Introducing a cover crop during the intercrop period in vegetable production
The technique consists of establishing a cover crop during an intercrop period (the time between the harvest of one crop and the establishment of the next). Depending on the objectives, the cover crop may have different names :
The cover crop can also play a role of competition against weeds and limit the use of herbicides, including glyphosate, during the intercrop period.
Description of the technique
Information originally from the Practical guide for designing vegetable cropping systems that are economical in phytosanitary products (2014) / Technical sheet T1.
Example of implementation
Here are some examples of rotations including cover crops in market gardening[1] :
- Tomato – arugula – cauliflowers – forage sorghum (summer cover) – lettuce
- Corn salad – pea + radish – eggplants – wheat heritage variety (winter cover)
- Before onions, a cover crop of ryegrass destroyed with a silage tarp (producing a thick mulch including residues from previous years)
- In the southeast, under shelter, forage sorghum can be established as an intercrop in spring or summer (after a melon, a zucchini, a late lettuce for example).
Details on the technique
The choice of cover crop species depends :
- on the objectives of the cover :
- Nitrogen capture,
- competition against weeds,
- improvement of soil structure or fertility,
- reduction of pathogens...
- on constraints related to sowing, to the crop and to the destruction of the cover :
- cost and availability of seeds,
- irrigation,
- availability of equipment...
- on the field conditions :
- climate,
- soil type,
- management...
- on the available duration for the intercrop, which varies depending on the previous crop-next crop pair. A cover crop with a development cycle adapted to this duration must be chosen. This may cause a shift in the planting date of the next crop.
Alternation of families between cover crops and crops is also taken into account for better regulation of bioagressors and complementarity of effects of different species.
Soil preparation and sowing
The sowing date is determined according to the species, water availability and the field situation (presence of weeds, next crop…). The objective is to quickly obtain a homogeneous and dense cover.
Depending on the situation, various techniques are possible :
- sowing before or during harvest without soil preparation
- sowing after harvest with soil preparation
- In all cases, sowing can be done broadcast or in rows.
Under shelter or in the absence of rain, sprinkler irrigation ensures rapid and regular growth.
The development of the cover crop may be subject to several mowings (sorghum for example) to avoid lignification and seed setting.
The date of cover destruction varies depending on :
- the objectives of establishing the cover,
- the species (to avoid seed setting and lignification of tissues),
- the soil type (the cover decomposes faster or slower),
- and the soil preparation time for the next crop establishment.
The destruction technique (ploughing, shredding, stubble cultivation, frost, rolling) varies depending on the chosen species, the season, the available equipment, the soil condition and the target objective.
Residues must be incorporated superficially into the soil (10-15 cm depth), immediately or after drying. To obtain a good seedbed and avoid the risk of seedcorn maggots, fresh residues should not be incorporated. A delay of 2 months before planting an industrial vegetable is necessary. For biofumigation purposes, residue incorporation must be immediate.
Application of the technique to...
All crops : Easily generalizable
The technique can be used both under shelter and in open field. All crops can be concerned depending on intercrop periods.
All soil types : Easily generalizable
Cover crops can be established in all soil types and in all regions if the species and technical itinerary are adapted. However, field conditions must be considered in species choice, both climatically (risks of drought, frost, heavy rain…) and regarding pH, texture and management (irrigation…).
All climatic contexts : Easily generalizable
Cover crops can be established in all soil types and in all regions if the species and technical itinerary are adapted. However, field conditions must be considered in species choice, both climatically (risks of drought, frost, heavy rain…) and regarding pH, texture and management (irrigation…).
Regulations
In vulnerable zones (nitrate directive) :
- establishment of a cover crop is mandatory; check sowing dates;
- for legumes in pure or mixed culture, check prohibitions and environmental contracts;
- regional regulations regarding cover destruction dates must be checked.
Effects on the sustainability of the cropping system
"Environmental" criteria
Effect on air quality : Increasing
- phytosanitary emissions decreasing
Effect on water quality : Increasing
- nitrogen and phosphorus discharge into water : decreasing
- pesticide discharge decreasing
Effect on fossil resource consumption : Increasing
- Fossil energy consumption increasing : cover establishment and destruction require more fuel than maintaining bare soil during intercrop
"Agronomic" criteria
Productivity : Variable
Generally, if practiced under good conditions, this technique improves the regularity and uniformity of the following crop. However, species from the Poaceae family may cause nitrogen hunger during their decomposition.
Soil fertility : Increasing
Introducing a cover crop during intercrop allows storage of organic matter, carbon and nitrogen in the soil, thus enhancing fertility. It also promotes soil biological activity and improves soil health depending on the species chosen. Moreover, this technique limits weed development, erosion, crusting and soil structure degradation.
Functional Biodiversity : Variable
Alternation of families between intercrop covers and crops allows better regulation of bio-aggressors and complementarity between effects of different species. Auxiliaries, pollinators and soil fauna can be favored by the cover presence, variably depending on the species chosen. However, soil auxiliaries may be disturbed by shredding and burying the cover crop at destruction.
Furthermore, some species have risks of regrowth or favor certain bio-aggressors.
"Economic" criteria
Operational costs : Increasing
Increase in operational and mechanization costs depending on the species planted and sowing and destruction techniques
Mechanization costs : Increasing
Margin : Variable
Fertilizer costs can be limited. Production and regularity of the following crop can be improved, hence a potential positive effect.
"Social" criteria
Working time : Increasing
Increase in mechanized work and overall working time for seedbed preparation, establishment and destruction of the cover.
Peak period : Increasing
Work to be planned during the intercrop period.
Favored or disadvantaged organisms
Bioagressors favored
| Organism | Impact of the technique | Type | Details |
|---|---|---|---|
| Snail | HIGH | pest, predator or parasite | Intercrop covers can serve as shelters for snails |
| Slug | HIGH | pest, predator or parasite | Intercrop covers can serve as shelters for slugs (e.g. rye and clovers) |
| Nematode (bioagressor) | HIGH | pest, predator or parasite | Certain Brassicaceae species (mustard, forage radish) maintain nematode populations in the soil (notably Meloidogyne sp.) |
| Flea beetle | MEDIUM | pest, predator or parasite | Many Brassicaceae species usable as intercrop covers are host plants for flea beetles (mustard, rapeseed, turnip, forage radish, rutabaga…) |
| brown Rhizoctonia | pathogen (bioagressor) | Certain Brassicaceae species are host plants for some Rhizoctonia species (mustard, rapeseed, turnip, rutabaga...) | |
| Rodent | HIGH | pest, predator or parasite | Intercrop covers can serve as shelters for rodents, except when made with some species toxic to rodents (e.g. bird's-foot trefoil) |
| Sclerotinia | HIGH | pathogen (bioagressor) | Certain Fabaceae species are host plants for some Sclerotinia species (faba bean, vetch, vetchling, forage pea, clover, lentil...) as well as some brassicas (Chinese radish) and sunflower |
| Thrips of vegetable crops | HIGH | pest, predator or parasite | Some intercrop plants can favor early development of thrips (phacelia, sweet clover) |
| Virus | HIGH | pathogen (bioagressor) | Some intercrop plants can be reservoirs of viruses (phacelia hosts viruses BYV, BMYV, PVY; buckwheat hosts CMV virus) |
Disfavored bioagressors
| Organism | Impact of the technique | Type | Details |
|---|---|---|---|
| Weeds | MEDIUM | weeds | Some intercrop plants can have allelopathic effects on weeds (certain sorghum varieties). When vegetables are planted directly in the intercrop cover, it can have a repellent effect against flea beetles. |
| Nematode (bioagressor) | HIGH | pest, predator or parasite | Some intercrop plants can act as trap plants for nematodes (certain sorghum varieties for example) |
| Flea beetle | MEDIUM | pest, predator or parasite | Some intercrop plants can prevent flea beetle establishment in crops (phacelia) |
| Pythium | HIGH | pathogen (bioagressor) | Use of intercrop plants that are not hosts of pythiaceous fungi can prevent pythium sp persistence in soil |
| brown Rhizoctonia | HIGH | pathogen (bioagressor) | Use of intercrop plants that are not hosts of rhizoctonia can prevent persistence of this bioagressor in soil |
| Rodent | MEDIUM | pest, predator or parasite | Some species like bird's-foot trefoil are toxic to rodents |
| Sclerotinia | HIGH | pathogen (bioagressor) | Use of intercrop plants that are not hosts of sclerotinia can prevent persistence of this bioagressor in soil |
Favored auxiliaries
| Organism | Impact of the technique | Type | Details |
|---|---|---|---|
| Spiders | HIGH | Natural enemies of bioagressors | Dense intercrop covers (grasses and legumes for example) can favor development of carabid beetles, rove beetles and spiders |
| Functional soil bacteria | Functional soil organisms | Intercrop covers stimulate soil microbial life | |
| Predatory and granivorous carabids | HIGH | Natural enemies of bioagressors | Dense intercrop covers (grasses and legumes for example) can favor development of carabid beetles, rove beetles and spiders |
| Mycorrhizae and functional soil fungi | Functional soil organisms | Intercrop covers stimulate soil microbial life | |
| Rove beetles | HIGH | Natural enemies of bioagressors | Dense intercrop covers (grasses and legumes for example) can favor development of carabid beetles, rove beetles and spiders |
| Earthworms | HIGH | Functional soil organisms | Intercrop covers that do not secrete toxic substances into the soil favor earthworms |
5. For further information
- Choosing and succeeding with your cover crop during intercrop in organic farming-Ghesquière J., Cadillon A, ITAB, Technical brochure, 2012
- Species characteristics - Cover crop during intercrop in organic farming-Cadillon A. et al., ITAB, Technical brochure, 2013
- Green manures in organic market gardening-Mazollier C., Vedie H., GRAB - ITAB, Technical brochure, 2008
- Cover crops, superficial techniques, Organic farming and Agroforestry-GABB 32, 2012, Page 25 : cover crops in market gardening
- Practical guide for designing vegetable cropping systems economical in phytosanitary products - Help sheet A3 : Characteristics of intercrop covers-Launais M., Bzdrenga L., Estorgues V., Faloya V., Jeannequin B., Lheureux S., Nivet L., Scherrer B., Sinoir N., Szilvasi S., Taussig C., Terrentroy A., Trottin-Caudal Y., Villeneuve F. Ministry of Agriculture, French Agency for Biodiversity, GIS PIClég, Publication, 2014
- Alternative weeding in market gardening - Preventive measures-Ferrier J-D. Chamber of Agriculture of Ain, Technical brochure, 2016. See page 11
- Intermediate crops-Chambers of agriculture Burgundy, Technical brochure, 2015
Appendices
Est complémentaire des leviers
S'applique aux cultures suivantes
Favorise les bioagresseurs suivants
- Snail
- Slug
- Nematode (bioagressor)
- Flea beetle
- Brown Rhizoctonia
- Rodent
- Sclerotinia
- Thrips of vegetable crops
- Virus
Favorise les auxiliaires
- Spiders
- Functional soil bacteria
- Predatory and granivorous carabids
- Mycorrhiza
- Mycorrhizae and functional soil fungi
- Rove beetles
- Earthworms
Défavorise les bioagresseurs suivants
