Water: Grow cover crops in arable fields
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Overall effectiveness category Trade-off between benefit and harms
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Number of studies: 19
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Effectiveness
55% -
Certainty
70% -
Harms
38%
Study locations
Supporting evidence from individual studies
A replicated, randomized, controlled study in 1986–1988 in an irrigated lettuce field in the Salinas Valley, California, USA, found less water in soils with winter cover crops, compared to winter fallows. Water availability: Less water was found in soils with cover crops, compared to fallows, in two of five comparisons (75 and 90 cm depth: 14–24 vs 16–20% soil moisture content). Implementation options: Less water was found in soils that were cover cropped with Secale cereale rye, compared to Vicia faba broad beans, in one of five comparisons (90 cm depth: 30% less water). Methods: There were six plots (10.7 x 1.1 m raised beds) for each of two winter cover crops (broad beans or rye) and there were six control plots (bare fallow, maintained with herbicide). The cover crops were seeded in November 1986–1987, irrigated until emergence, and chopped, disked, and chisel ploughed in spring (25–30 cm depth). Lettuces were planted in May and July 1987 and March and August 1988, and they were harvested in July and October 1987 and June and October 1988. The lettuces were irrigated (1–2 cm every 2–3 days until emergence, then 2 cm/week). Soil moisture was measured with a hydroprobe at five depths (25, 56, 75, 90, and 106 cm), 13 and 16 weeks after the cover crops were seeded (three measurements/depth).
Study and other actions testedA replicated, controlled study (years not reported) in a tomato field near Davis, California, USA, found that more water filtered into soils with cover crops, compared to bare soils. Water availability: More water filtered into soils with cover crops, compared to bare soils (8.0–8.3 vs 7.5 inches in four hours). Implementation options: Similar infiltration rates were found under oat-vetch and vetch cover crops (8 vs 8.3 inches in four hours). Methods: There were four plots for each of two cover crops (oat-vetch or vetch, planted in winter) and one control (no cover crop). Water infiltration was measured with an infiltrometer in spring, under the tomato crop that followed the cover crops, after three years of cover cropping.
Study and other actions testedA replicated, randomized, controlled before-and-after study in 1989–1991 in an irrigated lettuce field in Salinas, California, USA, found less water, but less nitrate leaching, in soils with cover crops, compared to bare fallows. Water availability: At the end of winter, less water was found in soils with winter cover crops, compared to bare fallows, at one of three depths (0–15 cm: 9–10% vs 13% soil moisture content), but similar amounts of water were found earlier in the winter (0–15 cm: 8–13% vs 9–14%), in 1991. Nutrients: At the beginning of spring, less nitrate was found in soils with winter cover crops, compared to bare fallows, in some comparisons (all cover crops in 1990: 2–6 vs 18–21 µg NO3-N/g dry soil; one of two in 1991: 66–79 vs 85–112). After the first rainfall in spring, more nitrate was found in soils with winter cover crops, compared to bare fallows (amounts of nitrate not clearly reported). The inference was that more nitrate was depleted by cover crops over winter, and more nitrate was leached from bare fallows in spring. Methods: In 1989–1990, six winter cover crops (Raphanus sativus oilseed radish, Brassica hirta white senf mustard, Brassica alba white mustard, Lolium multiflorum annual ryegrass, Secale cereale Merced rye, and Phacelia tanacetifolia) were grown on three plots each (two 12 m rows/plot), and bare fallows were maintained (with herbicide and hand cultivation) on three plots. In 1990–1991, two winter cover crops (Secale cereale Merced rye and Phacelia tanacetifolia) were grown on six plots each (two 8 m rows/plot), and bare fallows were maintained on six plots. Cover crops were tilled into the plots (15–20 cm depth in March 1990, depth not reported in February 1991). Lettuce was sown in April 1990–1991. All plots were irrigated and fertilized (56–85 kg N/ha, before sowing lettuce). Soil samples were collected in November 1989–1990, January 1990–1991, February 1991, and March 1990 (0–60 cm depth, 4 cm diameter, two cores/plot), weekly from late March to the end of June 1990 (0–15 cm depth), and every 2–7 days from mid-February to the end of March 1991 (0–15 cm depth).
Study and other actions testedA replicated, randomized, controlled study in 1991–1992 in an irrigated lettuce field in the Salinas Valley, California, USA, found less water in soils with winter cover crops, compared to bare soils. Water availability: Less water was found in soils with cover crops, compared to bare soils, in some comparisons (7 and 12 days after cover crops were incorporated into the soil: 7–9% vs 9–11% water; total number of significantly different comparisons not clearly reported). Methods: Three plots had winter cover crops (Merced rye Secale cereale, sown on 19 December 1991) and three plots had bare soils over winter. The plots (raised beds) were 8 x 4 m each. All plots were disked on 8 April (incorporating the cover crops). Soil samples were collected on 7–9 days between cover-crop incorporation and lettuce harvesting. Lettuce was sown on 8 May and harvested on 8 July 1992.
Study and other actions testedA replicated, randomized, controlled study in 1992–1993 in an irrigated broccoli field in the Salinas Valley, California, USA, found that less nitrate was leached from soils with winter cover crops, compared to bare soils, but cover crops had inconsistent effects on water availability. Water availability: Less water was found in soils with cover crops, compared to bare soils, in two of 16 comparisons (in March: 6–7% vs 8% soil moisture). Less water was lost through drainage from soils with cover crops, compared to bare soils (3.6–3.9 vs 6 mm/cm2). Nutrients: Less nitrate was leached from soils with cover crops, compared to bare soils (measured with ion-exchange resin bags or estimated from soil nitrate concentrations and drainage volumes: 7–9 vs 24–28 g NO3-N/m2; measured with suction samplers: 155 vs 281 g NO3-N/m2). Methods: There were three plots for winter cover crops (half Phacelia tanacetifolia and half Secale cereale Merced rye, sown in November 1992 and mown in March 1993) and three control plots with bare soil in winter. All plots (252 x 24 m) were tilled in March 1993 (15 cm depth), and the cover crops were incorporated into the soil. Two broccoli crops were grown on raised beds (first crop: April–August 1993; second crop: August–November 1993). All plots were irrigated (440–450 mm/crop, subsurface drip irrigation) and fertilized (41–42 g N/m2/crop). Soil samples were collected 16 times in November 1992–August 1993, including nine samples in March–April, when the cover crops were incorporated (0–75 cm depth, 6 cm diameter, four cores/plot). Leaching was measured with buried ion-exchange resin bags (60 cm depth, 10 g resin, excavated in March 1993) and suction samplers (60 cm depth, measured weekly in December 1992–March 1993).
Study and other actions testedA replicated, randomized, controlled study in 1994 in an irrigated wheat field in the Sacramento Valley, California, USA, found less water in soils with winter cover crops, compared to fallows. Water availability: Less water was found in soils with cover crops, compared to fallows (1.2–3.0 cm less water, 0.16–0.25 vs 0.20–0.35 m3 water/m3 soil, 0–90 cm depth). Methods: Legumes were grown as winter cover crops in some subplots, and other subplots were fallows (the number and size of the subplots was not clearly reported, but the main plots were 64 x 64 m). Half of the main plots were irrigated. In the wheat-growing season, half of the subplots were fertilized, but the cover crops and fallows were not fertilized. Soil samples were collected in August 1994 (0–90 cm depth), and water content was calculated by drying and weighing the soil (assuming a bulk density of 1.68 g/cm3).
Study and other actions testedA replicated, randomized, controlled study in 1991–1994 in an irrigated tomato field in the San Joaquin Valley, California, USA, found less water in soils with winter cover crops, compared to winter fallows. Water availability: Less water was found in soils with cover crops, compared to fallows, in some comparisons (e.g., about 150 days after planting the cover crops: 4.3–9.9 cm increase in soil water content vs 6.8 mm decrease to 4.0 mm increase in soil water content, 0–210 cm depth; number of significantly different comparisons not clearly reported). Methods: There were four plots (93 x 7 m) for each of three treatments, and there were four control plots (winter fallow). The treatments were Hordeum vulgare barley, Vicia dasycarpa Lana woollypod vetch, or barley and vetch as winter cover crops, planted in October 1991–1993 and incorporated into the soil in March 1992–1994. Soil water content was measured about every two weeks after the cover crops were planted (hydroprobe, six samples/plot, 15, 30, 60, 90, 120, 150, 180, and 210 cm depths).
Study and other actions testedA replicated, controlled study in 1996–1998 in an irrigated tomato field in the San Joaquin Valley, California, USA, found that winter cover crops had inconsistent effects on water availability. Water availability: In the tomato-growing season, more water was found in plots with winter cover crops (and no tillage in spring), compared to plots with bare soil in winter (and tillage in spring), in some comparisons (when irrigated; data not clearly reported). However, in in winter and spring, less water was found in plots with cover crops, in some comparisons. Methods: There were 12 plots (4.5 x 27.5 m plots) for each of two treatments (two grass-legume mixtures as winter cover crops, sown in October 1996–1997, killed and retained as mulch, with no tillage, in March 1997–1998) and there were 12 control plots (bare-soil fallows in winter, with herbicide, and conventional tillage in spring). Soil water was measured throughout the year with hydroprobes (0–6 feet depth until autumn 1997, then 0–7 feet depth). It was not clear whether these results were a direct effect of cover crops or tillage.
Study and other actions testedA replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more water in soils with cover crops, compared to soils without cover crops, in six of 12 comparisons. Water availability: More water was found in soils with cover crops, compared to soils without cover crops, in six of 12 comparisons (0.10–0.27 vs 0.07–0.26 g water/g soil; 0–15 cm depth). Methods: There were four plots (0.52 ha), for each of four treatments (reduced tillage or conventional tillage, with or without added organic matter). In plots with added organic matter, compost was added two times/year, and a cover crop (Merced rye) was grown every autumn or winter. Lettuce or broccoli were grown on raised beds. Sprinklers and drip irrigation were used in all plots. Soils were disturbed to different depths (conventional tillage: disking to 50 cm depth, cultivating, sub-soiling, bed re-making, and bed-shaping; reduced tillage: cultivating to 20 cm depth, rolling, and bed-shaping). Soils were collected, along the planting line, with 6 cm soil cores. It was not clear whether these results were a direct effect of adding compost or growing cover crops.
Study and other actions testedA replicated, randomized, controlled study in 2001–2004 in an irrigated maize field in southwest Spain found more water in soils with winter cover crops, compared to soils without winter cover crops. Water availability: More water was found in soils with short-term cover crops, compared to soils without cover crops, in one of nine comparisons (5–10 cm depth, in 2002: 0.33 vs 0.24 cm3 water/cm3 soil), and more water was also found in soils with long-term cover crops, compared to soils without cover crops, in five of nine comparisons (0.31–0.38 vs 0.24–0.30). Implementation options: More water was found in soils with long-term cover crops, compared to short-term cover crops, in six of nine comparisons (0.31–0.38 vs 0.25–0.30 cm3 water/cm3 soil). Methods: Cover crops (Avena strigosa lopsided oats) were sown on eight plots in September 2001–2003. Four of these plots had winter cover crops for six years before this (long-term cover crops), and four plots did not (short-term cover crops). Four other plots did not have winter cover crops from 2001–2004 or before. All plots were 20 x 10 m and were not tilled after 2001. Cover crops were suppressed with herbicide in April 2002–2004.
Study and other actions testedA replicated, randomized, controlled study in 2006–2008 in an irrigated maize field in the Ebro river valley, Spain, found that less nitrate was leached from soils with winter cover crops, compared to bare soils, but more water was lost through drainage. Water use: Similar amounts of water were used in plots with cover crops or bare soils (130–200 mm estimated evapotranspiration in the cover-cropping season). Water availability: More water was lost through drainage from plots with cover crops, compared to bare soils, in three of 10 comparisons (during the cover-cropping season: 4–7 vs 0–3 mm). Nutrients: Less nitrate was leached from soils with cover crops, compared to bare soils, in four of nine comparisons (during the maize-growing season: 2 vs 7–10 mg NO3-N/litre; 4–5 vs 23–27 kg NO3-N/ha). Implementation options: Less nitrate was leached from soils that were cover cropped with barley or winter rape, compared to common vetch, in two of three comparisons (during the maize-growing season: 2 vs 10 mg NO3-N/litre). Less water was lost through drainage from plots that were cover cropped with barley or winter rape, compared to common vetch, in two of four comparisons (during the cover-cropping season: 0–1 vs 7 mm). Methods: There were three plots (5.2 m2) for each of three winter cover crops (Hordeum vulgare barley, Brassica rapa winter rape, or Vicia sativa common vetch, sown in October 2006–2007), and there were three control plots with bare soil in winter. Similar amounts of nitrogen were added to all plots (300 kg N/ha), but less of it came from mineral fertilizer in plots with cover crops, to compensate for the organic nitrogen that was added to these plots when the cover crop residues were tilled into the soil. All plots were tilled in spring (March 2007–2008) and autumn (October 2006–2007). All plots were irrigated twice/week (drip irrigation, based on evapotranspiration). Maize was planted in April and harvested in October 2007–2008. Soil samples were collected before the cover crops were incorporated and after the maize was harvested (two soil cores/plot, 5 cm diameter, 0–120 cm depth). Drainage volume and nitrate leaching was measured every week (lysimeters, 5.2 m2 surface area, 1.5 m depth, 50 litre tank).
Study and other actions testedA replicated, controlled study in 2004–2008 in an irrigated maize field in the Garonne River corridor, southern France (same study as (13)), found that less water was lost through drainage from soils with winter cover crops, compared to bare soils. Water availability: Less water was lost through drainage from soils with winter cover crops, compared to bare soils, on 21 of 67 sampling dates (drainage volumes not reported for significant comparisons). Methods: Winter cover crops (2006–2007: white mustard; 2004–2006 and 2007–2008: oats) were grown on six plots, and bare soil was maintained in six plots. The plots were 20 x 50 m. Maize was sown in April–May 2005–2008 and harvested in October 2005–2008. Drainage from soils was measured with fiberglass-wick lysimeters (40 cm depth, two lysimeters/plot), on 67 sampling dates. A centre-pivot sprinkler was used for irrigation (857–943 mm water/year, irrigation plus rainfall).
Study and other actions testedA replicated, controlled study in 2004–2008 in an irrigated maize field in the Garonne River corridor, in southern France (same study as (12)), found that less herbicide was leached from plots with winter cover crops, compared to plots with bare soil. Pathogens and pesticides: Less herbicide was leached from plots with winter cover crops, compared to plots with bare soil (9% vs 16% of applied herbicide). Methods: Winter cover crops (2006–2007: white mustard; 2004–2006 and 2007–2008: oats) were grown on two plots, and bare soil was maintained in two plots. The plots were 20 x 50 m. The herbicide (75 g/L Isoxaflutole) was sprayed 1–3 days after the maize was sown, in April–May 2005–2008. Herbicide leaching was measured in drainage water, with fiberglass-wick lysimeters (40 cm depth, two lysimeters/plot, 11–21 samples/year, 6–272 days after treatment with herbicide). A centre-pivot sprinkler was used for irrigation (650–736 mm water/year, irrigation plus rainfall).
Study and other actions testedA replicated, randomized, controlled study in 2006–2009 in an irrigated maize field in the Tajo river basin, near Madrid, Spain, found that less nitrate was leached from soils with winter cover crops, compared to fallows. More water was used by cover crops, compared to fallows, but less water was lost through drainage and evaporation. Water use: More water was used by cover crops, compared to fallows (transpiration: 31–117 vs 0 mm). Water availability: Less water was lost through drainage from plots with cover crops, compared to fallows, in six of eight comparisons (47–301 vs 106–314 mm), and less water was lost through evaporation, in all comparisons (31–79 vs 51–101 mm). Similar amounts of water were lost as runoff from plots with cover crops or fallows (data not reported). Nutrients: Less nitrate was leached from soils with cover crops, compared to fallows, in five of eight comparisons during the cover-cropping seasons (13–36 vs 45–147 kg N-NO3/ha), and two of six comparisons during the maize-growing seasons (12–30 vs 42). Implementation options: Less nitrate was leached from soils that were cover cropped with barley, compared to vetch (129 vs 245 kg N-NO3/ha cumulative, in 2006–2009). Less water was lost through drainage from plots that were cover cropped with barley, compared to vetch, in two of four comparisons (47–234 vs 60–301 mm), but barley used more water than vetch, in three of four comparisons (transpiration: 63–117 vs 31–108 mm). Less water was lost through evaporation from plots that were cover cropped with barley, compared to vetch, in one of four comparisons (60 vs 79 mm). Methods: There were four plots (12 x 12 m plots) for each of two treatments (barley or vetch, as winter cover crops) and there were four control plots (fallow). Cover crops were sown in October 2006–2009 and maize was sown in April 2007–2009. The maize was irrigated (sprinklers) and fertilized (210 kg N/ha, split into two applications, 120 kg P/ha, and 120 kg K/ha). Soil water content was measured every hour with capacitance probes (10–130 cm depth, three probes/plot, after the cover crops and after the harvest), and nitrate in soil water was measured with ceramic suction cups (buried at 122–124 cm depth, 1 µm pore size). Water balance and nitrate leaching were calculated using the WAVE model.
Study and other actions testedA replicated, controlled study in 2007–2008 in an irrigated tomato field in Davis, California, USA, found similar rates of water infiltration into soils with winter cover crops or fallows. Water availability: Similar rates of water infiltration were found in soils with cover crops or fallows (6.7–7.6 vs 6.3–7.1 litres/foot/90 minutes). Methods: Conventional tillage or reduced tillage was used on four plots each (90 x 220 feet). Broadcast disking, subsoiling, land planing, and rebedding were used for conventional tillage. A Wilcox Performer was used for reduced tillage (two passes; beds were conserved). Winter cover crops (triticale) were grown on half of each plot, and the other half was fallow in winter. Sprinklers, furrow irrigation, and drip-tape (in furrows) were used to irrigate the tomatoes. All plots were fertilized. Water infiltration was measured in 2008 (using the blocked furrow method).
Study and other actions testedA controlled study in 2005–2006 in an irrigated tomato field in the Sacramento Valley, California, USA, found more phosphorus, but less ammonium, dissolved organic carbon, and sediment, in runoff from the part of the field that was cover cropped, compared to the part that was fallow. Water availability: Similar amounts of irrigation water were lost through discharge from each part of the field (42% vs 25%). Overall, less water was lost from the cover-cropped part, compared to the fallow part (44% less), and more water percolated deeply into the cover-cropped part (27% vs 15%), but it was not clear whether these differences were statistically significant. Nutrients: Similar amounts of nitrate were leached from each part of the field (measured in resin bags: 2.47 kg/ha). Higher phosphorus concentrations were found in runoff from the cover-cropped part of the field, compared to the fallow part, in one of two comparisons (in winter: 0.4 vs 0.2 mg dissolved reactive P/litre), but no differences were found in nitrogen or dissolved organic carbon concentrations (in winter: 0.1 mg NO3-N/litre; 0.1 mg NH4-N/litre; 5.8–7.4 mg C/litre; in summer: 1.6–2.2 mg NO3-N/litre; 0.1–0.2 mg NH4-N/litre; 3.3–3.9 mg C/litre). Lower loads (amounts/ha/irrigation or rainfall event) of ammonium and dissolved organic carbon were found in runoff from the cover-cropped part, compared to the fallow part (5.6 vs 8.3 g NH4-N/ha/event; 0.3 vs 0.7 kg C/ha/event), but no differences were found in nitrate or phosphorus loads (in winter: 0.1 kg NO3-N/ha/event; 20–22 g dissolved reactive P/ha/event; in summer: 0.4–0.9 kg NO3-N/ha/event; 61–118 g dissolved reactive P/ha/event). Sediments: Less sediment was found in runoff from the cover-cropped part of a field, compared to the fallow part, in two of four comparisons (concentrations, in winter: 0.1 vs 0.7 g total suspended solids/litre; loads, in winter: 0.9 vs 5 kg/ha/event). Methods: A field was divided into two parts: one part with a winter cover crop (mustard Brassica nigra, planted in autumn 2005, and disked into the soil in spring 2006), and one part fallow. Tomatoes were planted in both parts of the field in spring 2006. Runoff water was collected in autosamplers (250 mL samples, every four hours, if there was >5 cm of water in the flow meter). Cumulative nitrate leaching from the soil was measured with anion exchange resin bags (buried at 75 cm depth).
Study and other actions testedA replicated, randomized, controlled study in 2011–2014 in irrigated potato fields in Israel found less runoff from plots with cover crops, compared to bare soil. Water availability: No runoff was measured in some plots with cover crops, but up to 1.5 litres of runoff/second were measured in plots with bare soil (in 2011; no statistical comparisons were made for any years). Methods: Different plots were used in different years (2011–2012: 350 m2 plots, 20 plots with cover crops, eight plots without cover crops; 2012–2013: 695 m2 plots, 10 with, 10 without; 2013–2014: 1,800 m2 plots, four with, four without). Different mixtures of cover crops were used in different years, but oats were used in all years, and triticale was used in Years 1 and 2 (2011–2013). Plots without cover crops were weeded (tilled bare; some plots in all years) or weedy (not tilled; some plots in Year 1). Herbicide and fertilizer were used on all plots. Water was measured in runoff channels, after each rainfall event (one HS flume/plot). Plots had a 5–7% slope.
Study and other actions testedA replicated, randomized, controlled study in 2011–2013 in two irrigated tomato fields in central Italy found that winter cover crops had inconsistent effects on water availability. Water availability: More water was found in plots with winter cover crops (mulched in the spring), compared to control plots, in some comparisons in July–August (data on soil water content not clearly reported), but inconsistent differences in soil water content were found in May–June (sometimes more, sometimes less). Methods: Three species of winter cover crops (Vicia villosa hairy vetch, Phacelia tanacetifolia lacy phacelia, or Sinapis alba white mustard) were sown on three plots each, in September, and winter weeds were controlled with herbicide on three control plots (18 x 6 m plots). The cover crops were mown and mulched (strips, 80 cm width) in May, and the control plots were tilled (depth not reported). Tomato seedlings were transplanted in May (transplanted into the) and harvested in August. All plots were tilled (30 cm depth) and fertilized (100 kg P2O5/ha, harrowed to 10 cm depth) in September. Some plots were also fertilized (100 kg N/ha) in June–July. Plots were irrigated to replace 50–100% of water lost through evapotranspiration. Soil water content (soil moisture meter, 20 cm depth) was measured weekly, or within 48 hours of rainfall, in the tomato-growing season. It was not clear whether these results were a direct effect of cover cropping, mulching, herbicide, or tillage.
Study and other actions testedA replicated, randomized, controlled study in 2012–2014 in a mostly rainfed field in the Central Valley, California, USA, found less water in soils with winter cover crops, compared to winter fallows. Water availability: Over the winter, less water was found in soils with cover crops, compared to fallows, in some comparisons (2013: 5.3 cm less water; 2014: 0.67 less; number of comparisons not clearly reported). This was because water was lost from soils with cover crops, but gained in soils with fallows. Methods: There were three plots for each of three cover crops (legumes: 45% Vicia faba, 35% Pisum sativum, and 20% V. sativa; legumes and triticale: 40% P. sativum, 30% V. sativa, and 30% Tritocosecale; or brassica: 45% Brassica juncea, 40% Sinapsis alba, and 15% Raphanus sativus) and there were three fallow plots (kept bare with herbicide). Each plot was 10 x 30 m. All plots were irrigated only to establish the cover crop (10 cm/year). Plots with cover crops were fertilized (112 kg N/ha) and seeds were sown in November. Water content was measured twice/week in January–March (0–90 cm depth).
Study and other actions tested
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This Action forms part of the Action Synopsis:
Mediterranean FarmlandRelated Actions
| Actions | Effectiveness | Studies | Category | |
|---|---|---|---|---|
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Soil: Plant hedgerows Action Link |
Unknown effectiveness (limited evidence) | 1 |
Synopsis Link |
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Pollination: Plant flowers Action Link |
Likely to be beneficial | 8 |
Synopsis Link |
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Crop production: Plant hedgerows Action Link |
Unknown effectiveness (limited evidence) | 1 |
Synopsis Link |
Mediterranean Farmland - Published 2017
Mediterranean Farmland synopsis
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