Catch crop nitrate trap (CIPAN)

Technical articles - Soil and fertilization, Cost reduction

Except for specific exemptions, regulations require winter soil cover in Vulnerable Zones (and other special cases), to limit nitrate leaching and combat soil erosion.

Objective

Intermediate Nitrate Catch Crops (CIPAN) are part of the family of multi-service intermediate crops (CIMS) and meet, from a regulatory standpoint, an environmental objective to protect water quality against pollution by nitrates from agricultural sources. Indeed, planted between two crops, that is between July and September, they fix the excess nitrogen in the soil, preventing its leaching into groundwater.

CIPANs thus constitute a very interesting agronomic tool in a sustainable agriculture approach (soil protection and structuring, improvement of fertility, biological activity…).

Moreover, these covers help diversify autumn and winter agricultural landscapes, which promotes biodiversity in general and small game in particular.

It is possible to meet this regulatory requirement while simultaneously building forage stocks, or simply benefiting agronomically.

Two possible strategies:

Keep it simple and low cost
Rebuild forage stocks

Elements to consider

The goal is to establish an intermediate crop before a spring crop and achieve sufficient development to trap soil nitrogen present between the previous harvest and the start of drainage (around mid-November).

The choice of species must also consider ease of destruction.

In this situation, the use of mustard is often the most convenient and cheapest solution (possibility of broadcast sowing). It is also possible to use spring cereals such as oat.

Other species such as phacelia help break disease cycles while having real benefits in terms of nitrogen trapping, soil cover, and structuring the worked soil horizon.


Mustard	Oat
FALSE SOWING Priority technique if the plot has a significant seed bank of weeds. In this case, sowing the cover crop can be delayed.
Stubble cultivation with simultaneous sowing using a rotary seeder (8-10 kg/ha) + Rolling. or Sowing with rotary seeder + shallow stubble cultivation (*) + Rolling.	Sowing at 60-80 kg/ha with fertilizer drill in a grid pattern. Stubble cultivation. Rolling.

(*) if the stubble cultivation tool cannot work shallowly, it is better to sow on the stubble and roll afterwards.

Rolling may be optional depending on the compaction work done by the stubble cultivation tool.

The cost of specific establishment operations (sowing-stubble-rolling) ranges between €20 and €30.

Sowing should preferably be done before the end of August to ensure sufficient development during autumn. Early sowing increases the risk of frost damage. The stage of vegetation development makes the cover more frost-sensitive. Very early sowing of mustard can lead to premature flowering and limited nitrogen uptake over time. This does not allow capturing nitrogen from autumn mineralization.

Recently, seed companies have marketed "late" mustard varieties which are preferable if sowing before September 1st.

Cereals have a lower nitrogen uptake capacity than mustard and crucifers in general.

Legumes (to be sown only in mixtures when there is no harvest) have a real capacity to absorb soil nitrogen, in addition to fixing atmospheric nitrogen.

The nitrogen contained in these legumes is available in significant quantities (25 units if producing at least 1.5 t of dry matter), although it does not allow fertilizing the following crop, far from it.

Conditions to benefit from this nitrogen input are:

Sow early. A legume needs more heat and sunlight than crucifers and grasses to develop. If the cover is sown late (after August 15-20), sowing legumes becomes less beneficial.

Do not destroy early because nitrogen could be quickly leached: not before the end of January.

CIPAN at the rotation scale

The objectives, in addition to nitrate trapping, will be:

Good soil cover (to compete with weeds).
Varied root systems that explore a large part of the soil.
High biomass production for fresh organic matter in the rotation.

Introducing legumes into the rotation via the cover allows reducing nitrogen input on subsequent crops. In this case, mixtures of different species are interesting to combine the favorable factors of each and break disease cycles. However, a combined seeder or a tool for no-till seeding will necessarily be required (establishment cost €50 to €60/ha). Destruction of some species can be difficult (e.g., radish) and balancing species proportions can be delicate.

To benefit from the cover, it should preferably be sown before September 1st and ideally around August 15th. Climatic conditions after sowing and soil moisture will determine good emergence and development.

It is important to note that a cover crop will not "restructure" the soil. It will maintain good structural condition in the top 30 centimeters (very interesting in soils prone to compaction), but the short presence of the cover and limited root development do not allow it to recover a plow pan or heavily compacted zones.

A CIPAN can help control weeds in a plot, mainly by competition. This competition is sometimes supplemented by an allelopathic effect when substances emitted by the intermediate crop are unfavorable to weeds. In this context, the CIPAN must be sown on a clean soil and as soon as possible to effectively limit regrowth of the previous crop. Weather conditions play a major role in emergence speed, with varying coverage power depending on the year. Species to favor in this weed management case are: buckwheat (forage and baking types), black forage lentil, forage rape, camelina, spring vetch, and spring forage pea.

How to choose your mixture?

Species choice depends on coverage objectives, nitrogen input, desired soil structuring, complementarity of species in aerial and root systems, and ease of destruction.

How to establish covers in maize/maize rotation?

Currently, regulations do not require anything in the case of late harvest or very clayey soils (except specific cases), except for fine shredding of residues, or at least superficial incorporation in the case of grain maize, sunflower.

Otherwise, sowing a cover is mandatory in continuous silage maize cropping, within 15 days after ensiling (despite low agronomic and environmental interest).

Only no-till seeding under cover allows satisfactory results in terms of nitrogen trapping and cover development. The technique consists of sowing the cover at the 6-8 leaf stage of maize during a mechanical weeding operation (cultivator combined with a rotary seeder at the front of the tractor).

The CIPAN stagnates until harvest then develops rapidly after ensiling. Certainly, too rapid development of an IRG (Ryegrass Italiano) can harm yield. This species may also seem inappropriate without harvest (CIPAN destruction must be mechanical).

Destruction of nitrate trap

Technically, maintaining a cover no longer affects nitrate losses from late autumn. From then on, destruction must occur at least 6 weeks before the next crop is sown.

Before maize sowing, the cover can remain until February.

For pea sowing, destroy the CIPAN as early as possible after November 15 if possible.

Also beware of plots that are difficult to work in spring: for these, destruction must occur as soon as possible from November 15.

In case of very developed cover and conventional establishment technique, shredding is generally necessary to facilitate degradation of plant tissues, their attack by microorganisms, and incorporation into the soil.

Before maize or sunflower, it is possible to wait for significant frost windows (usually around the second half of January and mid-February). At this time, rolling on frost is effective if the cover is well developed and if done at the right time and speed (Rolling at the start of thaw is striking on phacelia, oat, or pea).

The mulch produced effectively protects against crusting soils.

On less developed cover, mechanical destruction (tines or discs) is sufficient. With heavy tools, beware of soil compaction!

Otherwise, apply systemic herbicide, especially after cover harvest.

Choosing frost-sensitive species is a good way to avoid specific destruction interventions.

Intermediate crops and legumes: how effective?

The association of legumes in CIPAN is a popular practice to enrich the soil or add value to a catch crop. Legume development, thus sowing date, determines nitrogen gain (maximum 40 units, generally between 10 and 20 useful units).

Legumes are interesting in rotations without effluent inputs, where nitrogen is sometimes limiting at the start of the intercrop period.

Best practices

Prefer a mixture of 2 to 4 species.
Sow the cover as early as possible after harvest.
Keep the cover as long as possible (January-February) when soil type allows.
In case of mechanical destruction (shredding), start in the center of the plot, at reduced speed and using a deterrent bar.

To avoid

Pure mustard at high density.
Early cover shredding (early November).
Sowing the same cover across the entire farm.

Appendices

See the following crops:

Sources