Management of cover crops in arable farming Carbon cycle and GHG Biodiversity Soil regeneration

1. Presentation

Characterization of the technique

Description of the technique:

Jean-Marie Machet	INRA	jean-marie.machet(at)laon.inra.fr	Laon (02)
Jean-François Dobrecourt	CA 89	jf.dobrecourt(at)yonne.chambagri.fr	Avallon (89)
André Chabert	ACTA	andre.chabert(at)acta.asso.fr	Lyon (69)
Rémy Ballot	INRA	remy.ballot(at)grignon.inra.fr	Grignon (78)

Shred, spread and mix straw and stubble into the soil by mechanical work, notably stubble cultivation. The burial must distribute the straw as homogeneously as possible within the profile. At harvest, it is essential to anticipate this residue management using the chopper spreader of the combine harvester. Re-chopping is always possible, allowing better management of stubble height but remains an additional competing operation. Straw decomposition is facilitated (on an annual scale) as soon as residues do not exceed 5 cm in length, are "broken" and well distributed, and are in close contact with soil and microorganisms. Stubble cultivation tools allow more or less easily achieving the targeted objectives: stubble cultivators equipped only with tines are not sufficient to ensure a homogeneous mixing of the straw; tools of the cover crop type often work at irregular depths. Combined tools: for example, stubble cultivators with rigid tines and leveling discs or disc-tine combinations are best suited to ensure good soil/straw mixing and work at a regular depth.

Implementation period During the intercrop period

Spatial scale of implementation Plot

Application of the technique to...

All crops: Easily generalizable

Repeated passes (if combined tools are not used) are sometimes difficult (short intercrop or early establishment of a cover crop). But the technique remains generalizable to all annual crops.

All soil types: Easily generalizable

All climatic contexts: Easily generalizable

Regulation

POSITIVE influence

Mandatory burial of corn stalks before spring crop (strongly recommended chopping)

Nitrate Directive

2. Services provided by the technique

3. Effects on the sustainability of the cropping system

"Environmental" criteria

Effect on air quality: Variable

Phytosanitary emissions: UNKNOWN

GHG emissions: VARIABLE

Effect on water quality: Increasing

N.P.: DECREASE

Pesticides: DECREASE

Turbidity: DECREASE

Effect on fossil resource consumption: Variable

Fossil energy consumption: VARIABLE

Other: No effect (neutral)

Pollutant transfer to water (N, P, phytosanitary ...): Decrease

Organized nitrogen is temporarily no longer available for leaching, which helps reduce loss risks during winter. Stubble cultivation can also contribute to reduced use of herbicides through its "false seedbed" effect. Finally, surface roughness creation helps limit runoff and thus direct pollutant transfers.

Pollutant transfer to air (N, P, phytosanitary ...): no knowledge on impact

Fossil energy consumption: variable

Depends on the "reference" situation (with or without deep tillage? With or without stubble cultivation?). The technique necessarily requires one or more tools for straw burial but may allow in the long term a reduced use of mineral fertilizers, whose manufacture is energy-intensive in fossil fuels.

GHG emissions: variable

Decrease by carbon storage in soil (humification) but increase by soil humus degradation (mineralization)

"Agronomic" criteria

Productivity: Increasing

Contributes in the long term to improving soil fertility but may cause in the short term a decrease in mineral nitrogen availability for the following crop (which can reach about twenty units).

Soil fertility: Increasing

Regular burial of straw contributes in the long term to enriching the soil in organic matter (OM), which helps improve its chemical and physical fertility.

Water stress: Decreasing

Regular burial of straw contributes in the long term to enriching the soil in OM, which favors an increase in its water storage capacity.

Functional Biodiversity: Increasing

In the long term, a soil richer in OM promotes soil microbial activity. No knowledge on types of microorganisms.

Other agronomic criteria: Decreasing

Crusting and erosion: Decreasing

Residue incorporation increases soil OM content and also helps limit climate impact on soil and combats crusting phenomena (surface residues protect soil from precipitation) and erosion (improvement of soil physical properties).

Soil acidification: Decreasing

Straw burial helps reduce the rate of soil acidification.

"Economic" criteria

Operational costs: Variable

Slight decrease in phosphorus fertilization costs, more significant for potassium fertilization. In the case of crops with nitrogen-rich residues, return can allow a reduction of nitrogen fertilization costs, provided residue mineralization coincides with crop uptake phase. Conversely, for crops with high C/N residues, the decrease in nitrogen availability for the following crop must be compensated by fertilization.

Mechanization costs: Increasing

Cost very variable depending on equipment availability on the farm: from 10 euros/ha if equipment is available, to 30 euros if subcontracted. Approximately 30 to 35 €/ha for straw chopping and 25 €/ha for stubble cultivation. This cost is reduced if chopping is done directly by the combine harvester during harvest.

Margin: Decreasing

No valorization of by-product (straw sale) if planned,

Possible increase in nitrogen dose on the following crop (0 to ~20 U/ha),

Increase in mechanization and fuel costs for straw burial.

"Social" criteria

Working time: Variable

Farmers are accustomed to stubble cultivating their plots (except plough direct or no-till), if residue chopping can be done by the combine harvester, there is no increase in overall workload. However, if chopping causes an additional pass (tractor-mounted chopper), workload will increase (half hour/ha).

chopping with combine => no increase in working time if farmer practices stubble cultivation
increase in mechanization time => if additional chopping and/or farmer does not practice stubble cultivation

Indicatively, work rates for chopping and stubble cultivation represent about 2 ha/h per pass. Chopping followed by stubble cultivation thus represents about 1 hour/ha.

Effect on farmer health: Decreasing

Solidarity among farmers: Decreasing

In difficult years for forage production (2003, 2010, 2011), straw can be harvested and sold to livestock farmers to feed their herds. The generalization of the technique could lead to a decrease in available quantities.

Observation time: No effect (neutral)

4. Favored or disadvantaged organisms

Favored Pests

Organism	Impact of the technique	Type	Details

Disadvantaged pests

Organism	Impact of the technique	Type
fusarium head blight	MEDIUM	pathogen (pest)
slug	MEDIUM	pest, predator or parasite
take-all	MEDIUM	pathogen (pest)
sharp eyespot	MEDIUM	pathogen (pest)
bean pyralid	MEDIUM	pest, predator or parasite
European corn borer	MEDIUM	pest, predator or parasite

Favored Auxiliaries

Organism	Impact of the technique	Type	Details

Disadvantaged Auxiliaries

Organism	Impact of the technique	Type	Details

Favored climatic and physiological accidents

Organism	Impact of the technique	Details

Disadvantaged climatic and physiological accidents

Organism	Impact of the technique	Details

5. For further information

Support for diagnosis and prescription of phosphorus and potassium fertilization of arable crops
-COMIFER

Book, 1995

Calculation of nitrogen mineralization and leaching in fallow using a simple dynamic model
-Mary B. (INRA)

European Journal of Soil Science, no. 50, p549-566, Peer-reviewed article, 1999

Export of straw: What consequences on NPK fertilization?
-Laurent F., Bouthier A., Castillon P., Le Souder C. (Arvalis)

Agricultural Perspectives no. 354, p16-19, Press article, 2009

Organic matter and soil sensitivity to crusting and compaction
-Guerif J.

Organic matter and agriculture, proceedings of the 4th soil analysis days and 5th forum of reasoned fertilization, Conference proceedings, 1995

Nitrogen management in intercrops and fallows
-Machet J.M. (INRA)

Nitrogen management in agroecosystems, Eds G Lemaire and B Nicolardot, p271-288, Conference proceedings, 1996

Better manage the intercrop for agronomic and environmental benefit
-Minette S. (Chambre d'agriculture Poitou-Charentes)

Professional report, 2005

Nitrate leaching in intensive agriculture in Northern France: Effect of farming practices, soils and crop rotations
-Beaudoin N. (INRA)

Agric. Ecosyst. Environ. No. 111, p292-310, Peer-reviewed article, 2005

Soil susceptibility to compaction by wheeling as a function of some properties of a silty soil as affected by the tillage system.
-Pereira J.O.

European Journal of Soil Science, no. 58, p34-44, Peer-reviewed article, 2007

Soil, vegetation, environment
-Duchauffour P.