Action: Use organic rather than mineral fertilizers
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- Seventeen studies (including three reviews) from Austria, Belgium, Germany, Ireland, Switzerland and the UK looked at the effects of using organic rather than mineral fertilizers. Fourteen studies (including two reviews and seven replicated and controlled studies, of which four also randomized) from Austria, Belgium, Germany, Ireland, Switzerland and the UK found that areas treated with organic rather than mineral fertilizers supported higher plant diversity and cover or species richness, increased earthworm abundance or diversity, biomass and density and increased abundance and/or species richness of some or all invertebrates investigated.
- A literature review found organic fertilizers without pesticides produced highest earthworm biomass. A small trial in Belgium found more predatory beetles on an arable field two years after organic fertilizer application than on a control plot.
- One randomized, replicated, controlled trial in the UK found that using organic rather than mineral fertilizers did not affect the abundance of three weed species. A replicated study from Ireland found that the application of farmyard manure had no long-term effect on invertebrates, whilst two studies from the UK found the increase in arthropod predators and springtails was only seen at a local not a field scale. A review found one study from the UK reporting that heavy applications of slurry can be toxic to common earthworms.
The use of chemicals in agricultural management, such as synthetic fertilizers, may have a detrimental effect on farmland biodiversity. Organic fertilizers such as farmyard manure (including green manure or crop residues), slurry and other composts provide an alternative to synthetic or mineral fertilizers. Mineral fertilizers are manufactured preparations including nitrogen N, phosphorous P or potassium K, or 'NPK'.
Supporting evidence from individual studies
A small unreplicated trial at Huele, Belgium, from 1978 to 1980 (Pietraszko & De Clercq 1982) found more predatory beetles (Coleoptera) on an arable field two years after manure application than on a control plot, or a plot manured the year before monitoring. A single two hectare field was split into three plots: one control plot and two plots with manure applied at 40,000 kg/ha. One plot had manure in October 1978, the other in October 1979. The field was planted with potatoes, then wheat. More ground beetles (Carabidae) and rove beetles (Staphylinidae) were found on the plot manured in 1978. There were 2,197 ground beetles and 1,456 rove beetles in total, compared to fewer than 1,800 ground beetles and less than 1,300 rove beetles on the other plots. There was no difference between plots in the total number of male spiders (Araneae), but there were significantly fewer female spiders on the plot manured in 1978 than on the other two plots (379 female spiders in total, compared to over 430 on the other plots). In all three arthropod groups, individual species responded differently, although most species were caught more often on a manured plot.
A replicated study in an arable field in Ireland (Purvis & Curry 1984) found that application of farmyard manure resulted in an initial, temporary increase in invertebrate taxa, including beneficial arthropods, but overall catch diversity did not differ significantly with organic fertilizer application. Inorganic fertilizers were applied in typical applications to sown sugar beet Beta vulgaris. Three treatments were applied, each replicated in two 10 x 25 m plots: application of pre- and post-emergence herbicides (control: Lenacil and Phenmedipham), application of pre- and post-emergence herbicides plus farmyard manure, and no herbicide application. Percentage weed cover was estimated in five quadrats (0.09 m²) in each plot in June 1979. Nine pitfall traps/plot (5.6 cm diameter) were set for four 7-day trapping periods (May-September).
A small study of seven cereal fields over one year in Belgium (Hance & Gregoirewibo 1987) found that organic manure increased the abundance and number of species of ground beetles (Carabidae). A field with a 60 t/ha application of organic manure (and organophosphorus insecticide) had significantly higher abundance (1,128 individuals) and number of species (20 species) than a field with no organic manure (and organochloride insecticide, 14 species). Ground beetle abundance was highest (1690 individuals) when, as well as applying organic manure (30 t/ha), green manure was applied in late summer and turned under the soil in early spring. Species diversity was highest with the highest concentration of organic manure (60 t/ha, 20 species). An application of aldicarb insecticide with organic manure did not affect the number of individuals, but slightly reduced the number of species. However, without manure, the insecticide resulted in a three-fold reduction in the number of individuals. Fields differed in organic manure (none, 30 t/ha, 60 t/ha) and insecticide (aldicarb, lindane, E-605). Ten pitfall traps were placed in a row in each field, 4 m apart and were sampled from April to September.
A replicated, controlled, randomized study from 1988 to 1991 of an upland permanent pasture at Bronydd Mawr Research Centre, Powys, UK (Jones & Haggar 1993) found that plant diversity and herb cover was significantly higher in grassland with organic fertilizer than mineral fertilizer applications. Plots with farmyard manure and slurry had significantly higher species diversity (both 28% of species) than high (300 kg N/ha, 13% herbs) and low (100 kg N/ha, 18%) mineral applications and similar to unfertilized plots (31%). Nitrogen fertilizers resulted in a significant decrease in species diversity in the hedge bottom; in 1991, only 11 hedgerow species were present on mineral N treatments, 50% less than organic and control treatments. Herb cover was also lower in high (16-21%) and low (18-23%) N applications compared to farmyard manure (28-34%), slurry (27-28%) and the control (33-34%). Vegetation production was significantly higher with high N applications (1697 g dry matter/m²) than other treatments (low N: 1413, farmyard manure: 1343, slurry: 1175, control 973 g dry matter/m²). Sheep grazed grassland plots (7 x 4 m) extending into the hedge bottom were established. A randomized block design with three replicates was set up with the five treatments. Vegetation was sampled monthly within plots between April-November 1988-1991 and hedge bottoms were sampled in spring, summer and autumn each year.
A replicated, randomized, controlled trial in 1986-1987 in Northern Ireland (Humphreys & Mowat 1994) found ground beetle (Carabidae) abundance was higher in plots of Brussels sprouts Brassica oleracea that received mineral fertilizer followed by organic (manure or slurry) fertilizer applications compared to control plots receiving mineral fertilizers only. Over the three year period, more ground beetles were caught in no-barrier pitfall traps in the manure or slurry-treated plots than control (inorganic fertilizer-only) plots (average number of total ground beetles/trap/day: 0.46 manure plots, 0.39 slurry, 0.36 control, 0.26 straw). Ground beetles were more abundant in manure plots than controls for both barrier and no-barrier traps. In 1985 and 1986 within the planted area of plots, total catches of ground beetles were 13% and 5% higher in manure and slurry plots and 26% lower in straw plots compared with controls. The most common ground beetle, Bembidion lampros, was also more abundant in manure plots than controls. In 1985 and 1986 the largest number of springtails (Collembola) was found in manure plots, control plots had the lowest number of springtails. In 1985 and 1986 fly larvae (Diptera) and earthworms (Lumbricidae) were more abundant in manure and straw plots but the differences were not significant (no numbers given). The largest number of cabbage root fly Delia radicum eggs were found in slurry followed by control plots when ground beetles were excluded. There were five replicates of four 10 x 10 m plots. In 1985 and 1986 all plots were treated with 100 kg N, 50 kg P and 100 kg K/ha, followed by four different treatments: 0.5 t cattle manure/plot, 455 l cattle slurry/plot, three bales winter barley/plot, control (no additional treatment except herbicide). Plots were then treated with herbicide. Brussels sprouts were planted on 27 May in 1985 and 21 May 1986. In 1985 there were three pitfall traps/plot, recording from May-December. In each plot, five soil samples were taken from around unprotected plants and five soil samples from plants protected with a plastic barrier (6 cm high, 38 cm diameter; internal soil level raised to allow beetles to escape but not enter). Similar sampling was carried out in 1986, with beetles recorded weekly from 6 January to 2 December from three pitfall traps, and collected weekly April-December from 10 pitfall traps surrounded by plastic barriers (barriers used to stop egg predation). Cabbage root fly eggs were counted 10 June-21 October and pupae were collected from soil from four plants/plot on 10 January. No organic or inorganic fertilizers were applied to the plots in 1987 but cauliflower plants were planted in the plots and beetles and cabbage root fly egg-laying surveyed.
A controlled study in 1991-1992 on two arable fields northeast of Wien, Austria (Idinger 1995) (same study as (Idinger et al. 1996, Idinger & Kromp 1997)) found that the number of emerging parasitic wasps (Hymenoptera) and flies (Diptera) was generally higher in a plot fertilized with compost than in the mineral fertilized control field. However, the effect of fertilizer on the number of emerging arthropods varied strongly between arthropod families. The parasitic wasp families (Ichneumonidae, Braconidae and Proctotrupoidea) all emerged in significantly higher numbers on the compost fertilized plot. The same was true for two of the more common fly families, gall midges (Cecidomyiidae) and non-biting midges (Chironomidae), and partly dark-winged fungus gnats (Sciaridae), whereas two families, balloon flies (Empididae) and humpbacked flies (Phoridae), were found more often in the control field. None of the presented families or species emerged in highest numbers in an unfertilized plot. Two plots (185 x 10 m each) were established in a 4 ha organic winter rye field. One was left unfertilized, the other was fertilized with compost. A nearby conventional winter cereal field served as a control. The control was fertilized with mineral fertilizer and treated with herbicides in 1991 only. Emerging arthropods were sampled from May-November 1991 and May-August 1992 in five photo-eclectors placed along a line (20 m apart) in each habitat. The eclectors were emptied every second week and moved every month. Data from six sampling dates are used in this paper.
A small controlled study in three fields on an organic farm at Obere Lobau, Austria (Idinger et al. 1996) (same study as (Idinger 1995, Idinger & Kromp 1997)) found that numbers of species, but not abundance of spiders (Araneae) and ground beetles (Carabidae) were higher in arable fields with compost rather than inorganic fertilizer applications. Numbers of ground beetle species were higher in compost and unfertilized plots (18 species) than inorganic plots (12), as was species diversity (Shannon’s H: unfertilized 2.1, compost 1.8, inorganic 1.2). Ground beetle abundance did not vary with treatment (4-5 individuals/trap). There were variations in the responses of different species with treatment. Numbers of spider species were higher in compost and unfertilized plots (30) compared to inorganic plots (21), species diversity did not differ (Shannon’s H: 2.2-2.3). Seven money spider (Linyphiidae) species made up approximately 85% of spiders in all treatments, thus numbers of additional species varied. Spider abundance did not vary with treatment (6-7/trap). Two plots (185 x 10 m) in a 4 ha wheat/rye field were either unfertilized since 1989 or fertilized with compost (80 t/ha in 1989 and 1991). A 7.6 ha field (potatoes/bean/cereal) received inorganic fertilizer (1990: 30 N, 75 P, 120 K kg/ha, 1991: 112 N, 104 Ca kg/ha) and herbicides. Five ground photoeclectors (0.25 m²) were placed 20 m apart in the centre of plots to sample arthropods. Traps were moved each month and emptied every two weeks, 5-6 times between May-November 1991-1992.
In the same small controlled study in three fields on an organic farm at Obere Lobau, Austria as (Idinger 1995, Idinger et al. 1996), (Idinger & Kromp 1997), dominant arthropod groups tended to have a higher abundance in arable fields with compost rather than inorganic fertilizer applications. In the second year, the majority of dominant arthropod groups (15 of 24) had significantly higher abundance in compost plots, these included springtails (Isotomidae, Entomobryidae), rove beetles (Staphylinidae), long-horned flies (Nematocera), dark-winged fungus gnats (Sciaridae). Three groups were more abundant in the unfertilized plots and six in inorganic plots. Differences between treatments were only consistent over two years for a few groups. Non-biting midges (Chironomidae) and long-legged flies (Dolichopodidae) were significantly more abundant in compost plots, spiders (Araneae) and hypogastrurid springtails (Hypogastruridae) in unfertilized plots and humpbacked flies (Phoridae) and slender springtails (Entomobryidae) in inorganic fertilizer plots.
A study of arable fields in 1989-1992 and 1994 in Germany (Pfotzer & Schuler 1997) found that soil microbial activity, feeding activity of soil fauna and the abundance of springtails (Collembola) and mites (Acari) were higher in plots with organic rather than mineral fertilizers. Soil microbial activity did not differ between treatments in April (17-20 micro fluorescein g/dry matter/h), but it was significantly higher with compost treatments (farmyard manure 25-32, farmyard manure plus hornmeal 24-31, composted organic household waste 25-34) compared to mineral fertilization (20-27). Compost application significantly increased feeding activity compared to mineral fertilization (farmyard manure 1-5 perforated baits/d, farmyard manure plus hornmeal 1-5, household waste 1-6, mineral fertilization 1-2). The abundance of springtails and mites showed the same pattern. Composts were applied at 60 Mg fresh matter/ha and hornmeal at 0.6 Mg/ha. Fields were on rotation from winter wheat to oil radish, potatoes and winter barley. Soil biological activity was measured with the bait-lamina test (April-August 1994) and rate of fluorescein diacetate hydrolysis (topsoil 0-10 cm samples). Springtails and mites were sampled 13 times between 1989 and 1992 using a modified Kempson extractor.
A randomized, replicated, controlled trial from 1990 to 1992 in Suffolk, UK (McCloskey et al. 1998) found that the use of organic rather than mineral fertilizers did not affect the abundance of three weed species, sterile brome Bromus sterilis, common poppy Papaver rhoeas and cleavers Galium aparine. Abundance of the three species did not differ between plots treated with organic poultry manure and those treated with conventional NPK fertilizer. From October 1989 winter wheat plots were treated with either composted poultry manure or conventional NPK fertilizer, applied at 240 kg N/ha/year. The weed species were sown either singly or together, or left to grow naturally in control plots. There were three 9 m2 replicate plots for each combination of treatments. Weed growth was monitored from 1990 to 1992.
A 1999 literature review (Kromp 1999) found six studies testing the effects of using organic rather than mineral fertilizers. Five studies found more ground beetles (Carabidae) with organic manure (in one case green manure) than mineral fertilizer, these included (Pietraszko & De Clercq 1982, Hance & Gregoirewibo 1987, Humphreys & Mowat 1994). One study (Idinger et al. 1996) found no difference in the total numbers of ground beetles between compost and mineral fertilizer.
A replicated, controlled, randomized study between 1978-1998 of arable farming in Switzerland (Fliessbach et al. 2000) investigated the effect of organic and conventional systems (including use of only mineral fertilizers) on arthropod, earthworm (Lumbricidae), weed and microorganism abundance and diversity. Organic systems had greater earthworm diversity (7-8 species vs 6), density (365-450 individuals/m² vs 247) and biomass (242-261 g/m² vs 183) compared to conventional systems. Earthworm density and biomass was lowest in conventional systems with mineral fertilizers (143 individuals/m², 117 g/m²) and unfertilized plots (217 individuals/m², 137 g/m²). Microorganism biomass was higher in organic systems (312-406 mg microbial C/kg) than conventional systems with manure and mineral fertilizer (271-285 mg microbial C/kg), conventional systems with mineral fertilizer only (171-244) and unfertilized plots (177-208). Ground beetle (Carabidae) diversity was higher in organic (35-38 species) than conventional systems (32), as was the density of ground beetles (99-113 vs. 55), rove beetles (Staphylinidae) (37-40 vs 23) and spiders (Araneae) (58-76 vs 33). Organic systems received approximately 50% less fertilizer (farmyard manure only), than conventional systems. The study was a randomized block design with treatments replicated in 3-6 plots in each of four blocks (96 plots of 100 m²).
A 2000 literature review (Holland & Luff 2000) looked at which agricultural practices can be altered to benefit ground beetles (Carabidae). It found four European studies (Purvis & Curry 1984, Hance & Gregoirewibo 1987, Humphreys & Mowat 1994, Idinger 1995) showing that adding organic manure or compost to agricultural soil increased the numbers of ground beetles relative to sites treated with mineral fertilizer.
A long-term replicated controlled trial from 1956 to 1995 on alpine pasture in the Bernese Oberland region of Switzerland (Koch & Meister 2000) found that the type of fertilizer used (slurry, PK or NPK) affected the number of plant species, with a significantly greater number of species found on plots fertilized with slurry (on average 36 species) than with NPK fertilizer (on average 29 species), and an intermediate number of species found on plots fertilized with PK. The type of fertilizer did not affect species diversity. Fertilization over a 40 year period reduced the number and diversity of plant species. Plant abundance and diversity (Shannon’s H) were greatest in unfertilized plots, where over 60 species were recorded. N was applied at 83 kg/ha, P as 90 kg/ha phosphate (P205) and K as 180 kg/ha potash (K20). There were four replicates.
A small 2000 literature review on aspects of organic farming (Pfiffner 2000) found that organic fertilizers can enhance ground-dwelling arthropods through a richer supply of detritus-eating soil invertebrates (saprophagous mesofauna) (Purvis & Curry 1984). Organic fertilizers without the use of pesticides produced the highest earthworm biomass (Bauchhenss 1991).
Bauchhenss J. (1991) Regenwurmtaxozönosen auf Ackerflächen unterschiedlicher Düngungs- und Pflanzenschutzintensitäten [Earthworm taxonomic communities on arable land with different fertilization and plant protection intensities]. Bayerisches Landwirtschaftliches Jahrbuch, 68, 335-354.
A 2000 literature review of grassland management practices in the UK (Wakeham-Dawson & Smith 2000) found one study that reported that although the abundance of common earthworms Lumbricus terrestris tended to increase with the addition of farmyard manure, heavy applications (more than 500 m³/ha/year) of slurry can be toxic (Curry 1994). Another study found that although densities of larger soil invertebrates did not differ in fields with and without farmyard manure applications, bird usage was higher in those that had received moderate applications (Tucker 1992).
Tucker G.M. (1992) The effects of agricultural practice on field use by invertebrate-feeding birds in winter. Journal of Applied Ecology, 29, 779- 790.
Curry J.P. (1994) Grassland Invertebrates. London, Chapman & Hall.
Two replicated controlled trials in Warwickshire, UK (Bell et al. 2008) found that adding compost or green manure to wheat fields increased numbers of arthropod predators and springtails (Collembola) in the soil at or close to where the compost was added. The effect was local and did not translate to a field-scale increase in numbers of ground active arthropod predators when 1.5 to 3 m-wide strips of compost were added to fields. There were also fewer cereal aphids (pests) (Aphidoidea) in plots with compost applied, but in field-scale experiments this difference was not statistically significant. In the small scale experiment, half of 160 plots 30 x 35 cm in size (2000) or 20 plots of 4 m2 (2001 and 2002) were treated with mushroom compost in April, half were not. Arthropod predators in the soil were sampled within sunken bowls between April and May each year. In the large-scale experiment, 20 x 10 m plots were treated with compost in one 3 m-wide strip, two 1.5 m-wide strips, or not given compost. There were six replicates of each treatment. Arthropod predators were sampled in a large pitfall trap and two 0.5 m2 quadrats 1-6 m away from the experimental treatments. Springtails were counted from soil cores in the compost strips and 1 m and 6 m away.
A replicated, controlled study in 2004 of grass/clover Trifolium spp. fields in Switzerland (Birkhofer et al. 2008) found that spider (Araneae), but not ground beetle (Carabidae) or rove beetle (Staphylinidae), abundance was significantly greater in plots with organic fertilizers compared to those with synthetic fertilizers. Spider activity density was 80% greater in organic plots in April and October (1.1/m²) than conventional plots (0.9/m²). Spider diversity did not differ significantly with treatment. Ground-running spider abundance (78% Pardosa spp.) was significantly greater in organic compared to conventional plots in April (1.0 vs 0.6/m²), August (1.2 vs 1.0/m²) and October (1.2 vs 0.9/m²). In contrast, foliage-running spiders were more abundant in conventional plots in May (0.5 vs 0/m²). There was no effect of treatment on potential prey (aphids (Aphididae), leafhoppers (Auchenorrhyncha), and globular (Sminthuridae) and slender (Entomobryidae) springtails (Collembola)). Treatments were replicated in a 12 x 4 Latin square design of 10 x 20 m plots. Half of each plot received high levels of manure or synthetic fertilizers. No pesticides were applied. Five pitfall traps were placed within a fenced enclosure (1.8 m²) established within each plot before each of the five annual cuts (April-November 2004). After 14 days invertebrates were identified to group and activity densities calculated. Potential prey taxa were sampled by suction sampling (2 m² area) and a soil core (20 cm diameter) in each subplot in October.
A replicated, controlled, randomized study of arable fields over two years in England (Eyre et al. 2009) found that wolf spider (Lycosidae), ground beetle (Carabidae) and true bug (Hemiptera) abundance tended to be higher in plots with organic fertilizers. In contrast, rove beetles (Staphylinidae), money spiders (Linyphiidae), hoverflies (Syrphidae) and parasitoid wasps (Braconidae) tended to be more abundant in plots with conventional fertilizer applications. Effects depended on year and crop type (grass/clover Trifolium spp., cereals, vegetables). There was no effect of treatments on net-winged flies (Neuroptera) and parasitic wasps (Proctotrupoidea). A field was divided into four blocks (122 x 122 m), each with 32 plots (24 x 12 m). Treatments were conventional or organic (no) pesticide applications, and conventional (inorganic) or organic (none or compost) fertilizers. Invertebrates were sampled using five monthly samples from five pitfall traps/plot from May-September and three 1 minute suction samples/plot in the first week of July, August and September 2005 and 2006.
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- Humphreys I.C. & Mowat D.J. (1994) Effects of some organic treatments on predators (Coleoptera, Carabidae) of cabbage root fly, Delia-radicum (l) (Diptera, Anthomyiidae), and on alternative prey species. Pedobiologia, 38, 513-518
- Idinger J. (1995) Ground photoeclector evaluation of Diptera and parasitoid Hymenoptera in unfertilized, mineral nitrogen and compost fertilized grain fields. Mitteilungen Der Deutschen Gesellschaft Fur Allgemeine Und Angewandte Entomologie Band 10, Heft 1-6, Dezember 1995, 10, 553-556
- Idinger J., Kromp B. & Steinberger K.H. (1996) Ground photoeclector evaluation of the numbers of carabid beetles and spiders found in and around cereal fields treated with either inorganic or compost fertilizers. Acta Jutlandica, 71, 255-267
- Idinger J. & Kromp B. (1997) Ground photoeclector evaluation of different arthropod groups in unfertilized, inorganic and compost-fertilized cereal fields in eastern Austria. Biological Agriculture & Horticulture, 15, 171-176
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- Bell J.R., Traugott M., Sunderland K.D., Skirvin D.J., Mead A., Kravar-Garde L., Reynolds K., Fenlon J.S. & Symondson W.O.C. (2008) Beneficial links for the control of aphids: the effects of compost applications on predators and prey. Journal of Applied Ecology, 45, 1266-1273
- Birkhofer K., Fliessbach A., Wise D.H. & Scheu S. (2008) Generalist predators in organically and conventionally managed grass-clover fields: implications for conservation biological control. Annals of Applied Biology, 153, 271-280
- Eyre M.D., Sanderson R.A., Shotton P.N. & Leifert C. (2009) Investigating the effects of crop type, fertility managemen and crop protection on the activity of beneficial invertebrates in an extensive farm management comparison trial. Annals of Applied Biology, 155, 267-276