 7 | 14.9 | 22.5 | 10 | 16.5 | 234.2 | 1,647 |
Annual max | 31.8 | 12.3 | 21.1 | -- | -- | -- | -- | -- |
Annual min | 17.1 | 2 | 8.5 | -- | -- | -- | -- | -- |
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Mean | 23.1 | 6.3 | 14.2 | 22.8 | 10.2 | 16.4 | 278.3 | 1,519 |
Annual max | 30 | 10.8 | 19.2 | -- | -- | -- | -- | -- |
Annual min | 12.5 | 2.6 | 7.6 | -- | -- | -- | -- | -- |
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Mean | 23.2 | 7.1 | 14.5 | 22.8 | 7.9 | 16 | 577.8 | 1,504 |
a Annual maximum (max) and annual minimum (min) indicate the greatest or lowest value observed during the respective year. b Total precipitation occurred during the annual winter rainy season, calculated from October of the preceding year through September of the following year (e.g., 2020 values were calculated from 1 October 2019 to 30 September 2020). c--, not applicable and GDD, growing degree days.
At both sites, air temperatures were consistent between years. However, the mean daily maximum temperature was 0.2°C higher in 2021 than 2020, while it was 1.3°C lower in 2021 compared to 2020 in Napa County. Daily maximum soil temperature was 0.9°C and 0.3°C higher in 2021 compared to 2020 in both Fresno County and Napa County, respectively. Daily average soil temperatures were also slightly higher by a degree of 0.1°C–0.2°C at both sites in 2021. Furthermore, average soil temperatures during both years were 0.3°C–0.5°C higher in Fresno County and 0.4°C–0.5°C higher in Napa County compared to the long-term average for the region over the past 10 years (2011–2021) (
At the Fresno County vineyard, approximately 199.0 mm of rain was received at the experimental site beginning in October of the preceding year until the harvest in year 1, while 152.5 mm of rain was received during the same period in year 2. In year 1 of the study, the greatest amount of precipitation was received in March (67 mm), while in year 2, the greatest amount (87 mm) was received in January followed by December and October. Therefore, compared to year 1, year 2 received more fall-to-winter precipitation. The Napa County vineyard received a greater amount of rainfall compared to that of Fresno County, as 234.2 mm of rain was received in year 1 and 278.3 mm of rain in year 2. December and January received the greatest amount of precipitation in both year 1 and year 2.
Soil texture was assessed using the hydrometer method (S-14.10) from the North American Proficiency Testing (NAPT) program. The SOC content was measured in the interrows of each experimental unit under dry conditions. In July 2020, bulk density was assessed at the centers of interrows (122 cm from the vine rows) and the edges of the berms (61 cm from the grapevine trunk) using brass rings of 10 cm internal diameter and 7.5 cm length. No differences in bulk densities were found in the soil samples between CT and NT interrows, thus all soil samples were taken at the same depth of 30 cm. Three soil cores were randomly collected per experimental unit to a depth of 30 cm and partitioned into 0–15 cm and 15–30 cm subsamples. Subsamples were homogenized and kept in a cool environment until analysis. At analysis, samples were dried, sieved to <2 mm, ball-milled, and analyzed for SOC by combustion method (S-9.30), and soil texture was determined by hydrometer analysis (S-14.10) according to the NAPT program. Soil pH was determined
To calculate the losses of soil C through Rs, soil CO2 efflux was measured
Eq. 1.
where Rs is the respiration rate (CO2 flux, or moles of CO2 unit area-1 unit time-1), Co is the CO2 concentration at T = 0, and Cn is the concentration at a time Tn later. A is the area of soil surface exposed (78 cm2), and V is the total system volume (1,171 ml). The air within the SRC-2 chamber was continuously and automatically mixed during the measurement period to ensure representative samples.
Rs measurements took place no more than 2 h after solar noon and was measured at six time points per experimental unit in each season in Oakville (24 January, 13 April, 21 April, 23 April, 22 May, and 19 June in 2020; 29 January, 14 April, 16 April, 14 May, 15 June, and 9 July in 2021) and five time points in Fresno (2 March, 25 March, 16 April, 17 April, and 12 June in 2020; 14 February, 24 March, 28 April, 29 April, and 1 July in 2021). Measurement time points were selected to represent soil conditions throughout the season, including the day before and after a tillage event and important precipitation events at both sites. Mean Rs values for the season were calculated for each treatment and the bare soil control. In the first year of the study, soil moisture was measured as the volumetric water content (VWC) at the time of each Rs measurement. No significant differences were found between treatments, and thus, soil moisture was not monitored the following season, and measurement dates were targeted before and after tillage and precipitation events.
NPPgrapevine was estimated as the summation of annual production (harvest yield, leaf biomass, and cane production) and permanent organs (trunk and root biomass). Harvest commenced when the fruit reached approximately 25°Bx in Oakville (25 August 2020 and 1 September 2021) and 21°Bx in Fresno (6 October 2020 and 7 September 2021). At both sites, clusters from three data vines per experimental unit were manually removed, counted, and weighed on a top-loading balance. Subsamples were collected from clusters within each experimental unit at harvest, and C content (% mass) was determined
To assess the leaf biomass at the Fresno vineyard, leaf area index (LAI) was measured in late spring to characterize the grapevine canopy growth by a smartphone program, VitiCanopy,
Cane production (pruning wood weights) was measured at dormancy among the three data vines per experimental unit. The C content (%) of pruning wood was estimated based on previous literature, which was 9% as the average percentage fractions of biomass of canes (
NPPcover crop was calculated by collecting aboveground and belowground biomass at crop physiological maturity as described previously (
The NECB (Mg C ha-1 year-1) was calculated as follows:
Eq. 2. NECB = NPPgrapevine + SOC + NPPcover crop – Rs: interrow – harvest – Rs: under vine
where NPPgrapevine is the summation of annual (leaves and fruits) and perennial (permanent organs) growth, SOC is the soil organic carbon sequestered to a depth of 30 cm adjusted for the interrow spatial coverage, NPPcover crop is the sum of aboveground and belowground cover crop biomass to 10 cm, Rs: interrow is the soil respiration of the portion of the vineyard where the cover crop is grown, harvest is the amount of C removed through yield, and Rs: under vine is the soil respiration of the portion of the soil left bare. Interrow coverage was estimated as 48% of one hectare and bare soil 52% of one hectare. A positive NECB signifies that the system is the net sink of C, and a negative NECB signifies a net source of C to the atmosphere.
Statistical analyses were conducted with R studio version 3.6.1 (RStudio: Integrated Development for R., Boston, MA, USA) for Mac OS. After normality assessment, data were submitted to a two-way analysis of variance (ANOVA) to assess the statistical differences between the different cover crop and tillage treatments and the respective interaction effects. Means ± standard errors (SEs) were calculated, and when the F value was significant (P ≤ 0.05), a Tukey’s “honest significant difference” (HSD)
The soil texture at the Fresno County vineyard is classified as a sandy loam with approximately 66% sand, 22% silt, and 12% clay and a bulk density value 1.4 g cm -3. The SOC (% mass C) was not affected by type of cover crop nor tillage system over the course of the experiment at either depth in the Fresno County vineyard (
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) |
|
Bulk density (g cm-3) |
|
C (t ha-1) |
|
Average SOC (% mass) |
|
Bulk density (g cm-3) |
|
C (t ha-1) |
|
|
|
||||||||||||
NT | 0.70 | ns | 1.4 | ns | 14.68 | ns | 1.44 |
** | 1.3 | ns | 28.15 |
** |
CT | 0.69 | 1.4 | 14.39 | 1.37 |
1.3 | 26.62 |
||||||
|
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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 | ||||||
|
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0–15 cm | 0.88 |
*** | 1.4 | ns | 18.50 |
*** | 1.45 |
** | 1.3 | ns | 28.18 |
** |
15–30 cm | 0.50 |
1.4 | 10.57 |
1.36 |
1.3 | 26.59 |
||||||
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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.
Across the five readings of Rs measured in the interrows at the Fresno County vineyard, when Rs readings were averaged to determine the seasonal mean Rs, no overall differences were observed over the duration of the experiment (
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 |
|
AG | RV | PG | Under vine |
|
|
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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 |
|
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14-Feb | 2.41 | 3.24 | ns | 3.42 |
2.20 |
2.86 |
1.92 |
* |
24-Mar | 3.35 | 5.35 | ns | 4.02 |
4.02 |
5.01 |
1.38 |
* |
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 |
|
AG | RV | PG | Under vine |
|
|
|
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24 January | 7.14 |
8.52 |
* | 10.02 |
6.19 |
7.29 |
5.29 |
* |
13 April | 6.70 |
9.61 |
* | 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 |
6.06 |
** | 6.20 | 5.12 | 5.85 | 3.71 | ns |
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29 January | 14.78 |
15.87 |
* | 15.60 |
10.06 |
20.32 |
12.48 |
* |
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 |
7.29 |
* | 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.
Progression of soil respiration (Rs) and daily precipitation amounts in two wine grape vineyards,
At the Fresno County vineyard, there was an effect of cover crop on pruning wood and leaf C contributions (
Components of the vineyard’s net primary production (NPP as t ha-1 of dry matter), the whole vine’s net carbon balance (NCB), and the vineyard’s net ecosystem carbon balance (NECB) calculated over the 2-year study for six different cover crop and tillage systems.a,b.
Treatment | Harvest (Mg C ha-1) | Pruning wood (Mg C ha-1) | Leaves (Mg C ha-1) | Permanent organs (Mg C ha-1) | Grapevine NPP (Mg C ha-1 year-1) | Rs Under vine (Mg C ha-1 year-1) | Grapevine NCB (Mg C year-1) | Cover Crop NPP (Mg C ha-1) | Rs Interrow (Mg C ha-1 year-1) | SOC (Mg C ha-1) | NECB (Mg C ha-1 year-1) | |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Tillage (T) | Cover crop (CC) | |||||||||||
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NT | AG | 1.39 | 1.76 | 3.02 | 11.5 | 17.7 | 1.84 | 15.35 | 1.80 | 2.81 | 17.71 | 23.36 |
PG | 1.41 | 1.30 | 2.97 | 11.5 | 17.2 | 1.84 | 14.83 | 1.70 | 4.02 | 19.25 | 22.96 | |
RV | 1.32 | 1.73 | 3.53 | 11.5 | 18.1 | 1.84 | 15.82 | 2.30 | 3.94 | 17.64 | 23.5 | |
CT | AG | 1.25 | 1.75 | 3.22 | 11.5 | 17.7 | 1.84 | 15.54 | 3.93 | 3.39 | 19.81 | 25.31 |
PG | 1.48 | 1.56 | 3.27 | 11.5 | 17.8 | 1.84 | 15.39 | 1.83 | 3.42 | 18.97 | 23.74 | |
RV | 1.65 | 2.17 | 2.93 | 11.5 | 18.3 | 1.84 | 15.66 | 1.17 | 3.74 | 17.64 | 22.89 | |
|
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NT | AG | 1.24 | 1.61 | 2.98 | 11.5 | 17.3 | 2.96 | 14.56 | 2.00 | 3.71 | 17.71 | 22.24 |
PG | 1.63 | 1.25 | 2.92 | 11.5 | 17.3 | 2.96 | 14.15 | 2.15 | 3.69 | 19.32 | 22.69 | |
RV | 1.80 | 1.53 | 3.48 | 11.5 | 18.3 | 2.96 | 14.99 | 1.83 | 3.81 | 17.71 | 22.54 | |
CT | AG | 1.11 | 1.75 | 3.18 | 11.5 | 17.6 | 2.96 | 14.91 | 4.08 | 5.81 | 19.88 | 23.63 |
PG | 1.21 | 1.50 | 3.09 | 11.5 | 17.3 | 2.96 | 14.58 | 2.07 | 5.06 | 18.97 | 22.25 | |
RV | 1.34 | 2.01 | 2.88 | 11.5 | 17.8 | 2.96 | 14.88 | 1.33 | 3.98 | 17.36 | 21.94 | |
CC | ns | * | * | -- | ns | -- | ns | ** | ns | ns | ns | |
T | ns | ns | ns | ns | ns | ns | ns | ns | ns | |||
CC × T | ns | ns | ns | ns | ns | ns | ns | ns | ns | |||
Year | ns | ns | ns | ns | * | * | ns | ns | ns | |||
Year × CC | ns | ns | ns | ns | ns | ns | ns | ns | ns | |||
Year × T | ns | ns | ns | ns | ns | ns | ns | ns | ns | |||
Year × CC × T | ns | ns | ns | ns | ns | ns | ns | ns | ns | |||
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NT | AG | 0.15 | 0.37 | 0.57 | 6.7 | 7.8 | 3.71 | 5.71 | 2.92 | 5.56 | 29.25 | 18.49 |
PG | 0.17 | 0.21 | 0.49 | 6.7 | 7.6 | 3.71 | 5.47 | 0.96 | 5.89 | 28.28 | 16.68 | |
RV | 0.14 | 0.43 | 0.44 | 6.7 | 7.7 | 3.71 | 5.63 | 2.59 | 4.73 | 28.76 | 18.41 | |
CT | AG | 0.16 | 0.51 | 0.55 | 6.7 | 7.9 | 3.71 | 5.83 | 2.96 | 6.85 | 29.25 | 18.00 |
PG | 0.16 | 0.32 | 0.64 | 6.7 | 7.8 | 3.71 | 5.72 | 1.19 | 5.82 | 27.30 | 16.61 | |
RV | 0.16 | 0.77 | 0.74 | 6.7 | 8.4 | 3.71 | 6.29 | 3.20 | 5.50 | 27.30 | 18.29 | |
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NT | AG | 0.44 | 0.56 | 0.61 | 7.0 | 8.6 | 4.40 | 5.88 | 3.20 | 7.25 | 28.76 | 17.74 |
PG | 0.33 | 0.39 | 0.53 | 7.0 | 8.3 | 4.40 | 5.63 | 1.62 | 7.70 | 27.79 | 16.05 | |
RV | 0.26 | 0.62 | 0.47 | 7.0 | 8.3 | 4.40 | 5.80 | 3.60 | 6.68 | 30.23 | 18.83 | |
CT | AG | 0.37 | 0.68 | 0.58 | 7.0 | 8.6 | 4.40 | 5.97 | 3.32 | 7.48 | 27.30 | 17.08 |
PG | 0.38 | 0.48 | 0.67 | 7.0 | 8.5 | 4.40 | 5.86 | 1.47 | 7.75 | 26.81 | 15.72 | |
RV | 0.46 | 0.96 | 0.77 | 7.0 | 9.2 | 4.40 | 6.45 | 3.46 | 5.64 | 26.81 | 18.27 | |
CC | ns | ns | ns | -- | * | -- | ** | ** | ns | ns | *** | |
T | ns | ** | * | *** | *** | ns | ** | ** | * | |||
CC × T | ns | ns | ns | * | * | ns | ns | ns | ns | |||
Year | *** | ** | ns |
|
ns | ns | ns | ns | * | |||
Year × CC | ns | ns | ns | ns | ns | ns | ns | ns | ns | |||
Year × T | ns | ns | ns | ns | ns | ns | ns | ns | ns | |||
Year × CC × T | ns | ns | ns | 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; NPP; net primary production; NCB, net carbon balance; Rs, respiration; SOC, soil organic carbon; NECB, net ecosystem carbon balance; ns, not significant; and --: not applicable.
When harvest mass and Rs under vine were subtracted from grapevine NPP to generate the grapevine net carbon balance (NCB), a year-to-year difference was observed at the Fresno County vineyard, as values in 2020 were greater than that of 2021 (
After 2 years of the adoption of treatments, there were no statistical differences between the type of cover crop on SOC at either experimental vineyard, which agreed with some previous studies when cover crops were implemented and the effects on SOC were monitored only for a short period of time (
At the Fresno County vineyard, while the soils under cover crop displayed differences in Rs in the early season Rs measurement events in 2021, ultimately no seasonal differences were observed. This may be due to the higher sand content in the soil at this experimental site (
A similar trend was observed at the Napa County vineyard, where Rs interrow showed differences in the early season, despite no significant differences of cover crop type over seasonal average R
On the other hand, high variability in biomass led to a significant effect of cover crop type on the NECB at both experimental sites. This was likely due to the compensation of C input through biomass from the cover crops implemented in this study, as the AG and RV all showed greater biomasses compared to the low-stature PG. AG and RV have generated greater biomasses compared to low-profile
Our findings provide more evidence of that the vineyard agroecosystem can serve as a C sink for short-term implementation of cover crops with NT practice. Corroborating previous research under sandy soils, tillage and type of cover crop had little to no effect on the NECB. However, under the finer-textured soils, CT reduced the NECB through a reduction in SOC and increase in Rs, or soil CO2 efflux. The type of cover crop also impacted the NECB, as cover crops that produced greater biomass increased the NECB. Ultimately, vineyard site characteristics, including soil texture and climate, were key determinants of the effectiveness of C storage potential, as they can determine SOC and Rs of vineyards in Mediterranean vineyard agroecosystems in both Napa and Fresno. Overall, the implementation of NT and cover crop practices should be carefully considered with a thorough understanding of the specific site characteristics to fully maximize their effectiveness.
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.
SK designed the trial and acquired the funding. MZ, NT, RY, and LM executed the trial. MZ and NT curated the data. MZ wrote the first version of the manuscript. All authors read and approved the final submitted version of the paper.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.