Providing evidence to improve practice

Action: Water: Add slurry to the soil Mediterranean Farmland

Key messages

Water use (0 studies)

Water availability (2 studies): One replicated, randomized, controlled study from Spain found similar amounts of water in soils with or without added slurry, and another one found similar amounts of water-filled pore space.

Pathogens and pesticides (0 studies)

Nutrients (5 studies): Two replicated, randomized, controlled studies from Spain found that more nitrate was leached from plots with added slurry, compared to plots without it. One of these studies also found that more nitrate was lost in runoff from plots with added slurry, in some comparisons. Two replicated, randomized, controlled studies from Portugal and Spain found that similar amounts of nitrate were leached from plots with or without added slurry. Two replicated, randomized, controlled studies from Spain found more dissolved organic matter in soils, or leached from soils, with added slurry.

Sediments (0 studies)

Implementation options (3 studies): One study from Spain found that less nitrate was leached from plots with surface application, compared to injection, of slurry. One study from Spain found that less nitrate was lost through runoff and leaching from plots with less added slurry, compared to more. One study from Spain found similar amounts of water-filled pore space in soils with digested or untreated pig slurry, and another found similar amounts of water-filled pore space in plots with less or more added slurry.

Supporting evidence from individual studies

1 

A replicated, randomized, controlled study in 2002 in irrigated farmland in Spain found that more nitrate was leached from plots with added slurry, compared to plots without it. Nutrients: More nitrate was leached from plots with added slurry (0.08–2 vs 0.1 g N/m2). Implementation options: Less nitrate was leached from plots with surface application, compared to injection, of slurry (0.8 vs 2 g N/m2). Methods: Plots (3 x 3 m) growing tall fescue Festuca arundinacea had pig slurry (surface application or injection, 200 kg N/ha) or no fertilizer (three plots each). Each plot had a lysimeter (1 x 1 m, 0.75 m depth) to measure leaching. Slurry was injected (5 L/m) or applied with a watering can. Water (5 L/plot) was added to the control plots. All plots were sprinkler-irrigated (June–August: daily; September: twice/week). Soil cores were taken from the centre of the plots (0–10 cm depth).

 

2 

A replicated, randomized, controlled study in 2009 in a rainfed barley field in Spain found similar amounts of water-filled pore space in soils with or without added slurry. Water availability: Similar amounts of water-filled pore space were found in soils with or without added slurry (20–60%). Implementation options: Similar amounts of water-filled pore space were found in soils with untreated or digested slurry (20–60%). Methods: Plots (30 m2) had no fertilizer or pig slurry (anaerobically-digested pig slurry or untreated), applied in January 2006 (125 kg N/ha; three plots for each) 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).

 

3 

A replicated, randomized, controlled study in 2007–2009 in an irrigated onion field near Madrid, Spain, found that more dissolved organic carbon was leached from plots with added slurry, compared to plots without it. Nutrients: Similar amounts of nitrate were leached from plots with or without added slurry (31 vs 17 kg/ha), but more dissolved organic carbon was leached from plots with added slurry (3 vs 2 kg/ha). Methods: Plots (20 m2) had anaerobically-digested pig slurry or no fertilizer (three plots each), added in 2007 and 2008 (110 kg N/ha). The slurry was 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.

 

4 

A replicated, randomized, controlled study in 2007 in an irrigated melon field in Spain found more dissolved organic matter in soils with added slurry, compared to soils without it. Nutrients: More dissolved organic carbon was found in soils with added slurry (22–34 vs 15–34 mg/kg). Methods: Plots (4 x 5 m) growing melon Cucumis melo (6,950 plants/ha) had digested pig slurry or no slurry, and were either drip or furrow irrigated (three plots for each). Slurry was applied using a hose pipe (175 kg N/ha). Additional fertilizers were added immediately after (phosphorous: 50 kg/ha; potassium: 150 kg/ha). Slurry and fertilizer were incorporated into the soil (15 cm) using a rotocultivator. For furrow irrigation (2 L/min), there were five furrows/plot (80 cm width, 15 cm depth, 100 cm apart). For drip irrigation (3 L/h), there were two lines/subplot (1.8 m apart). Irrigation was applied 20 times, on a weekly basis. Soil samples were taken (0–10 cm depth; frequency not reported).

 

5 

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 or without added slurry. Nutrients: Similar amounts of nitrate were leached from soils with or without added slurry (2006–2007: 78 vs 49 kg NO3-N/ha; 2007–2008: 28 vs 23). 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). Cattle slurry was added to three treatment plots (5.6 x 8 m), but not three control plots, in spring. Maize was grown in spring–summer, and oats were grown in autumn–winter.

 

6 

A replicated, randomized, controlled study in 2010–2013 in rainfed barley fields in Spain found similar amounts of water-filled pore space in plots with or without added slurry. Water availability: Similar amounts of water-filled pore space were found in plots with or without added slurry (25–26% vs 24%). Implementation options: Similar amounts of water-filled pore space were found in plots with less or more slurry (25% vs 26%). Methods: Plots (40 x 12 m) had pig slurry (75 or 150 kg N/ha) or no fertilizer (three plots each). Plots had conventional tillage (mouldboard plough: 25 cm depth; cultivator: 15 cm depth) or no tillage. Soil samples (0–5 cm depth) were collected every 2–3 weeks in 2011–2013.

 

7 

A replicated, randomized, controlled study in 2003–2004 in an irrigated maize field in Spain found that more nitrate was lost through leaching and runoff from plots with added slurry, compared to plots without it. Nutrients: More nitrate was lost through leaching (105–208 vs 10 kg/ha) and runoff (in three of four comparisons: 74–81 vs 3 mg/L) from plots with added slurry, compared to plots without it. Implementation options: Less nitrate was lost through leaching (208–226 vs 105 kg/ha) and runoff (34 vs 74–81 mg/L) from plots with less slurry, compared to more slurry (30 vs 60–120 Mg slurry/ha). Methods: Plots (30 x 40 m) had pig slurry (30, 60, 90, or 120 Mg/ha) or no slurry (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 plot was drip-irrigated, simulating flood irrigation (May–September, with 7–12 intervals). Water samples were collected after each irrigation or rainfall event in 50 L containers.

 

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.