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Providing evidence to improve practice

Action: Crop production: Use organic fertilizer instead of inorganic Mediterranean Farmland

Key messages

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Crop yield (11 studies)

  • Food crops (10 studies): Four replicated studies (three controlled, two randomized; one site comparison) from Italy and Spain found higher yields in plots with organic fertilizer, compared to inorganic fertilizer, in some comparisons. Three replicated, randomized, controlled studies from Spain and the USA found lower yields in plots with organic fertilizer, compared to inorganic fertilizer, in some or all comparisons. Three replicated, randomized, controlled studies from Greece and Spain found similar yields in plots with organic or inorganic fertilizer.
  • Forage crops (1 study): One replicated, randomized, controlled study from Spain found higher alfalfa yields in plots with organic fertilizer, compared to inorganic, in one of two comparisons.

Crop quality (0 studies)

 

Supporting evidence from individual studies

1 

A replicated, randomized, controlled study in 2002–2005 in a maize field in Greece found similar crop yields in plots with organic or inorganic fertilizer. Crop yield: Similar maize yields were found in plots with organic or inorganic fertilizer (12–14 vs 12–13 Mg/ha).  Methods: Plots (5.6 x 8 m) had organic fertilizer (liquid cow manure: 80 Mg/ha/year) or inorganic fertilizers (260 kg N ha/year and 57 kg P/ha/year) (six plots each). Fertilizers were incorporated into the soil with a disk harrow (12–15 cm depth) within two hours of application. Grain yield was measured in two rows (12.8 m2) in each plot, at the end of October.

2 

A replicated, randomized, controlled study in 2002–2005 in a barley field in Toledo, Spain, found higher grain and straw yields in plots with organic fertilizer, compared to inorganic fertilizer. Crop yield: Higher grain yields were found in plots with organic fertilizer, compared to inorganic fertilizer, in two of eight comparisons (with 20 t thermally dried sewage sludge/ha/year: 2.0 vs 1.6 t/ha; with 80 t composted sewage sludge/ha once in three years: 2.8 vs 1.6 t/ha), and higher straw yields were found in six of eight comparisons (2.7–4.2 vs 1.8 t/ha). Methods: There were four plots (10 x 3 m) for each of eight organic fertilizers (20 or 80 t thermally dried sewage sludge/ha, applied once in three years or once/year; 20 or 80 t composted sewage sludge/ha, applied once in three years or once/year) and one mineral fertilizer (15-15-15 NPK: 400 kg/ha/year). Plots were fertilized in mid-September and planted in mid-October. Barley was harvested in June 2005 (1 m2/plot).

 

3 

A replicated, randomized, controlled study in 2003–2004 in three maize-tomato fields near Davis, California, USA, found lower crop yields in organically-fertilized plots, compared to inorganically-fertilized plots. Crop yield: Lower maize yields were found in organically-fertilized plots, compared to inorganically-fertilized plots (4.1–6.7 vs 9.3–13.6 Mg grain/ha). Methods: Organic or inorganic fertilizer was used on six plots each (1.5 x 1.0 m plots). Urea was added to inorganically-fertilized plots (April: 60 kg N/ha; May: 200 kg N/ha). On organically-fertilized plots, inorganic fertilizer was replaced, every other year, with the residues of legume cover crops (100 kg N/ha). Maize was sown at different times (organically-fertilized plots: March; inorganically-fertilized plots: May), and different amounts of nitrogen were applied. It was not clear whether these results were direct effects of differences in the type of fertilizer (organic or inorganic), the amount of fertilizer, or the planting date.

 

4 

A replicated, randomized, controlled study in 2009 in a rainfed barley field in Spain found similar crop yields in plots with organic or inorganic fertilizer. Crop yield: Similar crop yields were found in plots with organic or inorganic fertilizer (1,032–1,508 vs 1,061 kg/ha). Methods: Plots (30 m2) had no fertilizer, organic fertilizer (pig slurry, anaerobically-digested pig slurry, municipal solid waste, or composted crop residue with sludge), or inorganic fertilizer (urea), which was applied in January 2006 (125 kg N/ha; three plots for each fertilizer) and incorporated into the soil (0–5 cm depth) using a roto-cultivator. Phosphate and potassium (75 and 40 kg/ha, respectively) were added to all plots.

 

5 

A replicated, randomized, controlled study in 2001–2009 in an irrigated nectarine orchard in Italy found higher yield in plots with organic fertilizer added compared to inorganic fertilizers added. Crop yield: Higher nectarine yields were found in plots with organic fertilizer, compared to inorganic fertilizer, in one of eight comparisons (38 vs 28 kg/tree). Implementation options: Higher nectarine yields were found in plots with compost, compared to manure, in one of six comparisons (39 vs 33 kg/tree). Methods: There were four plots for each of four organic-fertilizer treatments (5 t compost/ha in May; 5 t/ha split into two applications, in May and September; 10 t/ha split into two; or 5–10 kg dry cow manure/ha), and there were four plots for inorganic fertilizer (70–130 kg N/ha, 100 kg P/ha, 200 kg K/ha; plot size not reported). The compost was made from domestic organic waste and urban pruning material (50% each). Fertilizers were tilled into the soil (25 cm depth).

 

6 

A replicated, randomized, controlled study in 2006 in a barley field in the Henares river basin, Spain, found similar crop yield in plots with organic or inorganic fertilizer. Crop yield: Similar barley yields were found in plots with organic or inorganic fertilizer (1,879–2,381 vs 2,079 kg grain and straw/ha). Methods: There were three plots (30 m2) for each of four organic fertilizers (anaerobically digested thin fraction of pig slurry, untreated pig slurry, composted municipal solid waste, or sewage sludge and composted crop residues) and one mineral fertilizer (urea), applied in January (125 kg available N/ha). Plots were cultivated (0–5 cm depth) to incorporate the fertilizers. Barley was planted in January and harvested in June.

 

7 

A replicated, randomized, controlled in 2006–2008 in an irrigated field in Spain found higher alfalfa Medicago sativa yields in plots with organic fertilizer, compared to inorganic fertilizer. Crop yield: Higher alfalfa yields were found in plots with organic fertilizer, compared to inorganic fertilizer, in one of two comparisons (21 vs 20 Mg/ha). Methods: Plots (5 m2) had organic fertilizer (pig slurry: 170 or 340 kg N/ha/year) or inorganic fertilizer (phosphorous-potassium: 200 kg/ha/year; phosphorus pentoxide and potassium oxide: 150 kg/ha/yr). Yield was measured in each plot (mown to 8 cm height).

 

8 

A replicated, randomized, controlled study in 2000–2003 in an irrigated maize field in northeast Spain found lower crop yields in plots with organic fertilizer, compared to inorganic fertilizer. Crop yield: Lower maize yields were found in plots with organic fertilizer, compared to inorganic fertilizer, in one of four years (2003: 7–9 vs 10 Mg/ha). Methods: Plots (3.8 x 2.5 m) had inorganic fertilizer (150 kg N/ha) or organic fertilizer (pig slurry: 30, 60, 90, or 120 Mg/ha) (three plots for each). Maize was harvested in November each year.

 

9 

A replicated, randomized, controlled study in 2000–2005 in an irrigated barley-maize field in Spain found lower barley and maize yields in plots with organic fertilizer, compared to inorganic fertilizer. Crop yield: Lower yields were found in plots with organic fertilizer, compared to inorganic fertilizer (barley, in one of two comparisons: 4–6 vs 8 Mg/ha; maize: 4–6 vs 8 Mg/ha). Methods: Plots (3.8 x 2.5 m) had inorganic fertilizer (150 kg N/ha/year) or organic fertilizer (slurry: 30, 60, 90, or 120 Mg/ha/year) in 2000–2003. Phosphorus (120 kg P2O5/ha) and potassium (180 kg KCl/ha) were added to all plots in 2003 and 2004. Barley was sown in December 2003 and harvested in June 2004. Maize was sown in July 2004 and harvested in December.

 

10 

A replicated, randomized, controlled study in 2010–2013 in rainfed barley fields in Spain found higher barley yields in plots with organic fertilizer, compared to inorganic fertilizer. Crop yield: Higher barley yields were found in plots with organic fertilizer, compared to inorganic fertilizer, in seven of 12 comparisons (2,755–5,335 vs 1,308–3,885 kg/ha). Methods: Plots (inorganic: 50 x 6 m or 40 x 6 m; organic: 40 x 12 m) had inorganic fertilizer (60, 75, 120, or 150 kg N/ha) or organic fertilizer (75 or 150 kg N/ha) (three plots for each). Plots had conventional tillage (mouldboard plough: 25 cm depth; cultivator: 15 cm depth) or no tillage. Barley was harvested in June.

 

11 

A replicated, randomized, controlled study in 2003–2004 in an irrigated maize field in Spain found higher crop yields in plots with organic fertilizer, compared to inorganic fertilizer. Crop yield: Higher crop yields were found in plots with organic fertilizer, compared to inorganic fertilizer, in four of 12 comparisons (16–18 vs 14 Mg/ha). Methods: Plots (30 x 40 m) had organic fertilizer (30, 60, 90, or 120 Mg slurry/ha) or inorganic fertilizer (0, 180, 240, or 300 kg N/ha) (three plots for each). Slurry was immediately covered after application. Each plot was drip-irrigated, simulating flood irrigation (May to mid-September, with 7–12 intervals). Barley was harvested at the end of 2004.

 

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.