Water: Add slurry to the soil

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).

   Study and other actions tested

   Referenced paper

   Vallejo A., García-Torres L., Díez J.A., Arce A. & López-Fernández S. (2005) Comparison of N losses (NO3, N2O, NO) from surface applied, injected or amended (DCD) pig slurry of an irrigated soil in a Mediterranean climate. Plant and Soil, 272, 313-325.

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).

   Study and other actions tested

   Referenced paper

   Meijide A., García-Torres L., Arce A. & Vallejo A. (2009) Nitrogen oxide emissions affected by organic fertilization in a non-irrigated Mediterranean barley field. Agriculture, Ecosystems & Environment, 132, 106-115.

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.

   Study and other actions tested

   Referenced paper

   Sánchez-Martín L., Sanz-Cobena A., Meijide A., Quemada M. & Vallejo a. (2010) The importance of the fallow period for N2O and CH4 fluxes and nitrate leaching in a Mediterranean irrigated agroecosystem. European Journal of Soil Science, 61, 710-720.

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).

   Study and other actions tested

   Referenced paper

   Sánchez-Martín L., Meijide A., García-Torres L. & Vallejo A. (2010) Combination of drip irrigation and organic fertilizer for mitigating emissions of nitrogen oxides in semiarid climate. Agriculture, Ecosystems & Environment, 137, 99-107.

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.

   Study and other actions tested

   Referenced paper

   Carneiro J.P., Coutinho J. & Trindade H. (2012) Nitrate leaching from a maize × oats double-cropping forage system fertilized with organic residues under Mediterranean conditions. Agriculture, Ecosystems & Environment, 160, 29-39.

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.

   Study and other actions tested

   Referenced paper

   Plaza-Bonilla D., Cantero-Martínez C., Bareche J., Arrúe J. L. & Álvaro-Fuentes J. (2014) Soil carbon dioxide and methane fluxes as affected by tillage and N fertilization in dryland conditions. Plant and Soil, 381, 111-131.

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.

   Study and other actions tested

   Referenced paper

   Yagüe M. R. & Quílez D. (2015) Pig slurry residual effects on maize yields and nitrate leaching: a study in lysimeters. Agronomy Journal, 107, 278-286.