Action Synopsis: Soil Fertility About Actions

Amend the soil with formulated chemical compounds

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

Nutrient loss: Three of five replicated trials from New Zealand and the UK measured the effect of applying nitrification inhibitors to the soil and three found reduced nitrate losses and nitrous oxide emissions, although one of these found that the method of application influenced its effect [Thompson]. One trial found no effect on nitrate loss. One trial found reduced nutrient and soil loss when aluminium sulphate was applied to the soil.

Soil organic matter: Five of six studies (including three controlled, randomized and replicated and one randomized and replicated) from Australia, China, India, Syria and the UK testing the effects of adding chemical compounds to the soil showed an increase in soil organic matter or carbon when nitrogen or phosphorus fertilizer was applied. One site comparison study showed that a slow-release fertilizer resulted in higher nutrient retention. One study found higher carbon levels when NPK fertilizers were applied with straw, than when applied alone, and one replicated study from France found higher soil carbon when manure rather than chemical compounds were applied.

Yield: One replicated trial from India and a trial from the Philippines showed that maize, wheat and rice yield increased with increased fertilizer application.

Soil types covered: clay, fine loamy, gravelly-sandy loam, loam, loamy sand, sandy loam, silty, silty-clay, silt-loam.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, controlled study in 1984-1985 on a loam soil in Berkshire, the UK (Thompson et al. 1987) found that adding a nitrification inhibitor to cattle slurry injected into pasture reduced nitrogen losses from 58 kg N/ha (slurry with no inhibitor) to 28 kg N/ha, and to 34 kg N/ha by spreading slurry on the surface. The effect was less pronounced in spring. The slurry treatments – surface application, injection into pasture, and injection with the nitrification inhibitor nitrapyrin – were applied to ryegrass Lolium perenne in December and April at a rate of 80 t/ha. Slurry was poured into ploughed slots in the injection treatments. Each treatment was replicated four times.

    Study and other actions tested
  2. A site comparison study in 1984-1987 on a peat overlaying clay soil in Plynlimon, UK (Roberts et al. 1989) found that about 10% of phosphorus from quick-release fertilizers (superphosphate) was lost through leaching, compared to slow-release fertilizers (basic slag) for which phosphorus levels in the soil were not affected. There were two sites, the first comprising 1.5 ha of soft rush Juncus effusus and purple moor grass Molinia caerulaea. This site was disc harrowed, and lime, basic slag, fertilizer and a nitrogenous fertilizer were applied. The second site (19.5 ha) contained purple moor grass and small areas of blanket mire Calluna vulgaris-Eriophorum vaginatum. Lime and phosphate fertilizer were applied at this site and grass seed was sown using the spike seeding method (a reduced tillage method whereby ground is spiked with a spike-aerator, then seed is broadcast over the soil). Soil and water samples were collected. Water flow and phosphorus levels were measured.

    Study and other actions tested
  3. A controlled, randomized, replicated site comparison study in 1990-1994 on a sandy loam in the UK (Beckwith et al. 1998) found that applying the nitrification inhibitor dicyandiamide with manure had little to no effect on reducing nitrate leaching (50 kg N/ha lost manure only, 42.5 kg N/ha lost manure with inhibitor). There were two manure treatments at each site: pig/cattle slurry and farmyard cattle manure in Shropshire and poultry litter and farmyard cattle manure in Nottinghamshire. Manures were applied monthly at 200 kg N/ha between September and January to overwinter fallow or directly onto winter rye Secale cereale. An extra treatment was included to test dicyandiamide, which was applied at 20 l/ha. All treatments were replicated three times at both sites. Plots were 12 x 4 m and 15 x 4 m in the Shropshire and Nottinghamshire sites, respectively. Total soil mineral nitrogen was measured.

    Study and other actions tested
  4. An experiment in 1994-1995 on silty clay in the Philippines (Witt et al. 2000) found higher grain yields under high (7.15 t/ha) compared to low (6.15) or no (2.95 t/ha) nitrogen fertilizer application. There were two crop systems: continuous rice Oryza sativa, and a maize Zea mays-rice rotation. Maize was grown in the dry season, and rice in the dry. Within each 12 x 25 m cropping system were four 12 x 8 m nitrogen treatments: control (no nitrogen fertilizer), low (30 kg N/ha), medium (40 kg N/ha) and high application (50 kg N/ha). Within these were two 6 x 8 m sub-treatments: early (63 days before rice seedling transplanting) or late crop residue (rice or maize) incorporation (14 days before transplanting). Soils were sampled to 15 cm depth.

    Study and other actions tested
  5. A controlled, randomized, replicated experiment from 1984 to 1997 on loamy sand and sandy loam in the UK (Silgram and Chambers, 2002) found increased soil mineral nitrogen under increasing nitrogen fertilizer with 54, 60, 65 and 71 kg N/ha in soil receiving 0, 100, 150 and 200 kg N/ha respectively. Soil organic carbon was higher under 250 kg N/ha (14.91 g C/100g) compared to no fertilizer (0.91 g C/100g). There were three residue treatments at two sites: burned straw incorporated (into soil to 15 cm depth), chopped straw incorporated (15 cm depth), and chopped straw not incorporated. All treatments were mouldboard ploughed in autumn to 30 cm depth. Within each treatment were six nitrogen fertilizer treatments: 0-250 kg N/ha increasing by 50 kg a time (winter cereals: wheat Triticum aestivum, barley Hordeum vulgare, oats Avena sativa), 0-150 kg N/ha by 30 kg (spring cereals (barley) and sugar beet Beta vulgaris), and 0-300 kg N/ha by 60 kg (winter oilseed rape Brassica napus). Each nitrogen treatment was 64 m2 at Gleadthorpe and 69 m2 at Morley. Grain and straw samples were used to measure nitrogen content. Soils were samples to 90 cm depth.

    Study and other actions tested
  6. A replicated experiment from 1929 to 1999 on clay soil in France (Pernes-Debuyser and Tessier, 2004) found the highest soil organic carbon levels under manure application (37.2 g/kg soil) compared to the control (7.1 g/kg). The remaining treatments had carbon levels similar to or less than the control. Water retention was highest under manure application under low and higher water potential (0.32 g/cm3 and 0.009 g/cm3 respectively), compared to nitrogen and potassium treatments (0.17 g/cm3) (control figures not presented). Manure also had higher soil stability (81.9 % large soil aggregates) compared to phosphorus (22.2%) and nitrogen and potassium treatments (33.8%). Treatments included: no application (control, 10 plots); nitrogen (150 kg/ha/year); potassium (150 kg/ha/year); phosphorus (1t/ha/year); calcium (1 t/ha/year), horse manure (100 t/ha/year). Each treatment was replicated twice in 5 x 5 m plots. Soils were sampled at the end of the experiment.

    Study and other actions tested
  7. A replicated experiment from 1989 to 1997 on a clay soil in northern Syria (Ryan et al. 2008), found that increasing nitrogen fertilizer addition (0, 30, 60 and 90 kg N/ha) increased soil organic matter (246, 249, 262, 264 t/ha, respectively). Three replications of 36 x 120 m plots included the following crop rotations: continuous fallow, continuous wheat Triticum aestivum, and wheat grown in rotation with lentil Lens culinaris, chickpea Cicer arietinum, vetch Vicia sativa, pasture medic Medicago spp., or watermelon Citrullus vulgaris. Within each rotation were four smaller 36 x 30 m sub-plots with 0, 30, 60 or 90 kg N/ha applied. Within these were 12 x 30 m grazing treatments: no grazing/stubble retention, medium and heavy grazing. Soil organic matter, nitrogen/nitrates, and phosphorus were measured at the beginning of each cropping season.

    Study and other actions tested
  8. A replicated study in 2009 on loam, silt-loam and sandy loam soils in South Island, New Zealand (Di et al. 2009) found that adding the nitrification inhibitor dicyandiamide reduced nitrate loss by an average of 59% across different soil types and contrasting rainfall conditions. Soils in Canterbury, West Coast and Southland regions were fertilized with cow urine at a rate of 1,000 kg N/ha. Dicyandiamide was applied to half the soils at 10 kg/ha following urine application, and under two rainfall conditions (1,100 and 2,200 mm/year). There were four replicates of each treatment and soils were sampled in large (0.5 x 0.7 m), undisturbed sections.

    Study and other actions tested
  9. This controlled, replicated experiment in 2004-2008 on silt loam soil in New Zealand (McDowell & Houlbrooke 2009) found that applying alum (aluminium sulphate) after grazing of forage crops by cattle or sheep reduced phosphorus loss by 29% and 26%, and fine sediment loss by 16% and 43%, respectively, compared to normal forage crop grazing. Grazing cattle or sheep on forage crops increased phosphorus loss from fields by approximately 100% (1.3 kg/ha) and 33% (0.9 kg/ha) respectively, compared to normal sheep grazing on pasture (0.6 kg/ha).  Forage grazing by cattle or sheep increased fine sediment loss by 1,000% (0.7 mg/ha) and 500% (0.4 mg/ha), relative to grazing pasture with sheep (0.06 mg/ha). Twenty-eight 10 × 25 m plots included four replicates of combinations of the following treatments: cattle or sheep grazing on winter forage crops (triticale Triticosecale Wittmack, then kale Brassica oleracea), sheep pasture, restricted grazing, or alum addition on the forage crops (20 kg/ha following grazing).

    Study and other actions tested
  10. A controlled, randomized, replicated experiment in 2009 on gravelly sandy loams in the South Andaman Islands, India (Pandey & Begum 2010) found that adding phosphorus to a cover crop increased nitrogen levels by 16%. Nitrogen mineralization (the breakdown of organic matter, e.g. leaves, into mineral nitrogen) was greater in cover-cropped soils with added phosphorus than in cover-cropped soils without added fertilizer (73% and 39% greater than control, respectively). Nitrogen levels were 8% higher in soil with no cover crop plus phosphorus, compared to the control. There were six replicates of four treatments in a coconut palm Cocos nucifera plantation: no cover crop (control), no cover crop plus phosphorus (16% P (P2O5) at 24 kg/ha), cover crop (Kudzu Pueraria phaseoloides) and cover crop plus phosphorus (24 kg/ha). Each plot was 40 x 40 m and contained 28 coconut palms 7.5 m apart. Each month 10 soil samples were taken to 15 cm depth from each plot. Soil carbon, nitrogen and nitrogen mineralization were measured.

    Study and other actions tested
  11. A replicated experiment in 2000-2004 on fine loamy soil in Dehradun, India (Sharma et al. 2010) found that maize Zea mays yield increased from 1.2 to 2.1, 2.6 and 3.0 t/ha as nitrogen fertilizer rates increased from 0 to 30, 60, and 90 kg N/ha respectively. Wheat Triticum aestivum yields also increased with increased nitrogen fertilizer application (1.3, 2.1 and 2.8 t/ha for 0, 40 and 80 kg N/ha). Maize was grown followed by wheat and each crop had four mulching treatments in 130 m2 plots: no mulching (control), sunnhemp Crotalaria juncea, leucaena Leucaena leucocephala prunings/twigs, and sunnhemp and leucaena combined. Each treatment had 29 m2 subplots with fertilizer applied at a rate of 0, 30, 60 or 90 kg N/ha for maize, and 0, 40 or 80 kg/ha for wheat. There were four replications.

    Study and other actions tested
  12. A randomized, replicated experiment from 1968 to 2008 on clay soil in Australia (Dalal et al. 2011) found soil organic carbon was highest under high (20.40 Mg/ha), then medium (20.13 Mg/ha), compared to no nitrogen application (19.53 Mg/ha), in the topsoil. Fertilizer application only affected carbon levels when crop residue was retained, (1.8 Mg C/ha more carbon under high fertilizer with residues retained, compared to no fertilizer no residue).  Nitrogen was 125 kg N/ha higher under high fertilizer application compared to no fertilizer. Total soil nitrogen increased with nitrogen fertilizer application only when crop residues were retained. Average grain yield was highest under no-tillage plus crop residue and high fertilizer (2.86 Mg/ha) and lowest under conventional tillage plus crop residue, no fertilizer (2.28 Mg/ha). Wheat Triticum aestivum was the principle crop bar three years which were cropped with barley Hordeum vulgare. Treatments included: tillage (conventional tillage 10 cm depth, no-tillage); crop residue management (burned or retained); and nitrogen fertilizer application (none applied, low or high application (30 and 90 kg N/ha/year respectively). Plots were 61.9 x 6.4 m and replicated four times. Soil was sampled in each plot at the end of the experiment to 1.5 m depth.

    Study and other actions tested
  13. A replicated, controlled study in 2008 on sandy loam in New Zealand (Di & Cameron 2012), found that two nitrification inhibitors, dicyandiamide and 3,4-dimethylpyrazole phosphate (DMPP), were both effective at reducing nitrogen loss through nitrous oxide emissions and nitrate leaching. Adding dicyandiamide to pasture reduced nitrous oxide emissions by 62% and nitrate loss by 36%, while adding DMPP to pasture reduced nitrous oxide emissions by 66% and nitrate loss by 28%, compared to the control. The study used three treatments, replicated four times on pasture plots planted with a mixture of ryegrass Lolium perenne and white clover Trifolium repens. Treatments were control (cow urine, 1000 kg/ha), dicyandiamide (cow urine and dicyandiamide at 10 kg/ha) and DMPP (cow urine and DMPP at 1 kg/ha or 5 kg/ha). Treatments were applied in mid-winter and re-applied in early spring. Dicyandiamide and DMPP were both applied as liquid formulations.

    Study and other actions tested
  14. A controlled, randomized, replicated experiment from 1990 to 2005 on silty, silty-clay and clay soil at four sites in China (Tang et al. 2012) found higher soil organic carbon levels under nitrogen/phosphorus/potassium (NPK) plus straw (9.1 g C/kg soil) compared to NPK alone (8.4 g C/kg) or the control (7.7 g C/kg). Three treatments were applied to long-term wheat Triticum aestivum-maize Zea mays rotations at four sites: control (no fertilizer), NPK (at 165-362 kg N/ha, 25-41 kg P/ha, and 68-146 kg K/ha), and NPK plus straw (at 2.2-6 Mg/ha)). Weeds were removed manually and crops were irrigated when necessary. Soils were sampled to 20 cm depth at each site in autumn after maize harvest, and before the next fertilizer application.

    Study and other actions tested
Please cite as:

Key, G., Whitfield, M., Dicks, L.V., Sutherland, W.J. & Bardgett, R.D. (2020) Enhancing Soil Fertility. Pages 613-634 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.


Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Soil Fertility

This Action forms part of the Action Synopsis:

Soil Fertility
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust