Providing evidence to improve practice

Action: Soil: Use reduced tillage in arable fields Mediterranean Farmland

Key messages

Organic matter (14 studies): One meta-analysis from multiple Mediterranean countries found more organic matter in soils with reduced tillage, compared to conventional tillage. Eleven replicated studies (ten randomized and controlled, one site comparison) from Italy, Spain, Syria, and the USA found more organic matter in soils with reduced tillage, compared to conventional tillage, in some or all comparisons. Two replicated, randomized, controlled studies from Spain and the USA found similar amounts of organic matter in soils with reduced tillage or conventional tillage, in all comparisons. No studies found less organic matter in soils with reduced tillage, compared to conventional tillage.

Nutrients (15 studies)

  • Nitrogen (14 studies): Seven replicated studies (five randomized and controlled, one site comparison) from Italy, Spain, and the USA found more nitrogen in soils with reduced tillage, compared to conventional tillage, in some comparisons. Three of these studies also found less nitrogen in some comparisons. Two replicated, randomized, controlled studies from Spain found less nitrogen in soils with reduced tillage, compared to conventional tillage, in some or all comparisons. Five replicated, randomized, controlled studies from Spain, Syria, and the USA found similar amounts of nitrogen in soils with reduced tillage or conventional tillage, in all comparisons.
  • Phosphorus (6 studies): Five replicated, randomized, controlled studies from Italy, Spain, and the USA found more phosphorus in soils with reduced tillage, compared to conventional tillage, in some or all comparisons. One replicated, randomized, controlled study from Spain found similar amounts of phosphorus in soils with reduced tillage, compared to conventional tillage, in all comparisons.
  • Potassium (3 studies): Two replicated, randomized, controlled studies from Spain found more potassium in soils with reduced tillage, compared to conventional tillage, in some comparisons. One replicated, randomized, controlled study from Spain found similar amounts of potassium in soils with reduced tillage, compared to conventional tillage, in all comparisons.
  • pH (1 study): One replicated, randomized, controlled study from Spain found similar pH levels in soils with reduced tillage or conventional tillage.

Soil organisms (16 studies)

  • Microbial biomass (15 studies): Eleven replicated, randomized, controlled studies from Italy, Spain, and the USA found more microbial biomass in soils with reduced tillage, compared to conventional tillage, in some comparisons. Two replicated, randomized, controlled studies from Spain and Syria found less microbial biomass in soils with reduced tillage, compared to conventional tillage, in some comparisons. Two replicated, randomized, controlled studies from Spain found similar amounts of microbial biomass in soils with reduced tillage or conventional tillage, in all comparisons.
  • Bacteria (1 study): One replicated, randomized, controlled study from Spain found more denitrifying bacteria in soils with reduced tillage, compared to conventional tillage.
  • Other soil organisms (2 studies): One replicated, controlled study from the USA found similar numbers of mites and nematodes, but differences in mite and nematode communities, in soils with reduced tillage, compared to conventional tillage. One replicated site comparison from the USA found more earthworms in fields with fewer passes of the plough, in one of three comparisons.

Soil erosion and aggregation (9 studies)

  • Soil aggregation (8 studies): Three replicated, randomized, controlled studies from Spain found that soil aggregates had higher water-stability in plots with reduced tillage, compared to conventional tillage, in some comparisons. One of these studies also found that soil aggregates had lower water-stability in some comparisons. One replicated, randomized, controlled study from Spain found that water-stability was similar in plots with reduced tillage or conventional tillage. One replicated, randomized, controlled study from Spain found more large aggregates in soils with reduced tillage, compared to conventional tillage, in one of two comparisons. One replicated, randomized, controlled study from Spain found smaller aggregates in soils with reduced tillage, compared to conventional tillage. Three replicated, randomized, controlled studies from Spain and the USA found similar amounts of aggregation in soils with reduced tillage or conventional tillage.
  • Soil erosion (1 study): One replicated, randomized, controlled study from Egypt found less erosion with less tillage (one pass with the tractor, compared to two), but found more erosion with shallower tillage, compared to deeper.

Greenhouse gases (11 studies)

  • Carbon dioxide (9 studies): Three replicated, randomized, controlled studies from Spain found more carbon dioxide in soils with reduced tillage, compared to conventional tillage, in some or all comparisons. Three replicated, randomized, controlled studies from Spain and the USA found less carbon dioxide in soils with reduced tillage, compared to conventional tillage, in some or all comparisons. Three controlled studies from Italy, Spain, and the USA found similar amounts of carbon dioxide in soils with reduced tillage or conventional tillage, in all comparisons.
  • Nitrous oxide (3 studies): Two replicated, randomized, controlled studies from Spain and the USA found more nitrous oxide in soils with reduced tillage, compared to conventional tillage, in some or all comparisons. One controlled study from the USA found similar amounts of nitrous oxide in soils with reduced tillage or conventional tillage, in all comparisons.
  • Methane (1 study): One replicated, randomized, controlled study from Spain found similar amounts of methane in soils with reduced tillage or conventional tillage.

Implementation options (1 study): One replicated, randomized, controlled study from Egypt found that less soil was lost in runoff water from plots that were tilled at slower tractor speeds.

Supporting evidence from individual studies

1 

A replicated, randomized, controlled study in 1983–1996 in a rainfed wheat field in the Henares river valley, Spain, found no differences in soil stability between plots with reduced tillage or conventional tillage. Soil erosion and aggregation: No differences in soil stability were found between plots with reduced tillage or conventional tillage (pre-wetted soil aggregates: 78–89% were water-stable; air-dried soil aggregates: 1–4% were water-stable). Methods: Conventional tillage or reduced tillage was used on four plots each. Each plot had two subplots (20 x 30 m, with or without crop rotations). A mouldboard plough (30 cm depth) was used for conventional tillage, in autumn. A chisel plough (20 cm depth) was used for reduced tillage, in autumn. A tine cultivator (10–15 cm depth, two passes) was used for both conventional and reduced tillage, in spring. Fertilizer and post-emergence herbicide were used on all plots. Soil samples were collected in June or July 1996 (0–30 cm, four samples/subplot).

 

2 

A replicated, randomized, controlled study in 1998–2000 in an irrigated vegetable field in the Salinas Valley, California, USA, found more microbial biomass in soils with reduced tillage, compared to conventional tillage. Tillage had inconsistent effects on nutrients. Nutrients: Similar amounts of nitrogen were found in soils with reduced tillage, compared to conventional tillage (1.5–1.6 g total N/kg soil; 0–15 cm depth). At depths of 0–90 cm, less nitrate was found in soils with reduced tillage, compared to conventional tillage, in 12 of 14 comparisons (4–61 vs 5–64 g NO3-N/g soil), but more nitrate was found in one of 14 comparisons (34 vs 29). At depths of 0–15 cm, tillage had inconsistent effects on nitrate (0–64 vs 0–53 μg NO3-N/g soil) and ammonium (0–9 vs 0–6 μg NH4-N/g soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in two of 16 comparisons (120–130 vs 90–100 μg C/g soil). More microbial biomass (measured as nitrogen) was found in soils with reduced tillage, compared to conventional tillage, in three of 16 comparisons (12–15 vs 5–8 μg N/g soil). 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 crops were grown in 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.

 

3 

A replicated, randomized, controlled study in 1996–1999 in three rainfed barley fields in the Ebro river valley, Spain (same study as (20,25,26,30)), found less nitrogen in soils with reduced tillage, compared to conventional tillage. Nutrients: Less nitrogen was found in soils with reduced tillage, compared to conventional tillage, in two of nine comparisons (125–176 vs 219–247 kg/ha). Methods: Reduced tillage or conventional tillage was used on 27 plots each (50 x 6 m plots). A mouldboard plough (25–30 cm depth) and a cultivator (15 cm depth, 1–2 passes) were used for conventional tillage, in August–September. A cultivator (10–15 cm depth, 1–2 passes) was used for reduced tillage, in September. Two-thirds of the plots were fertilized (50–75 or 100–150 kg N/ha). Barley was sown, with a seed drill, in October–November. Soil samples were collected four times/year (0–50 cm in two of three fields, 0–100 cm in one field, two soil cores/plot).

 

4 

A replicated, randomized, controlled study in 2000–2002 in a rainfed sunflower-wheat field near Seville, Spain, found more phosphorus and potassium in soils with reduced tillage, compared to conventional tillage. Nutrients: More phosphorus and potassium were found in soils with reduced tillage, compared to conventional tillage, in three of 10 comparisons (26–29 vs 20–24 mg phosphorus/kg soil; 313–403 vs 261–313 mg potassium/kg soil). Methods: Reduced tillage or conventional tillage was used on three plots each (22 x 14 m plots). A mouldboard plough (25–30 cm depth, in 2000–2001), a cultivator (15–20 cm depth), and a disc harrow (15 cm depth) were used for conventional tillage, and crop residues were burned. A chisel plough (25–30 cm depth, in 2000), a disc harrow, and pre-emergence herbicide were used for reduced tillage, and crop residues were retained. Soil samples were collected in November 2001, January 2002, and December 2002 (six samples/tillage treatment, 0–40 cm depth). Sunflower was grown in 2001 and it was not fertilized. Wheat was grown in 2001–2002 and it was fertilized.

 

5 

A replicated, randomized, controlled, before-and-after study in 1999–2004 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (36)), found that tillage had inconsistent effects on nitrogen in soils. Phosphorus in soils increased after reduced tillage, but it did not change after conventional tillage. Nutrients: After four years, nitrogen increased in soils with conventional tillage (before: 1,300 lb/acre; after: 1,400–1,600), but decreased in soils with reduced tillage, in one of two comparisons (before: 1,400; after: 1,200), and increased in soils with reduced tillage, in one of two comparisons (before: 1,300; after: 1,600). After four years, nitrate increased in soils with reduced tillage, in one of two comparisons (before: 18 ppm; after: 25), but did not change in soils with conventional tillage (before: 16–17; after: 10–19). After four years, phosphorus increased in soils with reduced tillage (before: 7–8 ppm; after: 15–17), but did not change in soils with conventional tillage (before: 8; after: 7–9). Methods: Reduced tillage or conventional tillage was used on 16 plots each, in 1999–2009. The plots (9 x 82 m) had six raised beds each. Rainfed winter cover crops (triticale, rye, and vetch) were planted on half of the plots, in October 1999–2003, and crop residues were chopped in March. Different numbers of tillage practices were used (conventional tillage: 18–21 tractor passes, including disc and chisel ploughing; reduced tillage: 12–13 tractor passes, not including disc and chisel ploughing). Tomatoes and cotton were grown in rotation. Fertilizer and herbicide was used in all plots. Soil samples were collected in spring (before planting) and in autumn (after harvest), in 2000–2004 (0–30 cm depth; number and volume of samples not reported).

 

6 

A replicated, randomized, controlled study in 2003–2005 on rainfed farms in the Ebro river valley, Spain, found less greenhouse gas in soils with reduced tillage, compared to conventional tillage. Greenhouse gases: Less carbon dioxide was found in soils with reduced tillage, compared to conventional tillage, in 12 of 30 comparisons, in the two days after tillage (0.1–6.4 vs 0.1–13.3 g CO2/m2/hour). Methods: Reduced tillage or conventional tillage was used on seven plots each (33–50 x 7–10 m plots), on a total of two farms, with multiple crops. A mouldboard or subsoil plough was used for conventional tillage (25–40 cm depth). A cultivator (15 cm depth) or chisel plough (25–30 cm depth) was used for reduced tillage. Carbon dioxide was measured with a dynamic chamber (21 cm diameter, 900 mL airflow/minute, two samples/plot), 4–6 times in the 48 hours after tillage.

 

7 

A replicated, randomized, controlled study in 1992–2005 in a rainfed wheat-sunflower-pea field near Seville, Spain (same study as (28,33)), found more soil organisms in soils with reduced tillage, compared to conventional tillage. Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in one of six comparisons (0–5 cm depth, November 2004: 316 vs 183 mg C/kg soil). Methods: Conventional tillage or reduced tillage was used on three plots each (22 x 14 m plots). A mouldboard plough (25–30 cm depth), a cultivator (12–15 cm depth, 1–3 times/year), a disc harrow (5–15 cm depth, 1–2 times/year), and herbicide were used for conventional tillage. A chisel plough (25–30 cm depth), a disc harrow (5–7 cm depth), and herbicide were used for reduced tillage. Wheat, sunflowers, and peas were grown in rotation. Wheat was fertilized, but sunflowers and peas were not. Soil samples were collected in November 2004 and December 2005 (0–25 cm depth, two samples/plot).

 

8 

A replicated, randomized, controlled study in 1993–2000 in a rainfed field near Madrid, Spain, found more phosphorus and potassium in soils with reduced tillage, compared to conventional tillage, but tillage had inconsistent effects on nitrogen. Nutrients: More nitrogen was found in soils with reduced tillage, compared to conventional tillage, in six of eight comparisons (0.7–1.3 vs 0.4–0.9 mg/ha), but less was found in one of eight comparisons (0.5 vs 0.6 mg/ha). More phosphorus was found in soils with reduced tillage, compared to conventional tillage, in two of four comparisons in 1997 (12–13 vs 7–8 kg/ha). More potassium was found in soils with reduced tillage, compared to conventional tillage, in two of four comparisons in 1997 (230–260 vs 150–190 kg/ha). Similar pH was found in soils with reduced tillage or conventional tillage (pH 7.8). Methods: Conventional tillage or reduced tillage was used on 20 subplots each (10 x 25 m subplots). Barley-barley, barley-vetch, or barley-fallow rotations were used on the subplots. A mouldboard plough (30 cm depth) was used for conventional tillage. A chisel plough (20 cm depth) was used for reduced tillage. Barley was fertilized, but vetch and fallows were not. Herbicide was used when needed. Soil samples were collected after harvest (0–90 cm depth; nitrogen was measured at 0–30 cm depth; phosphorus and potassium at 0–80 cm depth).

 

9 

A replicated, randomized, controlled study in 1982–2003 in a rainfed wheat-sunflower-legume field near Seville, Spain, found more phosphorus in soils with reduced tillage, compared to conventional tillage. Nutrients: More phosphorus was found in soils with reduced tillage, compared to conventional tillage (961 vs 776 mg phosphorus/kg soil). Methods: Reduced tillage or conventional tillage was used on four plots each (180 x 15 m plots), in 1983–2003. Crop residues were burned, and a mouldboard plough (50 cm depth, once every three years, in summer) and a cultivator (15 cm depth, before seeds were sown) were used, for conventional tillage. A cultivator (15 cm depth, before seeds were sown) was used for reduced tillage. Fertilizer was used on wheat crops. Soil samples were collected in September 2003 (15 subsamples/plot, 5 cm depth).

 

10 

A replicated, randomized, controlled study in 2002–2005 on three rainfed farms in the Ebro river valley, Spain, found similar amounts of greenhouse gas in soils with reduced tillage or conventional tillage. Greenhouse gases: Similar amounts of carbon dioxide were found in soils with reduced tillage or conventional tillage (0.11–1.65 vs 0.12–1.76 g CO2/m2/hour). Methods: Reduced tillage or conventional tillage was used on ten plots each (Peñaflor: three plots each, 33 x 10 m plots; Agramunt: four plots each, 9 x 50 m plots; Selvanera: three plots each, 7 x 50 m plots). In Peñaflor, a mouldboard plough (30–40 cm depth) and a cultivator (10–15 cm depth) were used for conventional tillage. In Agramunt, a mouldboard plough (25–30 cm depth) and a cultivator (15 cm depth) were used for conventional tillage. In Selvanera, a subsoil plough (40 cm depth) and a cultivator (15 cm depth) were used for conventional tillage. A cultivator (Agramunt and Selvanera: 15 cm) or chisel plough (Peñaflor: 25–30 cm depth) was used for reduced tillage. Carbon dioxide samples were collected from December 2002 (Peñaflor, twice/month) or December 2003 (Agramunt and Selvanera, once/month) to June 2005, with an open chamber (900 mL airflow/minute, 21 cm diameter).

 

11 

A replicated, randomized, controlled, before-and-after study in 2004 in a barley field in the Ebro river valley, Spain, found that tillage had inconsistent effects on soil aggregation. Soil erosion and aggregation: Soil aggregates were smaller immediately after reduced tillage, compared to conventional tillage, in two of five comparisons (1.8–1.9 vs 2.3 mm dry mean weight diameter; 29–35 vs 2–16% reduction in dry mean weight diameter). Soil aggregates were smaller after 15 years of reduced tillage, compared to conventional tillage, in three of ten comparisons (1.8–2.2 vs 2.3–2.6 mm dry mean weight diameter). Soil aggregates were more stable after 15 years of reduced tillage, compared to conventional tillage, in four of ten comparisons (16–20 vs 12–15% water stability). Methods: Reduced tillage or conventional tillage was used on three plots each (33.5 x 10 m plots), in 1989–2004. A chisel plough was used for reduced tillage (20–25 cm depth). A mouldboard plough was used for conventional tillage (30–35 cm depth). Soil samples were collected before (8 November) and after (15 November) the soils were tilled (flat spade, 0–40 cm depth, two subsamples/plot).

 

12 

A replicated, randomized, controlled study in 2003 in rainfed farmland in the Ebro river valley, Spain, found similar amounts of soil aggregation in plots with reduced tillage, compared to conventional tillage. Soil erosion and aggregation: Similar amounts of large aggregates were found in soils with reduced tillage or conventional tillage (0–20 cm depth: water-stable aggregates >2,000 µm: 0.01–0.03 g aggregate/g soil). Methods: Conventional tillage or reduced tillage was used on three plots each (10 x 33 m). A mouldboard plough was used for conventional tillage (30–35 cm depth). A chisel plough was used for reduced tillage (25–30 cm depth). Soil samples were collected with a flat spade (0–20 cm depth) in July 2003.

 

13 

A replicated site comparison in 2004–2005 in 16 irrigated tomato fields in the Sacramento Valley, California, USA, found more earthworms in fields with fewer passes of the plough. Organic matter: More carbon was found in fields with fewer passes of the plough in the year before they were sampled (total carbon; data reported as model results). Nutrients: More nitrogen was found in fields with fewer passes of the plough in the year before they were sampled (total nitrogen; data reported as model results). Soil organisms: More earthworms were found in fields with fewer passes of the plough in the year before they were sampled, in one of three comparisons (individual earthworm biomass; data reported as model results). Methods: Earthworms were collected from 16 tomato fields, in February–April 2005. In 2004, these fields had different numbers of tillage operations (3–10 passes of the plough). Five fields were cover cropped, and seven were mulched with crop residues. All fields were fertilized and irrigated.

 

14 

A replicated, randomized, controlled study in 2003–2004 in three irrigated maize-tomato fields near Davis, California, USA, found higher greenhouse-gas emissions in soils with reduced tillage, compared to conventional tillage. Nutrients: Similar amounts of nitrogen were found in soils with reduced tillage or conventional tillage (1.8–2.6 vs 1.9–2.7 Mg N/ha). Soil erosion and aggregation: Similar amounts of soil aggregation were found in soils with reduced tillage or conventional tillage (1.2–1.7 vs 1.2–1.8 mm mean weight diameter). Greenhouse gases: Higher nitrous oxide emissions were found in soils with reduced tillage, compared to conventional tillage, in two of seven comparisons (emissions not reported for all of these comparisons, but the highest emissions were found in plots with reduced tillage: 29–40 g N2O-N/ha/day). Methods: Reduced tillage or conventional tillage was used on nine plots each (1.5 x 1.0 m plots). Nine tillage practices, in 12–15 tractor passes, were used for conventional tillage. Five tillage practices, in 5–10 tractor passes, were used for reduced tillage. Soil samples were collected with soil cores (two cores/plot, 4 cm diameter, 0–15 cm depth), when the maize was harvested (September). Greenhouse-gas emissions were measured with closed chambers (March–September, every three weeks, from each plot).

 

15 

A controlled study in 2003–2006 in an irrigated wheat-sunflower-chickpea field in Yolo County, California, USA, found similar amounts of greenhouse gas in soils with reduced tillage, compared to conventional tillage. Greenhouse gases: Similar amounts of greenhouse gas (carbon dioxide and nitrous oxide) were found in soils with reduced tillage, compared to conventional tillage (3–14 vs 3–15 Mg C/ha/year; 2–9 vs 1–4 kg N/ha/year). Methods: Conventional tillage was used on one half of a field, and reduced tillage was used on the other half, in 2003–2006. Different crops were planted in different years (2003: fallow; April 2004: maize; May 2005: sunflower; November 2005: chickpea). Ripping (45 cm depth), disking (15 cm depth), grading, listing beds were used for conventional tillage. Herbicide, stubble chopping, mulching, and disking were used for both conventional tillage and reduced tillage. Both treatments were fertilized and irrigated. Greenhouse gases were measured with closed chambers, in several places (crop row, crop bed, bottom of the furrow, and side of the furrow), 1–2 times/month, in 2003–2006 (nine samples/treatment).

 

16 

A replicated, randomized, controlled study in 1990–2006 on three rainfed farms in Spain found more soil organisms in plots with reduced tillage, compared to conventional tillage. Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in two of nine comparisons (0–10 cm depth, in Lleida: 420–490 vs 170–230 mg C/kg dry soil). Methods: Reduced tillage or conventional tillage was used on nine plots each in Lleida province (50 x 6 m plots, established in 1996), six plots each in Zaragoza province (33.5 x 10 m plots, established in 1990), and three plots each in Sevilla province (22 x 14 m plots). A mouldboard plough (25–40 cm depth, in Zaragoza and Sevilla), a cultivator (10–15 cm depth, 1–3 times/year), a disc harrow (5–15 cm depth, 1–2 times/year, in Sevilla), and herbicide (in Sevilla) were used for conventional tillage. A chisel plough (in Zaragoza but not in Lleida, 25–30 cm depth), a cultivator (10–15 cm depth, 1–2 passes), a disc harrow (5–7 cm depth, in Sevilla), and herbicide (in Sevilla) were used for reduced tillage. Soil samples were collected in March 2006 (0–25 cm depth).

 

17 

A replicated, randomized, controlled study in 1991–2008 on a rainfed wheat-sunflower-pea field near Seville, Spain (same study as (18)), found more soil organisms in plots with reduced tillage, compared  to conventional tillage. Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in two of three comparisons (0–10 cm depth: 978–1,058 vs 806–814 mg C/kg soil). Methods: Reduced tillage or conventional tillage was used on three plots each (22 x 14 m), in 1991–2008. A chisel plough (25–30 cm depth, every two years) and a disc harrow (5–7 cm depth, every year) were used for reduced tillage. A mouldboard plough (25–30 cm depth), a cultivator (15–20 cm, 2–3 passes), and a disc harrow (15 cm) were used for conventional tillage (every year). Wheat, sunflowers, and peas were grown in rotation. Wheat was fertilized, but sunflowers and peas were not. In 1991–2003, crop residues were burned on plots with conventional tillage. Crop residues were retained and herbicides were used on plots with reduced tillage. Soil samples were collected in March 2008 (three samples/plot, 400 g/soil core, 0–20 cm depth).

18 

A replicated, randomized, controlled study in 1991–2008 on a rainfed wheat-sunflower-pea field near Seville, Spain (same study as (17)), found more soil organisms in plots with reduced tillage, compared  to conventional tillage. Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in three of six comparisons (654–1,058 vs 806–814 mg C/kg soil). Methods: Reduced tillage or conventional tillage was used on three plots each (22 x 14 m), in 1991–2008. A chisel plough (25–30 cm depth, every two years) and a disc harrow (5–7 cm depth, every year) were used for reduced tillage. A mouldboard plough (25–30 cm depth), a cultivator (15–20 cm, 2–3 passes), and a disc harrow (15 cm) were used for conventional tillage (every year). Wheat, sunflowers, and peas were grown in rotation. Wheat was fertilized, but sunflowers and peas were not. In 1991–2003, crop residues were burned on plots with conventional tillage. Crop residues were retained and herbicides were used on plots with reduced tillage. Soil samples were collected in March and July 2008 (three samples/plot, 0–20 cm depth).

 

19 

A replicated, controlled study in 1993–2006 in an irrigated tomato-corn field in Davis, California, USA, found similar numbers of soil organisms, but different communities of soil organisms, in plots with reduced tillage, compared to conventional tillage. Soil organisms: Similar numbers of mites and nematodes were found in soils with reduced tillage or conventional tillage (596–888 vs 527–797 individuals/100 g fresh soil). However, the composition of nematode and mite communities differed between soils with reduced tillage or conventional tillage (reported as distance in multivariate space). Methods: Conventional tillage or reduced tillage was used on six plots each (0.4 ha plots). Plots were tilled about five times/year (conventional) or two times/year (reduced; depth not reported). All plots were irrigated. Half of the plots were fertilized, and compost was added to the other half. Soil samples were collected eight times in March 2005–November 2006 (three samples/plot). Mites were sampled with soil cores (5 cm diameter, 10 cm depth). Nematodes were sampled in soil cubes (20 x 20 x 20 cm).

 

20 

A replicated, randomized, controlled study in 1996–2008 in a rainfed barley field in the Ebro river valley, Spain (same study as (3,25,26,30)), found more greenhouse gas in soils with reduced tillage, compared to conventional tillage. Greenhouse gases: More carbon dioxide was found in soils with reduced tillage, compared to conventional tillage (amount of carbon dioxide not reported). Methods: Reduced tillage or conventional tillage was used on nine plots each (50 x 6 m). A mouldboard plough or a disc plough was used for conventional tillage (25–30 cm depth, 100% incorporation of crop residues). A cultivator was used for reduced tillage (10–15 cm depth, 50% incorporation of crop residues). Two-thirds of the plots were fertilized (60 or 120 kg N/ha). Greenhouse gas was sampled with an open chamber (2 samples/plot, 21 cm diameter, 900 mL airflow/minute), in 2005–2008 (several samples within 2 days before and after tillage).

 

21 

A replicated, randomized, controlled study in 2003–2005 in a vineyard in Napa Valley, California, USA, found less carbon dioxide in soils with reduced tillage, compared to conventional tillage. Greenhouse gases: Less carbon dioxide was found in soils with reduced tillage, compared to conventional tillage, in one of two years (8.57 vs 10.11 Mg CO2-C/ha). Methods: Three plots (518 m2 each, four vine alleys each) were disked in spring (conventional tillage: 30 cm depth), and three plots were not disked (reduced tillage). Short stature barley was grown as a winter cover crop on all plots. Cover crops were mown in spring, before disking. All plots were disked in autumn (5 cm depth), before the cover crops were planted.

 

22 

A replicated, randomized, controlled study in 2000–2009 on a farm in Sicily, Italy, found more organic matter, nitrogen, phosphorus, and soil organisms in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage (8–16 vs 6–11 g C/kg soil). Nutrients: More nitrogen or phosphorus was found in soils with reduced tillage, compared to conventional tillage, in one of two comparisons (2.2 vs 1.7 g N/kg soil; 20 vs 11 mg phosphorus/kg soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage (334–680 vs 241–464 mg C/kg soil), and more microbial biomass (measured as nitrogen) was found in one of two comparisons (102 vs 78 mg N/kg soil). Greenhouse gases: Similar amounts of carbon dioxide were found in soils with reduced tillage, compared to conventional tillage (69–71 vs 109–111 mg C-CO2/kg soil). Methods: Conventional tillage or reduced tillage was used on eight plots each (20 x 15 m plots), in 2000–2009. A mouldboard plough (20 cm depth) was used for both conventional tillage (6–8 ploughings/year) and reduced tillage (one ploughing/year, plus hoeing to control weeds). Compost was added to all plots (15–30 t/ha/year). Soil samples were collected in May 2009 (five sub-samples/plot, 0–20 cm depth).

 

23 

A replicated, randomized, controlled study in 1994–2007 in a rainfed wheat field near Madrid, Spain (same study as (35,39)), found more organic matter and higher stability in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage, in two of four comparisons (0–7.5 cm depth: 8–9 vs 6–8 Mg C/ha). Soil erosion and aggregation: Higher stability was found in soils with reduced tillage, compared to conventional tillage, in one of four comparisons (0–7.5 cm depth, October 2007: 51 vs 38% of aggregates were water-stable). Methods: Reduced tillage or conventional tillage was used on eight plots each (10 x 25 m plots), in autumn 1994–2007. A mouldboard plough (20 cm depth) and a cultivator were used for conventional tillage. A chisel plough (15 cm depth) and a cultivator were used for reduced tillage. All plots were fertilized. Soil samples were collected after the seedbeds were prepared (three samples/plot, 0–15 cm depth), in November 2006 and October 2007.

 

24 

A replicated, randomized, controlled study in 2008–2010 in a wheat-legume field in southwest Spain (same study as (31)) found more soil organisms in soils with reduced tillage, compared to conventional tillage. Soil organisms: More microbial biomass (measured as carbon or nitrogen) was found in soils with reduced tillage, compared to conventional tillage, in four of 18 comparisons (0–5 cm depth, in June 2009 or January 2010: 458–2,363 vs 263–957 mg C/kg soil; 37–69 vs 17–25 mg N/kg soil). Methods: Conventional tillage or reduced tillage was used on three plots each (30 x 10 m plots). A mouldboard plough was used for conventional tillage (25 cm depth). Herbicides and a chisel plough were used for reduced tillage (10–15 cm depth). All plots were fertilized. Soil samples were collected in January 2009, June 2009, and January 2010 (three samples/plot, nine soil cores/sample, 0–25 cm depth). No tillage was used on all plots in 1999–2008.

 

25 

A replicated, randomized, controlled study in 1996–2009 in a rainfed barley field in the Ebro river valley, Spain (same study as (3,20,26,30)), found higher greenhouse-gas emissions in soils with reduced tillage, compared to conventional tillage. Greenhouse gases: Higher carbon dioxide emissions were found in soils with reduced tillage, compared to conventional tillage, in three of four comparisons (amounts of carbon dioxide not clearly reported). Methods: Reduced tillage or conventional tillage was used on nine plots each (50 x 6 m plots). A mouldboard plough was used for conventional tillage (25–30 cm depth, 100% incorporation of crop residues). A cultivator was used for reduced tillage (10–15 cm depth, 50% incorporation of crop residues). Two-thirds of the plots were fertilized (60 or 120 kg N/ha). Carbon dioxide was measured with an open chamber (21 cm diameter, 900 mL airflow/minute, 2 samples/plot/day, every 7–14 days, in 2006–2009).

 

26 

A replicated, randomized, controlled study in 1996–2009 in a rainfed barley field in the Ebro river valley, Spain (same study as (3,20,25,30)), found less nitrate in soils with reduced tillage, compared to conventional tillage. Nutrients: Less nitrate was found in soils with reduced tillage, compared to conventional tillage (461 vs 852 kg N-NO3/ha), but no differences in ammonium were found (amounts of ammonium not reported). Methods: Reduced tillage or conventional tillage was used on nine plots each (50 x 6 m plots) in October or November. A mouldboard plough was used for conventional tillage (25–30 cm depth, 100% incorporation of crop residues). A cultivator was used for reduced tillage (10–15 cm depth, 50% incorporation of crop residues). Two-thirds of the plots were fertilized (60 or 120 kg N/ha). Soil samples were collected when sowing the crop in November 2005–2008 (two samples/plot, 4 cm diameter soil auger, 0–100 cm depth).

 

27 

A replicated, randomized, controlled study in 1996–2008 in a rainfed legume-cereal field near Aleppo, Syria, found more organic matter and fewer soil organisms in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic matter was found in soils with reduced tillage, compared to conventional tillage, in four of 10 comparisons (2003: 12–17 vs 10–13 g/kg). Nutrients: Similar amounts of nitrogen were found in soils with reduced tillage or conventional tillage (0.76 g/kg soil). Soil organisms: Less microbial biomass (measured as carbon and nitrogen) was found in soils with reduced tillage, compared to conventional tillage, in four of eight comparisons (carbon, 5–20 cm depth: 13–38 vs 90–91 mg/kg soil; nitrogen, 10–30 cm depth: 5–10 vs 19–28 mg/kg soil). Methods: The crop rotations were vetch–barley (two-course) or vetch–barley–vetch–wheat (four-course). Reduced tillage or conventional tillage was used on twenty plots each (25 x 25 m plots). A mouldboard plough (30 cm depth, after cereal crops) was used for conventional tillage. A cultivator (12 cm depth, after vetch) was used for both conventional and reduced tillage. All plots were fertilized in November. Soils were sampled in 2003 (0–30 cm depth) and 2008 (0–20 cm depth).

 

28 

A replicated, randomized, controlled study in 1991–2008 in a rainfed wheat-sunflower-pea field near Seville, Spain, found more organic matter, more soil organisms, and lower greenhouse-gas emissions in soils with reduced tillage, compared to conventional tillage. Tillage had inconsistent effects on soil stability. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage, in one of three comparisons (0–5 cm depth: 11 vs 10 g total organic C/kg soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in one of three comparisons (0–5 cm depth: 885 vs 620 mg C/kg soil). Soil erosion and aggregation: More stable soils were found in plots with reduced tillage, compared to conventional tillage, in one of nine comparisons (5–10 cm depth: 49 vs 39% water-stable aggregates), but less stable soils were found in one of nine comparisons (data reported as aggregation index). Greenhouse gases: Lower carbon dioxide emissions were found in soils with reduced tillage, compared to conventional tillage (0.31 vs 0.40 g CO2/m2/hour). Methods: Reduced tillage or conventional tillage was used on three plots each (22 x 14 m plots). A mouldboard plough and a chisel plough were used for conventional tillage (25–30 cm depth), and crop residues were burned (1992–2003, but not 2004–2008). A chisel plough and herbicide were used for reduced tillage (25–30 cm depth), and crop residues were retained. Wheat, sunflowers, and peas were grown in rotation. Wheat was fertilized, but sunflowers and peas were not. Soil samples were collected in 2008 (0–25 cm depth, four samples/plot).

 

29 

A replicated meta-analysis from 2013 of multiple Mediterranean countries found a higher percentage of organic matter in soils with reduced tillage, compared to conventional tillage. Organic matter: A higher percentage of organic carbon was found in soils with reduced tillage, compared to conventional tillage (15% higher). Methods: The Web of Knowledge database was searched, using the keywords, “Mediterranean”, “soil”, and “conventional”, and 17 data sets from 12 studies of reduced tillage were found and meta-analysed. The most recent studies included in this meta-analysis were published in 2011.

 

30 

A replicated, randomized, controlled study in 1996–2008 in a rainfed barley field in the Ebro river valley, Spain (same study as (3,20,25,26)), found more organic matter, but similar amounts of soil organisms, in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage (8.65 vs 7.39 g C/kg dry soil). Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with reduced tillage or conventional tillage (263 vs 231 mg C/kg dry soil). Methods: There were nine plots (50 x 6 m) for each of two tillage treatments (reduced tillage: cultivator, 10–15 cm depth; conventional tillage: mouldboard plough, 25–30 cm depth). Plots were tilled in October or November. Soil samples were collected in October 2008 (before tillage, three soil cores/plot, 4 cm diameter, 0–50 cm depth).

 

31 

A replicated, randomized, controlled study in 2008–2010 in a rainfed wheat-vetch field in southwest Spain (same study as (24)) found more organic matter and soil organisms in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage (17–23 vs 12–15 g C/kg soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in four of five comparisons (in soil aggregates <2 mm in diameter: 526–646 vs 339–346 g C/kg soil). Soil erosion and aggregation: Similar amounts of soil aggregation were found in soils with reduced tillage or conventional tillage (data reported for five soil fractions). Methods: Conventional tillage or reduced tillage was used on three plots each (300 m2 plots), in 2008–2009. From 1999–2008, no tillage was used on all plots. A mouldboard plough (25 cm depth, in 2008), or a chisel plough (10–15 cm depth, in 2009), and a disk harrow were used for conventional tillage, and crop residues were removed (in 2008 and 2010). A chisel plough (10–15 cm depth) and herbicide were used for reduced tillage, and crop residues were retained. Soil samples were collected in October 2010 (0–10 cm depth, five samples/plot).

 

32 

A replicated, randomized, controlled study in 2009–2012 in two irrigated vegetable fields in central Italy found more nitrate and ammonium in soils with reduced tillage, compared to conventional tillage. Nutrients: More nitrate was found in soils with reduced tillage, compared to conventional tillage, in two of 12 comparisons (in plots with oats or oilseed rape as the winter cover crop: 6 vs 2 mg NO3-N/kg dry soil), and more ammonium was found in one of 12 comparisons (11 vs 2 mg NH4-N/kg dry soil). Methods: Reduced tillage or conventional tillage was used on nine plots each (6 x 4 m plots). Each plot had a winter cover crop (hairy vetch, oats, or oilseed rape). Cover crops were sown in September 2009–2010 and suppressed in May 2010–2011. A mouldboard plough and a disk harrow (two passes) were used for conventional tillage (incorporating the cover crop residues to 30 cm depth). A rotary hoe was used for reduced tillage (incorporating the cover crop residues to 10 cm depth). Pepper seedlings were transplanted into these plots in May 2010–2011 and were last harvested in October 2010 and September 2011. After the pepper harvest, endive and savoy cabbage seedlings were transplanted into these plots, and they were harvested in December 2010 and November 2011 (endive) or March 2011 and February 2012 (cabbage). No fertilizer was added while the crops were growing, but the plots were irrigated. Nutrients were measured in soil samples (10 samples/plot, 0–30 cm depth, when these crops were harvested).

 

33 

A replicated, randomized, controlled study in 2008–2013 in a rainfed wheat-sunflower-pea field near Seville, Spain, found similar amounts of organic matter and nutrients in soils with reduced tillage or conventional tillage. Organic matter: Similar amounts of organic carbon were found in soils with reduced tillage or conventional tillage (9 g C/kg soil). Nutrients: Similar amounts of nitrogen, phosphorus, and potassium were found in soils with reduced tillage or conventional tillage (0.92–0.99 vs 0.91–0.97 g N/kg soil; 17.8–25.7 vs 22.2–26.1 g phosphorus/kg soil; 307–419 vs 367–428 g potassium/kg soil). Methods: Reduced tillage or conventional tillage was used on three plots each (6 x 33.5 m plots). A mouldboard plough (25–30 cm depth), a chisel plough (25 cm depth, twice/year), and a disc harrow (12 cm depth) were used for conventional tillage. A chisel plough (25 cm depth, once/year), a disc harrow (5 cm depth), and herbicide were used for reduced tillage. Wheat, sunflowers, and peas were grown in rotation. Wheat was fertilized, but sunflowers and peas were not. Soil samples were collected in October 2012 (0–25 cm depth).

 

34 

A replicated, randomized, controlled study in 1991–2011 in rainfed wheat-sunflower-pea fields near Seville, Spain (same study as (16,37)), found more organic matter and more soil organisms in soils with twenty years of reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage, in two of three comparisons, in long-term plots (1991–2011, 0–10 cm depth: 13–14 vs 10–11 g C/kg soil), but no differences were found in short-term plots (2008–2011: 6–9 vs 7–9 g C/kg soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in one of three comparisons, in long-term plots (1991–2011, 0–5 cm depth: 580 vs 474 mg C/kg soil), but no differences were found in short-term plots (2008–2011: 740–958 vs 689–868 mg C/kg soil). Methods: Reduced tillage or conventional tillage was used on three plots each, in each of two experiments: a short-term experiment (2008–2011, 20 x 9 m plots), and a long-term experiment (1991–2011, 20 x 14 m plots). A mouldboard plough (25–30 cm depth), a cultivator (15–20 cm depth, two passes), and a disc harrow (15 cm depth) were used for conventional tillage. A chisel plough (15–20 cm depth, every other year) and a disc harrow (5–7 cm depth) were used for reduced tillage, and crop residues were retained (>60% cover). Soil samples were collected in January 2011 (0–25 cm depth, five samples/plot).

 

35 

A replicated, randomized, controlled study in 1994–2013 in a rainfed field near Madrid, Spain (same study as (23,39)), found more organic matter, soil organisms, and greenhouse gas in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in plots with reduced tillage, compared to conventional tillage, in two of 12 comparisons (8 vs 6 g C/kg soil). Soil organisms: More microbial biomass (measured as carbon) was found in plots with reduced tillage, compared to conventional tillage, in three of 12 comparisons (380–400 vs 200–250 mg C/kg soil). Greenhouse gases: More carbon dioxide was found in plots with reduced tillage, compared to conventional tillage, in two of 12 comparisons (30–40 vs 20–28 mg CO2-C/kg soil/d). Methods: Conventional tillage or reduced tillage was used on eight plots each (10 x 25 m plots). A mouldboard plough was used for both conventional tillage (25 cm depth) and reduced tillage (20 cm depth). Wheat was grown on half of the plots, whereas wheat, vetch, and barley were grown in rotation on the other half. Wheat and barley were fertilized. Crop residues were shredded and retained. Soil sam  ples were collected six times in October 2010–April 2013 (soil cores, 0–15 cm depth, 5 cm diameter).

 

36 

A replicated, randomized, controlled study in 1999–2009 in an irrigated tomato-cotton field in the San Joaquin Valley, California, USA (same study as (5)), found similar amounts of organic matter in soils with reduced tillage or conventional tillage. Organic matter: Similar amounts of carbon were found in soils with reduced tillage or conventional tillage (24–29 vs 23–26 t total C/ha). Methods: Reduced tillage or conventional tillage was used on 16 plots each, in 1999–2009. The plots (9 x 82 m) had six raised beds each. Rainfed winter cover crops (triticale, rye, and vetch) were planted on half of the plots, in October 1999–2008, and crop residues were chopped in March. Different numbers of tillage practices were used for conventional tillage (19–23 tractor passes, including disc and chisel ploughing) and reduced tillage (11–12 tractor passes, not including disc and chisel ploughing). Tomatoes and cotton were grown in rotation. Fertilizer and herbicide were used in all plots. Soil samples were collected in autumn 2007 (0–30 cm depth, 7.6 diameter soil cores, 6–8 subsamples/plot).

 

37 

A replicated, randomized, controlled study in 1991–2010 in rainfed wheat-sunflower-pea fields near Seville, Spain (same study as (16,34)), found more organic matter, fewer soil organisms, and more aggregation in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage, in four of ten comparisons (6–9 vs 5–7 g C/kg soil). Soil organisms: Less microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage, in one of ten comparisons (in autumn, 1–2 mm aggregates: 67 vs 107 g microbial C/kg organic C). Soil erosion and aggregation: More large aggregates were found in soils with reduced tillage, compared to conventional tillage, in autumn (1–2 mm aggregates: 18 vs 16% of soil weight; 2–5 mm: 35 vs 31%), and fewer small aggregates were found in one of three comparisons, in autumn (0.25–0.5 mm aggregates: 14 vs 19% of soil weight). However, no differences in aggregate distributions were found in spring (data reported for five aggregate sizes). Methods: Reduced tillage or conventional tillage was used on three plots each (300 m2 plots). A mouldboard plough (25–30 cm depth), a cultivator (15–20 cm depth, two passes), and a disc harrow (5–7 cm depth) were used for conventional tillage. A chisel plough (15–20 cm depth, every other year) and a disc harrow (5–7 cm depth) were used for reduced tillage, and crop residues were retained (>60% cover). Wheat, sunflowers, and peas were grown in rotation. Wheat was fertilized, but sunflowers and peas were not. Soil samples were collected in spring and autumn 2010 (0–10 cm depth, five samples/plot).

 

38 

A replicated, randomized, controlled study in 2012–2013 in a rainfed wheat field in Wadi Madwar, northwestern Egypt, found less erosion of soils with less frequent tillage, compared to more frequent, more erosion of soils with shallower tillage, compared to deeper, and less erosion of soils that were tilled at slower speeds, compared to faster. Soil erosion and aggregation: Less soil was lost in runoff water from plots with reduced tillage, compared to conventional tillage (1.44 vs 1.66 t/ha). More soil was lost in runoff water from plots that were tilled to 15 cm depth, compared to 20–25 cm depth (1.31 vs 1.20–1.22 t/ha). Implementation options: Less soil was lost in runoff water from plots that were tilled at slower tractor speeds (0.69–1 m/s: 1.21–1.22 t/ha), compared to faster speeds (1.25–1.53 t/ha: 1.26–1.29 t/ha). Methods: Reduced tillage or conventional tillage was used on three plots each (0.45 ha plots). A chisel plough was used for both reduced tillage (one pass) and conventional tillage (two passes). Each plot had three subplots (0.15 ha subplots, tilled to 15, 20, or 25 cm depth). Each subplot had four sub-subplots (size not reported; tilled at 0.69, 1, 1.25, or 1.53 m/s). Runoff water was collected in buried containers, downhill from each sub-subplot, after each storm.

 

39 

A replicated, randomized, controlled study in 1994–2011 in a rainfed cereal-legume field near Madrid, Spain (same study as (23,35)), found higher greenhouse-gas emissions, more soil organisms, and more organic matter in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage (27.1 vs 11.2 mg dissolved organic C/kg soil). Nutrients: Similar amounts of nitrate and ammonium were found in soils with reduced tillage, compared to conventional tillage (1–18 mg NO3-N/ha; 0.2–3.5 mg NH4-N/kg). Soil organisms: More bacteria were found in soils with reduced tillage, compared to conventional tillage (denitrifying bacteria: 108 vs 106 gene copies), but no difference in microbial biomass (measured as carbon) was found (186 vs 94 mg C/kg soil). Greenhouse gases: Higher nitrous oxide emissions were found in soils with reduced tillage, compared to conventional tillage (0.12 vs 0.05 kg N2O–N/ha), but no difference in methane emissions was found (–473 vs –231 g CH4–C/ha). Methods: No tillage or reduced tillage was used on three plots each (10 x 25 m), in October. A chisel plough and a cultivator were used for reduced tillage (15 cm depth). A mouldboard plough and a cultivator were used for conventional tillage (20 cm depth). Soil and greenhouse-gas samples were collected 1–12 times/month, in November 2010–October 2011, in the vetch phase of a fallow-wheat-vetch-barley rotation (soil cores: 0–15 cm depth, 2.5 cm diameter; closed chambers: 19.3 cm height, 35.6 cm diameter, 20 mL gas samples, 0–60 minutes after chamber closure). The vetch was not fertilized.

 

40 

A replicated, randomized, controlled study in 2009–2011 in an irrigated eggplant field in central Italy found more nitrogen in soils with reduced tillage, compared to conventional tillage. Nutrients: More nitrogen was found in soils with reduced tillage, compared to conventional tillage, in one of four comparisons (30 vs 24 mg inorganic N/kg dry soil). Methods: A mouldboard plough (30 cm depth) was used on all plots in autumn, before winter cover crops were planted. Cover crops were mown or chopped in spring, before tillage. Reduced tillage or conventional tillage was used on 12 plots each (6 x 4 m plots). A mouldboard plough (30 cm depth) and a disc (two passes) were used for conventional tillage (which incorporated the cover crop residues into the soil). A rotary hoe (10 cm depth) was used for reduced tillage (which incorporated some of the cover crop residues into the soil). Eggplant seedlings were transplanted into the plots in May, and fruits were harvested four times/year in July–September 2010–2011. Soil samples were collected when the seedlings were transplanted and when the last fruits were harvested each year (0–30 cm depth, six samples/plot). All plots were fertilized before the cover crops were grown, but not after. All plots were irrigated.

 

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.