Introduction

The last century has seen food production be revolutionized. Nowadays, about half of the population rely on nitrogen fertilizers for their alimentation. The environmental impacts of, on one hand, the NO2 and CO2 emission during their synthesis, and, on the other hand, the NO2 emission and leaching in fertilized fields raise serious concerns [START_REF] Blottnitz | Damage costs of nitrogen fertilizer in Europe and their internalization[END_REF]Crews and Peoples, 2003).

Farmers have been affected by the volatility of fertilizer purchase prices in the last decades. It directly decreases profitability, strongly for productions where fertilizer account for a large part of production costs, such as corn or small grains [START_REF] Huang | Les légumineuses pour des systèmes agricoles et alimentaires durables. IFV and INAO[END_REF]. Facing these challenges, others approaches for fertilization would benefit from being better known in order to feed a growing population. The atmospheric dinitrogen is the largest reservoir of nitrogen on earth and it can be fixed by legumes with the energy derived from photosynthesis. Thus, legume-based agroecosystems are likely to be more sustainable than fertilizer-based systems (Crews and Peoples, 2003). Regenerating soil fertility through this biological fixation by legume-rhizobial symbiose is an alternative practice. Cover crops of legumes accumulate nutrients that will be released after cover crop death and available for the subsequent crop.

Although crop system is partly dependent to synthetic nitrogen fertilizer, inputs of biological fixed nitrogen still has a significant contribution to fertilization in pastures and field crops systems [START_REF] Evans | Net nitrogen balances for cool-season grain legume crops and contributions to wheat nitrogen uptake: a review[END_REF]. In perennial crops systems, green manuring showed interesting potentials in cultivation of sugarcane [START_REF] Ramesh | GREEN MANURING IN SUGARCANE -A REVIEW[END_REF], orchards [START_REF] Mouco | GREEN MANURES IN "KENT" MANGO ORCHARD[END_REF] and vineyards [START_REF] Garcia | Management of service crops for the provision of ecosystem services in vineyards: A review[END_REF] to increase nutrients availability and use efficiency. At least in winter, these perennial crops do not cover the empty space in between the rows, allowing growing intercrops. Performances assessment and technical references are more and more available in field crops systems. Yet, management of the cover crops in vineyards requires assessment of the potential competition with the perennial crop, and of the potential restitutions of nutrients by the green manure in order to build references and decision rules [START_REF] Rapidel | Analysis of Ecosystem Services Trade-Offs to Design Agroecosystems with Perennial Crops[END_REF][START_REF] Garcia | Management of service crops for the provision of ecosystem services in vineyards: A review[END_REF]. Also, the success of a green manure depends on its good development, [START_REF] Cherr | Green Manure Approaches to Crop Production[END_REF] deplore a need for assessment of potential effects of environment and management on candidate green manure survival, growth and decomposition. To better answer those concerns, the French Vine and Wine Institute first needs to connect with winegrowers' expectations and soil management itineraries. Therefore, this internship proposes to review and help understanding management methods used in the field in a precursor vineyard, the vineyard of Gaillac, and to study the effects of the environment and management choices on green manure development. 1. 1.1.1 The different soil management strategies in vineyard Grapevine (Vitis vinifera) is a perennial crop commonly grown as a monoculture. Soil management aims at improving physicochemical properties, water regime and limiting weed development. The operations can be different over the year, and between and under the grapevine row [START_REF] Reynier | Manuel de viticulture: guide technique du viticulteur[END_REF]. In the 20 th century, most farmers managed soils thanks to mineral fertilizers and tillage.

Since the middle of the 20 th century, herbicides have been widely adopted thanks to their great effectiveness. In the 70ies, the environmental contamination induced by mineral fertilizers led to a renewal in the use of manure and cover cropped with legumes [START_REF] Hartwig | Cover crops and living mulches[END_REF]. Cover crops are living, purposely seeded or resident plants grown into or after the main crop [START_REF] Hartwig | Cover crops and living mulches[END_REF]. Cover cropping in vineyard gained popularity for quality issues, indeed it can have a positive effect on grape composition [START_REF] Lopes | Cover cropping in a sloping non-irrigated vineyard: II Effects on vegetative growth, yield, berry and wine quality of 'Cabernet Sauvignon' grapevines[END_REF] and health conditions (Valdés-Gomez et al., 2011). Moreover, viticulture has been evaluated as one of the most erosion prone land use [START_REF] Cerdan | Rates and Spatial Variations of Soil Erosion in Europe: A Study Based on Erosion Plot Data[END_REF] and the main cause appears to be the typical late 20 th century crop management (Martinez-Casasnovas and Sanchez-Bosch, 2000), with winegrowers' practices aiming to maintain bare soils [START_REF] Rodrigo-Comino | Five decades of soil erosion research in "terroir". The State-of-the-Art[END_REF]. On the reverse, cover crops can be included in conservation agriculture practices, by providing a groundcover that reduces erosion [START_REF] Labreuche | Evaluation des impacts environnementaux des Techniques Culturales Sans Labour en France[END_REF].

Quite recently, a survey [START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF] recorded French vineyards' cultural practices, highlighting a contrasted situation. 45% of vineyards plots present a groundcover between the rows. In about half of the cases, the soil is cover cropped only one inter-row out of two. A few of the cover cropped inter-rows are sown and permanent (7%), even less are sown and temporarily (5%); most are spontaneous and permanent grass [START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF]. Temporarily groundcovers are mainly wintry, growing during the resting phase of grapevine. Under the rows, a vegetal cover is rarely tolerated [START_REF] Mezière | Ecophyto R&D, vers des systèmes de culture économes en produits phytosanitaires[END_REF][START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF]. A mulch is sometimes formed with cover crop residues, but it is not a majority practice [START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF]. Chemical weeding is a common practice, tillage is an alternative. Both can be combined in time and space. The latter is preferentially used between the rows rather than under the grapevine [START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF] where it calls for specific material [START_REF] Mezière | Ecophyto R&D, vers des systèmes de culture économes en produits phytosanitaires[END_REF].

The services and disservices provided by cover crops

Cover crops are a powerful lever to improve soil physical structure. They allow increases of infiltration, water holding capacity [START_REF] Tournebize | Impact de l'enherbement du vignoble alsacien sur le transfert des nitrates[END_REF], and aggregate stability thanks to the supply of organic matter (Garcia-Diaz et al., 2017). Consequently, a reduction of erosion is observed (Lieskovsky and Kenderessy, 2012), and they provide firm footing for cultural operations (Mc Gountry, 2004).

Cover crops in vineyard allow a reduction of phytosanitary chemicals transfer in the environment thanks to better infiltration of the run-off, retention and degradation of the molecules [START_REF] Benoit | Fonctions environnementales des dispositifs enherbés en vue de la gestion et de la maîtrise des impacts d'origine agricole : cas des pesticides[END_REF].

Meanwhile, vineyard consumption of pesticides is important. In France, they represent 37% of the agricultural lands but 20% of French pesticides consumption [START_REF] Mezière | Ecophyto R&D, vers des systèmes de culture économes en produits phytosanitaires[END_REF]. Also, a reduction of nitrogen leaching is observed [START_REF] Tournebize | Impact de l'enherbement du vignoble alsacien sur le transfert des nitrates[END_REF]. Moreover, cover crops help control weed community (Baumgartner et al., 2008)) and can be one step toward herbicide reduction.

Then, the presence of a groundcover provides board and lodging for soil organisms. Higher abundances were observed for nematodes and earthworms [START_REF] Coll | Viticultural soils quality: benefits of permanent grass cover on soil chemical characteristics and soil biological indicators[END_REF] for permanent grass).

Microbial biomass, respiration and nitrification are also increased [START_REF] Steenwerth | Cover crops and cultivation: Impacts on soil N dynamics and microbiological function in a Mediterranean vineyard agroecosystem[END_REF].

Finally, thanks to the organic matter supply and the enhancement of soil organisms' activity, cover crops can support soil fertility [START_REF] Ingels | Effects of Cover Crops on Grapevines, Yield, Juice Composition, Soil Microbial Ecology, and Gopher Activity[END_REF]. This role will be further explained in the following section.

On the other hand, cover cropping in vineyard may cause a vine vigour reduction [START_REF] Celette | Dynamique des fonctionnements hydrique et azoté dans une vigne enherbée sous le climat méditerranéen (Docteur de Montpellier Supagro[END_REF]Valdés-Gomez et al., 2011). Competition because of cover cropping a sensitive stages of vine growth such as blooming and berry setting can lead to important decrease in yields (Delpuech and Metay, 2018) and alter must and wine quality [START_REF] Guerra | Influence of Floor Management Technique on Grapevine Growth, Disease Pressure, and Juice and Wine Composition: A Review[END_REF]. In spring and summer, the groundcover gradually dries and impoverishes the superficial soil compartments [START_REF] Celette | Dynamique des fonctionnements hydrique et azoté dans une vigne enherbée sous le climat méditerranéen (Docteur de Montpellier Supagro[END_REF]. Cover crop root system occupy approximatively the sixty first soil centimetre, where also mineralisation, a process notably water condition dependent, stand. Labile organic nitrogen pool and nitrogen mineralization decrease with depth [START_REF] Gilmour | Soil testing and nitrogen mineralization[END_REF]Gaultier and Farenhorst, 2006). Mineral nitrogen stock may be significantly lower during spring and summer in cover cropped vineyards because of nutrients uptakes by the cover crop [START_REF] Celette | Dynamique des fonctionnements hydrique et azoté dans une vigne enherbée sous le climat méditerranéen (Docteur de Montpellier Supagro[END_REF], without any fertilizer supply). Depending on the context, different dynamics and scale of uptake can occur and be source of real concerns for water and nitrogen grape alimentation. For example, a well-established permanent cover crop appears to consume more nitrogen than a seeded barley, particularly before budburst, during barley young stages. After what, the developing barley consumed nearly 10 kg N/ha in a month [START_REF] Celette | Dynamique des fonctionnements hydrique et azoté dans une vigne enherbée sous le climat méditerranéen (Docteur de Montpellier Supagro[END_REF].

The balanced of the services provided highly depends on the context. If it is well managed, this competition control vegetative growth and improve grape quality (Delpuech and Metay, 2018;[START_REF] Rapidel | Analysis of Ecosystem Services Trade-Offs to Design Agroecosystems with Perennial Crops[END_REF].

.3 Green manures to support soil fertility for grapevine

Green manure (GM) is a crop designed to ensure a soil amendment and a nutrient source for a main crop (Cherr et al., 2009). The input is realized thanks to the entrance of supplementary nitrogen sources and thanks to organic nitrogen storage in soils (Huyghe and Schneider, 2015). In vineyards, one can define it as crops that will be mown or ploughed to restore nitrogen to grape [START_REF] Garcia | Management of service crops for the provision of ecosystem services in vineyards: A review[END_REF].

Grapevine is in dormancy during winter and knows different growth stages from budburst to senescence as detailed in figure 1. After bud burst, grapewine first uses its reserves from the previous year in the ligneous tissues [START_REF] Inédit Goutouly | L'azote chez la vigne : dynamique des besoins, de l'assimilation, du stockage et de la redistribution vers les fruits[END_REF][START_REF] Conradie | Utilisation of Nitrogen by the Grapevine as Affected by Time of Application and Soil Type[END_REF]. After a few weeks, grape roots elongation increases fast and is maximum at blooming [START_REF] Williams | Grapevine. Irrigation of Agricultural Crops[END_REF]. Soil nitrogen absorption is greatly enhanced from blooming to veraison stages [START_REF] Conradie | Utilisation of Nitrogen by the Grapevine as Affected by Time of Application and Soil Type[END_REF]. The nitrogen requirements concern mainly the leaves and grapes. They respectively represent 1.21 and 1.39 kg N per ton of grapes produced and more than 60% of total plant requirements [START_REF] Conradie | Seasonal uptake of nutrients by Chenin blanc in sand culture: I. Nitrogen[END_REF], studied on Chenin blanc). For controlled yield objectives (Protected Designation of Origin, or PDO, produced at around 45 hl/ha), nitrogen needs of grapevine are about 20-30 kg/ha per year, whereas for higher yield objectives (Protected Geographical Indication, or PGI, produced at 100 hl/ha) they reach 70 kg/ha [START_REF] Crespy | Legume versus fertilizer sources of nitrogen: ecological tradeoffs and human needs[END_REF]. As grape nitrogen needs are the most important from bud burst to veraison and reach a peak at blooming [START_REF] Conradie | Seasonal uptake of nutrients by Chenin blanc in sand culture: I. Nitrogen[END_REF], soil fertility here consists in a good availability of nutrients near blooming.

To reach great performance in terms of soil fertility support, the approach of implanting specific crops between the rows during winter is gaining popularity. Some species can be chosen notably because the amount of nitrogen available for the next crop depends on the C/N ratio of the service crop [START_REF] Finney | Biomass production and carbon/nitrogen ratio influence ecosystem services from cover crop mixtures[END_REF]. Organic residues in soils have generally C/N ratios between 10 and 30 [START_REF] Calame | Comprendre l'agroécologie : origines, principes et politiques Cavaillé, A[END_REF].

Legumes' richness in proteins (Huyghe and Schneider, 2015) classify them as good green manure, with low C/N ratios. Vetch and clover were reported as presenting higher plant-available nitrogen than wheat or rye [START_REF] Bair | Release of Available Nitrogen after Incorporation of a Legume Cover Crop in Concord Grape Department of Crop and Soil[END_REF]. Leguminous ability to capture atmospheric nitrogen is important; for example, from 45 to 80 % of the nitrogen content of pea is atmospheric nitrogen fixed by the symbioses [START_REF] Jensen | Symbiotic nitrogen fixation and nitrate uptake by the pea crop[END_REF].

Green manures including leguminous have already proved itself to provide nitrogen to grape.

Gontier (2013) reported a higher nitrogen release in soil cover cropped with Vicia faba compared with cover crops composed of Grasses or Brassicas. This performance must have been dued to a higher biomass production by Vicia faba (3.5 t/ha of dry biomass instead of 0.8 t/ha or 1.3 t/ha for grasses or brassicas) and nitrogen content (2.8 % of dry biomass instead of 1.2 % or 1 %). In this study, the effect on grapevine yield were little; an improvement in nitrogen content of must was sometimes observed.

Another key issue for the nutrient furniture to the main crop is that the green manure should have a great biomass production [START_REF] Vrignon-Brenas | Early assessment of ecological services provided by forage legumes in relay intercropping[END_REF]. Cereals well fit this criterion with important dry matter production. [START_REF] Fourie | Soil management in the Breede River Valley Wine Grape Region, South Africa[END_REF] reported dry matter production of triticale reaching 6 t/ha before grapevine budburst (sown at a seeding density of 100kg/ha). Finally, the nature of the GM strongly impacts its nutrients support. In this study, we have chosen to focus on wintry sown GM that have flourished in our studied area and to understand their complexed management which comes in addition to grapevine management.

1.1.2 Importance of the modalities of green manure's insertion into the soil management technical itinerary and its pedo-climatic context Constraints and objectives determine choices and management of the services crops, which are sum up along grapevine cycle on the figure 2. Cover crops management offer diverse options -seeding tool, duration, destruction tool, residue management -which are essential levers to reach one targeted service [START_REF] Garcia | Management of service crops for the provision of ecosystem services in vineyards: A review[END_REF]. In this section, we will develop technical itinerary options and their consequences.

We define a technical itinerary as the logical and ordered combination of cultural operations, implemented for a culture (Sebillotte, 1974). We focus only on soil management issue in settled vineyards implementing green manure.

To begin with, restitutions desired in spring imply a sowing period from late September to November, about 4-6 months before the GM accumulate enough biomass. Sowing conditions in late summer are often quite bad, notably because of bad temperatures and soil conditions. Some species can show preferences for early or late sowing; for example, Trifolium incarnatum and Vicia Faba seems to develop better in Gaillac when early sown [START_REF] Gontier | Incidence de différents modes de pilotage des couverts végétaux hivernaux sur l'alimentation azotée de la vigne et la qualité des vins du Sud-Ouest[END_REF]. Second, the sowing operation must be organised among the other steps of the main crop cultivation [START_REF] Justes | Réduire les fuites de nitrate au moyen de cultures intermédiaires : conséquences sur les bilans d'eau et d'azote, autres services écosystémiques[END_REF], notably grape harvest and an eventual soil preparation. To choose a tilled seedbed or a direct seeding imply differences for plant germination, as well as seeding method [START_REF] Jeon | Effect of different seeding methods on green manure biomass, soil properties and rice yiel in rice-based cropping systems[END_REF]. Direct seeding can pose technical problem because of the residues or the weeds present [START_REF] Labreuche | Evaluation des impacts environnementaux des Techniques Culturales Sans Labour en France[END_REF].

The choice species offer numerous possibilities to suit targeted services. Clovers, vetches, alphalfa and other medics, lupins are common temperated GM legumes in field crops systems. Cereal rye, mustards radishes, buckwheat, millet, oat and wheat are usual for nonlegumes service crops [START_REF] Cherr | Green Manure Approaches to Crop Production[END_REF].

Based on research on natural ecosystems showing that increasing plant diversity allows a greater biomass production [START_REF] Hector | Plant Diversity and Productivity Experiments in European Grasslands[END_REF][START_REF] Tilman | Biodiversity and stability in grasslands[END_REF], one can propose to use multispecies cover crop. [START_REF] Finney | Biomass production and carbon/nitrogen ratio influence ecosystem services from cover crop mixtures[END_REF] encounter a positive correlation (R²=0.15) between species richness and cover crop biomass. The authors measure an average increase in dry aboveground biomass of 533kg/ha for each supplementary cover crop specie. Also, nitrogen functional complementarity, studied in grass-legume bicultures, appears to be a great lever to reach high cover crop biomass production [START_REF] Finney | Biomass production and carbon/nitrogen ratio influence ecosystem services from cover crop mixtures[END_REF], with intermediary C:N ratio (Teasdale and Abdul-Baki, 1998). Even if an increased in cover crop mixture biomass in comparison to high yield cover crop monoculture is not reached in all contexts, it may allow to combine phenological complementarities to fulfil several agroecosystem services [START_REF] Finney | Biomass production and carbon/nitrogen ratio influence ecosystem services from cover crop mixtures[END_REF]. [START_REF] Justes | Quantifying and modelling C and N mineralization kinetics of catch crop residues in soil: parameterization of the residue decomposition module of STICS model for mature and non mature residues[END_REF] Then, decisions of tactical adjustments depend on the observed climate because of its impacts on GM growth and competition for nutrients with grapevine. Soil and climate strongly influence GM implantation and biomass production [START_REF] Gontier | Incidence de différents modes de pilotage des couverts végétaux hivernaux sur l'alimentation azotée de la vigne et la qualité des vins du Sud-Ouest[END_REF]. Soil temperature, excess and lack of water, can affect plant germination [START_REF] Labreuche | Evaluation des impacts environnementaux des Techniques Culturales Sans Labour en France[END_REF], and, for legumes, the symbiotic bacteria survival (Huyghe and Schneider, 2015). The symbiotic fixation of the legumes can be altered by a high soil mineral nitrogen content. To fertilize a green manure can be a tactical choice, but it makes it lazy to fix nitrogen, the legumes would rather use the mineral nitrogen available in soil [START_REF] Voisin | Quantitative effects of soil nitrate, growth potential and phenology on symbiotic nitrogen fixation of pea (Pisum sativum L.)[END_REF].

Finally, biomass production is the greatest in April and May, around 600 degree-days after sowing [START_REF] Alonso-Ayuso | The Kill Date as a Management Tool for Cover Cropping Success[END_REF]. Then, fear of frost, competition or inconvenience for cultural operations may be decision criteria for destruction.

The cover crops kill date is a key of the GM success [START_REF] Alonso-Ayuso | The Kill Date as a Management Tool for Cover Cropping Success[END_REF]. Comparison between ecosystem services provided by early kill and late kill cover crops in field crop system is presented in figure 3, showing that a majority of services are enhanced for late kill date. Time of destruction influence the quality and quantity of green manure. From emergence to bolting stage, nitrogen quantity increases in leguminous organs. Blooming is the period were the development of aerial and root system is maximum. Then, during maturation, a dilution is observed (Huyghe and Schneider, 2015).

In field crops, destruction of the GM is mainly done by tillage (with disks for example), rolling, chemical weeding or thanks to frost. The destruction mode can be decided in relation with the species of the green manure, and in relation with the residue management planned [START_REF] Labreuche | Evaluation des impacts environnementaux des Techniques Culturales Sans Labour en France[END_REF]. In vineyards, frost can't be used to kill the GM because the development is delayed and also climate conditions are generally warmer. Chemical destruction is neither expected.

After destruction, mineralization kinetic is influence by inherent soil properties but also residues nature and management. For important C/N ratio, cereal alone for example, nitrogen mineralization of the residues is often first locked, generating a nitrogen deficiency [START_REF] Justes | Quantifying and modelling C and N mineralization kinetics of catch crop residues in soil: parameterization of the residue decomposition module of STICS model for mature and non mature residues[END_REF]. After about one month, the mineralization significantly begins. The evolution of organic nitrogen released follow different trends as presented in figure 4. After two months, only 10% of organic nitrogen has been mineralized for cereal alone, in comparison with 40% for mixes including leguminous. Furthermore, the proportion of nitrogen mineralized may depend on the residue's management. In viticulture, the increases of soil nitrogen mineralization and nitrogen content of the must, observed in a Vicia Faba cover crop, are the highest when the residues are buried [START_REF] Gontier | Engrais verts en viticulture : incidence du type de couvert végétal et de son mode de destruction sur l'alimentation azotée e la vigne. Green manuring in viticulture: impact of cover crop species and way of destruction on nitrogen supply of the grapevine[END_REF] with burying five days after destruction by schredding). Depth of incorporation will impact nitrogen and water dynamic [START_REF] Justes | Réduire les fuites de nitrate au moyen de cultures intermédiaires : conséquences sur les bilans d'eau et d'azote, autres services écosystémiques[END_REF]. Residues management is essential to improve soil-residues interaction and can provide other services than nutrient supply such as reduction of soil evaporation if a mulch is formed [START_REF] Guerra | Influence of Floor Management Technique on Grapevine Growth, Disease Pressure, and Juice and Wine Composition: A Review[END_REF][START_REF] Celette | Dynamique des fonctionnements hydrique et azoté dans une vigne enherbée sous le climat méditerranéen (Docteur de Montpellier Supagro[END_REF].

On the top of that, a winegrower can have a multiannual strategy. This strategy can include a rotation of different soil management itineraries, on the model of field crop rotations. The objectives of such a strategy could be notably to increase weed control and support GM biomass production with an improved sanitary soil status [START_REF] Fourie | Soil management in the Breede River Valley Wine Grape Region, South Africa[END_REF]. According to the agricultural census of 2010 [START_REF] Urbain | Données INOSYS / RA2010 -traitement Chambres d'Agriculture Midi-Pyrénées[END_REF], 370 farms with grape production are in the AOP Gaillac area. Among them, 250 are significantly specialized in grape production, 55 are specialized both in field crops and grape, and finally the rest isn't specialized in grape production.

Average farm size in Gaillac area is 41.6 ha and average vineyard is 21.8 ha. Even the farms specialized in grape production often have other culture(s), mainly 15 ha of field crops, 2.4 ha of permanent pasture in average [START_REF] Urbain | Données INOSYS / RA2010 -traitement Chambres d'Agriculture Midi-Pyrénées[END_REF]. Based on the Agreste survey on cultivation practices of 2013, the part of organic vineyard in Gaillac area is 6% [START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF]. 48 % of the 250 specialized vineyards ensure the wine production in their own winery [START_REF] Urbain | Données INOSYS / RA2010 -traitement Chambres d'Agriculture Midi-Pyrénées[END_REF]. Otherwise, the production is intended to traderwinemakers and cooperative wineries.

Pedoclimatic context

The Gaillac area is commonly divided in three large terroirs broadly organised from north to south: the Cordais plateau in the north of the Vère River, the hill sides on the right bank of the Tarn, and finally lands of the left bank of the Tarn that are mainly alluvium terraces [START_REF] Courjault-Rade | Geological characterisation of plots belonging to the Gaillac vineyard (Tarn, Midi-pyrenees) -Consequences on the determination of the basic terroir units (BTU) and the choice of vegetative material[END_REF].

This distinction is locally very used and echoes to the landscapes. Nevertheless, it doesn't include part

Caption:

A translation of the caption is proposed above:

Figure 5: Map of the terroirs in the Gaillac AOC denomination zone (A. [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF] of the vineyard area east of Albi, and a finer soil study is presented on figure 5. Finally, we can sum up the pedoclimatic conditions with the following great groups. The first would be composed of hill sides and plateau of calcareous or marly dominance [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF], with eventually very shallow soils [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF]. They are mainly in the north of the area. According to the Pedological Referential [START_REF] Baize | Cover-Crop Systems Affect Weed Communities in a California Vineyard[END_REF], they are calcosols [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF]. The second would be alluvium terraces [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF], including the so-called "boulbène" which are here ancient alluvium terraces with leached loamy soils poorly drained [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF]. According to the Pedological Referential (1995), they are luvisol-redoxisol [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF]. Common in Aquitaine, these soils are humid in winter but dry in summer; soil crusting is often observed. They lack soluble elements, notably fertilizers (Cavaillé, 1951). They are located in the Tarn valley; they occupy largely the left bank (south). To finish, a block east of Albi [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF], in the Cunac municipality, is composed of hill sides and plateaus which are dissected, with gravel clays. Soils are also leached and loamy [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF]. According to the Pedological Referential (1995), they are luvisol [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF].

Climate of the area has Mediterranean influences, with strong heat, and oceanic humidity. Warm and dry Autan wind is also a component of the climate [START_REF] Courjault-Rade | Le Lauragais, une entité géologique et géographique[END_REF]. Globally, climate is warm and temperate, rainfall is significant even in summer. Average annual temperature in the city Gaillac is 13.1°C and the rainfall 732 mm/year (https://fr.climate-data.org/europe/france/midipyrenees/gaillac-8019). Climate show variations across the area, they are quite finely presented with colour gradient on the map (figure 5). The calcareous hill sides and plateau include the warmer zone of this region. Autan wind is particularly felt in southwest of the left bank and in the east of the Cunac block [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF].

In this landscape, vine cultivation rate is higher on calcareous hill sides and plateau (from 10-20% near Albi to more than 50%) than in Tarn valley, left bank or east block where it reaches between 2 and 20 % [START_REF] Delaunois | Adapting Cover Crop Soil Coverage to Soil Depth to Limit Competition for Water in a Mediterranean Vineyard[END_REF]. This practice adds up to traditional operations. In Gaillac, according to the 2013 census of cultural practice, the large majority (65%) of fertilizer inputs are mineral, 20% are foliar fertilizers, 4% only are organic and the rest is organo-mineral or unknown (Agreste, 2013). For half of the surface, fertilizer supply occurs each year; for 34% it takes place at least one time in four years; finally, for 15% of the surface no fertilizer was spread between 2009 and 2013 (Agreste, 2013). Concerning weeding, 46% of the surfaces are wed with chemicals, only 9% by mechanical weeding and on 43% of the surfaces both are used. In comparison with the other vineyards from southwestern France, occurrence of chemical weeding is higher (Agreste, 2013). In half of the plots of Gaillac zone, soil under the grapevine rows is kept bare; in 46% vegetal cover is temporary. On the inter-rows, surfaces are for 67% permanently cover cropped and for 28% temporarily cover cropped [START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF].

As explained before, cover crops management is quite complex, and an innovative practice that may be difficult to handle for winegrowers. In Gaillac, the presence of pluri-actives people [START_REF] Zahm | Assessing farm sustainability with the IDEA method -from the concept of agriculture sustainability to case studies on farms[END_REF] and the local dynamic [START_REF] Biarnès | Unexpected predominance of wine grower location over soil trafficability for vine management in southern France[END_REF] around cover cropping may have been a catalyser for a large adoption of green manure in vineyards. Cover crops imply complexity and an adaptative strategy while there is still a lack for convenient indicators [START_REF] Rapidel | Analysis of Ecosystem Services Trade-Offs to Design Agroecosystems with Perennial Crops[END_REF], therefore we expect the winegrower to be in need for support and research of such theme.

Problem statement, research questions and hypotheses

Like several innovative practices, GM in vineyards calls for a performance assessment and technical references. First, a review of the different operating methods used in the field is essential to suit with winegrowers' concerns. Thus, this internship aims at understanding the soil management itineraries including GM in Gaillac vineyards. To this end, we choose to focus on two questions. The first issue is to characterize diversity of GM implementation in Gaillac vineyards, as well as to note winegrowers' needs for research on grass growing issue, in order to guide IFV research works on GM for next years. A survey was carried out to achieve these goals and to build a typology of GM use. The second question addresses the potential effects of management choices on the GM performances. A field campaign aimed at assessing GM performances in vineyards of Gaillac, trying to study the effects of different management choices.

These guidelines will be sequentially covered in this report. After a presentation of the state of art for green manuring in vineyards and of the context of this study, we will give an overview of what types of soil management technical itineraries include green manure in Gaillac vineyards. Then, we will explain what links the field campaign highlight between soil management technical itinerary characteristics and green manure performances. To finish, we will step back to imagine what could be the project continuation at the heart of this diversity for IFV and go back over the challenges of green manuring.

2 How green manures are integrated into soil management strategies in the Gaillac vineyard?

2.1 Objectives of the survey:

The purposes of the survey are to note the solutions chosen by the winegrowers in terms of GM design and multi-annual strategy insides the plots, of sowing and management methods, also their decision rules, and finally the satisfactions or the barriers to GM adoption. Also, after data processing, it should allow to understand to what extent the adoption and the type of green manure depend on technicoeconomic characteristics, production objectives, pedoclimatic conditions and/or soil management logic.

Material and method

Method of data collection

This study was intended to concern a maximum of winegrowers from Gaillac denomination origin zone. There were two paths which could be taken: a quantitative census of the GM adoption and/or a collection of more qualitative information to understand the soil management strategies. For this second goal, personal interview of the winegrowers could be more appropriate. Nevertheless, we needed the results of the survey to be ready and spread before the destruction of their green manure.

Indeed, the idea was to use the data of the survey to select plots where the green manure performances could be measured (cf. part III). Therefore, we chose the use an online survey in order to contact a wider audience in a short time. This online survey should allow to identify the innovative soil management strategies including GM and to understand the decisions rules for the technical choices associated.

Primarily, a survey to census successively several soil management itineraries was built. First, the main soil management itinerary (in terms of surface area) was asked, whatever it includes GM or not; then a second itinerary including GM was asked but optional. The idea was to place the GM adoption among the others soil management. This first version of the survey has been tested by a winegrower. The survey was judged too long. It appeared that if the GM was used in less than half of the winegrowing estate surface, it was not described. Instead of being exhaustive, the survey has been redesigned to focus on GM use and to guide the surveyed to describe his GM. Consequently, some neutrality has been lost, as well as strict census of GM adoption.

The survey has been spread by V. Vigues, counsellor for winegrowers of the departmental Agricultural Chamber, to approximately 300 winegrowers working in Gaillac denomination of origin zone. It last between 05/04/2019 and 15/06/2019 with weekly reminders. It has been sent to almost all the winegrowers of Gaillac area since there are 370 farms with grapevine in this area, with 305 specialized in viticulture or in viticulture and field crops [START_REF] Urbain | Données INOSYS / RA2010 -traitement Chambres d'Agriculture Midi-Pyrénées[END_REF].

The survey was divided in three parts. First, a short description of the farm (see Annexe to evaluate if some wine estates were more likely to adopt GM. Various situations can be found across Gaillac vineyard and we analysed how size of the wine estate, its objectives of production, presence of a winery on the estate, labour force available, pluriactivity and methods of production (organic…) impact GM adoption. Then (see Annexe 2), the surveyed unit is one soil management technical itinerary.

We defined it as one same combination of soil management operations implemented in a block of plots for one common goal. We fixed our investigation on the itineraries implemented for the campaign 2018 (late summer 2017 to harvest 2018). The winegrowers implementing green manure were asked to describe their majority (in surface) soil management technical itinerary involving green manure and some decision rules associated. If a winegrower has no green manure, he was simply asked to describe it majority soil management itinerary (see Annexe 3). The surface on which each itinerary is implemented is collected. The survey also collected information to characterize soil type corresponding to the itinerary described. The description of a second itinerary was possible but optional. The end part of the survey was aimed to take note of satisfaction or barriers to GM adoption (see Annexe 4).

In order to reduce length of the survey, the great majority of the questions were multiple choice questions, based on terms and habits found in Labreuche et al. (2011) for field crop, on opinions of IFV experts and a chamber counsellor for adequacy with vine cultivation.

Data treatment method

The answers were sum up and divided in four sets of variables: farm characteristics, soil conditions, itineraries' description and winegrowers' decision criteria. Farm and soil characteristics aim at summarizing Gaillac context in farm and soil typologies. Itineraries were also summed up and graded to make emerged groups of soil management strategies related to GM use. Satisfaction, barriers and GM users' decision rules were treated separately, simply to highlight the most common.

The statistic treatments were done with R software, using RStudio. To build soil and farm clusters, two Multiple Correspondence Analysis (MCA) were carried out using the MCA function of the package FactoMineR. Then, an Ascending Hierarchical Classification were performed for each MCA using the HCPCshiny function of the package Factoshiny.

Once collected, a treatment on farm characteristic data was necessary to sum up with accurate modalities (figure 6). MCA for farm cluster was made with the following variables: size of the wine estate, destination of the harvest (co-operator or winery owner), presence of field crops activity on the farm, number of hectares per permanent worker on the wine estate, type of products in relation with the yields expected (AOP, IGP or without IGP), number of soil management itineraries implemented in the wine estate and finally any environmental approach. We gathered the vineyard (UAA in 10-fold steps (ha), the calculated vine surface per worker (ha) in two categories (]0; 15] and 15; inf[) by IFV expert opinion (C. Gaviglio, IFV). Two aberrant values in farm descriptions were treated as missing values.

One winegrower reported that half of his production was intended to a cooperative and half to his own winery. He was treated as owner of an independent winery because of its wine production activity. Two surveyed specified their grapes were intended to a trader winemaker, they were treated as cooperative users because they lack winery. The activities others than wine growing were only field crops, concerning 29 people, and breeding, concerning 3 people who also have field crops. We gathered the biodynamic and organic vineyards on one side (modality named organic_farming). When the surveyed was certified of high environmental value (the French HVE certification) or when he mentioned it involvement in the Ecophyto plan, the modality reasoned was assigned.

Analysis on soil data were made with the five following variables: texture, depth, calcareous rate, stoniness and slope. Proportion of missing values were so important for stone and slope that they were rather used as illustrative variables. We simplify data of stoniness in two ranges only (From 0 to 25 % and More than 25 %) because only two soils were characterized by a stoniness between 50% and 75%

and none was higher than 75%. The answers 'Unknown' and 'Impossible to give an average' were considered as missing values. Ultimately, the destruction mode using a "rotovator" was mentioned by two winegrowers and we treated it as disking for its quite similar effect (C. Gaviglio, IFV).

Itineraries including GM were dissected in details and clusters were made by expert opinion (figure 7).

The first level of segregation is the presence or absence of green manure, according to our definition.

The next levels deal with soil management multiannual strategy and the intensity of the practice across a plot.

Finally, this study aimed at highlighting links between GM implementation and farm characteristics, soil characteristics and building GM use typologies. First, at the scale of the soil management itinerary, we observed which production objectives (in terms of wine denomination, colour and in terms of targeted production volume) and which fertilization (in term of Nitrogen unit) correspond to our clusters of itineraries. Then, we tested if the soil management itineraries depend on the belonging to a soil or farm cluster thanks to Fisher tests. We visualized the repartition of the individuals across the clusters. To finish, univariate tests were carried out, testing impacts of soil and farm clusters on specific technical choices: sowing date, sowing mode, plant families in the mixtures of the GMs, destruction mode, destruction date, and residues management.

Results

Overview of the population surveyed

The survey link has been opened 87 times, but many didn't complete all the answers. No duplicate was found but one winegrower answered (and signed) two times the survey in order to describe two different Small wine estate with low surface per permanent worker and a single soil management GM per farm, and for a total surface of 1002.8 ha. On average, the winegrowers, when they adopted it, use GM on 77% of their vineyard surface.

Concerning soil management itineraries, 46 descriptions were completed. These 46 detailed descriptions of the itinerary cover 908 ha. Finally, we worked with the 46 individuals in order to build soil clusters, farm clusters and to analyse the soil management itineraries.

Clusters of soil and farm

Clusters of soil:

The first factorial plan explains 25.41 % of the data variability. Only the first nine dimensions have been used to build a more stable classification even if it covers 83.52% of the variability. The stoniness is very badly represented, even in the next dimensions.

Finally, the individuals are split in three groups (figure 8):

-The first group is composed of 23 individuals and coloured in black in figure 6. The modality clay characterised 91% of these soils. No clay loamy soil is present, nor sandy loamy. They are also calcareous (61%) to very calcareous (30%). The flat lands are poorly represented in this cluster in comparison with the global data set.

-The second group is formed by 9 individuals and is coloured in red. The five clay loamy soils are all in, yet they form 56% of the cluster. This last cluster also gather the individuals with missing values, notably for depth. Among these 9 individuals, two present the modalities clay and calcareous but have been assigned to this cluster probably because of their unknown depth and stoniness. By expert opinion, we decided to shift them to the first group.

-The last group gather 14 soils projected in green. The eight sandy loamy soils are all in, and they form 71% of the cluster. No clay soil is present here. The group is little calcareous for 86% of the individuals. The flat lands are over-represented.

The surveyed soils are mostly clay calcareous soil in hilly terrain. The low calcareous soils can be divided in two groups. One is composed of sandy loamy soils present mainly in plain. The second grouped different soils, a majority of which is clay loamy soils.

Clusters of farms:

The first factorial plan explains 34.20 % of the data variability. Likewise, only the first eight dimensions, covering 84.40 % of the variability, have been use for the classification. The classification formed the following five groups (figure 9):

-The first one is composed of 11 individuals. 90% of them have their own winery. It concentrates estates with a UAA between 20 and 20 ha and they represent 63% of the group. 80% have two different soil management itineraries. The absence of any environmental approach is rare in this group.

-In the second cluster, composed of 15 individuals, all the farms present a wine surface per permanent worker lower than 15 ha. There is no estate larger than 20 ha, 60% are less than 10 ha. A large majority has only one soil management itinerary.

-The third group has 8 individuals. 75% of them has between 30 and 40 ha of wine. The modality "High and low yield objectives" is poorly represented in comparison with the global dataset and this group includes all the estates which have only Low yield objectives (PDO).

-The last cluster gathers 12 farms. All of them have a field crops activity, yet only 41% of the pluriactive farms are in this cluster. 91% of the group intend their harvest to a cooperative or a trader winemaker. 75% present a wine surface per permanent worker larger than 15 ha. This group concentrates estate which are larger than 40 ha and those who have two soil management itineraries.

To synthetize, the first group represents most of the winery owner, includes estates of average size, generally cultivated according to organic or reasoned agriculture. Next, smaller estates with one soil management itinerary form the second group. Finally, large farms are divided in two groups. One of them concentrates wine estates with only one production objectives, particularly PDO. The other gather farm that all have field crops activity, most of them are co-operators and present large surface of wine per permanent worker.

2.3.3

The different itineraries and their distribution across the soil and farm clusters Among the 46 itineraries described, 13 don't included green manure. Two itineraries were called green manure but aren't annual sown cover crops. They consist in spontaneous groundcover which are returned to the soil during grape vegetative period.

A focus on itineraries including sown GM is detailed in annexe 6. Overall, for the campaign 2018, seeding occurred most of time in October. Direct seeding is little used (16%), almost half of the winegrower sow in lines after soil preparation. They all sow legumes, Vicia faba concerns 84% of the GM described. Legumes are alone in 39% of the cases, along with Grasses for 48%, and/or with Brassicas for 26%. Concerning GM destruction, it took place massively (55%) between 16 th of April and 30 th April 2018. Rolling is the main destruction mode with a score of 42%, and the second is grinding (32%). After that, the residues are kept in soil surface, forming a mulch, in 65% of the itineraries.

GM are sown in all inter-rows in 42% of the itineraries. Otherwise, GM are cultivated one inter-row out of two or three, alternating with another soil management practice on the second inter-rows: natural grass cover (32%), sown grass cover (10%), or weeding from winter season (10%). Under the grapevine rows, 52% of the winegrowers who implement GM accept a natural groundcover in winter, 39% don't and apply a wintry weeding. The others sown cover crops under the rows or didn't answer this question.

66

Average yield objectives of all the itineraries described 27 Average fertilization of all the itineraries described 13 itineraries 2 itineraries 5 itineraries 8 itineraries 7 itineraries 11 itineraries 66 27

(hl/ha)
Except one, all the surveyed winegrowers who sown green manure did it after the grape harvest in 2018. The last one sown half of his GM before and half after the harvest. They all use farm-saved seeds, 6 of them (6/31) complete with commercial seeds. 68% of them have their own seed drill, 16% use a CUMA seed drill, 13% ask to a neighbour and 3% for a service delivery.

Only four winegrowers reserve their use on GM to one production objective alone, red wine with Protected Geographical Indications (PGI) or Protected Designation of Origin (PDO). The others ticked several objectives. The most common answers are red PDO wines, white PDO wines, red PGI wines, white PGI wines, and rosé PDO wines, with respectively occurrences of 36, 31, 29, 22 and 21.

A classification of the itineraries in six clusters is proposed according to the segregation method already presented in figure 7. The population per cluster is small. Yet some characteristics can be underlined, notably in terms of yield objectives and fertilization (figure 10). The points raised here are only those who discriminate clearly the six clusters.

-The first cluster gather the itineraries without GM, but it includes plots were a groundcover is tolerated and plots where there is a systematic weeding. The large majority of these itineraries are achieved for low yields objectives corresponding to AOC production (<60 hl/ha).

-The second cluster is very little represented (only two individuals). The corresponding winegrowers declared their cover crops as green manures, but they are not GM as we would define it in this study. The winegrowers allow the resident vegetation to grow and manage it by mowing and grinding. The two itineraries have the lowest yield objectives and the lowest fertilization.

-The exceptional GM in the third cluster have the following common particularities: they are all applied in every rows of a plot, they all have been sown in October 2017, and they are all implemented for low yield objectives corresponding to AOC production. Four out of five of those GM include Vicia Faba and have been destructed in April 2017. It appeared that none of those itineraries was implemented for Rosé wine.

-The itineraries involving GM annually in all the inter-rows can be pooled in a fourth cluster. In those cases, non-leguminous plants are always sown, Grasses in 5 cases out of 8, otherwise they included Brassicas or Phacelia. The yields objectives and fertilization vary quite widely across this cluster.

-The next cluster gather itineraries where GM occupy only some inter-rows (one out of two or three) and where there is a rotation of the soil management between the inter-rows. 6 of these 7 itineraries involve non-leguminous plants (Grasses in 4 out of 6 cases, Brassicas in 3 out of 6 cases). Little quantity of fertilization is applied on those itineraries: 14 NU in average, the maximum surveyed is 25 NU. Those GM are rather implemented in plots for red and white wines with Protected Geographical Indications (PGI) than for Protected Designation of Origin (PDO). The residues management is homogenous in this cluster and consists in the creation of a mulch after rolling or burying. No disking is applied. This group contains 3 out of 7 itineraries with wintry weeding on the inter-rows without GM.

-To finish, a cluster gathers 11 individuals with GM in some inter-rows but without rotation, the GM is always sown on the same inter-rows. Except one individual who has a temporary grass cover (until mid-June), all the individuals have a permanent grass cover, maintained by mowing, on the inter-rows without GM. Burying the residues is a practice over-represented here (7 out of 11, meaning 64%) in comparison with the proportion among all the GM users (35%). This clusters concerns the red wines with Protected Geographical Univariate tests shown significant results for dependencies on one hand between soil clusters and the presence of non-leguminous species in the GM (p_value = 0.003403), and on the other hand between soil clusters and residues management (p_value = 0.01868). GMs only composed of legumes are exclusively found on clay calcareous soils whereas mixtures used on clay loamy or sandy loamy soils rather include at least grasses (figure 12 a). Concerning residues management, a mulch is always kept on sandy loamy soils of the plains (figure 12 b). Belonging to a soil or a farm cluster show no significant results on the other soil management technical choices (see annexe 9).

Decision rules, satisfaction, barriers and expectations

Decision criteria of the 31 GM users have been surveyed for choice of the species to sow and date of GM destruction. The main criteria for choice of the species (figure 13 a) are the targeted services, and the favourite ones are nitrogen supply, organic matter supply and soil structuring. The management issues of seed availability and easy implement also influence quite strongly the choice. Concerning Barriers to GM adoption are first of all lack of time and specific material for GM management. Then, the practice has been judged costly by several winegrowers. One surveyed declared that he stopped using green manure, because of economic reasons. 23 GM users answered to the last part of the survey.

Among them, 18 are satisfied with their GM settlement. Four winegrowers regret their sowing which was too late and penalized their success. To evaluate GM growth, they mostly rely on visual observation.

The height of the cover crops is a good indicator for them (figure 14a). Then, crop contamination by weeds and GM density are common criteria to evaluate it growth. Biomass measurement is very little used. With respect to GM effect on grapevine, 6 winegrowers chose the answer 'I don't know'. Among the others, 15 are satisfied, 2 are not. The improvements they observe mainly concern grapevine vigour (figure 14b). When asked, only 14 out of 24 winegrowers declared their use of GM does modify (diminution) their fertilization management. Yet, need for estimations of GM restitutions and knowledges on nitrogen deficiency has been raised (spontaneously in a comment). On another note, 3 out of 24 declared their GM use causes modification of their phytosanitary treatments.

Finally, 37 people answered what expectations they have for support and research structures on the theme of tillage, cover cropping and particularly green manuring. Winegrowers largely expect help in the choice of the GM crops (figure 15). Some winegrowers comment on the difficulties to adapt the choice of species to pebbly soils or to different objectives of yield and agronomic services. To a lesser extent, they require assistance for the choice of the kill date, for information on seed availability, for choice of the sowing date. One winegrower suggests broadcasting a monthly bulletin on GM and cover crop management. One deplores the absence of equipment for fast drilling.

To conclude, decision rules and management concerns that raised for GM are better known. The results show no strong links between production objectives, technico-economic characteristics and environmental approach of the farms and their facility to adopt GM. Pedoclimatic conditions does impact the choice of GM implementation.

3 What links can be established between soil management technical itinerary characteristics and green manure performances?

Objectives

The purpose of the field campaign is to assess GM performances across different Gaillac wine estates in a context of lack of references on GM uses in vineyards. The different management choices and pedoclimatic contexts may affect the performances and this field campaign should allow to highlight it.

It constitutes a first approach to set the scene to build a network of plots and propose in fine a monitoring protocol for coming years GM studies on Gaillac vineyard. In addition to that, GM biomass data will be transmitted for the calibration of the MERCI software (see Data treatment method for a short presentation of MERCI software).

Material and method

Data collection method

The initial objectives were to build a network of plots where the pedoclimatic context of Gaillac was well represented, to test different soil management itineraries (according to the main practices observed in Gaillac cf. part I) and to evaluate the GMs development.

Unfortunately, it took a lot of time to construct the online survey and the weather speed up the winegrowers to destruct their green manure. Therefore, we didn't have time to step back and look at the overall picture of how green manure are used in Gaillac. Consequently, the network of plots was formed on a voluntary basis, taking contact thanks to the repertory of V. Vigues, counsellor for winegrowers of the departmental Agricultural Chamber, with the same 300 winegrowers working in Gaillac denomination of origin zone than for the online survey. Finally, 9 winegrowers have been met and 17 assessments of the GM performances have been done. One winegrower had a spontaneous GM and we chose to focus only on sown GM in the presentation of the results. Then the results of 16 plots are explained in this report.

The appreciation of GM performances was made by measurements, for each GM specie, of number of plants, aerial fresh biomass, dry matter content, and also weed aerial fresh biomass near the time of destruction. Measures were carried on in plots selected after a short and informal interview of the winegrower. The selection was made so that the winegrower's main practices and pedoclimatic context are well represented. The interview allowed to collect information on the soil management technical itinerary. We determined the pedo-climatic conditions for each plot by cross checking the winegrower's comment and a map of the terroirs in Gaillac (see annexe 7). Measures were carried on a few days before the green manure destruction, on three replicates of 0,5 m² (0,5m x 1m installed perpendicularly to the inter-rows) per plot. Location of the replicates were chosen in order to well represent the plot, with the exception of two plots (V2P1 and V2P2) because the winegrower had destroyed his GM before the measurement and had left only GM strips. They took place from the 12 th of April to the 27 th of May 2019.

At grape blooming time, the Nutrition Balance Index -Dualex® developed by Force A, was measured on grape leaves to appreciate its nitrogen status. These measurements were decided lately in the monitoring. It should bring additional information to account for impact of GM on wine. Given its ease of measurement and the period of my internship, it was measured at blooming. Nutrition Balance Index considers two measures on leaf epidermis: chlorophyll fluorescence and flavones' absorbance. Those measures took place on the 12 th and 13 th of June 2019. At least sixty leaves were used to characterize each plot. Data on weather conditions for the 2019 campaign (see annexe 10) come from a network of meteorological data available on EPIcure information system. The station was chosen because of its central location in Gaillac denomination zone.

Data treatment method

The itineraries were sum up with variables allowing to aggregate data (such as the part of brassicas in the sown mixtures). To escape from the differences of surface sown across the plots, we expressed the biomass production in tonnes per hectare full of GM. Furthermore, fresh weed biomass is expressed in percentage of total fresh biomass. between the performances of GM sown before and after the 14 th of October 2018 was tested.

Then, student tests and correlation were carried on for univariate analysis. They were performed with variables of the itinerary and soil type to explain dry biomass production and then weed development.

Finally, we test correlation between dry biomass production, weed development and percentage of legumes in the dry matter produced on NBI.

The informal interviews also allow to note feelings of the winegrowers toward their GM use.

Results

A large variability is observed across the network of plots in terms of pedoclimatic context, grape varieties, production objectives and technical choices for GM management. Details of the itineraries are available in annexe 11. The plots sampled are well distributed across the Gaillac area (annexe 7), regarding vineyards importance among land uses. The GMs sampled have had lifetimes between 157 and 214 days. At those kill dates, from mid-April to end May, brassicas were at flowering stage or, at least, the tuber was developed. The phacelia was at flowering, the legumes also, or even at fruit-bearing stage. The stages were variable for cereals, from stage elongation to heading. Concerning grapevine stage, it varies from budburst for one winegrower to inflorescence emergence for another. Most winegrowers kill their GMs during the first grapevine leaves development. In the sample of winegrowers, there are experienced users of green manure and some who began two years ago. They were all interesting to estimate the potential restitutions of their GM thanks to MERCI®.

Performances of the GM:

The performances of the sampled GMs are heterogeneous (figure 16). The dry matter production is high for a handful of winegrowers including pioneers but also beginners. The performances are quite well represented in the first factorial plan of the PCA (figure 17). High coordinates on the first axis corresponds to GMs which were managed with high sowing densities, long lifetimes and which finally present great numbers of plants which sprouted. Those GMs were mainly sown before the 14 th of October 2018, implemented in luvisol-redoxisol from Tarn valley, and tend to produce more biomass.

The second axis segregates GMs according to the families of species used, weed percentage and dry matter. Among the samples, GMs composed exclusively of legumes tend to produce more biomass and present less weeds in comparison with GMs including brassicas or grasses.

Besides, Student tests and correlation tests have been carried out. The results are to be viewed cautiously as the sampling is very small -smaller than the bidding limit. After all, sowing date, lifetime of the GM, soil type and parts of the different plant families in the sown mixture have a significant effect on GM aerial dry matter production (table 1). GM development is greater when sown before the 14 th of October, remained in place for longer lifetime, on a luvisol-redoxisol, and with an important part of legumes in the mixture sown.

Factors significant for percentage of weeds in the total fresh biomass are different (table 1). Weed percentage is in average higher for GMs sown in line than for GMs broadcast. Unlike what is found in literature [START_REF] Labreuche | Evaluation des impacts environnementaux des Techniques Culturales Sans Labour en France[END_REF], it is here higher for GMs including grasses and brassicas and drops as part of legumes increases. Non-significant results are available in annexe 12.

Impact on grapewine:

The values of the NBI are very low (figure 18) in comparison with Cerovic et al. (2015) who recommended a NBI between 11 and 18 at flowering. They have the same order of magnitude than the 2016-2017 GM monitoring on the IFV estate at flowering which range from 4,3 to 5,0 [START_REF] Gontier | Incidence de différents modes de pilotage des couverts végétaux hivernaux sur l'alimentation azotée de la vigne et la qualité des vins du Sud-Ouest[END_REF]. This indicator concerns impact of GM on wine, yet it is also impacted by other practices and climate.

Given its ease of measurement and the period of my internship, it was measured at blooming. Monitoring this indicator at veraison stage may be interesting to better account for mineralization process and wine assimilation along its growth cycle. No correlation was observed between NBI and dry biomass production, weed development or percentage of legumes in the dry biomass production (annexe 12). Winegrowers' appreciation of their GM management:

Finally, dialogues with the winegrowers met draw an optimistic picture. A large choice of species allows to meet multiple needs and to combine objectives. They were globally satisfied of the GM emergence even if the success may not be equal for all species of the cover crop. Seeds are sometimes available on the farm and exchange possibilities have increased a lot during the last decade.

Seeding appears to be a delicate operation notably for seed placement depth and for access to appropriate material. Direct seeding has shown contrasted results according to the winegrowers' experiences.

Concerning destruction of GM, rolling is poorly suited to destruct cereals before heading but it allows to keep a mulch and to hence humidity. The constraint of frost compelled many of the interviewed winegrowers to destruct their GMs. A winegrower, who doesn't fear frost, deplores his uncertainty about the delay for peak of maximum restitution and prefers delaying the destruction date.

Effects of green manuring are rapidly visible. Evident successes are enhancement of grapevine vigour and improvement of soil structure. This method of organic matter supply has a fair cost-fertilizing ratio.

However, green manuring implies technical operations sometimes difficult or impossible because of short weather windows, a slopped plot, a pebbly soil or also needs for specific and costly material. To finish, it has been raised that in organic production organic seeds must be found.

To conclude, the performances of the sampled GM are heterogenous. This field campaign was carried out on soil management that differed on many points and it was difficult to study the effect of the sowing design on the GM development. We highlight some trends: luvisol-redoxisols seems to be more favourable to GM development than clay calcareous soils; early sowing dates and long lifetimes allows to increase biomass produced before destruction; high proportion of legumes in the sown mixture tends to favour high biomass production of the GM and to allow a better control of weeds.

Nevertheless, it progressively set the scene to monitor GM studies on vineyards of Gaillac. It allows to validate the feasibility of our measurements and exchange with concerned winegrowers. Also, the GM biomass data have been transmitted to improve the MERCI® software for its use in viticulture. The online survey allows to collect data on 68 vineyards, that is about 20% of the total number of vineyards in the Gaillac denomination zone. Gaillac vineyard, about 6400 ha, represent a very little part of the total 750 000 ha of the French vineyards [START_REF] Agreste | Statistique agricole annuelle 2017-2018 Données provisoires[END_REF]. This study has a local reach. As explained in the state of the art, clay calcareous plateau and hillsides are where wine cultivation is the most present and the online survey results represent them quite well. Farms size in our results in only a bit higher than the average in Gaillac.

A significant number of surveyed didn't complete the entire the questionnaire. The survey was probably too long. The diversity of practices made it difficult to anticipate when designing the questions. A lower degree of precision could have been more adequate to reach higher number of replies. The declared aim to tackle GM surely skew the representation of soil management given by the results. Considering the numbers of answer, it seems likely that it would have been difficult to survey so many winegrowers inperson interviews.

At least, in only 68 vineyards we count about 1000 ha with GM, meaning 15% of the Gaillac denomination zone. It confirms that the area is a territory of innovation on green manuring in comparison with the 7% of sown temporarily cover crops implemented in the inter-rows at national scale [START_REF] Agreste | Pratiques culturales en viticulture Campagne 2013[END_REF]. The diversity of implementation is also confirmed notably for multiannual strategies, mixtures sown, sowing and destruction tools. The common points shared by the different itineraries including GM and the points of divergence are summarized on figure 18.

The adoption of GM seems to be equal among the different farm clusters, meaning that this practice would be of interest for all and easily managed. Yet, the survey has an unfair sampling, notably the farms following Ecophyto plan and organic agriculture specifications are overrepresented. Also, the farm clustering has been based on criteria of our choice and some others should be accurate to test such as farmer age and level of competence. Furthermore, soil characteristics influence GM adoption and design. The reasons may be better conditions for GM implementation on some soil types or higher needs for GM services because of soil defaults. These trends should be taken into account when planning the IFV GM tests in Gaillac vineyards, with the objective to correspond to reality.

The field campaign was carried out on voluntary basis. In the light of the online survey results, the following design of GM are not represented: exceptional GM, annual GM sown in all inter-rows and annual GM sown only in part of the inter-rows with an annual rotation with another soil management.

It is probably partly due to the infrequency of the exceptional GM. Also, we wonder if the question on multiannual strategy were clear enough in the online survey. It seems likely that some winegrowers

Strengths

• Green manure emergence is generally satisfactory • Cost-fertilizing matter supply ratio is good • Green manure cover soils in winter • Soil response to green manure adoption is satisfactory (crust reduction, fertilizer supply) • Rolling enable to keep a mulch and humidity • A large choice a species allows to meet multiple needs and to combine objectives

• Direct seeding showed interesting results

• Some winegrowers already have hindsight of several years of experience

• Seed production is possible in some farms

Weaknesses

• Emergence success is sometimes variable across green manure species, at the expense of some services

• Rolling is poorly suited to destruct cereals before heading

• Need for knowledges on restitutions: When occurs the peak of maximum restitution in order to better choose destruction date and tools? How to avoid nitrogen deficiency? How much fertilizers can be saved?

• Seeding material doesn't always suit each specie (notably seed placement depth). Soil preparation and drilling are time-consuming. Direct seeding showed contrasted results.

• The soil management technical operations may be difficult or impossible because of short weather windows, soil type (pebbly soil) or slope.

• GM management calls for investment for specific costly material.

Opportunities

• GM is part of an approach respecting the environment for a positive image of the vineyard.

Threats

• Frost is feared and often bring forward destruction date • If a plot is certified organic production, organic seeds must be found for GM characterized their soil management as uniforms in all inter-rows even if it was different one inter-row out of two.

However, this field campaign enables to inform the winegrowers on the potential restitutions of their GM and give maybe a first anchor among new winegrowers. The data of biomass production have been transmitted to calibrate MERCI software for viticulture. The network of plots formed is too diversified to extract robust results of itinerary comparison. The initial plan was to select winegrowers thanks to the online survey, in order to test a few factors. Unfortunately, the online questionnaire was ready too late, and the GM destruction has been put forward by fear of frost. Nevertheless, it allowed to validate the feasibility of the measures in Gaillac vineyards and refine the IFV planning of GM tests.

Afterall, this field campaign shows some results, yet more years of study should be carried out to confirm this. Early sowing seems to be favourable. GM better developed on the luvisol-redoxisols than on the calcosols. Long lifetime appeared as a great determinant for high biomass production. Even a few days of delay for the destruction is likely make important differences of biomass accumulation because destruction occurs when productivity is the highest for these spring species. [START_REF] Guiducci | Total N supply and profit from several green manure crops[END_REF] observed an increase of the biomass by 54% on average when the kill date was delayed from the 26 th of March to the 8 th of April. On the other side, we expected the biomass production to be enhanced by the presence of non-legumes in the mixture as found in the literature [START_REF] Labreuche | Evaluation des impacts environnementaux des Techniques Culturales Sans Labour en France[END_REF][START_REF] Guiducci | Total N supply and profit from several green manure crops[END_REF]. Also, we expected the non-legumes to better control weed than legumes pure. This highlight the weakness of our network of plots and the difficulty to understand because of the multiple factors than vary across the plots. Yet, the majority legume presents it this field campaign was Vicia faba and this species may have higher productivity and provide a better weed control than the other legumes studied in literature.

Finally, after detailed reading of the online survey and meeting with farmers, I realized a SWOT analysis (figure 19) for green manure implementation. Needs for references raise particularly on estimation of the GM restitutions and on specificities of GM species notably in terms of adaptation to soil types and potential restitutions.

Up to agroecosystem services?

The performances of our network, in terms of nutrient supply, can be compared to the performances of a network in Charente-Maritime region during the 2017-2018 campaign. The averages dry matter production per hectare is 5,25 tonne per hectare [START_REF] Caillaud | Les engrais verts au service de la viticulture : Résultats de la campagne 2017/2018[END_REF], a value very close of the average 5,5 tonnes per hectare in our network. In terms of nitrogen potential restitutions, the average of our sampled GM is about 100 NU, but it corresponds to 25 NU when taking into account GM occupation on the interrows of the plots. It is very likely to have a significant contribution in comparison with the 20-30 nitrogen units needed by grapevine for controlled yield objectives [START_REF] Crespy | Legume versus fertilizer sources of nitrogen: ecological tradeoffs and human needs[END_REF]. The average fertilization of the online surveyed is 27 nitrogen unit. Even if the compensation of nitrogen fertilizer by green manuring remains shy, GM contribution seems to be able to make up for significant quantity of nitrogen units.

Framework on agroecosystem services quantification is wise and burgeoning [START_REF] Dominati | A soil change-based methodology for the quantification and valuation of ecosystem services from agro-ecosystems: A case study of pastoral agriculture in New Zealand[END_REF]. The assessment of GM performances we proposed was easy to perform but limited. It is important to explain from the outset that the commonly used C/N ratio of a green manure proved it accuracy to explain nitrogen supply service and yields [START_REF] Finney | Biomass production and carbon/nitrogen ratio influence ecosystem services from cover crop mixtures[END_REF], effects studied in corn cultivation). As part of this internship, the field campaign has more limited objectives. We made the hypothesis that aerial dry biomass matter just before destruction is correlated with agroecosystem services. [START_REF] Bair | Release of Available Nitrogen after Incorporation of a Legume Cover Crop in Concord Grape Department of Crop and Soil[END_REF] report that progressive improvement in soil soluble nitrogen quantity were directly correlated to higher GM biomass production. Also, increases of soil organic matter and microbial biomass pools related to GM biomass accumulation have been observed [START_REF] Cherr | Green Manure Approaches to Crop Production[END_REF]. Nevertheless, this assumption can be shaded, there is not necessary a correlation between cover crop productivity and performances [START_REF] Smith | Increased productivity of a cover crop mixture is not associated with enhanced agroecosystem services[END_REF]. The relation between cover crop biomass and its performances is service dependant. The online survey reveals the mayor services targeted by the winegrowers when choosing their GMs. Their role is manifold: nitrogen and organic matter supply, soil structuring and weed control, to mention the most important. The assessment of the GM proposed here is only based on aerial biomass quantity. Even if it fit well performance to restore nutrients, this indicator appears reductive when considering the other services expected. Biomass production is linked to weed suppression [START_REF] Finney | Biomass production and carbon/nitrogen ratio influence ecosystem services from cover crop mixtures[END_REF] but other indicators should be more informative. Plant density could

have been used to compare potential weed control. The root system was not considered for practical reasons whereas its importance for soil functioning is certain. Roots allow faster nitrogen releases because of their lower C/N ratio and because of roots exudates [START_REF] Collins | Decomposition interactions among wheat residue components[END_REF]. Once more, legumes may have interesting properties with exudates richer in nitrogen than other plants [START_REF] Eisenhauer | Earthworm and below ground competition effects on plant productivity in a plant diversity gradient[END_REF] and with nodosities being hotspots for microbial communities (Bédoussac et al., 2011 cited in Schneider and Huyghe). Some services appear to be more biomass quality dependent or relying on functional properties of the cover crop. Researches on functional traits are topical in agroecology framework (Martin and Isaac, 2017;[START_REF] Kazakou | A plant trait-based response-and-effect framework to assess vineyard inter-row soil management[END_REF]. Measures of functional traits were considered for GM leaf surface area and leaf dry matter content. Finally, they ended up being to inconvenient and the relations with agroecosystem services are still to be drafted.

An agroecosystem service is also context dependent. Soil organic matter supply by green manure is to be considered in light of the pre-existing SOM pool [START_REF] Cherr | Green Manure Approaches to Crop Production[END_REF]. Next research project would gain from soil analysis. Also, the release of nutrients after the kill date should offset the picking during GM growth. Depending on the context, there may be an important quantity of nitrogen available in winter that would be interesting to catch. The balance is not always simple to estimate and is strongly linked to pedoclimatic conditions [START_REF] Constantin | Concilier la réduction de la lixiviation nitrique, la restitution d'azote à la culture suivante et la gestion de l'eau avec les cultures intermédiaires[END_REF].

Conclusion

Soil fertility is the basis of food production and its maintenance is one of the today's challenge of agriculture. Green manuring is a practice which seems to flourish in order to restore nutrients to soil in a environmentally sound and sustainable way. We studied here the example of the adoption of green manure in vineyards of the Gaillac denomination zone, an innovative territory in terms of number and diversity of green manure implementation. This internship was quite an exploratory work and it try to review and organised main issues of green manures management. We manage to better understand the soil management itinerary associated to green manure and the decisions rules. We surveyed the interest of the winegrowers for support on green manure and more broadly grass growing strategies. It appears that the practice of green manuring has been largely adopted across our studied territory and the winegrowers are concerned and willing to work on green manure improvement. Their doubt and request particularly focus on species to seed and dates of sowing and destruction. In a second step, this work included meeting with a dozen winegrowers and samples of the green manures in their plots. It allows to complete our understanding of their soil management itinerary including green manure, to assess the green manure performances and to report some consequences of GM management and pedologic conditions on its development. The group, formed on a voluntary basis, showed in average good performances, even if some green manures have badly developed.

The increase of interest for green manuring is good news on the way to build sustainable agroecosystems. It has potential to achieve several agroecosystem services, support of soil fertility of course, but also notably improvement of soil structure, biological activity and water capacity.

Concerning fertilization control and reduction in a reasoned agriculture, the accurate adequacy of the inputs and the crop need is a strong lever to limits losses, with their economic and environmental costs.

After all, even a "green" manure may have some of the negative environmental impacts of any nitrogen losses in the environment. In a near future, precision agriculture may be able to integrate plot heterogeneity and guide nutrients supply management. Then, input management in agroecological systems would be achieved with sophisticated uses combining more sustainable sources of nutrients and enhanced efficiency (Crews and People, 2003;IFV and INAO, 2017). Abstract (1600 caractères maximum):

Green manuring has shown interesting potentials to increase soil organic matter. It consists in cover cropping intermediaries crops that accumulate biomass. This biomass will be released after cover crop death and available for the subsequent crop. Innovative green manure practices are burgeoning in Gaillac vineyard but still require technical references and assessment of potential services provided.

This study aimed at collecting technical information and decision rules of the soil management itineraries associated with these GM uses. An online survey has been carried out and allow to describe 46 soil management itineraries. A field campaign at green manure destruction period on 16 plots of Gaillac vineyard gave an illustration of green manure performances, in relation with technical choice and pedoclimatic context. This study finally allowed to build typologies of green manure uses and to census winegrowers' needs in terms of research on green manure. Such multi-species agroecosystems call for management tool in order to tackle the complexity of interactions.

Mots-clés : Engrais vert, entretien du sol, Vignoble de Gaillac, couverts végétaux en viticulture Key Words: Green manure, soil management itinerary, Gaillac vineyard, cover cropping vineyard * Elément qui permet d'enregistrer les notices auteurs dans le catalogue des bibliothèques universitaires

1

 1 Green manure into vineyard: what services?

Figure 1 :

 1 Figure 1: The different phenologic stages of grapevine (adapted from Naidu et al., 2015) and shape of nitrogen absorption during grapevine growth cycle (adapted from http://www.vignevin-occitanie.com/fiches-pratiques/lazote-en-viticulture/).

Figure 2 :

 2 Figure 2: Framework for the choice and management of service crops (SC) in vineyards (Garcia et al., 2018) H: harvest, LF: leaf fall, B: budburst, F: flowering, FS: fruit setting, V: veraison.

Figure 3 :

 3 Figure 3: Schematic representation of the effects of kill date on environmental variables and ecosystemic services (Alonso-Ayuso et al., 2014) The cover crop studied is a mixture of barley (Hordeum vulgare L.) and vetch (Vicia sativa L.) sown in October and killed on two different dates: mid-March and mid-April, in a field crop system. Fallow is used as reference conditions

  1.2.3 Innovative green manure practices in the Gaillac vineyardFor almost one decade, the IFV has observed innovative green manure practices in the Gaillac vineyard. The first field tests followed by the IFV began in 2010. It took place with a winegrower interesting in transferring its green manure practice from his field crops to his vineyard plots. In 2013, the IFV joined its forces to the Maison de la Vigne et du Vin de Gaillac; they candidated for a CASDAR project entitled "Innovative cover crops in vineyard for improvement of soil fertility, in order to conciliate reduction of inputs and durability of the production". The project tried to gather actors of developments, of research, and about fifteen winegrowers. One main objective was to learn collectively how to carry out green manure in theirs pedoclimatic local conditions. It last until 2018. Meanwhile, factorial tests were driven on the experimental estate associated to the Vinnopôle in Lisle-sur-Tarn. Yet, an explosion in green manure use and a diversity of management styles has been observed (IFV and Maison des Vins de Gaillac, 2017).

Figure 7 :

 7 Figure 7: Segregation of the soil management itineraries surveyed in 6 clusters x Criterium of segregation Final cluster

Figure 9 :

 9 Figure 8: First factorial plan of the MCA for soil data and the three clusters associated

Figure 10 :

 10 Figure 10: Yield objectives and fertilization across the itinerary clusters Yield objective of a winegrower belonging to the group (hl/ha) Average yield objective in the group (hl/ha) Fertilization of a winegrower belonging to the group (NU) Average fertilization in the group (NU)

Figure 12 :Figure 11 :

 1211 Figure 12: Number of individuals in function of the combinations of a soil cluster and a residues management (a) or the species sown (b).

  Indications (PGI) or Protected Designation of Origin (PDO) in a larger proportion than the average. The Fisher tests highlight a dependency between itineraries and soil clusters (p_value = 0.01841) but don't for farm clusters (p_value = 0.4729). Fisher tests focused on presence of a field crops activity on the farm show significant links with our soil management itinerary clusters (p_value = 0.002372), as well as yield objectives present on the wine estate (p_value = 0.03274). For the significant tests, repartitions of the itinerary clusters are presented on figure 11 (see annexe 8 for detailed of the non-significant tests). Concerning soil type dependency, the exceptional GMs concern only the clay calcareous soils. Annual GMs without rotation concern clay calcareous soils and clay, loamy or undefined soils. Annual GMs with rotation mostly concern the sandy loamy soils of plain. Itineraries with annual GM in all inter-rows are observed both in sandy loamy soils of plain and in the clay calcareous soils of the hillsides (figure 11 a).

Figure 13 :Figure 14 :

 1314 Figure 13: Occurrence of use concerning criteria for choice of GM species (a) and kill date (b) 31 winegrowers answered to these questions

Figure 15 :

 15 Figure 15: Occurrence of expectations of support and research structures with respect to tillage, cover cropping and particularly green manuring

Figure 16 :

 16 Figure 16: Performances of the green manure sampled Gaillac denomination zone in April and May 2019

  Potential restitutions were calculated thanks to MERCI software (version 2.9) based on dry biomass values. In field crops context, the French software MERCI -Estimation and restitution method for intermediary crops -allows to estimate the potential nitrogen restitution for the next crop. It calculates nitrogen furniture, thanks to the Stics model, based on measurements of the green manure in place just before destruction. The statistic treatments were done with R software (3.4.4 version), using RStudio. A Principal component analysis (PCA) was carried out with PCA function of the package FactoMineR. It tried to explain GM performances, in terms of biomass production, settlement and weed control, with variables of itinerary and soil type. The following variables were used: aerial dry biomass production (kg/ha), number of GM plants that grown (/m²), percentage of weed in the total fresh biomass, sowing mode, earliness of the sowing, presence of fertilization received by the GM, number of days between sowing and measurement, parts of the different families in the sowing mixture and finally soil denomination according to the Pedological referential (1995). The weather conditions during the GM implementation (see annexe 10) show a heavy rainfall on the 14 th of October 2018. It is the reason why difference

Figure 17 :

 17 Figure 17: Explanation of the performances of the green manure by variables of itinerary and soil nature Variables of the itinerary: sowing_density number_of_days: number of days between sowing and measurement sowing_density: sowing rate (kg/ha) Sown species: percentage of brassicas in the sown mixture (Brassicaceae) percentage of grasses in the sown mixture (Poaceae) percentage of legumes in the sown mixture (Fabaceae) Sowing mode: broadcast after soil preparation (broadcast)in line after soil preparation (line) direct sowing (direct) Sowing date: before 14/10/2018 (before_14oct) after 14/10/2018 (after_14oct) Fertilization: fertilized: the green manure did received fertilization during its lifetime non_fertilized: the green manure did not received fertilization during its lifetime

Table 1 :

 1 Figure 18: Values of NBI measured during the field campaign in Gaillac denomination zone in April and May 2019

Figure 18 :

 18 Figure 18: Common points (above) and points of divergence (below) between soil management itineraries involving GM. For the lower part of the figure, the colour and bold letter enable to highlight what differentiate the cluster

Figure 19 :

 19 Figure 19: SWOT (Strengths, Weaknesses, Opportunities and Threats) analysis for green manure implementation in soil management itineraries of Gaillac denomination zone.

Annexe 1 :

 1 The first part of the online survey corresponding to a simple description of the farm and to the presence or absence of green manure on the vineyard Annexe 2: Part of the survey concerning the winegrowers who do implement green manure and corresponding to the description of their main soil management itinerary including green manure Annexe 3: Part of the online survey concerning the winegrowers who don't implement green manure and corresponding to the description of their main soil management itinerary Annexe 4: Last part of the online survey to draw a review of the winegrowers' experience of green manure and collect their eventual requests Annexe 5: Description of the data from the online survey about farm and soil types Number of individuals Total of hectares concerned

Annexe 6 :

 6 Details on itineraries involving GM described in the survey Annexe 7: Localisation of the vineyards surveyed and the sampled plots in Gaillac denomination area Annexe 8: Non-significant test carried out to explain belonging to an itinerary cluster by farm characteristics thanks to a/ our farm clusters and b/ univariate tests. Non-significant test carried out to explain technical soil management choice in green manure adoption by belonging to our soil and farm clusters Annexe 10: Temperature and rainfall from late summer 2018 to summer 2019 recorded by the Epicure station "Laubarel" in Gaillac Caption: Rainfall (mm) Average daily temperature Minimum daily temperature Annexe 11: Description of main data of itinerary, performances of the green manures and Nutrition Balance Index Annexe 12: Non-significant test carried out to explain green manure performances (biomass production and weed control) and impact on grapevine (NBI) Etat des lieux des pratiques d'engrais vert dans le vignoble gaillacois Titre anglais: Situational analysis of green manure practices implemented in Gaillac vineyard Résumé (1600 caractères maximum) : La mise en oeuvre d'engrais vert a montré d'intéressants potentiels à augmenter la matière organique des sols. Cette pratique consiste à utiliser un couvert végétal qui accumule de la biomasse. Celle-ci sera restituée au sol après la mort du couvert, et disponible pour la culture suivante. Les pratiques d'engrais vert se multiplient dans le vignoble de Gaillac, néanmoins un besoin de références techniques et d'évaluations des services fournis se fait sentir. Cette étude vise à recueillir les informations techniques et les règles de décisions des itinéraires d'entretien du sol intégrant des engrais verts. Une enquête en ligne a été effectuée et a permis de décrire 46 itinéraires d'entretien du sol. Ensuite, une campagne de terrain au moment de la destruction des engrais verts sur 16 parcelles du gaillacois a donné une illustration des performances des engrais, en fonction des choix techniques de mis en oeuvre par le viticulteur et des conditions pédoclimatiques. Cette étude a finalement permis la construction de typologies d'usage d'engrais vert et de collecter les besoins des viticulteurs en matière de recherche sur les engrais verts. Ces agroécosystèmes multi-espèces ont grand besoin d'outils de pilotage pour faire face à la complexité des interactions qui s'y déroulent.

• Encouraging explosion of green manuring in the area.

	Seed availability is much higher
	since GM are widely used in Gaillac
	area
	The innovation has been launched,
	the Agricultural Chamber and the
	IFV took up the question and have
	resources to provide.
	• Specific material is already
	available in farm which have a
	field crop activity

Acknowledgments

I would like to give a sincere thank to all the IFV team for the pleasant atmosphere of these six months and for the help provided always with a smile. Thank you to Laure Gontier for the certain work of coaching me, rereading this report and for all the advices and knowledges transmitted. Also, thank you to Christophe Gaviglio for his tips that always allow to step back and unblock the situation.

Towards boom of green manuring in vineyards?

Green manure boom is a global trend, notably enhanced by the increasing consumer's demand for organic products which exclude synthetic nitrogen fertilizers (Crews and Peoples, 2003). On French field crop system only 20% of the surface are bare in winter. Intermediate crops in French field crop farms are 60% crucifers, 24% grasses, 9% mixtures, 2% are legumes alone [START_REF] Agreste | Une amélioration progressive des techniques de fertilisation en grandes productions végétales[END_REF]. Viticulture has been stubborn to adopt soil cover and today green manuring is still little used in comparison with field crop systems. The presence of perennial crops strongly modifies the technical operations and their scales in space, in time and in nutrients supply needed in comparison with field crop systems. Also, labour repartition allocates probably more to fertilization and soil management in field crops than in viticulture where it represents less than 20% of the total working times (figures transmitted by the Tarn Agricultural Chamber and produced by CER France and Agricultural chambers of Lot, Tarn and Tarnet-Garonne).

The cost-matter supply ratio has been judged interesting by the winegrower met. Still, need for supplementary machines specific to cover crop management is pointed out in this study and in the literature (Plass and Schûtte, 2017). Soil preparation (on the five first centimetres) costs are around 50-60 € per hectare, sowing costs range between about 60 and 150 € per hectares mainly depending on the tool and the soil preparation, finally the destruction costs are quite similar to the soil preparation costs [START_REF] Gastaldi | Les couverts annuels inter-rangs en viticulture -Fiche technique élaborée par l'Association Technique Viticole de Maine et Loire[END_REF]. Price of GM cultivation is variable, mainly depending on the specie, because of the seed prices [START_REF] Guiducci | Total N supply and profit from several green manure crops[END_REF], ranging from a dozen of euros per hectare to one hundred according to [START_REF] Ingels | Cover crop species and descriptions. Cover cropping in vineyards: a grower's handbook[END_REF]). Yet, production on the farm and exchanges of seeds are also possible.

On the other side, for other sources of nitrogen, if we sum up, one can considered that the price of 1kg of nitrogen is around 1€ [START_REF] Cohan | Prix des engrais azotés : quels impacts sur les céréales[END_REF] and is less expensive in labour than green manure. Then, the final cost saving of GM is not that obvious, mainly depending on species used. Also, in this study we didn't really consider spontaneous cover crop that contain managed as green manure. Without the seed costs, this low input approach appears to be the cheaper.

Furthermore, next step of GMs assessment is their effects on grapevine nutrition. The NBI is an indicator of grapevine nutrition but it depends notably on climate conditions and fertilization management what complicate the validation (or invalidation) of the impacts of GM on grapevine. Indeed, important issues remain unclear concerning effect on grapevine: coincidence of the nutrients release and grapevine needs, possibility of excess of nitrogen supply, possibility of nitrogen deficiency for low C/N ratio. From a different perspective, winegrowers monitor until the quality of their final product. Yet, grape quality is impacted by the presence of a green manure [START_REF] Guerra | Influence of Floor Management Technique on Grapevine Growth, Disease Pressure, and Juice and Wine Composition: A Review[END_REF][START_REF] Gontier | Engrais verts en viticulture : incidence du type de couvert végétal et de son mode de destruction sur l'alimentation azotée e la vigne. Green manuring in viticulture: impact of cover crop species and way of destruction on nitrogen supply of the grapevine[END_REF]. Nitrogen availability during grape formation affects yeast activity, and, for some grape varieties, it can be source of serious concern for aromatic precursor development [START_REF] Dufourcq | Azote foliaire et potentiel aromatique[END_REF]. Once more, the complexity of cover cropping calls for accurate management tools that still have to be built.