Introduction to integrated methods in the vegetable garden
Ploughing or no-ploughing?
Chapter : Crop soil
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⇒ Ploughing or no-ploughing ?
Introduction to integrated methods in the vegetable garden
Chapter : Crop soil
Previous or next articles ; click on a title to go to the page
⇒ Ploughing or no-ploughing ?
Tillage was immediately adopted when Neolithic man converted to agriculture over 5000 years ago. On all continents, early farmers found that tillage promoted seed germination and plant growth. In Europe, tillage was first carried out with rudimentary tools such as the adze used as a hoe. Before the Gallo-Roman era, the Celts were already using the plough, which splits the earth with a ploughshare, but does not turn it over.
Ploughing consists of turning over the soil with a spade for small areas or with a plough for large crops. In ploughing, the garden soil is not mixed. Everything on the surface of the soil, such as weeds, is buried 25 to 30 cm deep. In arable farming, mechanisation has led to deeper ploughing, which can go down to 80 cm.
Extract from the film: Les Gardiennes
The plough and ploughing have been known since at least the 5th century (1). However, ploughing did not become widespread overnight. Thus the plough was still used in France by some farmers on the eve of pre-industrial agriculture. This tool is mentioned in a very famous book written in the 19th century by Félicien PARISET (2), in which it is stated that the soil is decompacted to a depth of 10 to 12 cm three times a year for the cultivation of wheat, without worrying about the consequences for the earthworms.
With a few exceptions, the use of these different tillage techniques over thousands of years has never resulted in the desertification of cultivated soil in France. However, this is what is being criticised today in relation to tillage, and particularly ploughing. However, the plagic Anthrosols of north-western Europe (or Anthroposols in the French soil reference system), which support demanding crops where ploughing is frequently used, are characterised by a progressive accumulation over several thousand years of organic matter from agricultural activities mixed with the original soil. However, these same regions have suffered from humus loss in recent years and it is of course useful to know the reasons for this.
Is ploughing really responsible for this situation? Is it not the consequence of the generalisation of intensive monoculture and the disappearance of crop-livestock farms and the organic inputs they provide? Ploughing too deep ?But also of the generalisation of sewage systems prohibiting the spreading of human excrement in the fields for both sanitary and comfort reasons? Or particular local conditions? For example, in the US, more than a third of the Corn Belt in the Midwest has lost its carbon-rich topsoil. But this loss was mainly observed on hilltops and ridges, indicating tillage erosion with soil movement down slopes by repeated ploughing (3).
The organic matter content of the soil is mainly dependent on the amount of crop residues returned to the field. Shredded maize residues return a significant amount of straw to the soil. It is known that successive crops with few cereals, including tubers, beetroot, lettuce, onions, etc., bring little organic matter to the soil. Thus, there is a decrease in OM in regions such as the north of France where there is a lot of potato production.
In response to the loss of humus in intensive agriculture, other techniques comparable to spider or no tillage are proposed to replace ploughing. In " Simplified Cultivation Methods" (" Techniques Culturales Simplifiées" or TCS in french) or " No-Tillage farming " ("Techniques Culturales sans Labour" or TCSL in french), or "Regenerative Agriculture", ploughing is replaced by shallow tillage without turning the soil, as practised by our ancestors with the plough. In " conservation agriculture " (CA) (ACS in french), and in particular in direct seeding (no till), the soil is no longer worked except on the seed line to bury the seeds. The uncultivated part of the soil is covered with a non-productive plant cover to maintain humus.
According to the definition of the FAO (Food and Agriculture Organization of the United Nations), conservation agriculture, which involves direct seeding, refers to a cultivation system based on 3 main principles:
1) No tillage and minimal soil intervention during sowing, leaving no more than 25% of the surface area worked;
2) Organic mulch covering at least 30 percent of the soil surface immediately after sowing;
3) Crop diversity including at least three species in the crop rotation.
In regenerative agriculture, two other principles are added:
1) The integration of livestock farming (in particular the supply of manure);
2) Rooting the soil throughout the year.
In Germany, regenerative agriculture does not have the same meaning, including superficial milling or even deeper loosening of the soil.
In order to compensate for humus losses, specific non-productive plants are grown between the rows of the exportable crop, or after harvesting so that the soil is never bare. The nature of this plant cover is defined in such a way as to create complementary relationships between the different plants, including weeds. Farmers who have specialised in this type of cultivation have learned to adjust the composition of the cover crop every year, taking into account the nature and sowing dates of the exportable crops, the vegetative cycle and the depth of the plant species (6). For example, wheat is sown in November on a cover of trefoil, which is a perennial herb commonly grown as a forage crop. The trefoil is started in May when the wheat is already high to ensure soil cover after harvest. This association has not shown any harmful competition with the exportable crop.
It is essential to choose a cover crop variety that significantly improves soil fertility and contributes to input reduction. To give an example, in the USA much research undertaken by Mississippi State University has been devoted to the development of clover varieties with improved performance characteristics. Varieties deliberately selected for later maturity have shown a significant advantage in increasing soil nitrogen reserves. For example, when 13 different varieties were examined, the latest clover fixed 208 kg of nitrogen per hectare, while a less successful variety fixed only 46 kg of nitrogen per hectare (7).
In direct seeding, the maintenance of the topsoil is ensured by useful auxiliaries, in particular earthworms, which replace the work of the spade or plough. Direct seeding has been developed mainly in Brazil, Argentina, the USA and Australia, often under specific soil and climate conditions with a different cultivation context than in Europe. For example, in Argentina, direct seeding of PGM soybeans + glyphosate (18 million ha in 2010 (4)) has developed spectacularly. In France, direct seeding is still marginal (from 0.5 to 4% in 2013 depending on the type of crop (5)).
SCAs require a lot of plant debris to be left on site. When the field is not used for exportable crops, plants are grown (called cover crops) and then destroyed on site, usually with a weed killer, to increase the humus reserve. Apart from the mites, crustaceans and other bugs that feed on this plant debris, direct seeding requires a lot of earthworms that play a fundamental role in structuring the topsoil, notably its aeration and the mixing of organic matter with other soil elements to produce CAC.
The 3 main groups of earthworms
Black anecic (black head). Origin: author's vegetable garden
They are large and feed on the surface litter which they mix with the soil. These earthworms live in vertical tunnels underground to reach the surface and find their food. They release part of their excrement on the surface of the soil to form mounds, also known as « tortillons » in french. These earthworms live for several years in the soil, but their reproduction rate is limited. Anecic worms need compacted soil to build their galleries, which are destroyed after tillage resulting in a significant reduction in the surface area of the worm mounds.
Lightly pigmented and pale pink in colour, they live permanently in the soil by digging horizontal galleries and feeding on organic debris in the soil. Their droppings are left in the galleries.
They are small and often well coloured and prefer the surface litter of forests and meadows. Their reproduction rate is quite high. They are also found in abundance in composts.
Soil tillage by some species of earthworms is not negligible. In temperate regions, up to 15 species can be counted on, some of which are considered to be soil cultivators. Soil with a high organic matter content can contain 100 to 500 individuals per m². As an indication, the density can reach 2000/m² in temperate pastures in New Zealand or in some irrigated orchards in Australia (8).
In forest areas, ornamental gardens and grasslands, soil aeration is particularly ensured by tiller worms, whose presence can be recognised by the castings they leave on the surface. Tillage worms ploughman can ingest up to 20 to 30 times their own weight in soil every day and more than 1000 tons of dry soil per year. It is therefore easy to understand why some farmers and agricultural researchers believe that it is possible to replace ploughing with earthworms, provided that the right conditions are created for their optimal development as they exist in forest and grassland soils.
No-till techniques aim to preserve the biological characteristics of soils that would be degraded by ploughing, which is partly true when not enough organic matter is added to compensate for humus losses.
In ploughing, pathogenic bacteria living at depth are displaced to the surface. Beneficial insects and worms are attacked and eventually become scarce. Ploughing brings more oxygen into the soil, accelerating the decomposition of humus reserves. Some humus components are decomposed more quickly. In the presence of oxygen, mineralisation first degrades the fulvic acids in humus, which disappear after 1 to 3 years.
When the soil is not tilled, the mineralisation of other humus components takes much longer. In temperate regions, and according to some authors, any deep tillage, and especially ploughing, produces a loss of 1 to 3% of humus every year, whereas in no-till less than 0.5% of humus is mineralised (9).
Tillage is also blamed for modifying the chemical and physical characteristics of the soil, resulting in the deep storage of weed seeds and the alteration of aerobic bacterial colonies thriving on the soil surface. The seeds of the most resistant weeds buried by ploughing and protected from their predators (ants, beetles...), will germinate at the next ploughing after their return on the surface. The aerobic bacteria that thrive on the surface are buried and die of asphyxiation.
In terms of weed management, no-till also has its drawbacks. This practice has the effect of encouraging the return of perennial weeds such as creeping quackgrass whose rhizomes are no longer destroyed. Weed seeds accumulate in the first few centimetres of soil, favouring certain species such as ryegrass and wild oats (barren brome). Their competition on yield can be very strong in winter cereals (10). In conventional cultivation, there are eight to nine dominant weed species in a plot, whereas in shallow tillage, twenty to fifty species are commonly present (6).
tillage with mixing of horizons to a depth equivalent to ploughing (20 to 30 cm), but without turning over the topsoil. The swing-plough, which has been used in Mesopotamia since the 4th millennium BC before becoming widespread in other parts of the world (it is still used in the Far East, South America and North Africa), is considered a pseudo-plough. Nowadays, the principle of this tillage technique is to mix the original soil with bottom dressing, crop residues and other organic amendments. In field crops, the tools used are often heavy cultivators or rotavators (rotary tillers, motor hoes, etc.). The small tillers used by market gardeners and amateur gardeners are pseudo-tillage tools.
deep work (15 to 30 cm), but with the soil horizons kept in their original position (no turning of the soil, no mixing of layers). Some tools used in large-scale cultivation, such as the Morris dethatching machine, are capable of bringing the roots of weeds to the surface. The grelinette, also known as the organic fork, is a decompacting tool that is popular with some amateur gardeners and market gardeners who no longer wish to plough.
This is similar to pseudo-tillage, but at a lower depth (5 to 15 cm). It is often used to seed cereal land after a harvest, for example after a beet or potato harvest. In arable farming, the tools most often used are mouldboard stubble cultivators, disc tools or tine tools. For the amateur gardener, the claw (or hook) with a handle is the ideal tool for loosening the soil to a shallow depth, which can also be done with a rotovator by adjusting the position of the digging stand. The higher the position of the digging stand, the shallower the tiller will work.
No deep tillage. The soil is worked only on the seed line to initiate seed germination. Direct seeding implements are characterised by their sowing units consisting of discs or tines. Although they favour the positioning of the seed, they have the disadvantage of favouring the emergence of weeds. This technique allows for significant savings in fossil energy; for 3,000 tonnes of soil turned over per hectare, 50 litres of fuel will be needed for ploughing, compared with 6 litres for direct seeding. To rebuild the biological characteristics of the soil, crop residues must provide at least 30% cover in addition to plant cover. Direct seeding must be accompanied by permanent plant cover (juxtaposed with exportable crops or intercropping) to produce a green manure on site. After harvesting, the soil should never be left bare, even in winter. Before sowing, the vegetation cover is destroyed on site, usually with a weedkiller.
This is a variant of direct seeding. Its principle is to work the soil corresponding to the row of future seedlings to a depth of 10 to 25 cm while leaving plant residues on the surface on the unworked parts parallel to the profitable crops.
In no-till, crop residues are left on the surface where they are gradually degraded by earthworms and other bugs that feed on them. Most of the soil's organic matter is therefore concentrated in the first few centimetres of the soil. However, organic matter is much more exposed to oxidation when it is located near the surface where the concentration of oxygen is necessarily the highest.
If ploughing can be effectively replaced by earthworms, it takes years to achieve the same level of work as the plough does in a few hours. In addition, the earthworm population is more or less threatened by predators such as moles, birds and wild boars.
The absence of deep tillage in the autumn has an impact on the populations of certain pests that overwinter deep down, disrupting the sanitising action of winter frosts. The galleries dug by earthworms are used by pest larvae in the autumn to overwinter deep in the soil, protected from the winter frosts. The more earthworms there are in the soil, the more pest larvae will find a shelter to protect themselves.
The change from ploughing to no-till takes time. A transition of 5 years or even 10 years according to some authors (11) would be necessary to switch to no-till. Five years is the time needed for earthworms to turn over the entire topsoil over a distance of about 20 cm. This 5-year transition is also explained by the rather slow reproduction cycle of ploughing earthworms. Earthworms (epigeics) that like composts and concentrations of decomposing plant debris on the surface reproduce more quickly. Rebuilding an earthworm population in sufficient numbers requires a large quantity of organic matter to feed them, which represents a cost for the farmer (seeds, fertiliser, mowing, grinding, etc.).
No-till poses technical and economic challenges that are not easy to solve:
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Slug proliferation due to crop residues left behind.
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The soil is slower to warm up and does not dry out as quickly.
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Faster development of certain weeds such as vulpine, fireweed, dandelion, dock (12) and polyphagous predators. In southern vineyards there has been an increase in certain weeds such as wood mallow, scabious, despite the use of glyphosate to try to reduce them.
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Increased risk of diseases such as fusarium as a result of organic residues on the surface.
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Concentration of herbicide and other plant protection product residues on the surface when these are used.
In intensive agriculture as practised in France, ploughing is still the preferred solution for most farmers. However, some French farmers have adopted No-Tillage farming in response to problems associated with ploughing on certain plots, such as soil erosion and the reduction of humus reserves.
No-Tillage farming also has the advantage of producing significant time savings with a reduction in fuel costs in the case of direct seeding. There are studies that show that conservation agriculture practised over 14 years is overall superior to organic farming in terms of soil biomass development (13),
It should be noted that ploughing does not necessarily lead to a reduction in soil microflora as long as the quantity of humus present in the soil remains stable and is maintained by permanent inputs of plant waste from crops, farmyard manures and composts in addition to intercropping plant cover. The plant cover buried by ploughing produces the same advantages as direct seeding without the need to use a weedkiller.
Data collected over a long period of time from trials conducted by ARVALIS show that simplified tillage does not always result in a significant increase in carbon storage compared to ploughing, especially in temperate climates. Over an observation period of 40 years, episodes of carbon storage and destocking were observed for no-till and shallow tillage. Ultimately, compared to ploughing and over a long period of time, there was no significant difference in carbon storage for reduced tillage (14).
A meta-analysis conducted by the University of Basel and reported on the Agrarheure website in November 2021(15) shows that CO² storage, soil protection and increased crop yields cannot be achieved with no-till and direct seeding alone. These cultivation methods are therefore not more sustainable than ploughing with crop residue recycling. This meta-analysis confirms the studies conducted by ARVALIS mentioned above, but also the studies of the soil scientist Axel Don (16) from the Thünen Institute in Braunschweig, who came to very similar conclusions in 2019. The researchers from the University of Thünen had analysed more than a hundred field studies taking into account the entire soil profile and found that no-till methods stored on average only 150 kg/ha of carbon per year. In many studies, even humus loss was found.
Researchers at the Thünen Institute have noted that no-till is only possible in combination with increased use of plant protection products, especially glyphosate (a). A herbicide is essential to avoid burying the plant cover by ploughing (the use of a weed killer facilitates the transformation of the plant cover into biomass and prevents the germination of bad seeds). Studies carried out in France show that the development of no-till results in an increase in herbicide consumption ranging from 9% for grain maize to 26% for rape (17).
No-till would also have the advantage of improving carbon fixation in the soil through the formation of humus and would lead to better climate protection. In unplowed soils, the CO² fixed in the soil by the formation of humus would be greater than the release into the atmosphere of CO² resulting from the loss of humus. However, all greenhouse gas emissions must be taken into account. A study published on October 31, 2023 by the Wiley Online Library (18) analyzing around a hundred international publications showed that reduced tillage can at the same time increase emissions of nitrous oxide from the soil, a gas 300 times more harmful to the climate than CO2. Additional small amounts of nitrous oxide can destroy the climate protection effect of humus formation. Or even lead to an overall increase in greenhouse gases.
a) Glyphosate has been classified as "probably carcinogenic to humans" (Group 2A) by IARC, which carries out a carcinogenicity hazard assessment, while other agencies carry out a risk analysis. According to the health agencies, glyphosate is safe at the recommended doses and conditions of use.
Although tillage methods are considered by their detractors as aggressive because they modify the structure of the soil with the help of a tool, these techniques have advantages that are recognised even by those who practise organic farming. The following is a non-exhaustive list :
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Ploughing does increase the oxygenation of the soil at depth, but this allows beneficial aerobic bacteria to colonise a larger volume of the topsoil. And these bacteria have an important role in the balance of the soil ecosystem and its fertility. Rhizobium colonies (nitrogen-fixing bacteria) need oxygen, so ploughing increases their presence in a deeper layer of the soil. This increase in oxygenation by ploughing produces an increase in aerobic microbial agents involved in soil health. For example, Pseudomonas spp, which is a strict aerobic bacterium that thrives in the rhizosphere, is known to be a root protector (see article on rhizosphere and suppressive soils). It creates an adhesive and protective bio film called microbial mucilage. This bacterium is also known for its ability to solubilise iron.
List of some strict aerobic micro-organisms whose presence, favoured by good oxygenation, stimulates soil health.
fix atmospheric nitrogen to transform it into ammonium (20 to 40 kilos per hectare).
This bacterium produces a phythase enzyme that releases organic phosphorus from the soil. This bacterium colonises the roots and slows down harmful fungi. It also generates auxins (growth hormone) that promote root development.
associates with another strict bacterium, Rhizobium, which fixes atmospheric nitrogen in association with host plants such as legumes. Bacillus Radicola produces phytohormones that increase the development of the root system of plants.
specialise in the degradation of fresh organic matter containing lignin and cellulose. They also inhibit certain pathogenic germs.
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Manures used directly as manure have the disadvantage of losing part of their nitrogen through volatilization of ammonia during their transformation into nitrate. To limit volatilization losses, immediate burial is an effective technique, which is also the case for manure.
Forked carrots grown in insufficiently crumbled soil. ♦
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Deep ploughing followed by tillage to reduce clods prevents degeneration of root vegetables such as carrot and endive (forked roots).
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The potato is a very demanding plant in terms of soil preparation, especially as it is a fast-growing plant: 90 to 120 days; it is therefore important to encourage root development by mechanically working the soil to a depth of 15 to 20 cm. In order to obtain a well loosened soil, a deep tillage with a chisel is particularly desirable in clay and loam soils. Due to the special requirements of potatoes, a thin planting layer of about 10 cm should be built up, which is usually done in large-scale cultivation with scarifiers or vibratory cultivators.
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The turnover of bacteria on the surface is very fast. The distribution of anaerobic and aerobic bacteria in the different horizons corrects itself very quickly.
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Deep tillage creates many pores and micro-cracks that allow the roots to explore the active zone of the crop soil more easily. Some crops are very demanding on the structural quality of the soil. For example, sunflowers are very sensitive to areas of compaction. Any obstacle to its development can cause it to lose 5 quintals/ha and degrade its oil content (19). Deep cultivation is therefore necessary, as it is also for certain vegetable crops (melon, leek, chicory, carrot, etc.). It is much easier to obtain deep soil cultivation with mechanical tools than by leaving this work to earthworms, whose action can be hindered by uncontrollable factors, particularly climatic ones.
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Legumes have nodules on their roots that contain atmospheric nitrogen-fixing bacteria. These bacteria also consume oxygen to form nitrates, which contribute to the enrichment of the soil in nitrogen. For this reason, nodules are most numerous in the first few centimetres of the soil surface. Maintaining the soil with adequate deep tillage to facilitate gas exchange with the atmosphere increases the thickness of this zone of biological activity, and thus the soil's fertility potential.
Nodosities on bean roots
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The very fine elements suspended in the water tend to be washed away by rainfall to concentrate in layers of varying depth, which in turn generates erosion on the surface. After a few years, indurated areas are formed at depth and biological activity decreases. Deep tillage removes these indurated areas and reposition the very fine elements in the topsoil. The way in which clay is carried deep into the soil is described in another article by clicking here.
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In tilled soil, the soil is more porous, so there is less loss of fertilizer through runoff. Tillage facilitates the flow of water from irrigation or rain to the roots, which in turn receive more nutrients carried by the water. Unabsorbed mineral salts are more easily fixed in depth by CAC, whereas they would be lost through run-off when the soil is not sufficiently worked.
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Ploughing is very useful to control weeds by burying them and helping to enrich the soil with humus. Ploughing is known to be effective agains Knotweed. 90% of brome seeds (locally harmful in winter cereals, known to be favoured by simplified cultivation) disappear after ploughing. Sufficiently deep ploughing alters the establishment of woody weeds (phanerophytes, champhytes) and stumpy herbaceous species (hemicryptophytes) such as dock (20). The effect on annual plants is more or less nuanced, as ploughing brings back to the surface the seeds produced in previous years if they have resisted climatic and biological disturbances.
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For perennial species, the destruction can be partly offset by germination of the rhizome pieces. Success will depend on the way these propagules are treated (depth and frequency of ploughing, collection of rhizome residues, etc.), the climatic conditions. For example, ploughing in dry conditions in summer favours the drying out of bindweed and creeping bindweed. After ploughing in summer, it is possible to use a tine tool to remove the dried out ricehomes. The mechanisation of ploughing has made it possible to relegate to the edge of the field once emblematic rhizome weeds, such as creeping bentgrass.
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Ploughing is an effective tool for disrupting the life cycle of pathogenic microorganisms such as Fusarium, a serious disease affecting soft wheat or some vegetable crops (provided that fine grinding is carried out before residues are buried and rotations are undertaken to avoid incompatible combinations). Non-tillage crops are at greater risk if potentially contaminated residues are left on the surface and if no pre-harvest treatment for Fusarium has been applied.
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Autumn ploughing facilitates the destruction of eggs and pupae of insect pests that have burrowed into the soil to protect themselves from the cold of winter by offering them to birds or frost destruction. Some pests, such as wireworms, burrow deep into the soil to resist the cold. Another example: the pulp of the celery fly (Philophylla heraclei) overwinters in the soil between 5 and 10 cm. Shallow ploughing of a plot allows the winter frost to destroy the celery fly pulp without the use of pesticides. However, some beneficial ground beetles overwintering in the soil as larvae or adults are also destroyed, but their population can be largely maintained by preserving semi-natural habitats close to the crops. It should be noted that the shredding of plants deposited on the surface proposed by some Direct seedin followers is not sufficient to get rid of pests, as there is no turning of the soil to bring the pests or their eggs to the surface.
While it is true that mechanisation in arable farming has led to deeper ploughing than 30 cm, in recent years there has been a return to shallower ploughing to reduce OM losses. For this purpose, manufacturers offer stubble ploughs with low tractive power that work the soil to a depth of 10 to 15 cm. Some stubble ploughs with ploughshares can also be used for mechanical weeding while respecting the deep structure of the soil.
Cross-section of the soil in the author's garden at Oraison showing the thickness of the topsoil maintained by ploughing and certain soil conservation techniques (pseudo-tillage and shallow tillage) ♦
In conclusion, as far as the maintenance of the cultivated soil is concerned, there is no ideal technique that would supplant all the others, only techniques adapted to the pedoclimatic context of the place. For the amateur gardener, alternating ploughing, pseudo ploughing and shallow tillage is still the most practical method of soil maintenance, provided that a minimum volume of compost is spread every year to compensate for humus losses. Properly performed deep tillage with periodic additions of medium and long term composts will eventually produce topsoil corresponding to the thickness of the tilled soil. This topsoil layer improves every year and is easy to check. If the topsoil layer is removed, there is a break in colour between the tilled soil and the lighter layer below. The photo above shows a hole about 40 cm deep in my vegetable garden showing the 30 cm topsoil and the lighter underlying layer. The original soil was even lighter in colour 15 years ago, the underlying layer having received organic matter by infiltration from the topsoil in the meantime.
1) L'économie rurale et la vie dans les campagnes dans l'occident médiéval, Georges Duby
2) Mœurs et usages du Lauragais ; 1868 ; Marseille : Laffitte Reprints, 1979.
3) Study: Over a third of U.S. Corn Belt has lost its carbon-rich topsoil
4) Salambier et al., 2014
5) Terre-net https://www.terre-net.fr/observatoire-technique-culturale/strategie-technique-culturale/article/il-atteint-4-des-surfaces-cultivees-en-ble-tendre-217-96007.html
6) Pionnier en agriculture de conservation des sols : le goût d’innover ; INRA – science & impact 22-01-2019
7) Cover Crop Corner: What cover crops have gifted us | AGDAILY
8) Global Soil Biodiversity Atlas p 58
9) Fertilité des sols, importance de la matière organique – chambre d’agriculture Bas Rhin
10) Infloweb ; connaître et gérer la flore adventice
11) La fertilité des sols : l’importance de la matière organique – agriculture & terroirs, chambre d’agriculture du Bas-Rhin - dec 2011
12) Fried et al., 2012 Trajectories of weed communities explained by traits associated with species’ response to management practices
13) Fourteen years of evidence for positive effects of conservation agriculture and organic farming on soil life – agronomy for sustainable Development – janvier 2015, vol 35
15) https://www.agrarheute.com/management/betriebsfuehrung/pfluglos-ackern-bringt-nichts-neue-fakten-587321
16)https://www.agrarheute.com/management/betriebsfuehrung/humus-boden-pfluglos-arbeiten-bringt-nichts-559984
17) Enquête SSP 2017
18) https://onlinelibrary.wiley.com/doi/10.1111/gcb.16983
19) Le tournesol ; chambre d’agriculture Landes 2014 p 19
20) L’appauvrissement floristique des champs cultivés - Philippe Jauzein ; dossier de l’environnement INRA N° 21
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