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Providing evidence to improve practice

Action: Crop production: Plant or maintain ground cover in orchards or vineyards Mediterranean Farmland

Key messages

Crop yield (11 studies)

  • Grapes (8 studies): Two replicated, randomized, controlled studies from France and the USA found lower grape yields in plots that were seeded with grass between the vine rows, compared to plots with bare soil between the vine rows, in some or all comparisons. Six replicated, randomized, controlled studies from Italy, Portugal, Spain, and the USA found similar grape yields in plots with or without ground cover between the vine rows.
  • Other crops (3 studies): Two replicated, randomized, controlled studies from Portugal found higher chestnut yields in plots with resident vegetation, compared to plots without ground cover, but found no difference in chestnut yields between plots with seeded cover crops and plots without ground cover. One of these studies also found higher mushroom yields in plots with resident vegetation, compared to plots without ground cover. One replicated, randomized, controlled study from Chile found lower avocado yields in plots that were seeded with grasses and legumes, compared to plots with bare soil.

 

Crop quality (8 studies)

  • Grapes (6 studies): Five replicated, randomized, controlled studies from Italy, Portugal, and the USA found similar sugar contents in grapes with or without ground cover between the vine rows. Three of these studies found similar pH levels, and two of these studies found no differences in titratable acidity, but two of these studies found lower titratable acidity in grapes with ground cover between the vine rows. One replicated, randomized, controlled study from the USA found heavier grapes with ground cover between the vine rows, but two replicated, randomized, controlled studies from Italy and Spain did not. Two replicated, randomized, controlled studies from Portugal and Spain found other differences in grape quality with ground cover between the vine rows.
  • Other crops (2 studies): One replicated, randomized, controlled study from Portugal found larger chestnuts in plots with ground cover, compared to plots without ground cover. One replicated, randomized, controlled study from Chile found no difference in avocado quality in plots with or without ground cover.

 

Implementation options (6 studies)

  • Ground cover (5 studies)
    • Grapes (3 studies): One replicated, randomized, controlled study from the USA found similar grape yields in plots with different types of ground cover. However, this study found lighter-weight clusters of grapes in plots with seeded cover crops, compared to resident vegetation, in one of three years, and found inconsistent differences in cluster weights between plots with different types of seeded cover crops. Two replicated, randomized, controlled studies from Spain and the USA found other differences in grape quality between plots with different types of ground cover.
    • Other crops (2 studies): Two replicated, randomized, controlled studies from Portugal found lower chestnut yields in plots with seeded cover crops, compared to resident vegetation. One of these studies also found smaller chestnuts and lower mushroom yields.
  • Tillage (2 studies): One replicated, randomized, controlled study from the USA found higher grape yields, and heavier grape clusters, in plots without tillage between the vine rows, in one of six comparisons. Another replicated, randomized, controlled study from the USA found similar grape yields, with or without tillage between the vine rows.

Supporting evidence from individual studies

1 

A replicated, randomized, controlled study in 1989–1990 in an irrigated vineyard in the San Joaquin Valley, California, USA, found lower crop yields in plots with cover crops, compared to bare soils, between the vine rows. Crop yield: Lower grape yields were found in plots with cover crops, compared to bare soils, in two of four comparisons (in 1990: 16–20 vs 23 Mg/ha). Methods: There were three plots (one vine row and two interrows, 183 m length) for each of two cover crops (Bromus mollis bromegrass as a winter cover crop, treated with herbicide and mulched in summer, or followed by resident vegetation as a summer cover crop), and there were three control plots (bare soil, maintained with herbicide throughout the year). The bromegrass was seeded in January and December 1989 (and reseeded in March 1989 because of poor establishment). All plots were furrow irrigated until the water had advanced to the end of the furrow (five times in March–September 1989–1990), and thus more water was given to plots with faster infiltration (plots with cover crops). Grapes were harvested in September 1989–1990.

2 

A replicated, randomized, controlled study in 1998–2002 in a rainfed vineyard in southern France found lower crop yields in plots sown with grass between vine rows, compared to bare soil. Crop yield: Lower grape yields were found in plots with grass between the vine rows, compared to bare soil (8 vs 12 t/ha). Methods: In 1998, grass seeds (Festuca arudinacea tall fescue) were sown between the vine rows in four treatment plots, and herbicide was used to control weeds between vine rows in four control plots (12 x 15 m plots). The grass was mown three times/year, in the summer. Grape yield was measured from 1999–2002 (three vines/plots).

3 

A replicated, randomized, controlled study in 1996–2000 in an irrigated vineyard in the Sacramento Valley, California, USA, found no differences in grape yield or quality between plots with or without cover crops between the vine rows. Crop yield: Similar grape yields were found in plots with or without cover crops between the vine rows (18–28 vs 19–30 kg/vine). Crop quality: No consistent differences in grape quality were found in plots with or without cover crops (see publication for data on Brix, pH, and titratable acidity). Methods: There were four plots for each of four cover crops (1.8 m width, between vine rows of 3.4 width), and there were four control plots (periodically disked between the vine rows). Each plot was 10 contiguous vines and two adjacent interrows. The cover crops were Californian native grasses (not tilled, mown), annual clover (not tilled, mown), barley and oats (mown and disked), or legumes and barley (mown and disked in spring and used as a green manure). The Californian native grasses were seeded between the vine rows in autumn 1996. The others were seeded in autumn 1997–1999. All plots were drip irrigated, fertigated (20 kg N/ha/year), and the grass cover crops were also fertilized with urea (45 kg N/ha/year). Herbicide was used under the vines. Grape quality was measured in 150 grapes/plot.

4 

A replicated, randomized, controlled study in 2002–2004 in a rainfed vineyard in central Portugal found similar grape yields, but differences in grape quality, in plots with ground cover (without tillage), compared to tilled soils (without cover crops), between the vine rows. Crop yield: Similar grape yields were found in plots with or without ground cover (2.9 kg/vine). Crop quality: Lower acidity (2004: 6.7–7.2 vs 8.1 g tartaric acid/litre), higher phenol content (data not reported), and higher anthocyanin content (2004: 1,182–1,269 vs 1,027 mg/litre) were found in grapes from plots with ground cover, but there were similar sugar contents (22 oBrix) and pH levels (pH 3.35). Methods: There were four plots for each of two ground-cover treatments (resident vegetation or sown cover crops, both without tillage between the vine rows), and there were four control plots (with tillage between the vine rows; depth not reported). The plots were four vine rows each (100 vines/row). The cover crops were 60% grasses (Lolium and Festuca spp.) and 40% legumes (Trifolium spp.), sown in March 2002. The interrows of all plots were mown (treatments: twice/year, to 15 cm, in February and May–June; controls: once/year, in February, height not reported). All plots were fertilized, and herbicide was used under the vines. Two-hundred grapes/plot were collected for measurements of crop quality.

5 

A replicated, randomized, controlled study in 2002–2005 in an irrigated vineyard in the Napa Valley, California, USA, found similar grape yields in vine rows with ground cover, with or without tillage. Implementation options: Similar grape yields were found in vine rows with ground cover (either seeded cover crops or resident vegetation), with or without tillage (4.3–6.6 kg/vine). Methods: No tillage or conventional tillage was used on eight plots each, between the vine rows (three vine rows/plot). A disk plough was used for conventional tillage (15 cm depth, once/year in April–June). Four plots with conventional tillage had annual cover crops (seeded in October 2002–2004) and four plots had resident vegetation. Four plots with no tillage had annual cover crops (seeded in October 2002–2004), and four had perennial cover crops (seeded in October 2002). All plots were drip irrigated in July–October (85 kl/ha/week). Grapes were harvested from 18 vines/plot (September 2003–2004 and October 2005).

6 

A replicated, randomized, controlled study in 2000–2005 in an irrigated vineyard in the Salinas Valley, California, USA, found similar crop yields and qualities in plots with or without cover crops, except for lower acidity in plots with cover crops. Crop yield: Similar grape yields were found in plots with or without cover crops (6–6.5 vs 6.1 kg/vine; 46–48 vs 47 cluster/vine, 130–139 vs 132 g/cluster). Crop quality: Similar sugar content and pH levels were found in grapes from plots with or without cover crops (24 oBrix, 3.4 pH), but lower titratable acidity was found in plots with cover crops, in one of two comparisons (7.0 vs 7.3 g/litre). Methods: There were nine plots for each of two treatments, and there were nine control plots. The treatments were triticale (X Triticosecale) or Secale cereale Merced rye, planted in November 2000–2004 as cover crops (32 inches width) between the vine rows (8 feet width), mown in spring, and disked into the soil in the following November. Bare soils were maintained in the controls through disking in spring and summer (depth not reported). Each plot had 100 vines and the adjacent areas between the vine rows. All plots were drip-irrigated in April–October. Grapes were harvested from 20 vines/plot (for crop yield), and 200 grapes/plot (for crop quality). It was not clear whether these results were a direct effect of cover crops or tillage.

7 

A replicated, randomized, controlled study in 2001–2006 in a chestnut orchard in northeast Portugal (same study as (8)) found higher chestnut yields in plots with resident vegetation (without tillage), compared to plots without ground cover (with conventional tillage). Crop yield: Higher chestnut yields were found in plots with ground cover, compared to plots without ground cover, in one of two comparisons (with resident vegetation: 27 vs 19 kg dry matter/tree). Implementation options: Lower chestnut yields were found in plots with seeded grasses and legumes, compared to resident vegetation (20 vs 27 kg dry matter/tree). Methods: There were three plots for each of two treatments (no tillage with ground cover: grasses and legumes, sown in 2001, or resident vegetation), and there were three control plots (conventional tillage, 15–20 cm depth, thrice/year). Each plot (600 m2) had six chestnut trees (40 years old in 2001) and was fertilized but not irrigated. Chestnuts were collected thrice/plot in 2003–2006. It was not clear whether these results were a direct effect of ground cover or tillage.

 

8 

A replicated, randomized, controlled study in 2001–2008 in a chestnut orchard in northeast Portugal (same study as (7)) found higher mushroom and chestnut yields, and larger chestnuts, in plots with ground cover (without tillage), compared to plots with conventional tillage (without ground cover). Crop yield: Higher edible mushroom yields were found in plots with ground cover, compared to conventional tillage (43 vs 6 kg fresh weight/ha), and higher chestnut yields were also found in one of two comparisons (with resident vegetation: 27 vs 19 kg dry matter/tree). Crop quality: Larger chestnuts were found in plots with ground cover, compared to conventional tillage (10–11 vs 9 g/fruit; 26–27 vs 25 mm size index). Implementation options: Lower crop yields and smaller chestnuts were found in plots with seeded cover crops, compared to resident vegetation (edible mushrooms: 45 vs 59 kg fresh weight/ha; chestnuts: 20 vs 27 kg dry matter/tree; 11 vs 10 g/fruit; 26 vs 27 mm size index). Methods: There were three plots for each of two treatments (no tillage with ground cover: grasses and legumes, sown in 2001, or resident vegetation), and there were three control plots (conventional tillage, 15–20 cm depth, thrice/year). Each plot (600 m2) had six chestnut trees (40 years old in 2001) and was fertilized but not irrigated. Chestnuts were sampled thrice/plot in 2003–2006. Mushrooms were collected in 2006–2008 (weekly in May–July and September–November, under three trees/plot). It was not clear whether these results were a direct effect of ground cover or tillage.

 

9 

A replicated, randomized, controlled study in 2008–2011 in an irrigated avocado orchard in Chile found lower crop yields in plots with cover crops, compared to bare soil. Crop yield: Lower avocado yields were found in plots with cover crops, compared to bare soil (1.3 vs 5 kg fruit/tree; 7 vs 27 fruits/tree). Crop quality: Similarly-sized avocados were found in plots with cover crops or bare soil. Methods: Cover crops were grown in five treatment plots, and bare soil was maintained with herbicide in five control plots, in an avocado orchard, on a 47% slope (10 x 50 m plots). The groundcover (Lolium rigidum ryegrass and a legume, Medicago polymorpha) was sown in August 2008 and mown in February 2009–2010 (residues were retained). All plots were fertilized and irrigated. Avocado yield and quality were measured in 2011.

10 

A replicated, randomized, controlled study in 2008–2010 in an irrigated vineyard in the San Joaquin Valley, California, USA (same study as (14)), found lighter-weight clusters of grapes in plots with seeded cover crops, compared to resident vegetation, but found similar crop yields. Implementation options: Similar grape yields were found in plots with cover crops or resident vegetation (8–19 vs 11–19 kg/vine). Similar grape yields were found in plots with different types of seeded cover crops (oats only, or oats and legumes: 8–19 kg/vine). Higher grape yields were found in plots with no tillage, compared to conventional tillage, in one of six comparisons (in 2010, in plots that were cover cropped with oats and legumes: 13 vs 9 kg/vine). Heavier clusters of grapes were found in plots that were cover cropped with oats only, compared to oats and legumes, in one of three years (2010: 70 vs 65 g/cluster), but lighter clusters were found in one of three years (2009: 110 vs 125). Heavier clusters were also found in plots with no tillage, compared to conventional tillage, in one of six comparisons (in 2010, in plots that were cover cropped with oats and legumes: 85 vs 70 g/cluster). Lighter-weight clusters of grapes were found in plots with cover crops, compared to resident vegetation, in one of three years (2010: 65–70 vs 80 g/cluster). Methods: Either seeded cover crops or resident vegetation was grown between the vine rows on 16 plots each (two vine rows/plot, 190 vines/row). The cover crops were either oats or oats and legumes, on eight plots each, seeded in November. The plots were mown in spring, before tillage. No tillage was used on half of the plots, and conventional tillage was used on the other half. A disk plough (15–20 cm depth) was used for conventional tillage, in spring, summer (three times), and autumn. Herbicide was used to control weeds in the vine rows (50 cm width).

11 

A replicated, randomized, controlled study in 2005–2010 in an irrigated vineyard in Sardinia, Italy, found similar grape yields and similarly-sized grapes, of similar quality, in plots with ground cover (without tillage), compared to conventional tillage (without ground cover), between the vine rows. Crop yield: Similar crop yields were found in all plots (3.5–5.6 kg, 8.5–13.5 grape clusters/vine, 351–537 g/cluster). Crop quality: Similarly-sized grapes (1.8–3 g/grape), with similar compositions (sugar content: 19–22.5 oBrix; titratable acidity: 3.9–5.9 g/L; see publication for other measurements), were found in all plots. Methods: There were four plots (3 vine rows/plot) for each of four ground-cover treatments (all without tillage, with vegetation in the interrows: resident vegetation, complex grass-legume cover crop, simple grass-legume cover crop, or summer-dormant-grass cover crop), and there were four control plots (conventionally tilled interrow: 2–3 passes/year, 15 cm depth). Cover crops were sown in the interrows in October 2005. In the vine rows, weeds were controlled with herbicide. All vine rows were drip irrigated and fertilized. Grape yield and quality were measured in 2006–2010 (yield and size: 10 clusters/plot, 10 grapes/cluster; quality: 400 grapes every two weeks, from the beginning of ripening to harvest in 2007–2010; at harvest in 2006). It was not clear whether these results were a direct effect of ground cover or tillage.

12 

A replicated, randomized, controlled study in 2009–2011 in a rainfed vineyard in northern Spain found similar grape yields but differences in grape quality in plots with cover crops, compared to conventional tillage, between the vine rows. Crop yield: Similar grape yields were found in plots with cover crops or conventional tillage (4.2–6.2 vs 5.1–5.9 kg/vine; 14.1–16.8 vs 13.8–16.6 clusters/vine). Crop quality: Less yeast-assimilable nitrogen (which is needed for wine fermentation) was found in grapes from plots with cover crops, compared to conventional tillage, in one of six comparisons (with barley, in 2011: 48 vs 70 mg YAN/kg grape extract). Significant differences in amino acid content were found between plots with cover crops or conventional tillage (20 amino acids: see publication for details). Similar grape weight was found in plots with cover crops or conventional tillage (250–290 g/100 grapes). Implementation options: Less yeast-available nitrogen was found in grapes from plots that were cover cropped with barley, compared to clover (48 vs 77 mg YAN/kg grape extract). Methods: There were three plots (four vine rows/plot, 20 vines/row) for each of two cover crops (Hordeum vulgare barley or Trifolium resupinatum Persian clover between vine rows, sown in February 2009 and 2011), and there were three control plots (conventional tillage between vine rows: disk plough, 0–15 cm depth, every 4–6 weeks in February–August). No plots were fertilized. Herbicides were used under vine rows. Vine prunings were retained between rows. Grape yield and quality were measured in 2009–2011 (20 vines/plot, 500 grapes/plot).

13 

A replicated, randomized, controlled study in 2008 in an irrigated vineyard in southern California, USA, found larger grapes in plots with cover crops, compared to bare fallows, but found similar grape yields and sugar contents. Crop yield: Similar grape yields were found in plots with cover crops or bare fallows (75–80 vs 55 g/cluster). Crop quality: Similar amounts of sugar were found in grapes from plots with cover crops or bare fallows (24 oBrix/cluster). Larger grapes were found in plots with cover crops, compared to bare fallows, in two of four comparisons (11 vs 10 mm diameter). Methods: Cover crops (Fagopyrum esculentum buckwheat) were sown between the vine rows in four plots, in summer 2008, and the cover crops were irrigated throughout the summer (sprinklers: 10 sprinklers/plot, 45 litre/hour, two hours after sowing and six hours every 7–10 days; tree sprayer: 60.5 litres/plot, thrice/week). This irrigation system was also used on three plots that did not have cover crops. Conventional management was used on six plots (bare fallows were maintained between the vine rows through cultivation and no irrigation). The plots had two vine rows each (28.7 x 6 m plots). Grapes were harvested in September 2008 (10 clusters from 3 m in the centre of each plot).

 

14 

A replicated, randomized, controlled study in 2008–2010 in an irrigated vineyard in the San Joaquin Valley, California, USA (same study as (10)), found lower titratable acidity in grapes from plots with seeded cover crops between the vine rows, compared to resident vegetation. Implementation options: Grapes of similar quality were found in plots with cover crops or resident vegetation between the vine rows (23–25 oBrix; pH 3.3–3.6; 107–135 g/100 grapes; 25–33 g sugar/100 grapes), except that lower titratable acidity was found in grapes from plots with cover crops, in one of three years (2008: 5.7–5.9 vs 6.8 mg/L). Methods: Cover crops (2.5 m width) were grown in the alleys between the vine rows (3.1 m width) on 16 plots (two alleys/plot, 190 vines/row), and resident vegetation was allowed to grow on 8 plots, over the winter. There were two combinations of cover crops (oats only, or oats and legumes, seeded in November, on 8 plots each). All plots were mown in spring and tilled (15–20 cm depth) in spring, summer, and autumn. Herbicide was used to control weeds in the vine rows (50 cm width), but not in the alleys. Vines were drip-irrigated (60–70% of evapotranspiration).

Referenced papers

Please cite as:

Shackelford, G. E., Kelsey, R., Robertson, R. J., Williams, D. R. & Dicks, L. V. (2017) Sustainable Agriculture in California and Mediterranean Climates: Evidence for the effects of selected interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.