Establishing Intermediate Crops with Allelopathic or Biocidal Effect - Biofumigation

Technical articles

Carbon cycle and GHG Organic matter autonomy in vegetable farming Climate resilience Soil cover Biodiversity Soil regeneration

The technique consists in establishing during the intercrop period, or several months before sowing the main crop, an intermediate crop by choosing a species known for its allelopathic effect (release of chemical compounds that affect the development of other species, particularly weeds).

Presentation

The allelopathic effect can be summarized as the ability of certain species to produce toxic compounds which are released into the soil when plant tissues are incorporated.

For the control of weeds, the overall competitive ability of the intermediate crop must be considered. Some suggest destroying and incorporating the intermediate cover into the topsoil a few weeks before sowing the crop to avoid any negative impact on the crop. Others believe these operations should be done as late as possible so that the allelopathic compounds remain active. Biofumigation in the strict sense describes the phase of residue incorporation into the soil and their degradation into toxic compounds.

Examples of application

Brown mustard Brassica juncea

Soil preparation and sowing : soil preparation should be the same as for a main crop. Sowing must be as careful as possible and the seeding rate should be between 8 and 10 kg/ha. Under shelter and dry conditions, irrigation is recommended to facilitate emergence.
During crop growth : fertilization, irrigation and plant protection may be necessary. Indeed, the use of these cultural techniques depends on pedoclimatic conditions and farmer objectives. For good effectiveness of the technique, a production of at least 50 tons of fresh matter per hectare is sought.
Chopping and incorporation of the cover : the optimal stage to chop mustard is flowering. At this stage, the content of glucosinolates (toxic compounds) in stems and leaves is maximal; it decreases afterwards. Chopping must be as fine as possible to burst as many cells as possible. All tools are possible, but the hammer flail mower ensures better chopping. Immediately after chopping, residues must be incorporated into the soil using a rotary harrow, a rotavator or a rototiller, at a depth between 15 and 20 cm. The soil must then be pressed. Burial can be followed by mulching to maintain the moisture necessary for biofumigation and limit volatilization of toxic compounds. Ideally, soil temperature should be above 10 °C to allow glucosinolate transformation. The following crop can be planted or sown one week after incorporation, but a delay of 3 weeks to 1 month is preferable to avoid risks of nitrogen hunger (especially with Poaceae) or phytotoxicity.

Establishment of brown mustard (allelopathic effect on rhizoctonia) before a lettuce crop (experimental) : After two winter lettuce cycles, establish brown mustard. About 45 days later, chop and bury with a rotavator (horizontal axis rotary cultivator). To simplify the technique, water can be added to close the soil. Also, it is recommended to put a plastic film to avoid volatilization of biofumigant components. Leave at least 3 weeks.

Establishment of mustard against nematodes before sugar beet.
Establishment of crucifers before spring pea for the effect of glucosinolates on Aphanomyces.

Details on the technique

The definition of allelopathy is not fully consensual. Some include only interactions between plants, others between all types of living beings. Moreover, the existence of this phenomenon was long controversial. While now proven, this effect is very difficult to isolate from other interactions such as competition for resources.

Species with allelopathic effects (intensity of allelopathic effect from Sem-Partners catalog, see bibliography):

Diploid oat: allelopathic effect not demonstrated. Mechanisms and molecules involved poorly known.
Spring oat, Fenugreek, Vetch, Foxtail millet: medium allelopathic effect, mechanisms and molecules involved poorly known.
Camelina, Radish: strong allelopathic effect (glucosinolates).
Winter mustard, Spring mustard: glucosinolate action against nematodes (Heterodera Schaati and Meloidogyne chitwoodi) in biofumigation.
Buckwheat (Sarrazin): strong allelopathic effect. Mechanisms and molecules involved poorly known.
Niger, Winter pea, Spring pea: medium allelopathic effect.

Implementation period

During intercrop : The intermediate crop must develop sufficiently to express its allelopathic effects. Therefore, relevant sowing dates must be defined according to the chosen species, soil and climate.

Application of the technique to...

All crops : Easily generalizable, this technique can be applied to all vegetable crops in open field and under shelter depending on intercrop periods and durations.

All rotated crops can benefit from allelopathic effects of the preceding intermediate crop, notably :

Winter oat, Winter soft wheat, Einkorn (Small spelt), Spelt, Winter barley, Winter rye, Winter triticale: use of mustard against take-all.
Beet: use of mustard or radish against Rhizoctonia solani and nematodes.
Potato: against black scurf (also called Rhizoctonia solani).

It is not recommended to establish a species already present in the rotation (compost before sunflower, crucifer in short rotation with rapeseed, …).

All soil types : Easily generalizable, soil covers can be established in all soil types and in all regions if the species and technical itinerary are adapted (some interventions may be necessary, such as irrigation).

All climatic contexts : Easily generalizable.

Regulation

POSITIVE The Nitrate Directive requires soil cover during winter in vulnerable zone, this opportunity can be used to choose a cover with allelopathic effect.

No specific regulation exists for biofumigation. However, the regulations in force for intercrop covers in vulnerable zones (nitrate directive) concerning sowing date, chopping and crop management must be followed.

Effects on the sustainability of the cropping system

"Environmental" criteria

Effect on air quality :

phytosanitary emissions : DECREASE
GHG emissions : VARIABLE

Effect on water quality :

Increasing

N.P. : DECREASE
pesticides : DECREASE

Effect on fossil resource consumption :

Increasing

fossil energy consumption : INCREASE

Other :

Pollutant transfer to water (N, P, phyto ...) : Decrease : Reduction via reduced pesticide use (variable depending on molecules) and trapping of nitrogen and phosphorus by the cover.
Pollutant transfer to air (N, P, phyto ...) : Decrease : Reduction via reduced pesticide use variable depending on molecules.
Fossil energy consumption : Increase : Establishment and destruction of the cover cause higher fuel consumption than maintaining bare soil during intercrop (except legume intercrop which reduces nitrogen inputs) if there is no tillage during this period.
GHG emissions : variable : Establishment and destruction of the cover cause GHG emissions linked to fuel consumption. Cover development allows carbon storage in the soil. The balance is therefore "variable" at the crop scale.
Biodiversity : Increase : The presence of cover favors certain species by providing refuge and food (insects, soil macro and microfauna, birds, etc.). This effect varies depending on the nature of the cover, for example if it is a nectariferous species or not.
Landscape structure diversity : Increase : Soil cover diversifies the landscape during the intercrop period.

"Agronomic" criteria

Productivity :

Residue decomposition time more or less long which can cause a delay in sowing date.

If destruction is too late, the intermediate crop can cause depressive effects on the following crop (water and nitrogen availability). The allelopathic effect may also affect the following crop in addition to weeds. Be careful to adapt the cover choice to 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).

This technique promotes soil biological activity, allows storage of organic matter, carbon and nitrogen in the soil, thus enhancing its fertility.

This method limits nitrate leaching, erosion, crusting and soil structure degradation.

Water stress :

Increasing

Water uptake during cover development can reduce water available in the useful reserve, especially in case of dry winter. Cover destruction must be adapted to soil type and water requirements of the following crop.

Functional biodiversity :

Increasing

Beneficial organisms, pollinators and soil fauna can be favored by the presence of the cover, variably depending on the species chosen.

Selective method acting only on harmful organisms.

Other agronomic criteria :

Development of bio-aggressors : Variable : Intermediate crops can have variable effects on bio-aggressors. They break the cycle of some, but provide habitat and/or food to others (slugs, sawflies, flea beetles, aphids). Avoid choosing intermediate crops hosting bio-aggressors common to main crops (example: crucifers in rotation with frequent rapeseed).

"Economic" criteria

Operational costs :

Increasing

Depending on the species or species mixture chosen, seed cost can vary from 10 to 100 €/ha.

Increase in operational and mechanization costs varies depending on the species established and the sowing and destruction techniques chosen.

Mechanization costs :

Variable

Establishment cost can vary from 0 €/ha (sowing at harvest under the canopy) to 60 €/ha (direct sowing). Destruction cost also varies from 0 €/ha (frost) to 30 €/ha (chopping + burial).

Margin :

Variable

On one side, fertilizer savings (nitrogen restitution) and possible savings on phytosanitary products and passes, on the other side a cost linked to cover establishment. The effect on margin depends on the balance between these two elements. "Long-term" effects are difficult to quantify and usually not taken into account in margin calculations (soil structure improvement, erosion limitation, soil life, ...). The cover can also be valorized (harvest, fodder, ...).

"Social" criteria

Working time :

Variable

Depending on the mode of establishment and destruction, workload can be more or less important than that related to false seedbeds in intercrop. However, an increase in working time is observed for seedbed preparation, establishment, chopping and incorporation of the cover.

Peak period :

No effect (neutral)

However, work is to be expected during the intercrop period.

For more information

Allelopathy: Advances, Challenges and Opportunities - Mallik A. (Lakehead university, Canada) 4th world congress on allelopathy, august 2005, Wagga Wagga, Australia, Conference proceedings, 2005 article

Biofumigation : principle and application - Michel V. Technical brochure, 2008 Swiss Review Vitic. Arboric. Hortic. Vol. 40, 95-99

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) Agricultural Perspectives n°321, p22-29, Press article, 2006 link to article

Evaluation of alternative control methods against potato brown Rhizoctonia - Gaucher D. ; Loison R. ; Jaunatre V. ; Engel D. (Arvalis) Arvalis Plant Institute, 2010 link to poster

Practical guide for designing vegetable cropping systems saving phytosanitary products. Technical sheet T10. -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., Book, 2014 To access the Guide see link

Inhibition of weed growth after incorporation of plant residues into soil : allelopathy or nitrogen cycle modification? - Delabays N. (Agroscope RAC Changins, Switzerland) ; Munier-Jolain N. (INRA, UMR BGA) AFPP - 19th COLUMA conference. International days on weed control. Dijon, 8, 9 and 10 December 2004, Conference proceedings, 2004

Interest and feasibility of bio-disinfection with Brassicaceae in protected vegetable farming. - Parès L. 2011 Technical days Organic Fruits and Vegetables, 42-45.

Interest and feasibility of biofumigation with Brassicaceae in open field vegetable crops. - Montfort F. 2011 Technical days Organic Fruits and Vegetables, 37-41.

Intercrop period used to sanitize the soil - Beet Technical Institute The French Beet Grower's technique n°950 of 24 June 2011, Press article, 2011 article

Other means to limit weed risk - Pierre Mischler Agro-Transfert Resources and Territories, Technical brochure, 2011 link to brochure

New cover crops - comparison of different covers 2010 -SEM Partners Website, 2010

Website. Seed catalog of intermediate covers with details on their allelopathic effects (strip trials, weed biomass measurements, companion plant tests) CETIOM. site

Better managing intercrop for agronomic and environmental benefit - Minette S. (CRA Poitou-Charentes) Technical brochure, 2005 dossier

Nitrogen losses by leaching - Intermediate crops : immediate and lasting efficiency - Laurent F., Fontaine A. (Arvalis) Agricultural Perspectives n°327, p26-30, Press article, 2006 link to article

The role of allelopathy in agricultural pest management - Farooq M. , Jabran K. , Cheema Z.A. (University of Agriculture Faisalabad) and Wahid A. (University of Agriculture Faisalabad) ; Siddique K.H.M. (King Saud University) Pest Management Science 67, pp 493-506, 2011, Peer-reviewed article, 2011 Scientific review article. Provides a definition and its different uses in agriculture. abstract

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