Providing evidence to improve practice

Action: Water: Use organic fertilizer instead of inorganic Mediterranean Farmland

Key messages

Water use (0 studies)

Water availability (5 studies): Two replicated, randomized, controlled studies from Spain found similar amounts of water-filled pore space in plots with organic or inorganic fertilizer. Two replicated studies (one randomized and controlled, one site comparison) from France and Turkey found more water in plots with organic fertilizer, compared to inorganic fertilizer. One replicated, randomized, controlled study from Spain found less water in plots with organic fertilizer, compared to inorganic fertilizer, in one of two comparisons.

Pathogens and pesticides (0 studies)

Nutrients (6 studies): Two replicated, randomized, controlled studies from Italy and Spain found that less nitrate was lost from plots with organic fertilizer, compared to inorganic fertilizer, in some comparisons. One of these studies also found that more dissolved organic matter was lost, in one of two comparisons. One replicated, randomized, controlled study from Spain found more nitrate in runoff from plots with organic fertilizer, compared to inorganic fertilizer. Three replicated, controlled studies (two randomized) from Portugal and Spain found that similar amounts of nitrogen were lost from plots with organic or inorganic fertilizer.

Sediments (0 studies)

Implementation options (1 study): One study from Spain found that less nitrate, but more organic matter, was leached from plots that were fertilized with manure, compared to slurry.

Supporting evidence from individual studies

1 

A replicated, randomized, controlled study in 1995–1999 in arable farmland in southern Turkey found more water in soils with organic fertilizer, compared to inorganic fertilizer. Water availability: More available water was found in soils with organic fertilizer, compared to inorganic fertilizer (0.14–0.17 vs 0.09 cm3 water/cm3 soil). Methods: There were three plots (10 x 20 m) for each of three treatments: cattle manure (25 t/ha), compost (25 t/ha), or mineral fertilizer (160 kg N/ha, 26 kg P/ha, 83 kg P/ha). The compost was made of grass, stubble, and leaves. Wheat, sweet peppers, maize, and wheat were grown in rotation. Soils were sampled in 1999, after harvesting the last wheat crop (0–30 cm depth). The difference between water retention capacity at field capacity (–33 kPa) and at permanent wilting point (–1,500 kPa) was used to determine available water content.

 

2 

A replicated, controlled study in 1998–1999 in an irrigated maize field in Spain found that similar amounts of nitrogen were lost from plots with organic or inorganic fertilizer. Nutrients: Similar amounts of nitrogen were lost from plots with organic or inorganic fertilizer added (2.3–2.5 vs 2.5–2.9 g/m2). Methods: Plots (10 × 11 m) had pig slurry (165 kg/ha) or urea (165 kg/ha) (three plots each). Slurry was incorporated into the soil, five days after application, using a rotocultivator (0–5 cm depth). Water samples were taken during the first 15 days after application and every 2 weeks thereafter.

 

3 

A replicated, randomized, controlled study in 2009 in a rainfed barley field in Spain found similar amounts of water-filled pore space in plots with organic or inorganic fertilizer. Water availability: Similar amounts of water-filled pore space were found in plots with organic or inorganic fertilizer (20–60%). Methods: Plots (30 m2) had organic fertilizer (pig slurry, anaerobically-digested pig slurry, municipal solid waste, or composted crop residue with sludge) or inorganic fertilizer (urea), applied in January 2006 (125 kg N/ha; three plots for each fertilizer) and incorporated into the soil using a rotocultivator (0–5 cm depth). Phosphate and potassium (75 and 40 kg/ha, respectively) were added to all plots. Soil samples were taken every 1–2 weeks during crop period and three times during fallow period (0–10 cm depth), but no samples were taken in June–October (the soil was too dry).

 

4 

A replicated, randomized, controlled study in 2006 in a rainfed almond orchard near Granada, Spain, found less water in organically-fertilized soils, compared to inorganically-fertilized soils. Water availability: Less water was found in organically-fertilized soils, compared to inorganically-fertilized soils, in one of two comparisons (June: 4.6 vs 5.6 g water/100 g soil). Methods: Organic fertilizer (1,500 kg compost/ha, made from sheep manure and turf) or mineral fertilizer (250 kg/ha, 4.6% N, 1.2% P, 1.5% K) was used on 18 plots each (588 m2). Some organic fertilizer was used on all plots (30 t manure/ha), and one-third of the plots were grazed by sheep (7 kg organic C/ha from excrement). All plots had cover crops. Soil samples were collected on 7 June and 18 July 2006 (0–20 cm depth). It was not clear whether these results were a direct effect of the type or amount of fertilizer.

 

5 

A replicated, randomized, controlled in 2006–2008 in an irrigated alfalfa field in Spain found that similar amounts of nitrate were lost from plots with organic or inorganic fertilizer. Nutrients: Similar amounts of nitrate were lost from plots with organic or inorganic fertilizer (0.2–0.47 mg/L). Methods: Lysimeters (5 m2 and 1.5 m deep) 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). Water samples were collected from lysimeters (100 mL/week).

 

6 

A replicated, randomized, controlled study in 2007–2009 in an irrigated onion field near Madrid, Spain, found that less nitrate, but more organic matter, was leached from plots with organic fertilizer, compared to inorganic fertilizer. Nutrients: Less nitrate (1 vs 44 kg/ha), but more dissolved organic carbon (5 vs 3 kg/ha), was leached from plots with organic fertilizer, compared to inorganic fertilizer, in one of two comparisons (manure vs urea). Implementation options: More nitrate (31–44 vs 1 kg/ha), but less dissolved organic carbon (3 vs 5 kg/ha), was leached from plots with slurry, compared to manure. Methods: Plots (20 m2) had organic fertilizer (anaerobically digested pig slurry, or hen and goat manure) or inorganic fertilizer (urea), applied in May 2007 and 2008 (110 kg N/ha; three plots for each fertilizer). Fertilizers were immediately incorporated into the soil (10 cm depth), using a rotocultivator. Plots were irrigated 1–2 times/week (608–618 mm/year). Drainage water was collected in ceramic cups (80 cm depth, 40 kPa) thirty times during the experiment.

 

7 

A replicated, randomized, controlled study in 2006–2008 in a cereal field in the Castelo Branco region, Portugal, found that similar amounts of nitrate were leached from soils with organic or inorganic fertilizer. Nutrients: Similar amounts of nitrate were leached from soils with organic or inorganic fertilizer (2006–2007: 78–145 kg NO3-N/ha; 2007–2008: 26–35 kg). Methods: Water in the soil was collected in porous ceramic suction cup samplers (four/plot, 0.6–0.7 m depth, 50 kPa for 24 hours), whenever drainage occurred (October–November and April–May; 16 samples in total). There were three plots (5.6 x 8 m) for each of five organic-fertilizer treatments (single application in spring, or split application in spring and autumn, of municipal waste compost or sewage sludge, or split application of cattle slurry) and one mineral-fertilizer treatment. Maize was grown in spring–summer, and oats were grown in autumn–winter.

 

8 

A replicated, randomized, controlled study in 2010–2013 in a rainfed barley field in Spain found similar amounts of water-filled pore space in plots with organic or inorganic fertilizer. Water availability: Similar amounts of water-filled pore space were found in plots with organic or inorganic fertilizer (19–33% vs 16–33%). 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. Soil samples were collected at the end of the experiment (two samples/plot; 0–75 cm depth).

 

9 

A replicated, randomized, controlled study in 2003–2004 in irrigated arable farmland in Spain found that more nitrate was lost from plots with organic fertilizer, compared to inorganic fertilizer. Nutrients: More nitrate was found in runoff from plots with organic fertilizer, compared to inorganic fertilizer, in 12 of 16 comparisons (74–81 vs 3–24 mg/ha). More nitrate was found in leachate from plots with organic fertilizer, compared to inorganic fertilizer, in 14 of 16 comparisons (105–226 vs 10–54 kg/ha). Methods: Plots (30 x 40 m) had organic fertilizer (pig slurry: 30, 60, 90, or 120 Mg/ha) or inorganic fertilizer (0, 180, 240, or 300 kg N/ha) (three plots for each). Slurry was immediately covered after application. Lysimeters (2.6 x 2 m; 1.5 m depth), were installed in each plot, five years before the study. Each lysimeter was drip-irrigated, simulating flood irrigation (May to mid-September, with 7–12 intervals). Soil samples were collected after harvest (0–120 cm depth). Water samples were collected after each irrigation or rainfall event in 50 litre containers.

 

10 

A replicated, randomized, controlled study in 2009–2012 in an irrigated maize-ryegrass field in Italy found less nitrate in runoff from plots with organic fertilizer, compared to inorganic fertilizer. Nutrients: Less nitrate was lost in runoff from plots with organic fertilizer, compared to inorganic fertilizer, in one of two comparisons (manure vs inorganic: 42 vs 89 kg N/ha; 8% vs 20%). Methods: Plots (12 x 60 m) growing a double-crop rotation of silage maize and Italian ryegrass Lolium multiflorum had one of three types of fertilizer: cattle manure, cattle slurry, or inorganic fertilizer (four plots each). Soil samples were taken from each plot (two lysimeters/plot, 10 cm diameter, 50–90 cm depth).

 

11 

A replicated site comparison in 2009 in rainfed vineyards in southern France found greater water retention in organically-fertilized soils, compared to inorganically-fertilized soils. Water availability: Greater water retention was found in organically-fertilized soils, compared to inorganically-fertilized soils, in one of three comparisons (22% vs 14% water content at field capacity, by weight). Methods: In 146 plots of three soil types, inorganic fertilizer only (37–69% of plots in each soil type) or at least some organic fertilizer (31–63%) was used for at least five years before soil sampling. Soil samples were collected from the interrows in March–May 2009 (10 homogenized samples/plot, 0–15 cm depth).

 

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.