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Action: Soil: Use no tillage instead of reduced tillage Mediterranean Farmland

Key messages

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Organic matter (6 studies): Three replicated, randomized, controlled studies from Spain found more organic matter in soils with no tillage, compared to reduced tillage, in some or all comparisons. Three replicated, randomized, controlled studies from Spain found similar amounts of organic matter in soils with no tillage, compared to reduced tillage. No studies found less organic matter in soils with no tillage, compared to reduced tillage.

Nutrients (7 studies)

  • Nitrogen (6 studies): Three replicated, randomized, controlled studies from Italy and Spain found more nitrogen in soils with no tillage, compared to reduced tillage, in some comparisons. Two of these studies also found less nitrogen in some comparisons. One replicated, randomized, controlled study from Spain found less nitrogen in soils with no tillage, compared to reduced tillage, in some comparisons. Two replicated, randomized, controlled studies from Spain found similar amounts of nitrogen in soils with no tillage, compared to reduced tillage.
  • Phosphorus (2 studies): One replicated, randomized, controlled study from Spain found more phosphorus in soils with no tillage, compared to reduced tillage. One replicated, randomized, controlled study from Spain found similar amounts of phosphorus in soils with no tillage or reduced tillage. No studies found less phosphorus in soils with no tillage, compared to reduced tillage.
  • Potassium (1 study): One replicated, randomized, controlled study from Spain found similar amounts of potassium in soils with no tillage or reduced tillage. No studies found less potassium in soils with no tillage, compared to reduced tillage.

Soil organisms (8 studies)

  • Microbial biomass (6 studies): Five replicated, randomized, controlled studies from Spain found similar amounts of microbial biomass in soils with no tillage or reduced tillage. One replicated, randomized, controlled study from Spain found more microbial biomass in soils with no tillage, compared to reduced tillage, in some comparisons, but found less in some comparisons.
  • Bacteria (1 study): One replicated, randomized, controlled study from Spain found fewer denitrifying bacteria in soils with no tillage, compared to reduced tillage.
  • Other soil organisms (2 studies): One replicated, controlled study from the USA found similar numbers of mites and nematodes, but different communities of mites and nematodes, in soils with no tillage, compared to reduced tillage. One replicated, randomized, controlled study from Spain found more mites in soils with no tillage, compared to reduced tillage.

Soil erosion and aggregation (4 studies): One replicated, randomized, controlled study from Spain found more large aggregates in soils with no tillage, compared to reduced tillage, in some comparisons. One replicated, randomized, controlled study from Italy found similar aggregates in soils with no tillage or reduced tillage. One replicated, randomized, controlled study from Spain found higher water-stability in soils with no tillage, compared to reduced tillage, in some comparisons, but found lower water-stability in some comparisons. One replicated, randomized, controlled study from Spain found similar water-stability in soils with no tillage or reduced tillage.

Greenhouse gases (4 studies): Two replicated, randomized, controlled studies from Spain found less greenhouse gas in soils with no tillage, compared to reduced tillage, in some comparisons. Two replicated, randomized, controlled studies from Australia and Spain found similar amounts of greenhouse gas in soils with no tillage or reduced tillage.

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 that tillage had inconsistent effects on soil stability. Soil erosion and aggregation: Lower soil stability was found in plots with no tillage, compared to reduced tillage, in one of four comparisons (1–2 mm pre-wetted soil aggregates: 76.3 vs 77.8% water stable), but higher stability was found in two of four comparisons (1–2 mm air-dried soil aggregates: 11.0 vs 3.5% water stable; 4.38 mm air-dried soil aggregates: 12 vs 2%). Methods: No tillage or reduced tillage was used on four plots each. Each plot had two subplots (20 x 30 m, with or without crop rotation). A chisel plough (20 cm depth, in autumn) and a tine cultivator (10–15 cm depth, two passes, in spring) were used for reduced 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).

 

2 

A replicated, randomized, controlled study in 1996–1999 in three rainfed barley fields in the Ebro river valley, Spain (same study as (8,11,12)), found that tillage had inconsistent effects on nitrogen in soils. Nutrients: Less nitrogen was found in soils with no tillage, compared to reduced tillage, in one of nine comparisons (128 vs 176 kg/ha), but more nitrogen was found in one of nine comparisons (165 vs 125 kg/ha). Methods: No tillage or reduced tillage was used on 27 plots each (50 x 6 m plots). A cultivator (10–15 cm depth, 1–2 passes) was used for reduced tillage, in 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 (month of harvest not reported). 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).

 

3 

A replicated, randomized, controlled study in 2003–2005 on rainfed farms in the Ebro river valley, Spain, found less greenhouse gas in soils with no tillage, compared to reduced tillage. Greenhouse gases: Less carbon dioxide was found in soils with no tillage, compared to reduced tillage, in six of 20 comparisons, in the two days after tillage (0.1–0.6 vs 0.1–6.4 g CO2/m2/hour). Methods: No tillage or reduced tillage was used on seven plots each (33–50 x 7–10 m plots), on a total of two farms, with multiple crops. A cultivator (15 cm depth) or chisel plough (25–30 cm depth) was used for reduced tillage. Herbicide was used for 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.

 

4 

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 reduced tillage. Nutrients: More phosphorus was found in soils with no tillage, compared to reduced tillage (1,528 vs 961 mg phosphorus/kg soil). Methods: No tillage or reduced tillage was used on four plots each (180 x 15 m plots), in 1983–2003. A cultivator (15 cm depth, before seeds were sown) was used for reduced 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).

 

5 

A replicated, randomized, controlled study in 2003 in rainfed farmland in the Ebro river valley, Spain, found greater soil aggregation in plots with no tillage, compared to reduced tillage. Soil erosion and aggregation: More large aggregates were found in soils with no tillage, compared to reduced tillage, in four of six comparisons (0–10 cm depth, water-stable aggregates >2000 µm: 0.08–0.15 vs 0.02–0.03 g aggregate/g soil). Methods: No tillage or reduced tillage was used on three plots each (10 x 33 m). A chisel plough was used for reduced tillage (25–30 cm depth). Herbicide was used for no tillage. Soil samples were collected with a flat spade (0–20 cm depth) in July 2003.

 

6 

A replicated, randomized, controlled study in 1990–2006 on two rainfed barley fields in Spain (same study as (18)) 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 reduced tillage, in one of six comparisons (0–5 cm depth, in Zaragoza: 130 vs 60 mg C/kg dry soil), but less was found in one of six comparisons (0–5 cm depth, in Lleida: 360 vs 480). Methods: No tillage or reduced 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 chisel plough (in Zaragoza but not in Lleida, 25–30 cm depth) and a cultivator (10–15 cm depth, 1–2 passes) were used for reduced tillage. A seed drill and herbicide were used for no tillage. Soil samples were collected in March 2006 (0–25 cm depth).

 

7 

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 reduced tillage. Soil organisms: Similar numbers of mites and nematodes were found in soils with no tillage or reduced tillage (822 vs 888 individuals/100 g fresh soil). However, the composition of nematode and mite communities differed between soils with no tillage or reduced tillage (reported as distance in multivariate space). Methods: No tillage or reduced tillage was used on three plots each (reduced: 0.4 ha plots; no tillage: 3 m2 microplots). Plots with reduced tillage were tilled about two 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).

 

8 

A replicated, randomized, controlled study in 1996–2008 in a rainfed barley field in the Ebro river valley, Spain (same study as (2,11,12)), found similar amounts of greenhouse gas in soils with no tillage or reduced tillage. Greenhouse gases: Similar amounts of carbon dioxide were found in soils with no tillage or reduced tillage (amounts of carbon dioxide not reported). Methods: No tillage or reduced tillage was used on nine plots each (50 x 6 m). 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).

 

9 

A replicated, randomized, controlled study in 1994–2007 in a rainfed wheat field near Madrid, Spain (same study as (19)), found no differences in organic matter or soil stability in soils with no tillage or reduced tillage. Organic matter: Similar amounts of organic carbon were found in soils with no tillage or reduced tillage (7–11 Mg C/ha). Soil erosion and aggregation: No differences in soil stability were found in plots with no tillage, compared to reduced tillage (25–65% of aggregates were water-stable). Methods: No tillage or reduced tillage was used on eight plots each (10 x 25 m plots), in autumn 1994–2007. A chisel plough (15 cm depth) and a cultivator were used for reduced 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.

 

10 

A replicated, randomized, controlled study in 2008–2010 in a rainfed wheat-legume field in southwest Spain (same study as (13)) found similar numbers of soil organisms in soils with no tillage or reduced tillage. Soil organisms: Similar amounts of microbial biomass (measured as carbon or nitrogen) were found in soils with no tillage or reduced tillage (199–1,612 vs 120–2,363 mg C/kg soil; 9–40 vs 9–69 mg N/kg soil). Methods: No tillage or reduced tillage was used on three plots each (30 x 10 m plots). A chisel plough was used for reduced tillage (10–15 cm depth). A seed drill was 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.

 

11 

A replicated, randomized, controlled study in 1996–2009 in a rainfed barley field in the Ebro river valley, Spain (same study as (2,8,12)), found less nitrate in soils with no tillage, compared to reduced tillage. Nutrients: Less nitrate was found in soils with no tillage, compared to reduced tillage (270 vs 461 kg N–NO3/ha), but no differences in ammonium were found (amounts of ammonium not reported). Methods: No tillage or reduced tillage was used on nine plots each (50 x 6 m plots). A cultivator was used for reduced tillage (10–15 cm depth, 50% 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).

 

12 

A replicated, randomized, controlled study in 1996–2008 in a rainfed barley field in the Ebro river Valley, Spain (same study as (2,8,11)), found more organic matter, but no difference in soil organisms, in soils with no tillage, compared to reduced tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to reduced tillage (9.25 vs 8.65 g C/kg dry soil). Soil organisms: No difference in microbial biomass (measured as carbon) was found between soils with no tillage or reduced tillage (295 vs 263 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 and seed drill; reduced tillage: cultivator, 10–15 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).

 

13 

A replicated, randomized, controlled study in 2008–2010 in a rainfed wheat-vetch field in southwest Spain (same study as (10)) found similar amounts of organic matter, soil organisms, and aggregation in soils with no tillage or reduced tillage. Organic matter: Similar amounts of organic carbon were found in soils with no tillage or reduced tillage (14–22 vs 17–23 g C/kg soil). Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with no tillage or reduced tillage (452–549 vs 373–646 g C/kg soil). Soil erosion and aggregation: Similar amounts of soil aggregation were found in soils with no tillage or reduced tillage (data reported for five soil fractions). Methods: No 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. Herbicide was used for no tillage. A chisel plough (10–15 cm depth) and herbicide were used for reduced tillage. Soil samples were collected in October 2010 (0–10 cm depth, five samples/plot).

 

14 

A replicated, randomized, controlled study in 2002–2012 in a rainfed cereal field in Spain found more mites in soils with no tillage, compared to reduced tillage. Organic matter: Similar amounts of organic matter were found in plots with no tillage or reduced tillage (data not reported). Nutrients: Similar amounts of nitrogen were found in plots with no tillage or reduced tillage (data not reported). Soil organisms: More oribatid mites were found in plots with no tillage, compared to reduced tillage (5,162 vs 3,121 individuals/m2). Methods: Plots (11 x 12.5 m or 7 x 12.5 m) had reduced tillage (disc-harrowing, 15 cm depth) or no tillage (with herbicide). Straw was removed from all plots. Soil samples were collected in October 2011, February 2012, and May 2012 from plots without fertilizer and plots with 25 t/ha/year (three cores/plot, 0–5 cm depth). The other plots were sampled in May 2012.

 

15 

A replicated, randomized, controlled study in 2009–2012 in two irrigated vegetable fields in central Italy found that tillage had inconsistent effects on nutrients in soils. Nutrients: More nitrate was found in soils with no tillage, compared to reduced tillage, in one of 12 comparisons (in plots with hairy vetch as a winter cover crop: 10 vs 6 mg NO3-N/kg dry soil), but less nitrate was found in one of 12 comparisons (in plots with oats as the winter cover crop: 3 vs 6). More ammonium was found in soils with no tillage, compared to reduced tillage, in one of 12 comparisons (in plots with hairy vetch as a winter cover crop: 9 vs 5 mg NH4-N/kg dry soil), but less ammonium was found in one of 12 comparisons (in plots with oilseed rape as the winter cover crop: 4 vs 11). Methods: Reduced tillage or no 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 rotary hoe was used for reduced tillage (incorporating the cover crop residues to 10 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.

 

16 

A replicated, randomized, controlled study in 2008–2013 in a rainfed wheat-sunflower-pea field near Seville, Spain, found more organic matter (in one of three comparisons), but found similar amounts of nutrients, in soils with no tillage, compared to reduced tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to reduced tillage, at one of three depths (0–5 cm: 11 vs 9 g C/kg soil). Nutrients: Similar amounts of nitrogen, phosphorus, and potassium were found in soils with no tillage or reduced tillage (0.76–1.06 vs 0.92–0.99 g N/kg soil; 14.5–25.6 vs 17.8–25.7 g phosphorus/kg soil; 290–508 vs 307–419 g potassium/kg soil). Methods: No tillage or reduced tillage was used on three plots each (6 x 33.5 m plots). A chisel plough (25 cm depth), a disc harrow (5 cm depth), and herbicide were used for reduced 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).

 

17 

A replicated, randomized, controlled study in 2010–2011 in an irrigated wheat field in Western Australia found similar greenhouse-gas emissions in soils with no tillage or reduced tillage. Greenhouse gases: Similar nitrous oxide emissions were found in soils with no tillage or reduced tillage (0.04 g ha/hour). Methods: No tillage or reduced tillage was used on three plots each (1.4 x 40 m plots) in 2010, when the plots were fallow. A rotary hoe (12 cm depth) was used for reduced tillage. Herbicide was used for no tillage. Wheat was grown on all plots in 2011. Fertilizer (150 kg/ha) and herbicides were used on all plots in 2011. Nitrous oxide was sampled in closed chambers (two chambers/plot; one hour/sample; five sample dates/plot).

 

18 

A replicated, randomized, controlled study in 2008–2011 in a rainfed wheat-sunflower-pea field near Seville, Spain (same study as (6)), found similar amounts of organic matter and soil organisms in soils with no tillage or reduced tillage. Organic matter: Similar amounts of organic carbon were found in soils with no tillage or reduced tillage (7–10 vs 6–9 g C/kg soil). Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with no tillage or reduced tillage (581–746 vs 740–958 mg C/kg soil). Methods: No tillage or reduced tillage was used on three plots each (20 x 9 m plots). A chisel plough (15–20 cm depth, every other year) and a disc harrow (5–7 cm depth) were used for reduced tillage. A seed drill was used for no tillage. More than 60% of crop residues were retained in all plots. Soil samples were collected in January 2011 (0–25 cm depth, five samples/plot).

 

19 

A replicated, randomized, controlled study in 1994–2011 in a rainfed cereal-legume field near Madrid, Spain (same study as (9)), found more organic matter, but fewer soil organisms and lower greenhouse-gas emissions, in soils with no tillage, compared to reduced tillage. Organic matter: More organic carbon was found in soils with no tillage, compared to reduced tillage (29.7% more dissolved organic carbon). Nutrients: Similar amounts of nitrate and ammonium were found in soils with no tillage, compared to reduced tillage (1–18 mg NO3–N/ha; 0.2–3.5 mg NH4–N/kg). Soil organisms: Fewer bacteria were found in soils with no tillage, compared to reduced tillage (denitrifying bacteria: 106 vs 108 gene copies), but no difference in microbial biomass (measured as carbon) was found (304 vs 186 mg C/kg soil).  Greenhouse gases: Lower nitrous oxide emissions were found in soils with no tillage, compared to reduced tillage (0.05 vs 0.12 kg N2O–N/ha), but no difference in methane emissions was found (–137 vs –473 g CH4–C/ha). Methods: No tillage or reduced tillage was used on three plots each (10 x 25 m). A chisel plough and a cultivator were used for reduced tillage (15 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).

 

20 

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 reduced tillage. Nutrients: More nitrogen was found in soils with no tillage, compared to reduced tillage, in one of four comparisons (37 vs 30 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 reduced tillage was used on 12 plots each (6 x 4 m plots). A rotary hoe (10 cm depth) was used for reduced tillage (which incorporated some of 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.

 

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.