Amend the soil with manures and agricultural composts
Overall effectiveness category Trade-off between benefit and harms
Number of studies: 14
Background information and definitions
Soil microbial biomass is the amount of tiny living organisms in a given amount of soil. Soil microbial respiration is the production of carbon dioxide (CO2) when soil organisms respire (breaking down molecules to produce energy). Arbuscular mycorrhizal fungi are a group of fungi that live around the roots of plants. By living together, the fungi and host plant benefit each other: the fungi can live in a habitat without having to compete for resources and have a supply of carbon from the plant, while benefit the plant with an enhanced supply of nutrients, improved growth and ability to reproduce, and tolerance to drought. Arbuscular mycorrhizal fungi colonise a wide variety of host plants, including grasses, herbs, agricultural crops and legumes (Bardgett 2005). They are associated with less intensively cultivated and undisturbed soils.
Soil aggregates are groups of soil particles held together by moist clay, organic matter (such as roots), organic compounds (from bacteria and fungi) or fungal hyphae (long, branching structures of a fungus). Some soil particles fit closely together (high soil density), some do not (low density), creating different-sized spaces. These spaces (or pores) within and between soil aggregates can store air and water, microbes, nutrients and organic matter. Large aggregations of particles retain the most nutrients. Since organic amendments act as strong binding agents between particles, mean weight diameter (MWD) of the aggregates (in mm) soils are likely to increase with applications of organic material such as manures and composts. Soil penetration resistance MPa is the soil’s ability to withstand penetration by water or roots. Often with low penetration resistance comes higher hydraulic conductivity, which is the ease with which a fluid (usually water) can move through pore spaces in the soil. Higher hydraulic conductivity is an indicator of a healthy soil.
Excess levels of soluble salts in the soil can adversely affect plant life by changing a plant’s water balance and basic function, resulting in wilting or scorching. Electrical conductivity is a general measure of the soluble salt content or nutrient level of a soil (high conductivity values typically indicate high salt levels). Good quality topsoil should have an electrical conductivity value within the range of 100-1500 microSiemens/cm (μS/cm). Ceramic cup sampling measures the electrical conductivity of a soil, using a vacuum is connected to tubes in the soil. On the end of the tubes are small ceramic cups which filter moisture from the soil when suction is applied.
Ammonium-nitrate is often added to soils as a fertilizer and if plants do not take it up immediately, the ammonium-nitrate gets converted to nitrate by soil bacteria (nitrification) and can be lost from the soil (leaching). A nitrification inhibitor stops or slows down this conversion, and can reduce the loss of nitrate from the soil.
Bardgett R. (2005) The Biology of Soil: A community and ecosystem approach. Oxford University Press, Oxford.
Supporting evidence from individual studies
A controlled, randomized, replicated study in 1990-1994 on sandy loam in the UK (Beckwith et al. 1998) found lower nitrate losses for farmyard manure (10 and 19 kg N/ha from sites A and B respectively) than for broiler litter (24 kg N/ha) or slurry (56 kg N/ha) treatments. Nitrate losses were greatest following manure application in September-November (23 and 12 mg N/l for sites A and B), but were tiny when applications were made in December or January (less than 0.5 mg N/l for both sites). There were two manure treatments at each site: site A (Shropshire) received pig/cattle slurry and cattle farmyard manure, and site B (Nottinghamshire) received broiler (poultry) litter and farmyard manure. Manures were applied at 200 kg N/ha monthly between September and January to overwinter fallow or onto winter rye Secale cereale. All treatments were replicated three times at both sites. Plots were 12 x 4 m and 15 x 4 m at sites A and B respectively.Study and other actions tested
Referenced paperBeckwith C.P., Cooper J., Smith K.A. & Shepherd M.A. (1998) Nitrate leaching loss following application of organic manures to sandy soils in arable cropping. I. Effects of application time, manure type, overwinter crop cover and nitrification inhibition. Soil Use and Management, 14, 123-130
A controlled; randomized, replicated experiment in 2000-2001 on fine sandy-silty loam in the USA (Motavalli et al. 2003) found increased soil inorganic nitrogen with increased rates of poultry manure (from 4 to 83 mg N/kg). Corn Zea mays yield was highest under medium manure application (7,466 kg/ha) then high (7,339 kg/ha), low (6,437 kg/ha) and no application (4,464 kg/ha). Corn was planted in 3.8 x 10.6 m plots. Treatments consisted of: deep tillage to 30 cm depth (also called subsoiling), and three levels of soil compaction (0, 2 and 4 passes with a vibrating roller). Four rates of composted poultry manure (at 0, 6, 11, and 18 Mg/ha) were applied in spring to the deep tillage and compaction treatments. All treatments were then disced twice to 15 cm depth. There were four replications. Soils were sampled to 40 cm depth.Study and other actions tested
A controlled, replicated experiment in 1998-2001 on sandy loam in Madrid, Spain (Díez et al. 2004) found the highest nitrate leaching from soil under excessive pig slurry (329 kg N/ha), followed by medium (215 kg N/ha) and low application (173 kg N/ha), compared to the control (78 kg/ha). Dissolved salts in the soil were higher under high (6,058 kg salts/ha) compared to medium application (2,019 kg salts/ha). Maize Zea mays grain yield was higher under high (11,961 kg/ha), medium (10, 984 kg/ha) and low application (10,797 kg/ha) compared to the control (9,363 kg/ha). Four slurry treatments were applied to a maize crop: control (no fertilizer), suboptimal/low (as urea), optimal/medium (170, 162 and 176 kg N/ha for 1998, 1999 and 2001), and excessive/high application (not specified). Slurry was applied to soil through a band spreader connected to a tanker and then incorporated into the soil by rotivation. There were three replicates of 9.9 x 11.1 m plots. Barley Hordeum vulgare was grown in 2000 to avoid excessive repeat-cropping with wheat, but results of that year were not reported in the study. Soils were sampled 33 times throughout the experiment using ceramic cups.Study and other actions tested
A controlled, randomized, replicated experiment in 2000-2002 on clay loam in India (Ramesh and Chandrasekaran 2004) found 4% higher soil organic carbon under poultry manure (6.6 g C/kg) compared to unmanured plots (6.4 g C/kg). Soil organic carbon under dual cropping (6.4 g C/kg) and farmyard manure (6.4 g C/kg) were comparable to unmanured plots. There were five combinations of rice and sesbania consisting of: fallow-rice-rice, sesbania-rice-rice, sesbania-rice-sesbania-rice, sesbania-rice-rice-sesbania, and sesbania-rice-sesbania-rice-sesbania. Each combination was divided into four manure treatments: control (none applied), farm yard manure (12.5 t/ha), poultry manure (5 t/ha), and dual cropping with fern Azolla hybrid. There were three replications of each crop combination. Plot size was not specified. Soils were sampled after each rice harvest (depth not specified).Study and other actions tested
A replicated experiment from 1981 to 2002 on sandy loam in Denmark (Thomsen and Christensen 2004) found that pig slurry had no effect on soil carbon and nitrogen levels. Four straw management treatments were applied to barley Hordeum vulgare crops: straw removed (control: 0 t/ha), low (4 t/ha), medium (8 t/ha) and high straw application (12 t/ha). From 1981 to 1988 35 t/ha of pig slurry was applied to the straw treatments. After, a ryegrass Lolium perenne catch crop was grown. Plot sizes were not specified. In 1999-2002, wheat Triticum aestivum was sown into the straw treatments. Each treatment was divided into 21.25 m2 plots and received 0, 60, 120 or 180 kg N/ha. There were three replicates. Soil was sampled to 20 cm depth.Study and other actions tested
A randomized, replicated experiment in 2003 on sandy-loam soil in Quebec, Canada (Jiao et al. 2006) found that the application of 30 and 45 Mg/ha/y of composted manure produced a higher proportion of large soil aggregates (35% and 41% respectively) than inorganic fertilizer application. There were four replicates of two tillage systems: conventional (tandem disk to 10 cm soil depth, mouldboard plough 20 cm) and no-tillage. Within these were maize Zea mays, soybean Glycine max/maize and maize/soybean rotations (in 20 x 24 m plots) and then within these were four fertilizer treatments: inorganic fertilizers, composted cattle manure at 30 or 45 Mg/ha/y, and the two mixed together (in 20 x 6 m areas of plots). Soil samples (to 10 cm depth) were taken after crop harvest. Soil carbon, nitrogen, phosphorus and the size of aggregates were measured.Study and other actions tested
A controlled, replicated experiment in 2002-2004 on sandy clay loam in Edinburgh, the UK (Jones et al. 2006) found higher total soil carbon under cattle slurry (32.3 kg C/m3), sewage (36.5 kg C/m3) and poultry manure (44.5 kg C/m3) compared to the control (26.8 kg C/m3). Soil carbon under mineral fertilizers was no higher than under the control. Soil microbial respiration was highest under poultry manure (10,748 kg CO2/ha), followed by cattle slurry (9,835 kg CO2/ha) and sewage sludge (9,284 kg CO2/ha) treatments, compared to the control (5,636 kg CO2/ha). Respiration was lower in both mineral fertilizer treatments compared to poultry manure. Six fertilizer treatments were applied to 12 x 6 m plots of perennial ryegrass Lolium perenne grassland over two years. Treatments were sewage sludge, cattle slurry, poultry manure, urea, ammonium nitrate (all applied at 300 kg/ha/y) and a control receiving no fertilizer. Treatments were replicated three times. Soil microbial respiration was determined by measuring carbon dioxide levels in closed cylindrical chambers placed on the soil surface clear of vegetation. Soil samples were collected to 10 and 20 cm depths in April each year.Study and other actions tested
A review of 120 papers testing interventions on a range of soils largely in Japan (Komatsuzaki & Ohta 2007), found enhanced soil organic carbon storage under manure (and other organic by-products) application, cover crop management, and no-tillage practices. Balanced and integrated increases in the soil organic carbon pool, lessening of non-carbon dioxide emissions, and control of soil nutrients based on location-specific recommendations are also needed. No review methods were specified. Tillage systems reviewed included: no-tillage, conservation tillage (surface residues retained), conventional tillage (mouldboard plough, rotary tillage, disced). Cover crops reviewed included a mix of leguminous and grass covers: rye Secale cereale, hairy vetch Vicia villosa, and crimson clover Trifolium incarnatum.Study and other actions tested
An experiment in 2001-2005 on silty loam soil in Villmar-Aumenau, Germany (Möller 2009) found no obvious changes in soil carbon or nitrogen under different manure and cover crop management. Available nitrogen increased when manures were digested before application (70 kg N/ha), compared to undigested manures (61 kg N/ha). There were two trials. Trial 1 had eight treatments: (1-2) clover/grass ley; (3) wheat Triticum aestivum plus cover crops receiving farmyard manure (FYM) as slurry or effluents; (4) potatoes Solanum tuberosum receiving FYM and solid effluents, or maize Zea mays receiving FYM; (5) rye Secale cereale plus cover crops plus FYM; (6) peas Pisum sativum plus cover crops; (7) spelt T. aestivum ssp. spelta plus cover crops plus FYM, and (8) wheat undersown with clover/grass ley plus FYM and solid manures. Trial 2 included: (1) clover/grass ley; (2) potatoes plus solid effluents; (3) winter wheat plus liquid effluents; (4) peas; (5) winter wheat plus liquid effluents; (6) spring wheat plus solid effluents. All manuring treatments were applied before ploughing. Five soil samples were taken from each plot to 30 cm depth and measured soil nitrogen and carbon.Study and other actions tested
A controlled, randomized, replicated experiment from 1996 to 2008 on clay-loam soil in Turkey (Celik et al. 2010) found 69%, 32% and 24% higher soil organic matter content in soil under manure, compost and mycorrhizal-inoculated compost applications respectively, compared to the control. Mineral fertilizer had no effect on organic matter accumulation. The largest soil aggregations were found under manure (0.05 mm), mycorrhizal-inoculated compost (0.11 mm) and compost (0.07 mm) applications. The lowest soil density was under compost (1.1 Mg/cm3) compared to the control (1.4 Mg/cm3). Lower penetration resistance was found under compost (1.06 MPa) and manure (1.17 MPa) application, with the highest under mineral fertilizer application (1.29 MPa) and in the control (1.51 MPa) plots. Combined wheat Triticum aestivum and maize Zea mays yield was highest under mineral fertilizer (13,720 kg/ha) followed by manure (10,500 kg/ha), compost (8,780 kg/ha) and mycorrhizal-inoculated compost (7,630 kg/ha), compared to the control (5,900 kg/ha). Within a wheat-maize rotation were three replicates of five 10 x 20 m treatments: control, mineral fertilizer (300-60-150 kg N-P-K/ha), manure (25 t/ha), compost (equal mixture of grass, wheat stubble and plant leaves, 25 t/ha), mycorrhizal Glomus caledonium-inoculated compost (10 t/ha). Soil samples were taken to 30 cm depth 2008.Study and other actions tested
A controlled, randomized, replicated experiment in 2001-2011 on sandy clay loam in India (Bhattacharyya et al. 2012) found 34% higher soil organic carbon and 53% more total carbon (including inorganic carbon) under rice straw plus green manure (using Sesbania aculeata) compared to the control (5.2 g/kg). Microbial biomass (measured by quantities of carbon) was highest under farmyard manure plus green manure (250 mg/kg), followed by farmyard manure (233 mg/kg) compared to the control (153 mg/kg). Rice yield was highest under farmyard manure plus green manure (3.51 t/ha), followed by rice straw plus green manure (3.35 t/ha), farmyard manure alone (3.25 t/ha), and green manure alone (3.09 t/ha), compared to the control (1.93 t/ha). Treatments were applied to plots of paddy 20 days before plots were planted with transplanted rice Oryza sativa var. Geetanjali seedlings. Treatments included: control (no amendment), farmyard manure, green manure, farmyard manure plus green manure, and rice straw plus green manure (both incorporated into the soil 20 days before seedling transplantation). There were three replications. Soils were sampled at the beginning and end of the experiment to 60 cm depth.Study and other actions tested
A controlled, randomized, replicated experiment in 2007-2010 on sandy silt-loam in India (Ghosh et al. 2012) found lower soil loss (3.4 t/ha) and runoff (234 mm of water) when organic manures, mulching and minimal tillage were applied to plots with a palmarosa Cymbopogon martini vegetation barrier than when conventional inputs were applied to plots with no vegetation barrier (7.1 t/ha and 428 mm respectively). The palmarosa barrier treatment was also more effective than a panicum Panicum maximum barrier treatment with conventional inputs (5.2 t/ha, 356 mm). Maize Zea mays yield was 13% lower in the palmarosa compared to panicum treatment, but 43% higher than having no vegetation barrier. Wheat Triticum aestivum yield was on average 73% higher in the palmarosa relative to panicum treatment, and 99% higher than with no vegetation barrier. It is not clear whether these results were due to organic amendments, mulching or reduced tillage. There were three replications (using 100 x 20 m plots) of three treatments in a maize-wheat crop rotation: no vegetation barrier with conventional tillage, fertilizers and chemical weed control; panicum barrier with conventional inputs; and a palmarosa barrier (with farmyard manure, vermicompost (produced by worms), poultry manure, minimal tillage, or weed mulching.Study and other actions tested
A controlled, replicated experiment in 2005-2009 on loam in Michigan, USA (Nair & Ngouajio 2012) found higher microbial biomass under perennial ryegrass Lolium perenne and compost (195-210 μg/g dry soil) than under ryegrass without compost, or ryegrass/vetch Vicia sativa with and without compost (145-160 μg/g dry soil). Microbial respiration was highest in soil under the ryegrass-compost combination (282 μg carbon dioxide/g dry soil), compared to ryegrass/vetch with no compost (126 μg carbon dioxide). Tomato Lycopersicon esculentum yield was higher in soils after the ryegrass-compost treatment (44 kg/ha) than in ryegrass/vetch with no compost (22 kg/ha). It was not clear whether these effects were due to the cover crop or compost treatments. Two cover crop treatments were sown into soil between crops: ryegrass and ryegrass with vetch. Within these were two compost treatments: compost (25 t/ha dairy compost, but reduced to 12.5 t/ha in 2009) and no compost. There were four replications. Cover crops were mowed and incorporated into the soil before tomato seedlings were transplanted into 7.6 x 0.6 m beds. Four soil samples were taken to 15 cm depth from each treatment during the growing season.Study and other actions tested
A controlled, replicated experiment in 2009 on loamy soil in Colorado, USA (Hurisso et al. 2013), found higher soil microbial biomass under high levels of composted dairy manure (239 μg C/g soil, 80.8 μg N/g soil) or an alfalfa Medicago sativa crop (277 μg C/g soil, 90.9 μg N/g soil) when added to grass pasture, compared to medium (158 μg C/g soil, 38 μg N/g soil), low (144 μg C/g soil, 38 μg N/g soil) or no additions (157 μg C/g soil, 29.3 μg N/g soil). There were three replicates (in 3 x 12 m plots) of four treatments: composted dairy manure applied at low (22.4 Mg/ha), medium (33.6 Mg/ha) and high rates (44.8 Mg/ha), and alfalfa interseeded into the grass mixture (including orchardgrass Dactylis glomerata, meadow brome Bromus biebersteinii, and smooth brome B. inermis). Soil samples were taken up to 15 cm depth after roughly 1.5 years, and measured soil microbial biomass (levels of carbon and nitrogen) and the size of accumulated soil particles.Study and other actions tested