Providing evidence to improve practice

Action: Soil: Use no tillage in arable fields Mediterranean Farmland

Key messages

Organic matter (20 studies): One meta-analysis of studies from Mediterranean countries found more organic matter in soils without tillage, compared to soils with tillage. Fourteen replicated studies (eleven randomized and controlled, one controlled, one site comparison) from Italy, Spain, and the USA found more organic matter in soils without tillage, compared to soils with tillage, in some or all comparisons. One replicated, randomized, controlled study from Portugal found less organic matter in soils without tillage, compared to soils with tillage, in some comparisons. One replicated, randomized, controlled study from Spain sometimes found more organic matter, and sometimes found less, in soils without tillage, compared to soils with tillage. Three replicated, controlled studies (two randomized) from Italy and Spain found similar amounts of organic matter in soils with or without tillage.

Nutrients (19 studies)

  • Nitrogen (18 studies): Six replicated studies (five randomized and controlled, one site comparison) from Italy, Spain, and the USA found more nitrogen in soils without tillage, compared soil with tillage, in some or all comparisons. Six replicated, randomized, controlled studies from Spain found less nitrogen in soils without tillage, in some or all comparisons. Two replicated, controlled studies from Spain and the USA sometimes found more nitrogen and sometimes found less nitrogen in soils without tillage, compared to soils with tillage. Four replicated, controlled studies (three randomized) from Italy, Portugal, Spain, and the USA found similar amounts of nitrogen in soils with or without tillage.
  • Phosphorus (5 studies): Three replicated, randomized, controlled studies from Spain and the USA found more phosphorus in soils without tillage, compared to soils with tillage, in some or all comparisons. One replicated, randomized, controlled study from Portugal found less phosphorus in soils without tillage, compared to soils with tillage, in some comparisons. One replicated, randomized, controlled study from Spain found similar amounts of phosphorus in soils with or without tillage.
  • Potassium (3 studies): One replicated, randomized, controlled study from Spain found more potassium in soils without tillage, compared to soils with tillage, in some comparisons. One replicated, randomized, controlled study from the USA sometimes found more potassium and sometimes found less potassium in soils without tillage, compared to soils with tillage. One replicated, randomized, controlled study from Spain found similar amounts of potassium in soils with or without tillage.
  • pH (2 studies): One replicated, randomized, controlled study from Portugal found lower pH levels in soils without tillage, compared to soils with tillage, in some comparisons. One replicated, randomized, controlled study from the USA found similar pH levels in soils with or without tillage.

Soil organisms (18 studies)

  • Microbial biomass (13 studies): Five replicated, controlled studies (four randomized) from Italy and Spain found more microbial biomass in soils without tillage, compared to soils with tillage, in some or all comparisons. Two replicated, randomized, controlled studies from Spain sometimes found more microbial biomass, and sometimes found less, in soils without tillage, compared to soils with tillage. Six replicated, randomized, controlled studies from Spain and the USA found similar amounts of microbial biomass in soils with or without tillage.
  • Earthworms (2 studies): Two replicated studies (one controlled, one site comparison) from the USA found more earthworms in soils without tillage, compared to soils with tillage.
  • Nematodes (2 studies): Two replicated, controlled studies (one randomized) from the USA found similar numbers of nematodes in soils with or without tillage. However, one of these studies found different communities of nematodes in soils with or without tillage.
  • Mites (1 study): One replicated, controlled study from the USA found different communities of mites, but similar numbers of mites, in soils with or without tillage.
  • Other soil organisms (1 study): One replicated, randomized, controlled study from Spain found similar amounts of denitrifying bacteria in soils with or without tillage. Another replicated, randomized, controlled study from Spain found more microorganisms in soils without tillage, compared to soils with tillage, in some comparisons. One replicated, randomized, controlled study from Portugal found more fungus in soils without tillage, compared to soils with tillage.

Soil erosion and aggregation (9 studies): Seven replicated studies (six randomized and controlled, one site comparison) from Spain and the USA found that soils without tillage were more stable than tilled soils, in some or all comparisons. Two replicated, randomized, controlled studies from Spain found that soils without tillage were sometimes more stable, and were sometimes less stable, than tilled soils.

Greenhouse gases (10 studies)

  • Carbon dioxide (7 studies): Three replicated, controlled studies (two randomized) from Italy and Spain found more carbon dioxide in soils without tillage, compared to soils with tillage. Two replicated, randomized, controlled studies from Spain found less carbon dioxide in soils without tillage, compared to soils with tillage, in some comparisons. Two replicated, randomized, controlled studies from Spain sometimes found more carbon dioxide, and sometimes found less, in soils without tillage, compared to soils with tillage. One replicated, randomized, controlled study from Spain found similar amounts of carbon dioxide in soils with or without tillage.
  • Nitrous oxide (3 studies): One replicated, randomized, controlled study from Spain sometimes found more nitrous oxide, and sometimes found less, in soils without tillage, compared to soils with tillage. Two replicated, randomized, controlled studies from Spain found similar amounts of nitrous oxide in soils with or without tillage.
  • Methane (3 studies): One replicated, randomized, controlled study from Spain found less methane in soils without tillage, compared to soils with tillage. One replicated, randomized, controlled study from Spain sometimes found more methane, and sometimes found less, in soils without tillage, compared to soils with tillage. One replicated, randomized, controlled study from Spain found similar amounts of methane in soils with or without tillage.

Implementation options (1 study): One replicated, randomized, controlled study from Spain found more organic matter in soils that had not been tilled for a long time, compared to a short time, in one comparison. This study also found greater stability in soils that had not been tilled for a long time, in some comparisons.

Supporting evidence from individual studies

1 

A replicated, controlled study in 1996–1998 in an irrigated tomato field in the San Joaquin Valley, California, USA (same study as (2)), found more soil carbon and earthworms in plots with winter cover crops and no tillage, compared to plots with bare soil in winter and conventional tillage in spring. Organic matter: More soil carbon was found in plots with no tillage, compared to tillage (0.66–0.72% vs 0.62% carbon, 0–0.6 inches depth). Soil organisms: More earthworms were found in plots with no tillage, compared to tillage (2.1 vs 0.6 earthworms/square foot). 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 fallow in winter, with herbicide, and conventional tillage in spring). Soil carbon was sampled in September 1998 (eight subsamples/plot, 0–0.6 inches depth). Earthworms were sampled in March 1998 (two cylinders/plot, 16.5 inches diameter, 6 inches depth, sprinkled with mustard powder so that earthworms would come to the surface). It was not clear whether these results were a direct effect of cover crops or tillage.

 

2 

A replicated, controlled study in 1996–1998 in an irrigated tomato field in the San Joaquin Valley, California, USA (same study as (1)), found less nitrate in winter and spring, but more nitrate in summer, in plots with winter cover crops (and no tillage in spring), compared to plots with winter fallows (and tillage in spring). Nutrients: Less nitrate was found in plots with cover crops, compared to fallows, when measured in winter or spring (19 of 32 comparisons: 0.9–4.1 vs 3.8–7.9 ppm, 0–30 cm depth), but more nitrate was found when measured in summer (27 of 32 comparisons: 21–41 vs 8–14 ppm, 0–30 cm depth). Methods: There were 12 plots (4.5 x 27.5 m plots) for each of four treatments (two grass-legume mixtures, or two legumes without grasses, as winter cover crops, sown in October 1996–1997, killed and retained as mulch, with no tillage, in March 1997–1998) and each of two controls (bare-soil fallows in winter, with or without herbicide, and conventional tillage in spring). Tomato seedlings were transplanted in April 1997–1998. The tomatoes were irrigated (two inches/week) and fertilized (0, 100, or 200 lb N/acre, in March 1997 and May 1998). Soil nitrate was sampled four times in 1998 (0–30 cm depth, three samples/plot). It was not clear whether these results were a direct effect of cover crops or tillage.

 

3 

A replicated, randomized, controlled study in 1983–1996 in a rainfed wheat field in the Henares river valley, Spain, found that tillage had inconsistent effects on soil stability. Soil erosion and aggregation: Lower soil stability was found in plots with no tillage, compared to conventional tillage, in one of four comparisons (1–2 mm pre-wetted soil aggregates: 76.3% vs 78.4% water stable), but higher stability was found in two of four comparisons (1–2 mm air-dried soil aggregates: 11% vs 2.9% water stable; 4.38 mm air-dried soil aggregates: 12% vs 1%). Methods: No tillage or conventional tillage was used on four plots each. Each plot had two subplots (20 x 30 m, with or without crop rotation). A mouldboard plough (30 cm depth, in autumn) and a tine cultivator (10–15 cm depth, two passes, in spring) were used for conventional tillage. A seed drill and pre-emergence herbicide were used for no tillage. 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).

 

4 

A replicated, randomized, controlled study in 1996–1999 in three rainfed barley fields in the Ebro river valley, Spain (same study as (17,23,24,26)), found less nitrogen in soils with no tillage, compared to conventional tillage. Nutrients: Less nitrogen was found in soils with no tillage, compared to conventional tillage, in three of nine comparisons (82–165 vs 104–247 kg/ha). Methods: No 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. Herbicide was used for no tillage. 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).

 

5 

A replicated, randomized, controlled study in 2003–2005 on rainfed farms in the Ebro river valley, Spain (same study as (10)), found less greenhouse gas in soils with no tillage, compared to conventional tillage. Greenhouse gases: Less carbon dioxide was found in soils with no tillage, compared to conventional tillage, in 18 of 39 comparisons, in the two days after tillage (0.1–2.3 vs 0.1–13.3 g CO2/m2/hour). Methods: No tillage or conventional tillage was used on ten plots each (33–50 x 7–10 m plots), on a total of three farms, with multiple crops. A mouldboard or subsoil plough was used on plots with conventional tillage (25–40 cm depth). Herbicide was used on plots with no 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.

 

6 

A replicated, randomized, controlled study in 1993–1997 in a rainfed barley field near Madrid, Spain (same study as (19,37,39)), found more organic matter, phosphorus, and potassium in soils with no tillage, compared to conventional tillage, but tillage had inconsistent effects on nitrogen. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in six of eight comparisons (8–11 vs 4–6 Mg/ha), but less was found in one of eight comparisons (6 vs 7 Mg/ha). Nutrients: More nitrogen was found in soils with no tillage, compared to conventional tillage, in six of eight comparisons (0.7–1.4 vs 0.4–0.9 Mg total N/ha), but less was found in one of eight comparisons (0.5 vs 0.6 Mg/ha). More potassium and phosphorus were found in soils with no tillage, compared to conventional tillage, in two of four comparisons (in 1997: 13–17 vs 7–8 kg extractable P/ha; 250–310 vs 150–190 kg extractable K/ha). Similar pH was found in soils with no tillage or conventional tillage (pH 7.8). Methods: No tillage or conventional tillage was used on four plots each (five 10 x 25 m subplots/plot, with barley monocultures or barley rotations). A mouldboard plough (30 cm depth) and a cultivator (10–15 cm depth, when needed for weed control) were used for conventional tillage. Pre-emergence herbicide was used for no tillage. The barley was fertilized (NPK: 200 kg/ha; ammonium nitrate: 200 kg/ha). Soil samples were collected after the harvest in 1994–1997 (0–90 cm depth; organic matter and nitrogen were assessed at 0–30 cm depth).

 

7 

A replicated, randomized, controlled study in 2003–2004 in irrigated farmland in Davis, California, USA, found more organic matter and phosphorus in soils with no tillage, compared to conventional tillage. Tillage had inconsistent effects on potassium. Organic matter: More carbon was found in soils with no tillage, compared to conventional tillage, in one of two comparisons (in rotations with fallows: 4 vs 3.8 kg total C/m2). Nutrients: Similar amounts of nitrogen were found in plots with no tillage or conventional tillage (450–460 g total N/m2). More potassium was found in soils with no tillage, compared to conventional tillage, in two of six comparisons (10.3–12.9 vs 6–7.7 mg K/litre), but less was found in one of twelve comparisons (4.8 vs 6.3 mg/L). More phosphorous was found in plots with no tillage, compared to conventional tillage, in one of six comparisons (27 vs 19 mg P/kg soil). Similar pH levels were found in soils with no tillage or conventional tillage (pH 6.8–7.3). Soil organisms: Similar amounts of microbial and nematode biomass (both measured as carbon) were found in plots with no tillage or conventional tillage (60–80 vs 60 g microbial C/m2; 0.1–0.2 vs 0.2–0.25 g nematode C/m2). Methods: No tillage or conventional tillage was used on six plots each (67 x 4.7 m plots, three beds/plot). Crop residues were incorporated to 20 cm depth, and the beds were shaped, on plots with conventional tillage (disk, lister, and ring roller). Crop residues were flail mown and spread on the plots with no tillage. All plots were fertilized in 2003, but not thereafter (112 kg P/ha phosphorous, 50 kg NPK/ha, and 67 kg N/ha). Cultivation was used to control weeds on plots with conventional tillage. Hand weeding was used on plots with no tillage. Herbicide was used on all plots. Some plots were irrigated. Soil samples were collected in December 2003, and June, September, and December 2004 (0–30 cm depth, three samples/plot).

 

8 

A replicated, randomized, controlled study in 2002–2004 in an irrigated maize field in southwest Spain found less nitrogen and more microorganisms in soils with no tillage, compared to conventional tillage. Tillage had inconsistent effects on soil stability. Nutrients: Less nitrogen was found in soils with no tillage, compared to conventional tillage, in one of nine comparisons (0–5 cm depth, in 2002: 0.11 vs 0.12 g total N/kg soil). Soil erosion and aggregation: Lower stability was found in soils with no tillage, compared to conventional tillage, in two of nine comparisons (0–10 cm depth, in 2002: 31–35% vs 48–58% of aggregates were stable), but higher stability was found in two of nine comparisons (0–10 cm depth, in 2004: 61–69% vs 41–58%). Soil organisms: More microorganisms were found in soils with no tillage, compared to conventional tillage, in one of three years (0–5 cm depth, in 2004: 437 vs 261 colony forming units/g dry soil). Methods: Conventional tillage or no tillage was used on four plots each (20 x 10 m plots). A mouldboard plough (0–30 cm depth, in October 2001–2003 and March and April 2002–2004) was used for conventional tillage, and maize residues were burned in September–October 2002–2004. Herbicide was used for no tillage (April and May–June 2002–2004), and maize residues were not burned. For organic carbon, nitrogen, and aggregate stability, soil samples were collected in March, June, and October 2002–2004 (three samples/plot, 0–30 cm depth). For microorganisms, soils samples were collected every two months (0–5 cm depth). It was not clear whether these results were a direct effect of tillage or residue burning.

 

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 no tillage, compared to conventional tillage. Nutrients: More phosphorus was found in soils with no tillage, compared to conventional tillage (1,528 vs 776 mg phosphorus/kg soil). Methods: No 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. Herbicide and a double-disk planter were used for no 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 (same study as (5)), found less greenhouse gas in soils with no tillage, compared to conventional tillage. Greenhouse gases: Less carbon dioxide was found in soils with no tillage, compared to conventional tillage, in three of 13 comparisons (0.27–0.85 vs 0.54–1.19 g CO2/m2/hour). Methods: No 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. Herbicide and a seed drill were used for no 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 study in 2003–2004 in rainfed farmland in the Ebro river valley, Spain, found more stable soils in plots with no tillage, compared to conventional tillage. Soil erosion and aggregation: More large aggregates were found in soils with no tillage, compared to conventional tillage (in Selvanera, 0–20 cm depth, aggregates >2,000 µm: 0.17–0.37 vs 0.06–0.15 g aggregate/g soil). More large water-stable aggregates were also found in soils with no tillage, compared to conventional tillage, in four of six comparisons (in Peñaflor, 0–10 cm depth, water-stable aggregates >2,000 µm: 0.08–0.15 vs 0.01–0.03 g aggregate/g soil). Methods: No tillage or conventional tillage was used on six plots each (three in Selvanera, 7 x 50 m each; three in Peñaflor, 10 x 33 m each). Herbicide was used for no tillage. In Selvanera, a subsoil plough (50 cm depth) and a cultivator (15 cm depth) were used for conventional tillage. In Peñaflor, a mouldboard plough was used for conventional tillage (30–35 cm depth). Soil samples were collected with a flat spade (0–20 cm depth) in July 2003 and 2004.

 

12 

A replicated site comparison in 2004–2005 in 11 irrigated tomato fields in the Sacramento Valley, California, USA, found more earthworms, more carbon and nitrogen, and greater soil aggregation in soils with no tillage, compared to tillage. Organic matter: More carbon was found in soils with no tillage, compared to tilled fallows (1.6 times as much total carbon). Nutrients: More nitrogen was found in soils with no tillage, compared to tilled fallows (1.5 times as much total nitrogen). Soil organisms: More earthworms, and larger earthworms, were found in soils with no tillage, compared to tilled fallows (85 vs 19 g earthworms/m2; 2.9 times larger). Soil erosion and aggregation: Greater aggregation was found in soils with no tillage, compared to tilled fallows (larger mean weight diameter; data presented as model results). Methods: Earthworms were collected from 11 tomato fields (four fields that were tilled, incorporating the tomato residues into the soil, and seven fields that were not tilled, retaining the tomato residues as mulch), in three 30 cm3 soil pits/field, in February–April 2005. Organic matter and nutrients were measured in horizontal soil cores, collected from the walls of the soil pits (0–15 cm length). All fields were tilled in 2004, after the tomatoes were harvested. All fields were fertilized and irrigated.

 

13 

A replicated, randomized, controlled study in 1990–2006 in two rainfed barley fields in Spain (same study as (33,38)) found that tillage had inconsistent effects on soil organisms. Soil organisms: More microbial biomass (measured as carbon) was found in soils with no tillage, compared to conventional tillage, in three of six comparisons (0–5 cm depth in Lleida and Zaragoza, and 5–10 cm depth in Lleida: 130–370 vs 100–230 mg C/kg dry soil), but less microbial biomass was found in one of six comparisons (10–25 cm depth, in Zaragoza: 70 vs 110). Methods: No tillage or conventional tillage was used on nine plots each in Lleida province (50 x 6 m plots, established in 1996) and six plots each in Zaragoza province (33.5 x 10 m plots, established in 1990). A mouldboard plough (25–40 cm depth) and a cultivator (10–15 cm depth, 1–2 passes) were used for conventional tillage. A seed drill and herbicide were used for no tillage. Soil samples were collected in March 2006 (0–25 cm depth).

 

14 

A replicated, randomized, controlled study in 2005–2008 on two rainfed wheat-sunflower-pea fields near Seville, Spain (same study as (15)), found similar amounts of microbial biomass in soils with no tillage or conventional tillage. Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with no tillage or conventional tillage (291–791 vs 127–472 mg C/kg soil). Methods: No tillage or conventional tillage was used on three plots each (200 m2 each). A mouldboard plough (25–30 cm depth), a cultivator (15–20 cm, 2–3 passes), and a disk harrow (15 cm) were used on plots with conventional tillage. Herbicides and a seed drill were used on plots with no tillage. Wheat, sunflowers, and peas were grown in rotation. Wheat was fertilized, but sunflowers and peas were not. Soil samples were collected in March and July 2008 (three samples/plot, 0–20 cm depth).

 

15 

A replicated, randomized, controlled study in 1982–2008 on a rainfed wheat-sunflower-legume field near Seville, Spain (same study as (14)), found similar amounts of microbial biomass in soils with no tillage or conventional tillage. Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with no tillage or conventional tillage (272–766 vs 314–378 mg C/kg soil). Methods: No tillage or conventional tillage was used on three plots each (15 x 18 m). A mouldboard plough and a cultivator (depths not reported) were used for conventional tillage, and crop residues were burned. A seed drill and herbicide were used for no tillage, and crop residues were retained. Herbicide was used on all plots. Wheat, sunflowers, and legumes were grown in rotation. Wheat was fertilized, but sunflowers and legumes were not. Soil samples were collected in March 2008 (three samples/plot, 400 g/soil core, 0–20 cm depth).

 

16 

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 soils with no tillage, compared to conventional tillage. Soil organisms: Similar numbers of mites and nematodes were found in soils with no tillage or conventional tillage (822 vs 797 individuals/100 g fresh soil). However, the composition of nematode and mite communities differed between soils with no tillage or conventional tillage (reported as distance in multivariate space). Methods: No tillage or conventional tillage was used on three plots each (conventional tillage: 0.4 ha plots; no tillage: 3 m2 microplots). Plots with conventional tillage were tilled about five times/year (depth not reported). Plots with no tillage were hand weeded. 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).

 

17 

A replicated, randomized, controlled study in 1996–2008 in a rainfed barley field in the Ebro river valley, Spain (same study as (4,23,24,26)), found more greenhouse gas in soils with no tillage, compared to conventional tillage. Greenhouse gases: More carbon dioxide was found in soils with no tillage, compared to conventional tillage (amounts of carbon dioxide not reported). Methods: No tillage or conventional tillage was used on nine plots each (50 x 6 m). A mouldboard plough or a disk plough was used for conventional tillage (25–30 cm depth, 100% incorporation of crop residues). Two-thirds of the plots were fertilized (60 or 120 kg N/ha). Greenhouse gas was sampled in 2005–2008 (two samples/plot, open chamber, 21 cm diameter, 900 mL airflow/minute, several samples within two days before and after tillage).

 

18 

A replicated, randomized, controlled study in 2003–2005 in an occasionally irrigated oat field in Portugal found less organic matter and phosphorus, lower pH, and fewer fungal colonies in plots with no tillage, compared to tillage. Organic matter: Less organic carbon was found in soils with no tillage, compared to tillage, in three of four comparisons (5.6–6.2 vs 6.0–7.7 g organic C/kg soil). Nutrients: Similar amounts of nitrogen were found in plots with or without tillage (30–45 mg mineral N/kg soil). Less phosphorus was found in soils with no tillage, compared to tillage, in three of four comparisons (47–70 vs 75–81 mg extractable P/kg soil). Lower pH levels were found in soils with no tillage, compared to tillage, in two of four comparisons (pH 5.5 vs 5.7–5.8). Soil organisms: More fungal colonies were found in plots with no tillage, compared to tillage (2004–2005: 3.6 vs 4.5 colonies/mg soil). Methods: Tillage or no tillage was used on four plots each (400 m2 plots). A disk plough was used for tillage (two passes, 15 cm depth). The plots were intercropped with oats and Lupinus albus lupins in 2003–2004 (residues were retained, and incorporated into the soil in the plots with tillage) and oats were grown in monoculture in 2004–2005. The plots were fertilized in 2003–2004 (60 kg P/ha; 100 kg N/ha), but not in 2004–2005. Soils samples were collected in October, November, January, March, May, and July each year (15 cm depth, 15 samples/plot).

 

19 

A replicated, randomized, controlled study in 1994–2007 in a rainfed wheat field near Madrid, Spain (same study as (6,37,39)), found more organic matter and higher stability in soils with no tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in two of four comparisons (0–7.5 cm depth: 45% more organic carbon). Soil erosion and aggregation: Higher stability was found in soils with no tillage, compared to conventional tillage, in one of four comparisons (0–7.5 cm depth, October 2007: 63% vs 38% of aggregates were water-stable). Methods: No 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. Herbicide and direct seeding were used for no 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.

 

20 

A replicated, randomized, controlled before-and-after study in 1993–2008 in a rainfed wheat-maize-wheat-sunflower field in central Italy found more organic matter and nitrogen in soils with no tillage, compared to conventional tillage. Organic matter: After 15 years, more carbon was found in soils with no tillage, compared to conventional tillage, at one of two depths (0–10 cm depth, in 2008: 16 vs 11 g C/kg soil), and carbon increased over time (0–30 cm depth, from 1993 to 2008: 9% increase vs 1% decrease in C/ha). Nutrients: More nitrogen was found in soils with no tillage, compared to conventional tillage, at one of two depths (0–10 cm depth, in 2008: 1.7 vs 1.2 g total N/kg soil), and nitrogen increased over time (0–30 cm depth, from 1993 to 2008: 0.6% increase vs 0.5% decrease in N/ha). Methods: No tillage or conventional tillage was used on 64 plots each (21 x 11 m sub-sub-plots). A mouldboard plough was used for conventional tillage (30–35 cm depth), and crop residues were incorporated into the soil. Pre-emergence herbicide was used for no tillage, and crop residues were mulched onto the surface. Post-emergence herbicide and fertilizer were used on all plots. Some plots had winter cover crops. Soil cores were collected in 1993, 1998, and 2008 for nutrients and organic matter (0–30 cm depth; two samples/plot in September).

 

21 

A replicated, randomized, controlled study in 1986–2008 in a rainfed wheat field in southern Spain (same study as (27)) found more organic matter and nitrogen in soils with no tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in two of five comparisons (772–815 vs 684–699 g/m2). Nutrients: More nitrogen was found in soils with no tillage, compared to conventional tillage, in 10 of 20 comparisons (50–180 vs 30–150 g total N/m2). Methods: No tillage or conventional tillage was used on three plots each (five subplots/plot, 10 x 5 m subplots, with different wheat rotations). Mouldboard ploughing, disk harrowing, and/or vibrating tine cultivation was used for conventional tillage (depth not reported). Pre-emergence herbicide was used for no tillage. The wheat phase was fertilized with nitrogen in some sub-subplots (0–150 kg N/ha/year) and phosphorus in all plots (65 kg P/ha/year). Crop residues were retained. Soil samples were collected in October 2008 (0–50 cm depth), before tilling the soil and sowing wheat.

 

22 

A replicated, randomized, controlled study in 2008–2010 in a rainfed wheat-legume field in southwest Spain (same study as (28)) found more microbial biomass in soils with no tillage, compared to conventional tillage, in two of 18 comparisons. Soil organisms: More microbial biomass (measured as carbon and nitrogen) was found in soils with no tillage, compared to conventional tillage, in two of 18 comparisons (0–5 cm depth, in January 2010: 445 vs 263 mg C/kg soil; 31 vs 17 mg N/kg soil). Methods: No tillage or conventional 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 seed drill were used for no tillage. 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.

 

23 

A replicated, randomized, controlled study in 1996–2009 in a rainfed barley field in the Ebro river valley, Spain (same study as (4,17,24,26)), found less nitrate in soils with no tillage, compared to conventional tillage, in one of two comparisons. Nutrients: Less nitrate was found in soils with no tillage, compared to conventional tillage (270 vs 852 kg N–NO3/ha), but no differences in ammonium were found (amounts of ammonium not reported). Methods: No 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), in October or November. A seed drill and herbicide were used for no tillage. 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).

 

24 

A replicated, randomized, controlled study in 1996–2009 in a rainfed barley field in the Ebro river valley, Spain (same study as (4,17,23,26)), found that tillage had inconsistent effects on greenhouse-gas emissions from soils. Greenhouse gases: Higher carbon dioxide emissions were found in soils with no tillage, compared to conventional tillage, in three of four comparisons, but lower emissions were found in one of four comparisons (amounts of carbon dioxide not clearly reported). Methods: No 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 seed drill and herbicide were used for no tillage. 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).

 

25 

A meta-analysis in 2013 of studies from multiple Mediterranean countries found a higher percentage of organic matter in soils with no tillage, compared to conventional tillage. Organic matter: A higher percentage of organic carbon was found in soils with no tillage, compared to conventional tillage (in herbaceous crops: 18% higher). Methods: No tillage included herbicide use. The Web of Knowledge database was searched, using the keywords, “Mediterranean”, “soil”, and “conventional”, and 33 data sets from 21 studies of no tillage were found and meta-analysed. The most recent studies included in this meta-analysis were published in 2011.

 

26 

A replicated, randomized, controlled study in 1996–2008 in a rainfed barley field in the Ebro river Valley, Spain (same study as (4,17,23,24,26)), found more organic matter and more soil organisms in soils with no tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage (9.25 vs 7.39 g C/kg dry soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with no tillage, compared to conventional tillage (295 vs 231 mg C/kg dry soil). Methods: There were nine plots (50 x 6 m) for each of two tillage treatments (no tillage: pre-emergence herbicide; conventional tillage: mouldboard plough, 25–30 cm depth). Plots were tilled in October or November. Soils samples were collected in October 2008 (before tillage, three soil cores/plot, 4 cm diameter, 0–50 cm depth).

 

27 

A replicated, randomized, controlled study in 1986–2010 in a rainfed wheat field in southern Spain (same study as (21)) found less nitrate in soils with no tillage, compared to conventional tillage. Nutrients: Less nitrate was found in plots with no tillage, compared to conventional tillage (104 vs 112 kg NO3-N/ha). Methods: No tillage or conventional tillage was used on three plots each (10 x 5 m plots). A mouldboard plough, a disk harrow, and/or a vibrating tine cultivator were used for conventional tillage (depth not reported). A seed drill and pre-emergence herbicide was used for no tillage. Post-emergence herbicide was used on some subplots (which had different wheat rotations), and some subplots were fertilized (0–150 kg N/ha/year). Soil samples were collected before sowing (Eijkelkamp auger, three samples/plot, 0–90 cm depth), in 1993–2010.

 

28 

A replicated, randomized, controlled study in 2008–2010 in a rainfed wheat-vetch field in southwest Spain (same study as (22)) found more organic matter, soil organisms, and aggregation in soils with no tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in three of five comparisons (soil aggregates <1 mm in diameter: 18–22 vs 13–15 g C/kg soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with no tillage, compared to conventional tillage, in three of five comparisons (in smaller soil aggregates with diameters of 1–2, 0.25–0.5, or <0.5 mm: 504–549 vs 341–346 mg C/kg soil). Soil erosion and aggregation: More large aggregates were found in soils with no tillage, compared to conventional tillage (2–5 mm macroaggregates: 31% vs 24% of soil weight), and fewer smaller aggregates were found, in two of four comparisons (0.5–1 mm aggregates: 21% vs 26% of soil weight). Methods: No tillage or conventional tillage was used on three plots each (300 m2 plots), in 2008–2009. In 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 seed drill and herbicide were used for no tillage, and crop residues were retained. Soil samples were collected in October 2010 (0–10 cm depth, five samples/plot). It was not clear whether these results were a direct effect of tillage or residue removal.

 

29 

A replicated, randomized, controlled study in 1990–2010 in a winter cereal field in the Ebro river valley, Spain, found more organic matter and greater stability in soils with no tillage, compared to conventional tillage. The most organic matter and the greatest stability were found in soils with 11–20 years of no tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in three of sixteen comparisons (0–5 cm depth: 17–24 vs 12 g C/kg soil). Soil erosion and aggregation: More water-stable macroaggregates (0.25–8 mm diameter) and fewer water-stable microaggregates (0.053–0.25 mm diameter) were found in soils with no tillage, compared to conventional tillage (macroaggregates, in eight of 32 comparisons, 0–10 cm depth: 0.12–0.32 vs 0.02–0.04 g aggregate/g dry soil; microaggregates, in six of 16 comparisons, 0–10 cm depth: 0.25–0.41 vs 0.44–0.50). More large, dry macroaggregates (2–8 mm diameter) were found in soils with no tillage, compared to conventional tillage, in three of 16 comparisons (10–20 cm depth: 0.52–0.56 vs 0.38–0.40 g aggregate/g dry soil). Fewer small, dry macroaggregates (0.25–2 mm) were found in soils with no tillage, compared to conventional tillage, in four of 16 comparisons (10 –30 cm depth: 0.27 – 0.32 vs 0.36–0.41 g aggregate/g dry soil). Implementation options: More organic carbon was found in soils with 11–20 years of no tillage, compared to 1–4 years, at one of four depths (0–5 cm depth: 24 vs 11–17 g C/kg soil). More large, water-stable macroaggregates (2–8 mm diameter) were found in soils with 11–20 years of no tillage, compared to 1–4 years, at one of four depths (0–5 cm depth: 0.30–0.32 vs 0.02–0.12 g aggregate/g dry soil). More small, water-stable macroaggregates were found in soils with 4–20 years of no tillage, compared to one year, at one of four depths (0–5 cm depth: 0.13–0.16 vs 0.04 g aggregate/g dry soil). More large, dry macroaggregates (2–8 mm diameter) and fewer small macroaggregates (0.25–2 mm diameter) were found in soils with 4–20 years of no tillage, compared to 0–1 year, at one of four depths (10–20 cm depth: large: 0.52–0.56 vs 0.38–0.40 g aggregate/g dry soil; small: 0.30–0.32 vs 0.39–0.41). Methods: No tillage was used on four plots for 1–20 years (beginning in 1990, 1999, 2006, and 2009). Conventional tillage was used on the same four plots, before no tillage began, and also on one control plot for 20 years (1990–2010). Plots were 1,500 m2. Soil samples were collected in July 2010 with a flat spade (0–30 cm depth).

 

30 

A replicated, randomized, controlled study in 2009–2012 in two irrigated vegetable fields in central Italy found more nitrogen in soils with no tillage, compared to conventional tillage. Nutrients: More nitrate was found in soils with no tillage, compared to conventional tillage, in three of 12 comparisons (in plots with hairy vetch as a winter cover crop: 10–16 vs 6–12 mg NO3-N/kg dry soil), and more ammonium was found in one of 12 comparisons (in plots with hairy vetch as a winter cover crop: 9 vs 4 mg NH4-N/kg dry soil). Methods: No 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). The cover crop residues were gathered into strips of mulch (50 cm wide, along crop rows) in plots with no tillage. 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). It was not clear whether these results were a direct effect of tillage or mulch.

 

31 

A replicated, controlled study in 1991–2010 in a rainfed durum wheat field in Sicily, Italy, found more microbial biomass and carbon dioxide in soils with no tillage, compared to conventional tillage. Organic matter: Similar amounts of organic carbon were found in soils with no tillage or conventional tillage (20–21 vs 19–21 g C/kg soil). Nutrients: Similar amounts of nitrogen were found in soils with no tillage or conventional tillage (1.1–1.3 vs 1–1.4 g total N/kg soil). Soil microbial biomass: More microbial biomass (measured as carbon) was found in soils with no tillage, compared to conventional tillage (330–509 vs 208–293 mg C/kg soil). Greenhouse gases: More carbon dioxide was found in soils with no tillage, compared to conventional tillage (19–22 vs 14–17 mg C/kg soil/day). Methods: No tillage or conventional tillage was used on four plots each (18.5 × 20 m plots), with either wheat-faba bean or wheat-wheat rotations. Fertilizer and herbicide were used on all plots. Ploughing (30 cm depth) and harrowing (1–2 passes, 10–15 cm depth) were used for conventional tillage. Soil samples were collected after the harvest, in June 2009 (three samples/plot, 0–15 cm depth). Carbon dioxide was measured on 36 days in April 2008–April 2009 (closed chambers, 12 measurements/plot, 9–11 am).

 

32 

A replicated, randomized, controlled study in 2008–2013 in a rainfed wheat-sunflower-pea field near Seville, Spain, found more organic matter and more nitrogen in soils with no tillage, compared to conventional tillage, in some comparisons. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, at one of three depths (0–5 cm: 11 vs 9 g C/kg soil). Nutrients: More nitrogen was found in soils with no tillage, compared to conventional tillage, at one of three depths (0–5 cm: 1.06 vs 0.91 g N/kg soil), but no differences were found in other nutrients (0–25 cm: 14.5–25.6 vs 22.2–26.1 g phosphorus/kg soil; 290–508 vs 367–428 g potassium/kg soil). Methods: No 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 disk harrow (12 cm depth) were used for conventional tillage. A seed drill and herbicide were used for no 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).

 

33 

A replicated, randomized, controlled study in 2004–2011 in rainfed wheat-sunflower-pea fields near Seville, Spain (same study as (13,38)), found more organic matter in soils with no tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in one of three comparisons, in medium-term plots (2004–2011, 0–5 cm depth: 11 vs 9 g C/kg soil), but no differences were found in short-term plots (2008–2011: 7–10 vs 7–9 g C/kg soil). Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with no tillage or conventional tillage (581–746 vs 604–858 mg C/kg soil). Methods: No tillage or conventional tillage was used on three plots each (20 x 9 m plots), in each of two experiments: a short-term experiment (2008–2011), and a medium-term experiment (2004–2011). A mouldboard plough (25–30 cm depth), a cultivator (15–20 cm depth, two passes), and a disk harrow (15 cm depth) were used for conventional tillage. A seed drill was used for no tillage, and crop residues were retained (>60% cover). Soil samples were collected in January 2011 (0–25 cm depth, five samples/plot).

 

34 

A replicated, randomized, controlled study in 2010–2012 in a rainfed barley field in northeast Spain found less nitrate and greater stability in soils with no tillage, compared to conventional tillage. More greenhouse gas was absorbed by soils with no tillage. Organic matter: Similar amounts of organic matter were found in soils with no tillage or conventional tillage (6 g C/kg dry macroaggregates). Nutrients: Less nitrate was found in soils with no tillage, compared to conventional tillage (93 vs 110 mg NO3-N/kg dry macroaggregates), but there were similar amounts of ammonium (13 vs 20 mg NH4-N/kg dry macroaggregates). Soil organisms: Similar amounts of microbial biomass (measured as carbon and nitrogen) were found in soils with no tillage or conventional tillage (954 vs 866 mg C/kg soil; 237 vs 228 mg N/kg soil). Soil erosion and aggregation: More water-stable aggregates were found in soils with no tillage, compared to conventional tillage, in one of three comparisons (0.2 vs 0.1 g). Greenhouse gases: More methane was absorbed by soils with no tillage, compared to conventional tillage (–0.2 vs 0.07 µg/kg macroaggregates/h). Similar carbon-dioxide emissions (1,406 vs 1,334 µg/kg macroaggregates/h) and nitrous-oxide emissions (0.92 vs 0.75 µg/kg macroaggregates/h) were found in soils with no tillage or conventional tillage. Methods: No tillage or conventional tillage was used on three plots each (plot size not clearly reported). Some plots were fertilized (0–150 kg N/ha). A disk plough (20 cm depth) was used for conventional tillage, in October. Pre-emergence herbicide was used for no tillage. Soil samples (0–5 cm depth) were collected in March 2012 (greenhouse gases were measured in soil samples).

 

35 

A replicated, randomized, controlled study in 1996–2013 in two rainfed barley fields in northeast Spain (same study as (36)) found that tillage had inconsistent effects on greenhouse gases. Organic matter: Similar amounts of organic carbon were found in soils with no tillage or conventional tillage (short-term field: 96 vs 99 Mg/ha). Greenhouse gases: More methane was absorbed by soils with no tillage, compared to conventional tillage, in one of two comparisons (long-term experiment: –2.4 vs –1.1 kg C/ha), but less was absorbed in one of two comparisons (short-term experiment: –1.1 vs –2.7 kg C/ha). More carbon dioxide was emitted from soils with no tillage, compared to conventional tillage (3,985–4,480 vs 2,611–3,313 kg C/ha). Methods: No tillage or conventional tillage was used on three plots each, in each of two fields (2010–2013 in the short-term field, and 1996–2013 in the long-term field; plots size not clearly reported). A mouldboard plough (25 cm depth) and a cultivator (15 cm depth) were used for conventional tillage in the long-term field, and a chisel plough was used in the short-term field (depth not reported), in September–October. For no tillage, the residues were chopped and spread, and pre-emergence herbicide was used. Some plots were fertilized (0–150 kg N/ha). Soil samples were collected in June 2013 in the short-term field (0–75 cm depth). Greenhouse-gas samples were collected every 2–3 weeks in 2011–2013, in the long-term field, and 2011–2012 in the short-term field (closed chambers, 15 mL samples, 0, 30, and 60 minutes after closing).

 

36 

A replicated, randomized, controlled study in 1996–2013 in two rainfed barley fields in northeast Spain (same study as (35)) found less nitrate in soils with no tillage, compared to conventional tillage. Tillage had inconsistent effects on greenhouse gases. Nutrients: Less nitrate was found in soils with no tillage, compared to conventional tillage, in one of two comparisons (long-term experiment: 36 vs 56 kg/ha), but similar amounts of ammonium were found (10–11 vs 9–11 kg/ha). Greenhouse gases: More nitrous oxide was emitted from soils with no tillage, compared to conventional tillage, in one of two comparisons (short-term experiment: 0.20 vs 0.14 mg N2O-N/m2/day). Less greenhouse gas was emitted, per kilo of barley, in plots with no tillage, compared to conventional tillage (0.05 vs 0.10 kg CO2 equivalent/kg barley). Methods: No tillage or conventional tillage was used on three plots each, in each of two fields (2010–2013 in the short-term field, and 1996–2013 in the long-term field; plots size not clearly reported). A mouldboard plough (25 cm depth) and a cultivator (15 cm depth) were used for conventional tillage. For no tillage, the residues were chopped and spread, and pre-emergence herbicide was used. Some plots were fertilized (0–150 kg N/ha). Soil samples (0–5 cm depth) and greenhouse-gas samples (closed chambers, 15 mL samples, 0, 30, and 60 minutes after closing), were collected every 2–3 weeks in 2011–2013.

 

37 

A replicated, randomized, controlled study in 1994–2013 in a rainfed wheat field near Madrid, Spain (same study as (6,19,39)), found that tillage had inconsistent effects on organic matter, soil organisms, and greenhouse gases. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in seven of 12 comparisons (9–13 vs 6 g organic C/kg soil), but less was found in one of 12 comparisons (6 vs 5 g). Soil organisms: More microbial biomass (measured as carbon) was found in soils with no tillage, compared to conventional tillage, in six of 12 comparisons (390–750 vs 200–300 mg C/kg soil), but less was found in one of 12 comparisons (200 vs 300 mg). Greenhouse gases: More carbon dioxide was found in soils with no tillage, compared to conventional tillage, in six of 12 comparisons (40–60 vs 20–30 mg CO2–C/kg soil/d), but less was found in one of 12 comparisons (18 vs 22 mg). Methods: No tillage or conventional tillage was used on four plots each (in which a total of 24 subplots, 10 x 25 m each, were used for this study). A mouldboard plough was used for conventional tillage (25 cm depth). Pre-emergence herbicide was used for no tillage. The subplots had wheat monocultures or fallow-wheat-vetch-barley rotations. The cereals were fertilized (NPK, 200 kg/ha, twice/year, in October and March). The crop residues were shredded and retained. Soil samples were collected in October 2010, April 2011, November 2011, May 2012, October 2012 and April 2013 (50 mm diameter, 0–15 cm depth).

 

38 

A replicated, randomized, controlled study in 2004–2010 in rainfed wheat-sunflower-pea fields near Seville, Spain (same study as (13,33)), found more organic matter and more soil aggregation in soils with no tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage, in four of ten comparisons (6–10 vs 5–6 g C/kg soil). Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with no tillage or conventional tillage (20–75 vs 27–87 g microbial C/kg organic C). Soil erosion and aggregation: More large aggregates were found in soils with no tillage, compared to conventional tillage, in autumn, in one of two comparisons (1–2 mm aggregates: 20 vs 17% of soil weight), and fewer small aggregates were found in autumn, in one of three comparisons (<0.25 mm aggregates: 15 vs 21% of soil weight). However, no differences in aggregate distributions were found in spring (data reported for five aggregate sizes). Methods: No tillage or conventional tillage was used on three plots each (200 m2 plots). A mouldboard plough (25–30 cm depth), a cultivator (15–20 cm depth, two passes), and a disk harrow (15 cm depth) were used for conventional tillage. A seed drill and pre-emergence herbicide were used for no 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).

 

39 

A replicated, randomized, controlled study in 1994–2011 in a rainfed cereal-legume field near Madrid, Spain (same study as (6,19,37)), found more organic matter and more soil organisms in soils with no tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to conventional tillage (30.2 vs 11.2 mg dissolved organic C/kg soil). Nutrients: Similar amounts of nitrate and ammonium were found in soils with no tillage, compared to conventional tillage (1–18 mg NO3-N/ha; 0.2–3.5 mg NH4-N/kg). Soil organisms: More microbial biomass (measured as carbon) was found in soils with no tillage, compared to conventional tillage (304 vs 94 mg C/kg soil), but there were similar amounts of bacteria (denitrifying bacteria: 106 gene copies). Greenhouse gases: Similar nitrous-oxide and methane emissions were found in soils with no tillage or conventional tillage (0.05 kg N2O-N/ha; –137 vs –231 g CH4-C/ha). Methods: No tillage or conventional tillage was used on three plots each (10 x 25 m). A mouldboard plough and a cultivator were used for conventional tillage (20 cm depth) in October. A seed drill and herbicide were used for no tillage. Soil and greenhouse-gas samples were collected 1–12 times/month, in November 2010–October 2011 (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 closing).

 

40 

A replicated, randomized, controlled study in 2009–2011 in an irrigated eggplant field in central Italy found more nitrogen in soils with no tillage, compared to conventional tillage. Nutrients: More nitrogen was found in soils with no tillage, compared to conventional tillage, in one of four comparisons (37 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. No tillage or conventional tillage was used on 12 plots each (6 x 4 m plots). A mouldboard plough (30 cm depth) and a disk (two passes) were used for conventional tillage (which incorporated the cover crop residues into the soil). Cover crop residues were mulched and herbicide was used for no tillage. 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. It was not clear whether these results were a direct effect of cover crops or tillage.

 

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.