Planting cover crops as nitrate traps
1. Presentation
An intermediate crop nitrate trap (CIPAN) is a temporary crop of fast-growing plants intended to protect plots between two crops for sale.
Characterization of the technique
Description of the technique:
Establish a cover crop during the intercrop period that will capture mineral nitrogen before the drainage period begins (autumn/winter), thus limiting its leaching.
The cover can be made up of a single species (mustard, phacelia, oat...) or a mixture of species allowing to combine the qualities of each (different root systems allowing absorption of nitrogen in different soil horizons, species with rapid establishment and more "perennial" species...).
The cover can be destroyed by frost, mechanically (mowing, rolling, ploughing...) or chemically. The amount of nitrogen absorbed depends on the nitrogen available in the soil and the biomass produced.
The absorbed nitrogen will then be gradually released after the cover is destroyed, through residue mineralization. Part will be available for the following crop.
Example of implementation:
In the case of a succession "winter soft wheat => spring barley": Establishment of mustard between a winter soft wheat and a spring crop. Sowing is done late August / early September broadcast, at 10 kg/ha. The cover is mowed early December.
Details on the technique:
Intermediate crops
Diploid oat, Camelina, Fenugreek, Vetch, Spring mustard, Rape, Phacelia, Italian Ryegrass, Common Vetch...
Implementation period
During the intercrop period
Spatial scale of implementation
Plot
Application of the technique to...
All crops:
Generalization sometimes difficult
The intercrop period must be long enough to allow sowing of the cover, its development and destruction sufficiently long before sowing the next crop to avoid water or nitrogen deficit linked to residue mineralization, allelopathic phenomena (example: mustard before corn). The establishment of CIPAN is therefore particularly justified for long intercrops, leaving the soil bare during the drainage period, such as between a crop harvested in summer and a crop planted in the following spring.
After harvesting a spring crop, no CIPAN species sown late October grows fast enough to produce sufficient biomass to trap a significant amount of nitrogen before drainage resumes. In this case, it is possible to establish ryegrass or rape in the corn at the 5-10 leaf stage, using a hoe equipped with a broadcast seeding system and firming with a comb. The CIPAN germinates before the corn canopy closes and resumes growth in September when the corn dries out. The CIPAN covers the soil after corn harvest. But this undersowing technique in corn has very variable success depending on weather conditions (CIPAN drying out if too dry, slug attacks if too wet).
All soil types:
Generalization sometimes difficult
CIPAN establishment can be justified on all soil types. However, on some soils (e.g. clay), establishment or destruction of the cover can be very difficult. It will be necessary to carefully consider the species planted (e.g. frost-sensitive) and the destruction technique (frost, mowing, ...).
All climatic contexts:
Generalization sometimes difficult
The success of the technique depends on sufficient rainfall in autumn (September-October) to allow cover development before winter.
In pedo-climatic contexts subject to strong summer water deficits (Midi-Pyrénées, Poitou-Charentes), cover emergence and development are sometimes difficult.
Regulations
POSITIVE
The 4th action program of the Nitrate Directive requires, in most departments, total soil cover during winter in vulnerable zone since 2012. Regrowth of oilseed rape is considered as cover.
2. Effects on the sustainability of the cropping system
Environmental criteria
Effect on air quality:
Variable
GHG emissions: VARIABLE
Effect on water quality:
Variable
N.P.: DECREASE
pesticides: VARIABLE
Effect on fossil resource consumption:
Variable
fossil energy consumption: VARIABLE
Other:
No effect (neutral)
Air: Establishment and destruction of the cover cause GHG emissions linked to fuel consumption, but also allow carbon storage (if cover develops) and reduce indirect N2O emissions. The GHG balance is therefore "variable" at the crop scale.
Water: CIPAN establishment strongly reduces nitrogen transfer by leaching and to a lesser extent phosphorus. However, if non-frost-tolerant species are established, cover destruction may require the use of herbicides.
Fossil energy: Establishment and destruction of the cover cause higher fuel consumption than maintaining bare soil during the intercrop. But loosening of the profile by the cover may allow reduced tillage for the next crop establishment. Moreover, depending on species choice, this technique reduces mineral nitrogen inputs for the next crop and thus reduces fossil energy consumption for mineral nitrogen production.
Biodiversity: Increase
Choosing melliferous species can help feed pollinator insects.
Agronomic criteria
Productivity:
Variable
If destruction is too late, the intermediate crop can cause depressive effects on the following crop (water and nitrogen availability). Some intermediate crops can also have an allelopathic effect on the following crop.
But if destruction is early enough and cover choice appropriate, the cover has a neutral to positive effect on the following crop.
Soil fertility:
Increasing
Nitrogen captured by the cover during its development is gradually released after destruction. Part will be directly available for the following crop.
The cover also improves phosphorus and potassium availability for the following crop (element remobilization).
Water stress:
Variable
Water uptake during cover development can increase water deficit. Cover destruction must be adapted to soil type and water requirements of the following crop.
Functional biodiversity:
Increasing
Domestic plant biodiversity is increased by planting species different from the main crops. Moreover, the intermediate crop provides favorable cover for many animal species (birds, small game, micro and macrofauna...).
Other agronomic criteria:
Variable
Disease pressure: variable
Establishing intermediate crops helps "break" rotations and thus disease cycles (e.g. fusariosis, take-all) in cereal rotations. However, the cover can also increase disease pressure if planted species host the same pathogens as the main crops (planting crucifers in rotations with high frequency of oilseed rape, oat or rye in straw cereal rotations, some legumes in rotations including pea, ...).
Pest pressure: variable
Establishing intermediate crops can reduce or regulate some pests (e.g. nematodes of beet // mustard and radish anti-nematodes). However, the cover can also increase some pests (slugs, sawflies, flea beetles, aphids) by providing refuge and food.
Weed pressure: variable
A CIPAN that starts quickly and covers the soil well can compete with weeds. Conversely, a poorly developed cover leaves space for weeds while preventing stubble cultivation.
Soil structuring: Increase
Development of the cover root system promotes soil restructuring.
Economic criteria
Operational costs:
Increasing
Depending on the species or species mixture chosen, seed cost can vary from 10 to 100 €/ha.
Mechanization costs:
Increasing
Establishment cost can vary from 0 €/ha (sowing at harvest under the crop) to 60 €/ha (no-till). Destruction cost also varies from 0 €/ha (frost) to 30 €/ha (mowing + incorporation).
Margin:
Decreasing
Nitrogen returns for the following crop after cover destruction generally do not cover the costs related to its establishment and destruction.
The short-term overall margin will therefore be reduced, however "long-term" effects are difficult to quantify and usually not taken into account in margin calculations (restructuring, erosion limitation, soil life, ...). The cover can also be valorized (harvest, fodder, ...).
Other economic criteria:
Variable
Fuel consumption: variable
Establishment and destruction of the cover cause higher fuel consumption than maintaining bare soil during the intercrop. But loosening of the profile by the cover may allow reduced tillage for the next crop establishment.
Social criteria
Working time:
Variable
Depending on the mode of establishment and destruction, the workload can be more or less important than that related to false seedbeds during intercrop.
Observation time:
No effect (neutral)
3. For further information
- Choosing your intercrop: some points for reflection
- -Maurice R. (CRA Pays de la Loire) Technical brochure, 2006 link to brochure
- Cover crops in intercrops: 6 keys to success
- -Riou V., Fourmond S., (CA 49), Cornuault F. (UDCUMA Pays de la Loire) Anjou Cultures n°134, Press article, 2009
- Covering soils in autumn
- -Bodilis A.M. (Arvalis), Fougère M. (CA 44), Cozannet H. (CA 49), Lebreton J.C. (CA 53), Gendry M. (CA 72), Chauvin M. (CA 85), Moinaud H. (CRA Pays de la Loire) Technical brochure, 2003
- Intermediate crops: Water protection for an additional cost of 20 to 45 €/ha
- -Labreuche J., Laurent F., Moquet M., Protin P.V., Aubrion G. (Arvalis) Perspectives agricoles n°321, p22-29, Press article, 2006 link to article
- Effects on mineral nitrogen stock in soil - Ability to trap nitrate and contribute to nitrogen nutrition of the following crop
- -Cohan J.P., Castillon P. (Arvalis) Perspectives agricoles n°357, p 30-36, Press article, 2009 paid article
- Sheet n°9: Intercrop management
- -Coufourier N., Lecomte V., Le Goff A. (CA76), Pivain Y. (CA27), Lheriteau M., Ouvry J.F. (AREAS) AREAS, Technical brochure link to brochure
- Managing cover crop: Make the most of the nitrogen effect
- -Delpech C. Cultivar n°530, p14-15, Press article, 2002
- Guide to nitrate trap intermediate crops
- -CRA Brittany Technical brochure, 2009 link to brochure
- CIPAN much more than nitrate traps
- -Vanhaesebroucke R. Horizons, Press article, 2010
- Intermediate crops: better intercrop management for agronomic and environmental benefits
- -Minette S. (CRA Poitou-Charentes) Technical brochure, 2009 link to brochure
- Nitrogen losses by leaching - Intermediate crops: immediate and lasting efficiency
- -Laurent F., Fontaine A. (Arvalis) Perspectives agricoles n°327, p26-30, Press article, 2009 paid article
- Nitrate trap or cover crop: destruction date guided by the agronomic objective
- -Labreuche J. (Arvalis) Perspectives agricoles n°295, p26-28, Press article, 2003 paid article
- What happens to nitrogen trapped by CIPAN?
- -Hanocq D. Cap Agri, Press article, 2009
Appendices
Favorise les bioagresseurs suivants
- Cabbage flea beetle
- Black spot of inflorescences
- Slug
- Small flea beetle
- Cabbage aphid
- Green aphid of foliage
- Crown rust
Défavorise les bioagresseurs suivants
