Question 3. How can organic farming contribute to environmental conservation?
p. 250-260
Texte intégral
Methodological difficulty of comparing the environmental impact of organic and conventional farming
1Several hundred studies have attempted to assess the environmental impact of organic farming compared with conventional farming. They compare different types of production, under varied ecological conditions. However, each study covers a limited number of technical criteria and a particular cropping system in a given climatic zone. The results therefore cannot be generalised.
2Any comparison of OF and CF also raises a methodological difficulty because the term "conventional farming" covers a range of different systems, from productivist monoculture, involving the use of large quantities of mineral and chemical inputs, to combined crop/livestock systems based on integrated management of organic matter and the use of manure. Compared with the former, the advantages of OF are numerous, but compared with the latter, the positive effect of OF is smaller or unknown, because an integrated conventional system already employs some OF techniques.
3Thus, for any comparison of OF and CF, it is important to clarify which systems are being compared and the type of environment considered. With this reservation, an examination of several hundred studies shows that the effects of OF on the environment are better than, or at least as good as, CF. Only one study reports less beneficial overall effects from OF. Although few comparative OF/CF studies have been conducted in tropical zones, they generally show similar results to temperate-zone studies.
4Some of the experts stress that improving CF practices on large areas (reduction of inputs, crop rotation, fallowing, etc.) would have a greater positive effect on the environment than practising OF on small areas. A large number of conversions to OF would nonetheless provide better environmental protection, particularly in ecologically sensitive zones (water offtake zones, protected areas, areas around nature reserves), as studies by INRA and Cemagref1 on the Vittel Plateau have shown.
5The environmental benefits of OF stem from the techniques employed, which include crop rotation, fallowing, organic fertilisers, fewer toxic products sprayed on the soil (hence increased flora and fauna), and use of disease-resistant local varieties and species. Some of these techniques can also be used with favourable environmental effect in other types of farming that seek to reduce the negative impact of CF on the environment (e.g. IFS). It would be useful to synergy between research projects developing techniques for OF and IFS.
Overall, organic farming has a more favourable impact on the environment than conventional farming
6Table 12 below, based on a study of more than 300 bibliographical references that compare the environmental impact of conventional farming and organic farming, shows that, for most environmental quality factors, organic farming performs better overall than conventional farming.
7The main known facts concerning the environmental impact of OF compared to CF, and on which these general statements are based, are cited below for each of the generally recognised components of the environment: soil, landscape, biodiversity, water and air.
Effect of organic farming on environmental parameters
Organic farming has a significant beneficial effect on soil quality
8The organic content of organically farmed soils is higher than in conventionally farmed soils. Microbial biomass is greater, more active and more varied. Several studies show that plant roots are more frequently colonised by mycorrhizae. Earthworms are also more numerous in organically farmed soils. All these factors have a positive influence on soil structure (structural stability, porosity/permeability and water retention).
9Total nitrogen content and the amount of potentially mineralisable nitrogen are higher in OF, while the soluble nitrogen (nitrates) content is usually lower. The difference in soil nitrate content can be related to research findings that show that organic produce is less rich in nitrates but contains higher quality proteins and a higher dry content (in root vegetables, bulbs, tubers and green vegetables) than CF produce.
Table 12: Comparison of the impact of organic farming (OF) and conventional farming (CF) on five environmental criteria.

Source : Lotter (2003) from a review by Stolze et al. (2000) based on almost 300 publications.
10OF is also frequently associated with higher phosphorus levels, but not always; results are sometimes higher in CF owing to significant inputs in intensive farming. The presence of larger quantities of mycorrhizae in organically farmed soils is also a factor that improves the availability of phosphorus for plant nutrition. Trace elements have not been studied much.
11All in all, the positive effect of OF on several important soil properties generates better mineral nutrition and water supply conditions for plants and makes crop more resistant to some pests and diseases.
12However, as Table 13 below shows, the aggregate data available are still limited and rarely consider differences between OF and CF in tropical zones.
13Various studies also show that OF crops perform better during droughts, e.g. maize and tomatoes in the United States. This may be due to improved soil properties, mainly physical and biological properties, which improve the soil's water retention capacity and foster root and mycorrhiza development.
14Yields of organic crops have been observed to vary less from year to year, particularly in organic rice in Japan, where an unusually cold summer in 1993 destroyed conventional rice crops but only reduced organic rice output to 60 % to 80 % of a normal year's output. A review of 208 projects in Africa, Asia and Latin America shows that practices comparable to OF are liable to generate a significant increase in yields over traditional agriculture: from 50 % to 200 % in rain-fed crops, and 5 % to 10 % for irrigated crops.
15However, a study in the Rhône-Alpes region of France stresses that the beneficial effects of OF on soil properties are not found in some intensive OF systems with short crop rotation cycles and frequent tillage for weed control. The frequent tillage, sometimes carried out when the ground is too wet, compacts the soil so that crop rooting and nutrition are adversely affected.
Organic farming's favourable impact on erosion and landscapes
16Organic farming methods help to prevent erosion. Improved physical properties – porosity, permeability, water retention – and ground cover with green manure protect the soil effectively at field level, even in tropical climates where erosion is common.
Table 13 - Comparison of soil parameters in OF and CF (23 studies)

Source: Lotter 2003, modified and extended by Moreau et al. (2004)
17At a broader scale, the spatially coherent mosaic of varied land uses, with hedges, ditches etc., is also a favourable factor. The various barriers found in OF systems, formed by vegetation or by topographical features, help filter surface runoff, hold back solid matter and slow down surface runoff. Transfers of matter due to surface runoff are reduced at farm scale and catchment scale. In the tropics, studies in Rwanda, Kenya, Nicaragua and Chile have shown that diversifying land use patterns has a positive impact on erosion.
18It is mainly in Europe that the notion of landscape has developed. Research funded by the European Union in several countries assessed the impact of OF on landscapes, using the same methodology in each country. Table 14 below sums up the results. Landscape quality criteria generally score higher in OF, with more diverse and varied landscape elements creating a greater diversity of biotopes, linked to longer rotations, a wider range of crops growing at the same time and more varied land use (grass strips, hedges, copses, ditches, tracks etc.).
19OF encourages farmers to pay more attention to utilising the ecological potential of their farms in order to reduce external input use. This results in better vertical cohesion of the landscape on OF farms (match between the use of a place and its particular characteristics).
20OF also gives the landscape greater horizontal cohesion. The arrangement of different landscape elements such as fields, woodland, hedges, grass strips etc. and the denser network of tracks, ditches, buildings etc. allow for greater cohesion and a more functionally complex general environment on OF farms. Criteria for seasonal and historical cohesion (the presence of recognisable signs of local history and season) also appear more favourable under OF.
21However, OF will only make a positive contribution to landscape if the farmer is sufficiently aware of the issue and motivated by it. We should also point out that references on this question are lacking for tropical regions.
22Lastly, the impact of OF on the general environment and landscape is all the greater when it is part of a concerted approach to regional planning, with environmental goals for an area jointly defined by its farmers and society.
Tableau 14 - Comparaison d'exploitations en AB et en AC d'après différents critères de qualité du paysage

Source: Mansvelt et al., 1998, modified and completed by Moreau et al. (2004).
Organic farming increases biodiversity
23OF augments biodiversity, both in terms of a wider range of livestock breeds and crop species on the farm and in terms of wildlife and flora. By avoiding synthetic chemicals for crop protection, creating more varied biotopes and ensuring greater spatial cohesion, OF fosters a more abundant and biologically diversity wild fauna and flora.
24As well as involving more species and breeds than CF, OF maintains greater genetic diversity than CF, which with its systematic use of the most productive breeds and varieties has greatly reduced its gene pool. While OF does not forego modern, productive breeds and varieties, it helps to maintain and optimise the use of traditional species, breeds and varieties which are generally well adapted to local conditions and can be used to diversify and improve crops and herds under OF. Old vegetables are being grown anew in Europe, amaranth in Mexico, maca (Lepidium meyenii, a root crop) in Peru, and in the tropics some wild food plants could potentially be domesticated and grown as crops. Many seed banks and programmes to conserve local varieties are linked to OF – e.g., for tropical climates, in Kenya and Cuba.
25All in all, OF reflects the characteristic ecological diversity of an area better than CF. Because of its beneficial effects on biodiversity, OF is ideally suited for nature parks and reserves and surrounding localities, wherever farming is permitted there. Studies in this connection have been carried out on coffee crops in Salvador, and in the Ampay forest sanctuary in Peru.
26Organic farming does not contribute to the spread of genetically modified organisms (GMOs) and their attendant risks (more or less scientifically demonstrated) of damage to useful insects, acquisition of resistance by insect pests or weeds, danger to indigenous fauna and inefficacy in terms of crop protection. On the contrary, OF fosters "natural balance", based particularly on pest and disease management. Nonetheless, pest and disease control is difficult or even economically impossible in some heavily infested regions, especially when OF systems are starting up. The risk of spreading pests and diseases from organic crops to conventional crops cannot be excluded, because organic farms can maintain reservoirs of them.
27Floral and faunal diversity favours functional biodiversity and helps make OF's biological pest management methods effective. Better disease resistance under OF has been show with tomato, grapevine and cucumber in particular. By contrast, some herbicides used in CF may reduce crops' disease resistance. Studies have shown that glyphosate use reduces resistance to various root pests in beans (Phaseolus vulgaris) because it reduces root lignification and alters the composition of the plant's root exudates.
28Organic crops are more weed-tolerant than conventional crops (higher density possible without reducing yields) and OF practices such as rotation, green manure and preventing seeding) make it more difficult for weeds to spread.
Organic farming reduces the risk of water pollution
29Compared to CF, OF reduces the risk of water pollution by solid and dissolved substances (no synthetic pesticides or fertilisers, and less erosion). INRA has shown that OF is helping to protect water quality at the Vittel mineral water source and in stream basins tapped for drinking water.
30The absence of mineral nitrogen fertilisers in OF does not eliminate the risk of water pollution by nitrates; there remains some risk from excess soil nitrates, especially during the conversion period. However, with the exception of pig and poultry farming and some intensive organic market gardening systems, these risks (per unit of output) are often less than, and at most comparable with, those for CF. In the Caribbean, this has been shown with citrus growing in Cuba. There is also generally less excess phosphorus, potassium and other elements in organically farmed soils and the risk of resulting water pollution and eutrophication is less than in CF.
31The beneficial role of OF for preserving water quality is recognised in some parts of Europe where water supply companies are paying subsidies to help farmers convert to OF in water offtake zones. They consider this a cost-effective solution, reducing the cost of treating drinking water by reducing contamination of groundwater by nitrates and pesticides. In Germany, the city of Munich has been subsidising OF for some twenty years in the Mangfall river catchment, while in France the Vittel Perrier mineral water group is working with farmers in the company's offtake zones to encourage them to convert.
32The beneficial effect of OF on diffuse erosion should also mean less sedimentation further downstream, in reservoirs and in coastal areas (could reduce Martinique's frequent problems with turbid water).
33If OF became sufficiently widespread it could help preserve the abundance and functioning of aquatic ecosystems by reducing pollution and eutrophication in surface waters and coastal waters.
Can organic farming help combat global warming?
34Organic farming uses several agricultural practices that are recommended for increasing the soil carbon store and reducing emissions of greenhouse gases, particularly C02 and N20. These are crop rotation, use of organic fertiliser, integrated crop management and biological pest control. However, although increasing the soil's carbon store has a beneficial effect on the atmospheric C02 balance, soil carbon ceases to accumulate once the soil has reached a new equilibrium, after a few decades at most. OF can help to reduce C02 emissions from fossil fuels, because it uses less energy than CF per unit area of farmland, and often also per unit of farm produce obtained. It has not been clearly established that OF can help reduce release of N20 into the atmosphere.
35Energy efficiency (ratio of energy produced to energy consumed) is generally greater in OF than in CF. Overall greenhouse gas emissions per unit area appear to be generally less in OF than in CF, but this is less clearly established and not always borne out when assessed in terms of emissions per unit of produce, because of the lower yields in OF.
36All in all, in the present state of knowledge it has not so far been shown that OF is advantageous for combating global warming, especially when assessed per unit of output.
Possible negative effects of organic farming
37Organic farming is not free of all risk of negative effects. It is not easy to regulate soil fertility using natural fertilisers such as organic matter and crushed rock, especially with short-cycle crops. The result is often lower yields or excesses of soluble minerals (nitrogen and others) that can pollute water, especially during the first years under OF. There is less risk where there is full proficiency in the particular methods of OF. But ecological conditions can also affect the degree of risk. In Martinique, any excess soil nitrates due to organic inputs (e.g. for market gardens or Caribbean food crops) may increase drainage water nitrate content more significantly in the drier south than in the north, where the water balance is more often in surplus, and to a greater degree.
38There is a risk of under- or over-fertilising the soil in OF, because composted organic matter is more complex and varied in content than chemical fertilisers. For example, the variability of compost made from poultry manure and sugar refinery waste has caused problems for developing organic sugar cane growing in Mauritius.
39Risks from poor management of manure by farmers who are not fully proficient in OF methods requires some consideration. They include contamination by pathogenic germs or dissemination of weed seeds from poorly composted manure, and excessive manure application.
40Copper from the copper-based products used against fungal diseases and helminths in OF can accumulate in the soil and ultimately reach toxic levels. Particular attention should be paid to this factor in Martinique, whose soils naturally have a high copper content.
41The natural organic inputs authorised for OF are often complex in composition and have not been officially tested and proven. Not all natural materials are entirely non-toxic and some may pose problems. For example, rotenone administered to rats at a dose of 2-3 mg/kg caused symptoms similar to Parkinson's disease, and the plant-based pesticide pyrethrin is classed as carcinogenic by the US Environmental Protection Agency. However, the agricultural use of these substances in OF is permitted at considerably lower doses than those used in toxicological studies. They are also rapidly biodegradable, which greatly reduces their toxic potential.
42Organic crops can also act as reservoirs for diseases that then spread to neighbouring CF crops. This has been reported in the Netherlands.
Predictable positive effects of organic farming on the environment in Martinique
43The development of OF can be expected to have beneficial effects on the environment.
44OF can improve soil quality. Soil organic matter content should increase most in soils that have formerly gown market garden crops, Caribbean food crops and pineapple, as this is where the carbon store has been most severely depleted. Soil flora and fauna and related factors should improve in all cases due to the reduced use of toxic substances and a more diverse input of crop waste. The availability of potassium and phosphorus, often a problem in Martinique's soils, should also be improved and better regulated in OF because there is more organic matter and biological activity in the soil.
45Improving the physical and biological properties of the soil should make it possible to make more economical use of irrigation water – a definite advantage in the drier parts of Martinique.
46Concerted land management, with OF in a water offtake zone or stream basin, could help reduce surface runoff and river pollution.
47The spread of OF should conserve and make better use of local breeds. Increased wild biodiversity is also to be expected where land is managed in a concerted manner.
Notes de bas de page
1 Cemagref: Centre national du machinisme agricole, du génie rural et des eaux et forêts.
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