How do organic management practices contribute to these outcomes?
A study by the team led by the Organic Research Centre for Defra (DEFRA, 2018) reviewed a range of practices mentioned in organic standards and their impact on a variety of environmental outcomes. Results from the work highlighted the substantial benefits that can accrue from organic management techniques in terms of environmental performance. In particular, this applies for the impact categories of soil quality, non-renewable resource-use efficiency and biodiversity. As some management practice(s) can lead to lower yields compared to high-input-output approaches, this can lead to reduced positive/more negative environmental impacts when comparisons are made per unit of product. Conversely, systems applying such management practices will generally perform better when comparisons are made on a unit of land-area basis.
The ORC team reviewed organic standards and worked with experts to identify a range of techniques and management practices and scored them against their environmental impact including biodiversity. The outcomes for biodiversity can be found in Table 3.1. Their overall assessment was that organic management practices have considerable potential to improve a range of environmental performances including biodiversity.
Table 3.1: Biodiversity impact assessment for organic management techniques
A report by FiBL (Pfiffner and Balmer, 2011) identified the main causes of higher biodiversity in organic systems as:
- Forgo use of herbicides;
- Forgo use of chemically-synthesized pesticides;
- Less and purer organic fertilizer;
- Fewer cattle per square meter;
- More diversified crop rotation with higher clover-grass percentage;
- Conservation tillage;
- Higher percentage of semi-natural areas;
- Higher percentage of arable and ecological areas;
- More diversified farm structure.
In addition, the reductions in nitrogen and phosphorus fertiliser result in reduced eutrophication impacts on aquatic ecosystems, and reduced impacts on nitrogen-sensitive species from atmospheric depositions.
System diversity/mixed farming
The ORC literature review (DEFRA, 2018) highlighted the substantial benefits that can be achieved through a closer integration of crops and livestock within mixed farming systems. In particular, benefits can accrue where the inclusion of livestock prompts the utilisation of nitrogen-fixing-legume-containing leys, which can contribute to soil fertility-building, biodiversity and pest, disease and weed control, whilst reducing dependence on manufactured N fertiliser (Knox et al., 2011; Lemaire et al., 2014).
An observation by Ulber et al. (2009) was that the increased plant diversity on organic farms arose from multiple aspects of the system, such as longer crop rotations and the absence of herbicides and synthetic fertilisers. This was emphasised by the observation that, under non-organic conditions, a change of only a single factor, in this case the introduction of crop rotation, did not affect plant diversity.
Organic farms tend to have more favourable habitats such as hedgerows, grass margins, grassy ditches, small fields etc. than conventional farms. Norton et al. (2009) studying farms in England that had some arable crops found that the organic farms were located in more diverse landscape types; had smaller field sizes; higher, wider and less gappy hedgerows subjected to less frequent cutting; use rotations that include grass; and are more likely to be mixed. Even within diverse landscapes, organic systems had greater field and farm complexity than non-organic systems. This has prompted considerable discussion about whether benefits are derived from the farming system or from the habitat that is independent of the farming system. Some researchers e.g. Chamberlain et al. (2010) argue that the benefits of organic farming – in this case for farmland bird populations – come “primarily through greater habitat heterogeneity” and not from organic farming practice, but as discussed below, even in diverse landscapes, organic farms are more complex.
Several studies covering the range of taxa found that the biodiversity benefits of organic systems are of particular value in simple agricultural landscapes where organic farms are both spatially and temporally more diverse than their conventional counterparts e.g. Clough et al. (2007b), Boutin et al. (2008). Batáry et al. (2010). However, Norton et al. (2009) found that even within diverse landscapes, organic systems had greater field and farm complexity than non-organic systems. Some studies have also shown that organic farms can influence biodiversity in the surrounding landscapes with higher diversity recorded on conventional farms in organic ‘hotspots’ e.g. Rundlöf et al. (2008), Gabriel et al. (2010), Hodgson et al. (2010) suggesting that species are ranging across neighbouring conventional farms.
The increased systems diversity and complexity will impact positively on biodiversity by producing an increased number of potentially interconnected habitats that benefit both flora and fauna above and below ground. The spatial separation of different habitats on a farm at the same time i.e., leys with floriferous plants, species rich grassland, headlands and hedgerows plus cropped areas provides sites for pollinators, arable weeds, grassland fauna etc at any one moment in time. They also provide habitats and refuges for crop pest predators allowing reduced applications of pesticides. System diversity also allows for a wider range of habitats for a wider range of fauna including birds, mammals, and a range of insects i.e., pollinators.
Crop rotations are an essential part of an organic system and organic standards require certain principles to be observed within the rotation. These include a balance between fertility and exploitative phases of the rotation, the inclusion of a leguminous crop to provide nitrogen for following crops, the inclusion of crops with different root systems, and that plants with similar pest and disease susceptibilities must be separated by a suitable time period. They may also include a more diverse range of sowing (winter/spring) for weed control purposes.
A systematic comparison of organic and conventional crop rotations at the global scale based on a meta-analysis of the scientific literature by Barbieri et al. (2017), summarised in Dimambro et al. (2018), found that organic farming has differences in land-use compared to conventional, with increased complexity of organic crop rotations considered likely to enhance ecosystem service provisioning to agroecosystems. Some key findings when comparing organic with conventional farming were:
- Catch crops and undersown cover crops in cereal fields are more frequent in organic systems;
- Lower proportion of cereals;
- Higher frequency of cereal intercropping with legumes;
- More nitrogen fixing crops, including mixed legume-grass temporary leys;
- More diverse crop rotations;
- Longer crop rotations.
Organic mixed farming practices and the rotations they rely on can play an important role in enhancing biodiversity in farming systems. The association during different parts of the rotation between cropping and livestock enterprises through transfer of manure, feed and/or through the use of grazing livestock on grass/clover leys is an important component that delivers many environmental services including improved soil quality, water quality and biodiversity. Increased landscape mosaic diversity created by rotations can encourage populations for a large range of taxa (plants, insects, small animals and birds), in particular by providing permanent vegetation within undisturbed fields (i.e. forage and grasslands Lemaire et al. (2014)).
Introducing crops and varieties that increase the diversity and distribution of crop architecture and biomass above and below ground is also important in delivering environmental services. The number of crops in a sequence, combined with the frequency of return of those crops, can alter the ecosystem services provided by a rotation. The inclusion of species mixtures or intercrops may enhance effects also. Venter et al. (2016) showed the soils under more diverse crop rotations had higher microbial richness (+15.11%) and diversity (+3.36%) scores, possibly resulting from different organic matter inputs, as well as soil structure and habitat changes. Above-ground biodiversity can be enhanced by the crop species selected, which provide a range of habitats. Differences in flowering times can attract a wider variety of pollinators.
Similarly, the use of diverse or herbal species in ley swards, for permanent or temporary pasture and either grazed or ungrazed, can improve biodiversity with the farming system. It is shown to improve soil structure, N availability, biodiversity, weed cover and drought resistance. This approach reduces monocultures in swards (Wilkinson, 2017). Diverse mixtures support more pollinators throughout the season and provide a larger food range for birds. Mixtures with higher diversity do not compromise wild plant diversity (Zaralis et al., 2016). The inclusion of forage crops such as lucerne, sainfoin and chicory within pasture areas on livestock farms is a common technique employed by organic farmers. Novel forages can be grown as a pure stand but are usually grown in a grazing mix (e.g., with clover to help supply N through biological fixation) to improve productivity, biodiversity, resource use efficiency and soil health. Lucerne hay fields can encourage on-farm biodiversity by providing a habitat for microorganisms and invertebrates (Veronesi, Huyghe and Delgado, 2006). Increased floral abundance and longer flowering periods can also improve the availability of nectar and pollen, driving bumblebee community composition and pollinator populations (Knight et al., 2009; Potts et al., 2009; Stanley, Knight and Stout, 2013).
Leys can also be established by sowing during or after the sowing of a crop. This is usually done with a cereal and allows the ley to establish while the main crop is still in the ground; this can be before or after the main crop is harvested and reduces the need for tillage in preparation for sowing the ley. Undersown leys can provide an uncultivated overwinter bridge, which allows many insects to pupate in the soil and emerge as adults in spring. These adults lay eggs all through the neighbouring cereal crops and, by the time game chicks hatch in mid-summer, there are lots of small sawfly caterpillars around for them to eat (GWCT, 2018). Arthropod abundance, density and species richness was higher in undersown spring barley and undersown grass fields compared to mono-cropped fields (Huusela-Veistola and Hyvönen, 2006). A study in Finland found that fallow plots established by undersowing spring barley with grass or grass and red clover had more spiders and fewer pest insects than a control plot of spring barley, but similar numbers of ground beetles (Fletcher, 2018).
Rotations and the inclusion of both crops and livestock systems within them allows ruminants to be predominantly forage fed. This allows the production of meat/milk from forage, through grass-based diets with lower concentrate feed rates, and reduces the need for manufactured inputs, especially fertiliser and purchased compound feed. The use of forage/grassland areas can conserve and encourage on-farm functional biodiversity (Wilkins, 2008) although the wider adoption of such methods may result in less land available for conservation or forestry (Basset-Mens and Van Der Werf, 2005; Fischer et al., 2014). Although outdoor grazing systems can promote greater species diversity in grassland compared to cutting for silage and mulching (Lampkin et al., 2015), the use of extensive grazing practices can result in greater agricultural land use, limiting the amount of land available for conservation and other purposes (Green et al., 2005).
Rotations add a temporal aspect to the spatial diversity produced by mixed farming systems. Rotational systems generally have a wider range of crops, livestock and leys/grassland. The increase in range of crops and grassland will promote increased diversity of flora and fauna within the crops and swards as well as in the soil. The use of multispecies leys within rotations increases the range of plant species in themselves but also reduces the amount of synthetic fertilisers needed and promotes biological activity in the soil. The lower fertility levels within the cropping systems also promotes arable weeds that can be rare in intensive systems. The temporal features of a rotation mean that within a given farm or landscape there will be a range of habitats that can promote more mobile types of biodiversity such as birds, mammals and a range of mobile insects.
Avoidance of agrochemicals
The use of synthetic nitrogen and phosphate fertilisers has direct impacts on biodiversity, which organic farming avoids. These impacts include:
- Suppression of nitrogen sensitive species, in part through competition from more nitrogen-responsive species;
- Eutrophication of aquatic habitats and algal blooms as a result of nitrate leaching and phosphate loss through soil erosion and run-off from manure and slurry applications;
- Nutrient accumulation, acidification, and organic matter reduction in soils (affecting in particular earthworms and mycorrhizae).
Organic farming has a unique approach to the development and management of soil fertility that is not seen in other non-organic farming systems with the prohibition of synthetic nitrogen fertilisers and the use of more complex rotations (see above), primarily based on legume/grass leys supplemented by the application of manures. The inclusion of a legume or grass ley in the arable rotation is to build soil fertility and biological activity, increase soil organic matter, prevent disease, control weeds, increase farm biodiversity and promote crop and animal health. Ley species richness increases the diversity of insects, small animals and birds (Weibull, Östman and Granqvist, 2003).
The application of home produced or imported manures and composts are also an important approach to improving soil fertility. Litterick et al. (2004) define compost as “solid particulate organic material that is the result of composting, that has been sanitised and stabilised, and that confers beneficial effects when added to soil and/or used in conjunction with plants”. This is already a well-used practice in non-organic farming, but it is important in such systems to carefully account for the nutrients available and balance fertiliser application accordingly.
Using manures and composts replaces the macro- and micro-nutrients removed in crop and livestock produce, as well as increasing soil organic matter content. A major benefit is provision of micronutrients that are not present in pure chemical fertilisers. In a long-term field trial comparing rotations using manure or compost with artificial fertiliser-based systems, distinct communities of microbes were found in the treatments with organic materials. Organic manure application increased the richness and decreased the evenness of the soil microbiota (Hartmann et al., 2015b).
The use of fertility building legume-based leys, green manures, animal manures and composts replaces the need for synthetic fertilizers. These increase the biological activity of the soil, through the supply of energy as well as nutrients, and allow a wider range of weed and other flora that do not grow in more high fertility intensive systems. The use of leys with a range of floriferous legumes provides feed sources for pollinators: if managed carefully they can do so from spring to autumn.
The use of herbicides in intensive conventional farming systems can largely eradicate non-crop plants (not only weeds) from the system, which reduces the seed rain – a food source for birds and mammals but also threatening the survival of rare plants themselves.
Organic systems are prohibited from using chemical herbicides and must rely on rotations (see above) or physical approaches to weed management such as the use of tined, brush-based implements and/or comb harrows for weed removal in field crops. Weeds are rarely if ever eradicated within a crop and so provide both seed for diverse and rare weeds to persevere within the system, and as a feed source for birds and mammals. The use of mechanical weeding is likely to encourage improved diversity of flora and fauna compared to chemical methods, as the method(s) applied are unlikely to remove weeds entirely. Some remaining flora diversity is likely to remain in the field, providing biological diversity, offering habitats for beneficial/biocontrol insects, as well as insects as a food source for birds, and helping to keep the soil covered and supporting mycorrhizal fungi populations (Melander et al., 2017; Pesticide Action Network, 2017).
Pest, disease and parasite control
That the use of pesticides for insect control has a significant impact on non-target as well as target organisms is widely documented over many decades. The impact may be direct, due to lack of selectivity of a specific product, or it may be indirect, by removing a host or food source for the non-target organisms, including beneficial insects and birds. Conversely, the use of sown refuges such as field margins and beetle banks, and other landscape elements including trees and hedges, can support a more diverse and abundant range of natural predators, providing opportunities for passive biological control of pests.
The use of fungicides for disease control is also severely restricted in organic farming, although a number of fungicides are permitted, including copper compounds which do have negative environmental impacts. Copper is used primarily as a fungicide on top fruit, vines and potatoes, but although permitted, its use is restricted in organic farming. Processes are in place to reduce and eventually ban copper use in organic farming completely (IFOAM EG, 2018). Significant research is being undertaken to find alternative controls for fungal diseases in the relatively few crops that still rely on these products.
The reduced use of anthelmintics for parasite control in livestock can have a positive impact on dung beetle species richness and diversity (Hutton and Giller, 2003; Tonelli, Verdú and Zunino, 2017). The use of anthelmintic and the prophylactic use of veterinary medicines is permitted under limited conditions in organic farming. Parasites are managed through the rotation with a strong reliance on grazing management and clean grazing systems. There is some evidence that alternative forages such as Lotus corniculatus and Chichorium intybus can help with management of parasites (Marley et al., 2003).
Conservation/wildlife promotion areas (e.g., beetle banks, hedges, field margins, agroforestry) in farmed landscapes encourage natural predators, reducing the need for imported pesticides and providing a range of ecosystem services such as soil protection, reduced run-off and nutrient retention. Ecological infrastructure manipulation considerably enhances biodiversity and species richness, providing a habitat and food supply for a range of invertebrates, birdlife and mammals whilst encouraging increased numbers of natural predators (Smith et al., 2011). Margins sown with wild bird seed mixes could be considered a valuable offset to the low-biodiversity arable field centres treated with herbicides. Such areas also provide vital forage opportunities for farmland birds during the winter period, when other food availability is limited (Williams, Audsley and Sandars, 2006). Crops grown for game cover, for example, have been shown to support up to 100 times more farmland birds and significantly more species than surrounding arable habitats (Parish and Sotherton, 2004). The use of pollen and nectar mixes sown into field margins can also significantly increase the number of bumblebees (Carvell et al., 2007).
The benefit of landscape within organic farming systems is important. Organic farms tend to have smaller fields resulting in increased field boundaries – headlands, hedges etc. This provides habitat for a wide range of biodiversity. Many species need specific landscapes features and near natural features. If these features are not available in the landscape, no major effects are to be expected from the cultivation system. Otherwise, the importance of organic farming can be very high locally. The work by Gabriel et al. (2010) showed not only are the more mobile elements of biodiversity (birds, mammals, insects) affected by landscape but that plants can also be affected at both a farm and landscape level.
The practices considered in the chapter, including the integration of landscape elements to benefit agricultural systems, illustrate the potential of a land-sharing approach to contribute to resolving the tensions between agriculture and biodiversity (Tscharntke et al., 2012; Fischer et al., 2014; Finch et al., 2020). While it is clear that many species prefer and would benefit from undisturbed natural habitat and nature restoration, there are a number of key species, including farmland birds and arable wildflowers, that have adapted to agricultural systems, and which would be negatively impacted by a land sparing approach built on agricultural intensification. Lower intensity, land-sharing approaches such as organic farming have a key role to play in the mix of approaches, including nature restoration, that might be needed to deliver on biodiversity conservation goals.
The biodiversity benefits delivered by organic farming are a consequence both of the practices prohibited under organic regulations, such as the use of synthetic nitrogen fertilisers, herbicides and most pesticides and fungicides, as well as the agroecological practices adopted by organic farmer to solve production issues without them.
The complete avoidance or substantial reduction in the use of agrochemical inputs in organic farming contributes to biodiversity by avoiding or reducing the:
- Direct toxic impacts of herbicides and pesticides on non-target organisms;
- Indirect impacts of herbicide and pesticide use on food sources and habitat for insects, birds and other organisms;
- Impacts of surplus nutrient use on soil ecosystems, including organic matter loss and soil acidification due to nitrogen use and mycorrhizal decline due to phosphate use;
- Impacts on aquatic ecosystems from nitrate leaching and phosphate losses from agricultural land;
- Impacts on sensitive habitats and low nitrogen tolerance species from nitrogen depositions, including ammonia from livestock systems;
- Impacts on insects colonising animal faeces as a result of the use of certain anthelmintics;
- Climate change impacts on biodiversity associated with emissions from agricultural input use and manufacture, as well as loss of soil carbon.
By completely avoiding the use of most of these inputs, the benefits go significantly beyond those that might be expected from a 10-20% improvement in input use efficiency within conventional systems. However, yields are also reduced as a consequence of the input use reductions, so that benefits per unit output may be lower than per unit of land used.
However, the benefits are not only derived from avoided practices and inputs. Key biodiversity-enhancing practices used include the use of:
- Mixed farming systems integrating crops, trees and livestock;
- More diverse and complex rotations and cropping systems;
- Leguminous crops for biological nitrogen fixation, supporting pollinators if managed appropriately;
- Heterogenous genetic materials (variety mixtures, populations, landraces) using genetic diversity to support pest and disease control;
- Sown refuges and other landscape elements for natural predators (passive biological pest control);
- Smaller field sizes, contributing to a more complex landscape mosaic;
- Trees and hedges with complex understoreys for shelter, erosion control and fertility management;
- Alternation of sowing times of crops for weed control, benefiting farmland birds;
- Organic matter, leys and green manures for fertility building, providing energy-rich carbon sources to help maintain soil ecosystems;
- Reduced tillage and soil cultivation depths to protect soils;
- Diverse species mixtures including legumes, herbs and novel forages for grassland;
- Land-based livestock production systems with grazing and reduced stocking rates supporting biodiversity in grassland.
While none of the practices adopted are unique to organic farmers, the combination of many biodiversity-enhancing practices in a systems-based approach allows for synergies to be exploited with the potential for greater impacts. Organic farming practices and the related biodiversity benefits illustrate how a land sharing approach can be used constructively, as an alternative to a complete separation of intensive, land sparing but low-biodiversity agricultural production from land prioritised for nature.