Conservation agriculture (CA)

Technical articles - Soil and fertilization

Crop association in arable crops Permanent cover crops in arable crops Management of cover crops in arable crops Organic matter autonomy in vegetable farming Carbon cycle and GHG Climate resilience Soil cover Biodiversity Weeding in arable crops Soil regeneration

Direct seeding in a cover crop

Conservation agriculture (ACS) is a set of cropping techniques aimed at maintaining and improving the agronomic potential of soils, while maintaining a regular and efficient production both technically and economically.

Principle

Conservation agriculture restores the soil to the primary role in plant production. The soil is considered not as a mere growing medium, but as a living environment. Protecting it improves its functioning, restores or increases fertility. Biological activity then replaces mechanical work, which is considered disruptive to structure and balances.

Conservation agriculture goes beyond Simplified Cropping Techniques (TCS). It is based on 3 major pillars:

• No tillage

• Permanent soil cover

• Diversity and long rotation of crops

For standardization purposes and because these techniques can be implemented to varying degrees, the FAO has set a minimum threshold of soil cover by residues of the previous crop at 30% after sowing, this coverage rate being the minimum necessary to limit erosion phenomena, according to the USDA (United States Department of Agriculture, department of the US federal administration responsible for agriculture and food policy).

Starting Conservation Agriculture implies revisiting the overall system of the farm with the 3 principles as a guiding thread. It means accepting to change one's practices, train, experiment, change one's benchmarks (transmitted by peers from conventional agriculture), and become the pilot of one's Soil. This requires time, motivation, and a good dose of energy. Effective collective support accelerates the process. It is possible to join networks such as the APAD to exchange experiences and have simple, effective tools to ensure this transition.

Cropping practice

The main objective of conservation agriculture is to combat the degradation of arable soils, or the soil regeneration of degraded soils. To do this, it seeks to increase biodiversity and stimulate natural biological processes while increasing the amount of organic matter in the soil. These three elements are essential factors to ensure soil fertility. Conservation agriculture mainly relies on the following three pillars to generate or regenerate this fertility.

Reduction of soil tillage

Reducing or even eliminating mechanical soil work allows the surface humus layer created by decomposing plant debris to be preserved, which also protects the soil against erosion and crusting. The absence of soil tillage, especially plowing, also favors the quantity of earthworms present in the soil.

Only disturbance of the seed line is tolerated. It is possible to practice no-till seeding whose objective is to limit to the strict minimum the disturbance of biological activity during seed placement in the soil, to promote the natural vertical porosity of the soil, and to increase the organic matter content.

Diversification of plant species

Long rotations alternating different plant families (legumes, cereals, crucifers) and use of cover crops and crop associations. Agronomic reflection on crop succession is essential and diseases present on crops are reduced thanks to species complementarity. It is possible to integrate non-productive crops but with agronomic benefits, such as soil restructuring or reduction of diseases and pests thanks to complementary effects among species.

Permanent soil cover

By residues of previous crops (called mulch) or by the establishment of cover crops during intercrop periods or as permanent living covers. The cover crop performs multiple functions including soil structuring thanks to the root network, nitrogen storage, recycling of mineral elements, and development of aerial and underground biodiversity by providing habitat and food for present species.

Advantages

For widespread adoption, any new technology must present interest and advantages likely to attract many farmers, farmers who understand the difference between what they do and what they need. In the case of conservation agriculture, these advantages are threefold:

Social and economic advantages that improve production efficiency

• Reduction of working time and thus reduced labor needs

• Innovative approach dynamic that places agronomy back at the heart of the profession

• Improved quality of life thanks to optimization of time and labor costs

• Quality and abundant production

• Restoration of pleasant landscapes

• Reduction of expenses incurred, for example, for fuel purchase, machinery operation and maintenance, as well as labor

• Increased efficiency, since production increases with a lower amount of inputs

• Income security

• More resilient agricultural system facing economic crises

The positive impact of conservation agriculture on labor distribution during the production cycle and, above all, the reduction of labor needs are the main factors that have led farmers in Latin America, especially those using family labor, to adopt conservation agriculture.

Agronomic advantages that improve soil productivity

• Increase in organic matter content

• Soil water conservation

• Improvement of soil structure and thus rooting zone

The accumulation of crop residues leads to an increase in soil organic matter. This phenomenon is initially limited to the topsoil layer before extending to deeper layers. Organic matter plays an important role in the soil: fertilizer use efficiency, water retention capacity, soil aggregates, root system environment, and nutrient retention are strongly dependent on soil organic matter content.

Environmental advantages that protect the soil and make agriculture more sustainable

• Reduction of soil erosion, and thus decreased maintenance costs for roads, dams, and hydroelectric installations

• Better soil bearing capacity to reduce compaction and bogging of agricultural machinery

• Improvement of water quality

• Improvement of air quality

• Increase in biodiversity

• Carbon sequestration and reduction of greenhouse gas emissions

• Increase in soil fertility

• Reduction in diesel consumption

The presence of residues on the soil attenuates the impact of raindrops. When the energy of droplets is absorbed, they infiltrate the soil without harmful effects. Infiltration increases, runoff and erosion decrease. Residues also form a physical barrier that reduces wind speed and surface water flow. The reduction in wind speed reduces evaporation.

In conservation agriculture, maintaining permanent soil cover provides habitat for a number of species that feed on pests, and attracts insects, birds, and other animals. Crop rotation and cover crops promote genetic biodiversity, which is impoverished in monoculture systems.

Agricultural systems based on maintaining a cover crop and no-tillage store more carbon than plow-based systems, which release a lot of carbon into the atmosphere. During the first years of conservation agriculture implementation, soil organic matter content increases due to root decomposition and the contribution of crop residues remaining on the surface. Organic matter decomposition is slow and a good part of this matter is incorporated into the soil, slowing carbon release into the atmosphere. Overall, carbon is trapped in the soil, which becomes a net carbon sink. This phenomenon could significantly help in the fight to reduce greenhouse gas emissions and prevent the disastrous effects of global warming.

Limitations

Weed management

The main limitation to abandoning or greatly reducing soil tillage is that it removes producers' main means of controlling weeds. The use of tillage for mechanical destruction of weeds or false seedbed preparation, for example, is indeed the main alternative to the use of herbicides, often preferred for its effectiveness and lower cost.

Moreover, without tillage, seeds remain more easily on the surface and the presence of a permanent mulch modifies germination conditions, favorable to certain species but limiting germination of most species requiring light induction. Some seeds left on the surface are also consumed or damaged by the often richer biodiversity in ACS, and some weeds are disadvantaged by these particular conditions. Thus, ACS selects a different weed flora than would be selected in conventional. Currently, in the absence of tillage, chemical weed control is still the most effective option and therefore the most widespread.

Transitioning to ACS thus requires a radical change in the weed management model. However, human resources, tools, and even weed control strategies in ACS are still too scarce to support conversion.

In practice, transitioning to ACS currently involves increased herbicide use in the first years, during a transition phase mainly linked to farmer learning and system maturation (biotic and abiotic soil transformation notably). However, after a few years of well-managed ACS adopting an integrated weed management approach combining chemical and non-chemical methods (mainly mechanical destruction, extended rotation, cover crops during intercrops), a decrease in weed emergence after sowing and a reduction in herbicide use, becoming equivalent or even lower than conventional systems, are observed. Also, Farooq and Siddique in their book "Conservation Agriculture" place weed control as the "4th pillar" of ACS, highlighting the importance of this issue for these systems. Skillful use of cover crops is a particularly decisive lever for weed management in ACS, but expertise on covers, both from farmers and advisors, is still too rare and poorly adapted to local condition variations.

Soil saturation in winter

The fact that in ACS water is potentially better retained in soils implies that they are more saturated in winter and have limited infiltration capacity for rainwater, potentially causing higher winter and spring runoff than in tilled systems.

However, it is reasonable to think that with the very strong difference in structural stability between a tilled soil and a no-till soil, the presence of cover and mulch, combined with irregularities of the untilled soil (which does not have deep and regular furrows, often along the slope), the impact of runoff is greatly reduced in ACS compared to more conventional agriculture, due to slower runoff speed and less soil loss.

Pests

No tillage and no-till seeding do not disturb the habitat of rodents and slugs, which proliferate in crops, potentially causing significant plant losses.

For example, not mowing alfalfa preserves them from predators (foxes, cats, raptors,...).

Solutions to limit their population development must therefore be anticipated (mowing, localized rodenticide, slug control,...), and the presence of their predators can also be encouraged by installing perches for raptors.

Diagnosing your soil

The VESS spade test

Spade test

Implementation period	All year round
Observation to be made	In the field
Objective	Make a quick diagnosis of the physical state of the soil (up to 30cm)
Equipment	Spade, evaluation grid
Difficulty	Quick, little expertise required
Example of Method

Visual Soil Assessment (VSA, Graham Shepherd)

Visual Soil Assessment

Implementation period	All year round
Observation to be made	In the field
Objective	Make a quick diagnosis of the physical state of the soil (up to 30cm)
Equipment	Spade, basin, tarp, evaluation grid
Difficulty	Requires the VSA evaluation grid, more complete than the classic spade test but longer
Example of Method	Field guide (Downloadable - Guide complet téléchargeable ici here)

The 3D mini profile

3D mini profile

Implementation period	All year round
Observation to be made	In the field
Objective	Make a diagnosis on a greater soil depth (up to 60 cm)
Equipment	Telescopic loader pallets, a knife, a meter to evaluate rooting
Difficulty	Quick but requires some training
Example of Method	Agro transfer guide (Downloadable here)

The cropping profile

Cropping profile

Implementation period	All year round
Observation to be made	In the field
Objective	Make an in-depth diagnosis at surface and depth (120cm)
Equipment	Elbow grease, spade
Difficulty	Long, requires expertise
Example of Method	Cropping profile methodological guide (Downloadable here)

The penetrometer rod

Penetrometer rod

Implementation period	All year round
Observation to be made	In the field
Objective	Identify compaction zones in the plot (80cm)
Equipment	Penetrometer rod
Difficulty	Easy
Example of Method	Penetrometer rod methodological guide (Downloadable here)

Granulometric analyses

Granulometric analysis

Implementation period	All year round
Observation to be made	In laboratory
Objective	Know the texture, clay, silt and sand (fine and coarse) content. This information will allow you to know the Soil Crusting and porosity indices of your soil, as well as your soil's cracking aptitude and BiodivSol index
Equipment	Auger, sampling bag to collect a soil sample
Difficulty	Easy but requires paying for an analysis
Example of Method	Consult the nearest laboratory

Technique development

The cultivated area worldwide using this method was estimated at 106 million hectares in 2008/2009 and reached about 180 million hectares in 2015/2016, or about 12.5% of cultivated land worldwide. The European Conservation Agriculture Federation estimates about 5% of land cultivated under conservation agriculture, without distinguishing it from no-till areas.

In 2020, APAD established a label "At the Core of the Soils" to promote farms undertaking conservation agriculture.

Techniques and equipment

Strip-till

Passage of a Strip-till equipment

The Strip-till, widely used in North America, is beginning to appear in France. This technique consists of preparing and cracking the seed rows of row crops. Strip-tillers consist of several blades or tools mounted on a frame and adapted to a type of soil or crop: cracking blades, concave rollers to accelerate soil warming, V-wheels or finger wheels, smooth or notched discs. There is no universal solution in Strip-till. On clay soils, it is recommended to pass the strip-tiller in autumn so that the alternation of frost defrost completes the work. For rapeseed, strip-till is compatible with direct seeding but will precede it by a few days or weeks for spring sowing to allow the cracked soil time to warm up and mineralize.

To perform no-till seeding, adapted seeders are necessary; they locally open the soil (with a disc or a tine), create some fine soil, and place the seed in a favorable environment by disturbing a minimum surface at the plot scale. These seeders are generally heavier and more expensive than conventional seeders. However, they can be adapted to all conditions. AFDI (Agriculteurs Français et Développement International) and CEMAGREF (Centre d'Étude du Machinisme Agricole et du Génie Rural des Eaux et Forêts) have designed a no-till seeder that allows sowing with very low mechanical force and can be used with human or animal traction. Manufacturers market complex equipment whose performance can vary depending on working conditions. Test reports have been compiled to assist in choosing these machines.

Seeders

• "Straight" disc seeders. The straight disc creates a furrow in which the seed is deposited.
  • Advantages: disturbs the soil less, allows working through heavy vegetation.
  • Disadvantages: more expensive due to complexity, difficult to work in wet conditions. This is true for all seeders, but the phenomenon is accentuated for disc seeders. Seeds may rot before germinating.

• Tine seeders. The tines are equipped with a narrow share.
  • Advantages: they create fine soil on the seed line. The tines lightly work the soil and facilitate germination. Caution on fragile soils such as sandy soils that easily disintegrate. They are also better suited for starting conservation agriculture, as this equipment offers more versatility and does not require high surface porosity.
  • Disadvantages: beware of the rake effect if vegetation is too dense or if the tines are too close, tends to bring stones to the surface, lightly working the soil on the seed line can bring some weed seeds back into germination conditions.

• "Angled" disc seeders. These seeders are less common in the field, but users highlight their good work quality and versatility. The principle: the angled disc opens the soil (no furrow) and the seed is deposited inside. The closing wheel presses everything back. Unlike other seeders (tines and straight discs) where no-till is compensated by the heavy weight of the seeding elements requiring more power, angled discs change the attack angle. This technique allows opening the soil without needing heavy seeding elements. This type of seeder therefore requires less power.

Be careful not to roll too fast (no more than 10-12 km/h), as this could create too much fine soil.

A seeder cannot meet all situations, but trends can be outlined:

• If I have just started direct seeding and my soil is not yet well structured: the tine seeder could be the most suitable.
• If my soils are ready and well structured: the disc seeder is feasible.
• In wet conditions on clay soils, the results of disc seeders are catastrophic – angled disc seeders are very promising and the most versatile.

The seeder is only the last link in the chain; this technique requires a global approach on rotations and especially the importance of cover crops, both in summer and winter. Investment in a latest-generation seeder is costly. To start, it is necessary to work with the equipment you have. Failures will be part of the learning process and will allow progress in the technique. Working in groups is essential to feel supported and why not invest together?

Earthworms and glyphosate

While many researchers have warned about the harmful effects of glyphosate on earthworm populations, notably during the renewal of its authorization in 2023, farmers practicing CA observe an increase in earthworm populations despite frequent use of this herbicide. A recent study, compiling the conclusions of 63 studies conducted between 1982 and 2022, finds no significant impact of glyphosate at recommended doses, but suggests possible negative effects on reproduction and population structure of earthworms with multiple applications per year. However, most of these studies were conducted in laboratories, and long-term field studies are needed to better understand the real impact of glyphosate on these populations.

The reduction of tillage and other agronomic practices implemented in CA can explain the observed increase in earthworm populations.

Sources

• Conservation agriculture - Terre net
• The 3 pillars of CA - APAD
• Wikipedia page on conservation agriculture
• Conservation agriculture - FAO
• The tripod of conservation agriculture - INRAE
• Soil conservation agriculture and ecosystem services - CAIRN.Info
• Is conservation agriculture synonymous with specific equipment? - Agri 53

Annexes

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