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Providing evidence to improve practice

Action: Soil: Add manure to the soil Mediterranean Farmland

Key messages

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Organic matter (8 studies): Five replicated, controlled studies (two randomized) from Italy, Tunisia, Turkey, and the USA found more organic matter in soils with added manure, compared to soils without it. Three replicated, randomized, controlled studies from Italy, Spain, and Greece found similar amounts of organic matter in plots with or without added manure.

Nutrients (5 studies)

  • Nitrogen (5 studies): Three replicated, controlled, studies (one randomized) from Italy and Tunisia found more nitrogen in soils with added manure, compared to soils without it, in some comparisons. Two replicated, randomized, controlled studies from Greece and Italy found similar amounts of nitrogen in soils with or without added manure.
  • Phosphorus (3 studies): One replicated, randomized, controlled study from Greece found more phosphorus in soils with added manure, compared to soils without it. One replicated, randomized, controlled study from Italy found similar amounts of phosphorus in soils with or without added manure. One replicated, controlled study from Italy found inconsistent differences in phosphorus between soils with or without added manure.
  • Potassium (2 studies): Two replicated, randomized, controlled studies from Italy and Greece found more potassium in soils with added manure, compared to soils without it.
  • pH (3 studies): One replicated, randomized, controlled study from Tunisia found lower pH levels in soils with added manure, compared to soils without it. One replicated, controlled study from Italy found higher pH levels in soils with added manure. One replicated, randomized, controlled study from Italy found similar pH level in soils with or without added manure.

Soil organisms (3 studies)

  • Microbial biomass (2 studies): Two replicated, randomized, controlled studies from Italy and Spain found similar amounts of microbial biomass in soils with or without added manure.
  • Nematodes (1 study): One replicated, randomized, controlled study from Greece found similar numbers of nematodes in soils with or without added manure.

Soil erosion and aggregation (4 studies): One replicated, randomized, controlled study from Spain found less erosion in plots with added manure, compared to plots without added manure. Three replicated, randomized, controlled studies from Spain and Turkey found higher soil stability in plots with added manure, compared to plots without added manure, in some or all comparisons. One replicated, controlled study from the USA found similar soil stability in plots with or without added manure.

Greenhouse gases (2 studies): One replicated, controlled study from the USA found higher carbon dioxide emissions in plots with added manure, compared to plots without added manure. One replicated, randomized, controlled study from Spain found higher nitrous oxide emissions in plots with added manure, compared to plots without added manure.

Implementation options (1 study): One study from Tunisia found no differences in organic matter or pH between soils with different amounts of added manure, but found less nitrate in soils with less added fertilizer.

Supporting evidence from individual studies

1 

A replicated, controlled study in 1997–1998 in irrigated fallow land in California, USA, found more organic matter and higher carbon dioxide emissions in plots with added manure, compared to plots without manure added. Organic matter: More organic matter was found in soils with added manure (16 vs 10 g/kg). Soil erosion and aggregation: Similar aggregate stability was found in soils with or without added manure (366 vs 300 g/kg). Greenhouse gases: Higher carbon dioxide emissions were found in plots with added manure (3 vs 1 carbon dioxide µg/g/day). Methods: Plots (2 x 2 m) had poultry manure (25 Mg/ha) or no added fertilizer (five plots each). Manure was added in April 1987, February 1988, and October 1988 and was immediately incorporated into the soil (15 cm depth). Plots were irrigated weekly (100 mm/day). Five soil samples (25–100 mm depth) were taken from each plot.

 

2 

A replicated, randomized, controlled study in 1995–1999 in arable farmland in southern Turkey found more organic matter and greater soil stability in soils with added manure, compared to soils without added manure. Organic matter: More organic matter was found in soils with added manure, compared to soils without added manure, in one of two comparisons (1.8% vs 1.6%). Soil erosion and aggregation: Larger soil particles were found in plots with added manure, compared to plots without added manure (0.38–0.43 vs 0.18–0.29 mm mean weight diameter). Methods: Cattle manure (25 t/ha) was added to three treatment plots (10 x 20 m), but not three control plots. Wheat, sweet peppers, and maize were grown in rotation. Soils were sampled in 1999, after harvesting the last wheat crop (0–30 cm depth). Wet sieving was used to determine mean weight diameter.

 

3 

A replicated, randomized, controlled study in 2002–2005 in an irrigated maize field in Greece found similar amounts of organic matter in soils with or without added manure. Organic matter: Similar amounts of carbon were found in soils with or without added manure (5.7 vs 5.3 g/kg). Nutrients: Similar amounts of nitrogen were found in soils with or without added manure (0.81 vs 0.72 g N/kg). More phosphorus and potassium was found in soils with added manure, compared to soils without added manure (15–21 vs 4–11 mg P/kg; 67–85 vs 46–75 mg K/kg). Methods: Plots (5.6 x 8 m) had liquid cow manure (80 Mg/ha/year) or no added fertilizer (six plots each). The manure was incorporated into soil with a disk harrow (12–15 cm depth) within two hours of application. Soil samples were collected at the end of the growing season in 2005 (three samples/plot, 0–30 cm depth).

 

4 

A replicated, randomized, controlled study in 2001–2005 in the Guadalquivir Valley, Andalusia, Spain, found greater stability and less erosion in soils with added manure, compared to soils without added manure. Soil erosion and aggregation: More stable soils were found in plots with added manure, compared to plots without added manure, in two of four years (data reported as log instability index). Less soil was lost from plots with added manure, compared to plots without added manure, after rainfall (60 mm rainfall/hour, in two of four years: 175–192 vs 210–211 kg/ha; 140 mm rainfall/hour, in three of four years: 390–439 vs 508–520). Methods: There were four plots (9 x 9 m) for each of two treatments (5.8 or 11.6 t poultry manure/ha) and there wre four control plots (no manure). The manure was added in October 2001–2004, and soils were ploughed (25 cm depth). Soil samples were collected one day before the manure was added, in 2002–2004, and also in October 2005 (30 mm diameter gauge augers, 25 cm depth). Soils were watered to simulate rainfall in October 2002–2005 (60 or 140 mm rainfall/hour), and soil loss was measured in plots (1 x 1 m) that overlapped the borders of the treatment and control plots by 0.5 m.

 

5 

A replicated, randomized, controlled study in 1999–2004 in bare plots in Tunisia found more organic matter and nitrogen, but lower pH levels, in soils with added manure, compared to soils without added manure. Organic matter: More carbon was found in soils with added manure, in one of four comparisons (28 vs 9 g/kg). Nutrients: More nitrogen was found in soils with added manure (1.3–2 vs 1 g/kg). Lower pH levels were found in soils with added manure, in one of four comparisons (8 vs 8.3). Implementation options: Less carbon and nitrogen was found in plots with less fertilizer, compared to more fertilizer (carbon, in one of two comparisons: 12 vs 28 g/kg; nitrogen: 1 vs 2 g/kg). Similar pH levels were found in plots with different amounts of added manure (pH 8). Methods: Bare plots (1.5 x 1.5 m) had added manure (0, 40, or 120 t/ha) or no added manure (four plots for each). Manure was incorporated into the soil (10–15 cm depth). Soil samples (five samples/plot, 0–40 cm depth) were collected in September 2004.

 

6 

A replicated, randomized, controlled study in 2001–2009 in an irrigated nectarine orchard in Italy found more potassium in plots with added manure, compared to plots without added manure. Organic matter: Similar amount of organic matter were found in plots with or without added manure (2–3% vs 2%). Nutrients: Similar amounts of ammonium (1–6 vs 2–6 mg/kg) and phosphorus (20 vs 13 mg/kg), and similar pH levels (pH 7.8) were found in plots with or without added manure. More potassium was found in plots with added manure (312 vs 227 mg/kg). Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in plots with or without added manure (2–13 vs 4–10 mg/g). Methods: Four plots received 5–10 kg dry cow manure/ha, and four plots received no fertilizer. The manure was tilled into the soil (25 cm depth). Soil samples were collected in September (3–40 cm depth for organic matter in 2001–2008 and phosphorus in 2006) and four times in spring and summer in 2008–2009 (0–80 cm depth for nitrogen, and 4–20 cm depth for microbial biomass).

 

7 

A replicated, randomized, controlled study in 2007–2009 in an irrigated onion field near Madrid, Spain, found higher nitrous oxide and methane emissions in plots with added manure, compared to plots without added manure. Greenhouse gases: Higher nitrous oxide and methane emissions were found in plots with added manure (nitrous oxide: 1 vs 0.4 kg/ha; methane: 0.08 vs –1.15 kg/ha). Methods: Plots (20 m2) had manure (a mixture of hen and goat manure) or no fertilizer (three plots each), added in 2007 and 2008 (110 kg N/ha). The manure was immediately incorporated into the soil (10 cm depth), using a rotocultivator. Plots were irrigated 1–2 times/week (608–618 mm/year). Greenhouse-gas samples (closed chambers, 19 litre volume, 10 mL samples, 0, 30, and 60 minutes after closing) and soil samples (0–10 cm depth) were collected four times/week in the first two weeks after fertilizer was applied, twice/week during the first month, and once/week until the end of cropping season.

 

8 

A replicated, controlled study in 2006 in an almond orchard in Italy found more organic matter, nitrogen, and higher pH levels in plots with added manure, compared to plots without added manure. Organic matter: More carbon was found in plots with added manure, compared to plots without added manure, in four of six comparisons (8,173–9,420 vs 7,339–8,263 mg/kg). Nutrients: More nitrogen was found in plots with added manure (1,027–1,280 vs 727–827 mg/kg). Higher pH levels were found in plots with added manure, in one of six comparisons (8.57 vs 8.31). Methods: Plots (495 m2) had manure pellets (1.5 t/ha) or no fertilizer (three plots for each). Plots were drip-irrigated (2,000 m³/ha/year). Soil samples were collected in 2006 (five samples/plot, 0–15 cm depth).

 

9 

A replicated, controlled study in 2006–2007 in an almond orchard in Italy found more organic matter and nitrogen, but inconsistent difference in phosphorus, in soils with added manure, compared to soils without added manure. Organic matter: More carbon was found in soils with added manure, in five of six comparisons (0.81–0.91% vs 0.52–0.63%). Nutrients: More nitrogen was found in soils with added manure (0.10–0.17 vs 0.06–0.08%). Less phosphorus was found in soils with added manure, in five of six comparisons (1–6 vs 7–16 µg/g), but more was found in one of six comparisons. Methods: Plots (85 x 17.5 m) had added manure (commercial cow manure pellets: 1.5 t/h) or no added manure (three plots for each). Manure was incorporated into the soil (15 cm depth). Soil samples (five samples/plot, 0–15 cm depth) were collected in November 2006 and 2007.

 

10 

A replicated, randomized, controlled study in 2009 in an abandoned wheat field in Greece found similar numbers of nematodes in plots with or without added manure. Soil organisms: Similar numbers of nematodes were found in soils with or without added manure (368–559 vs 308–567 individuals/100 cm3). Methods: Plots (1 x 1 m) had added manure (4 kg/m2) or no added manure (four plots for each). Manure was added in January and incorporated into the soil with a mattock. Soil samples (three/plot, 3–20 cm depth) were collected in March and June.

 

11 

A replicated, randomized, controlled study in 2008–2011 in a wheat-barley field in northeast Spain found similar amounts of organic matter and microbial biomass, but greater soil stability, in soils with added manure, compared to soils without added manure. Organic matter: Similar amounts of organic carbon were found in soils with or without added manure (amounts not reported). Soil organisms: Similar amounts of microbial biomass (measured as carbon) were found in soils with or without added manure (579–1,230 vs 591–900 mg C/kg soil). Soil erosion and aggregation: More water-stable macroaggregates, and larger macroaggregates, were found in soils with added manure, compared to soils without added manure (0.43 vs 0.39 kg water-stable macroaggregates/kg soil; 3.23 vs 3.02 mm mean weight diameter). Methods: Poultry manure (100 kg N/ha) was added to three treatment plots, but not to three control plots (5 x 12 m plots). Soil samples were collected seven times, from March 2010 to July 2011, with a flat spade (0–5 cm depth, two samples/plot).

 

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.