Destroying green manure in vineyards
The destruction of cover crops present in the inter-row of the vine follows their establishment before the winter period as they are not intended to be harvested. When destroyed, the cover crops represent a contribution of organic matter, allowing to:
- combat soil erosion and runoff
- limit the development of weeds.
Several methods of destroying cover crops are commonly used, with different effects, particularly on the speed of degradation of the cover and its mineralization.
Destruction Methods
Destruction Timing
The destruction of the cover must occur at the latest by the flowering of the plants to avoid seed set and reseeding[1].
Until flowering, the plant accumulates photosynthesis products in reserves of simple elements. After flowering and from fertilization, these elements migrate to the seeds to form reserves of complex elements (such as starch, etc.). Flowering plants are at their maximum biological activity, so it is the most interesting time to destroy cover crops[2].
However, it is necessary to adapt and take into account[2] :
- the species present in the mixture,
- the development of the cover crop relative to the vine (examples: interference with treatments, risk of frost, risk of too late mineralization or on the flower increasing susceptibility to diseases…),
- flowering, or seed set of an invasive species, or the dominant species of the mixture.
The management of cover crop destruction must be linked to the needs of the vine: it must develop long enough while limiting its negative effects, and make its destruction and peak mineralization period coincide with the vine's needs. However, its mineralization is highly dependent on the climatic conditions of the vintage, which is why management mainly aims to limit competition from the cover, rather than to synchronize its nutrient release with vine needs.
Choosing a Method
The choice of destruction method depends on the objectives sought[1] :
Rolling
It consists of laying the cover crops down on the ground and pinching them to stop sap flow, with a high work rate (up to 12 km/h) and low energy demand (3.6 to 4.1 L fuel/h).
The slow degradation of the pinched part and the stop of cover growth allow a compensation or even gain in organic matter. However, it may result in incomplete destruction of the cover if the cover crop is composed of several species not all at the end of their cycle.
| Advantages | Disadvantages |
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There are different types of rollers. The main differences lie in the design of the elements that pinch the stems. For all, the common principle is a distribution of ground pressure by offsetting the elements, to prevent the roller from bouncing due to terrain irregularities and to improve the pressure exerted on the ground.[3]
Rolofaca
- Straight blades arranged in crenellations.
- Stems are cut more than crushed due to the sharp edges of the roller.
- Front mounting is possible.
- The Clemens roller is designed identically but has an interesting option to extend the roller to adapt to different vineyard row widths.
Actisol [1] roller
- Inclined blades on 4 interchangeable sections allow distribution of effort on the ground.
- Many stems are cut more than pinched.
- The roller can lift soil if the attack angle is too steep.
Martin Raucoules roller
A more artisanal design for this roller with two sections of inclined blades to channel the vegetation flow and prevent covers from lying under the vine feet. Crushing is a bit less homogeneous.
Rolojack
The particularity of this roller offered by VITIMECA lies in several features that distinguish it from others:
- Wavy blades for distributing ground effort,
- Presence of a support cylinder at the 3rd point to adjust pressure on the cover by transferring tractor weight,
- Presence of a small diameter solid counter-roller in front of the main roller.
- The crushing of the cover obtained is very homogeneous.
Mowing, cutting
It is interesting when the vegetation is lightly developed or if you want to leave it on the ground to ensure soil cover.
There are many machines available to mow vineyard inter-rows.
Equipment
- Hydraulic mower
- Inter-row mower
- Roto-fil mower for inter-rows
Shredding
This destruction is useful when the vegetation is dense and incorporation into the soil and decomposition must be rapid.
Shredding a heavily developed cover can be quite energy-consuming. Measurements made with a shredder on a 120 cm high cover gave a consumption of 10.8 L/h at a speed of 3.8 km/h. For a cover planted every other row, consumption is 7.75 L/h.
In viticulture, to avoid rapid mineralization or conversely a "nitrogen hunger", mulching appears as an interesting compromise that avoids abrupt changes at the soil and vine level.
Equipment
- mower with sections or rotary,
- vertical axis gyro-shredder,
- knife shredder with horizontal axis.
Mounted equipment is preferable because vegetation is not crushed by tractor wheels.[4]
Incorporation
Incorporation is optional; it depends on the objective sought. In all cases, some rules must be followed:
- Never incorporate a cover crop on wet soil.
- Respect a delay of 3 weeks between shredding and incorporation to avoid a mineralization peak or a "nitrogen hunger" phenomenon
- Vegetation can also be left on the soil for 30 to 60 days to dry before incorporation.
- Organic matter should not be incorporated deeply if still fresh and incorporation can be done in one or two passes, depending on species, with a tine or disc tool.
Equipment
Incorporation is then done with a covercrop-type implement. One to two passes are necessary depending on species.
Instantaneous consumption measured varies between 5.14 and 7.22 L/h for a working speed of 6 km/h.
Under these conditions, and always for covers planted every other row, consumption per hectare is between 2.3 and 3.3 L.
The total of the two operations, shredding and incorporation, therefore requires 10 to 11 L of fuel per hectare, i.e. 10 times more than simple rolling.
Grazing
Sheep grazing in grassed vineyards has a dual interest, both for the farmer and the viticulturist. But beware: sheep cannot graze all year round because there would be too great a risk for the vine. Grazing is possible from the end of lignification (end of October) until budburst of the vines (end of February or even March depending on varieties and areas).
Services Provided by the Technique
Nutrient supply
Destruction of cover crops, especially by shredding and shallow incorporation, allows the return to the vine of mineral elements in an assimilable form from insoluble forms that were unusable as such by the vine (example: Brassicaceae with potash, or atmospheric nitrogen with Fabaceae).
One can also let the cover lignify to adjust its C/N ratio, with the aim of increasing the organic matter content of the plot.
Physical stability and soil structuring
Destruction of the cover ensures soil cover, whether the cover has been shredded or not. This cover limits erosion and runoff phenomena and is all the more effective if there is mulch resulting from shredding.
Weed regulation and weed management
In the case of shredding with displacement under the row with or without inter-row tillage, this destruction allows covering the row with mulch and limits weed development by coverage.
Effects on the sustainability of the cropping system
"Environmental" criteria
Effect on water quality The role of weed management ensured by soil cover and mechanical intervention helps limit soil tillage. Moreover, soil cover ensured after cover crop destruction, as long as it is not incorporated, limits inter-row erosion and thus turbidity risk. Finally, a cover crop can act as a nitrate catch crop.
Effect on fossil resource consumption
Destruction of cover crops requiring one or more mechanical interventions increases fuel consumption and induced GHG emissions. However, these can be offset by limiting the use of mineral fertilizers (thanks to nutrient supply and weed management services), whose manufacture consumes fossil resources. Using cover crops to improve soil organic matter content also allows carbon storage in soils.
"Agronomic" criteria
Productivity Care must be taken regarding the timing of destruction and incorporation of cover crops, which can cause a mineralization peak and thus an increase in vine vigor at a time when it is rather sought to limit it (spring and veraison), and conversely, in some low fertility situations, too late destruction can generate competition with the vine.
Soil fertility
Cover crops stimulate soil biological activity rapidly and intensely during their growth and especially after incorporation. The amounts of humus formed help maintain the soil organic matter level but are often insufficient to increase it.
Water stress
Be careful in dry areas and during periods of strong vine growth to destroy the cover crop before it competes with the vine for water.
Functional Biodiversity
Cover crops, depending on the species composition of the mixture, can provide a favorable habitat for auxiliaries of the vine, however this is destroyed before the vine's vegetative period.
"Economic" criteria
Operational costs
Fuel consumption for cover crop destruction is higher than for chemical destruction. It depends on the tool and cover biomass. For covers planted every other row, IFV Southwest estimates between 10 and 11 L/ha consumption for shredding a heavily developed cover (120 cm height) followed by incorporation with a cover-crop type tool. This consumption is 10 times higher than for simple rolling.
Mechanization costs
They depend on the price of the equipment considered.
Margin
The destruction cost, including equipment price and associated labor time, is between 20 and 30 €/ha. To this must be deducted the saved inputs costs (fertilizers), which can amount to €75 per ha in the most favorable case. The price of the entire technique (sowing, seed cost, destruction) must be taken into account in the margin impact analysis.
"Social" criteria
Working time
Mechanical destruction of cover crops requires more working time than chemical destruction, especially since the intervention consists of working one row at a time.
Work rates vary depending on equipment, cover density... Rolling is the fastest intervention (8 to 12 km/h).
Peak period
Favor rolling which is the fastest destruction method (up to 12 km/h).
For more information
- Cover crops in viticulture (CA du Var) (PDF)
- Cover crops in viticulture (ITAB) (PDF)
- Cover crop destruction (IFV)
- cover crops in viticulture (Agrobio du Périgord) (PDF)
- ↑ 1.0 1.1 Chamber of Agriculture of Var, 2018, Cover crops in viticulture
- ↑ 2.0 2.1 Auxiliary Bio, No. 3, May 2017, Cover crops in organic viticulture, AgribioPérigord
- ↑ French Institute of Vine and Wine, online, Destruction of cover crops
- ↑ ITAB, Cover crops in viticulture
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