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International audience; Sustainable cropping systems that balance agricultural productivity and ecological integrity are urgently needed. Overreliance on soil tillage and herbicides to manage weeds has resulted in a number of major environmental problems including soil erosion and degradation, biodiversity loss, and water quality impairment. Combining organic farming and conservation agriculture is a viable alternative to address these challenges. In particular, mulch-based no tillage systems can be used to reduce tillage in organic production, improving soil quality while decreasing labor and fuel requirements. This technique involves planting cash crops directly into terminated cover crops that remain on soil surface and serve as mulch to prevent weeds establishment and protect soil from erosion. Despite potential benefits, adoption of organic mulch-based no tillage is limited due to challenges with cover crop termination, weed suppression, and yields. Here, we (i) review international research on organic mulch-based no tillage systems (soybean and maize), (ii) identify production issues that limit the success of this technique, and (iii) outline research priorities. As result, organic mulch-based no tillage is knowledge intensive and requires advanced planning and careful management of the cover crop. Primary challenges include timely cover crop establishment and termination, nutrient management, reduced soil temperature and moisture at planting, and achieving adequate seed-to-soil contact when planting into thick mulch on soil surface. Long-term research is needed to better understand the effects of this technique production on soil health and on the broader environmental and economic impacts. To increase adoption of organic mulch-based no tillage, future research should focus on (i) screening species and cultivars to identify cover crop and crop combinations that optimize cropping system performance and (ii) developing equipment for improving cover crop termination and seed placement. Research conducted in partnership with farmers will be valuable for developing guidelines and increasing adoption of this technique.

In organic farming, weeds are one of the threats that limit crop yield. An early prediction of weed effect on yield loss and the size of late weed populations could help farmers and advisors to improve weed management. Numerous studies predicting the effect of weeds on yield have already been conducted, but the level of uncertainty about weed effect is expected to be very high in organic crops. It is thus more appropriate to provide farmers and advisors with distributions of possible production levels, rather than with point values. The purpose of this study was to estimate the effect of early weed density at the end of the tillering stage of organic winter wheat on subsequent yield and on late weed density at flowering, by using quantile regression. Results showed that this method can be applied to a hyperbolic model and to an allometric density-dependent model, to describe the distribution of yield values and of late weed density respectively, as functions of early weed density measurements. Mechanical weed control showed no significant effect on the relationship between early weed density and grain yield, but it decreased late weed density. Yield and late weed density distributions derived by quantile regression provided sound information on the possible effect of weeds on organic winter wheat production.

In organic agriculture, weeds and nitrogen deficiency are the main factors that limit crop production. The use of relay-intercropped forage legumes may be a way of providing ecological services such as weed control, increasing N availability in the cropping system thanks to N fixation, reducing N leaching and supplying nitrogen to the following crop. However, these ecological services vary considerably depending on the forage legume biomass. The aim of this study was to identify factors that affect forage legume establishment and growth to help farmers adjust the management of the cover crop. Sixteen field experiments were conducted over a period of five years. In each experiment, winter wheat was grown as sole crop or intercropped with one of two species of forage legumes; Trifolium repens L. or Trifolium pratense L. After the intercropping stage, the cover crop was maintained until the end of winter and then destroyed by plowing before maize was sown. Climatic conditions, and the accumulation of legume and weed biomass were monitored from when the legume was sown to destruction of the cover crop. Our results showed that a minimum threshold of about 500 kg ha−1 biomass in the aboveground parts of the cover crop was needed at the end of intercropping to obtain the minimum biomass of 2000 kg ha−1 in September necessary to guarantee ecological services. To obtain sufficient legume biomass at the end of intercropping period, a thermal time greater than 1900 °Cd and more rainfall than 300 mm are required for legume growth. Moreover, a legume density of at least of 300 plants per square meter at the wheat flowering stage was a good indicator of legume biomass at the end of the intercropping period. Rainfall was a limiting factor of legume growth between the end of the intercropping period and September. Legume density at wheat flowering and climatic conditions during the intercropping period thus appear to be good indicators to predict to capacity of cover crop to produce sufficient biomass in September. These indicators can be used by farmers as a management tool for the cover crop.

The interest of organic farmers in adopting conservation agriculture principles, including minimal soil disturbance, permanent soil cover and crop rotation has been growing since the early 2000s. However, currently there is no network for organic farmers practicing conservation agriculture, and a lack of knowledge on how organic farmers implement conservation agriculture in practice. Consequently, few technical references are available for organic farmers when they start applying conservation agriculture practices, in particular on controlling weeds without the use of herbicides. The main objectives of this study were: (1) to explore the diversity of conservation agriculture techniques (i.e., reduced tillage, no-tillage and green manures) practiced among European farmers, and (2) to identify farmers’ main strategies for implementing conservation agriculture and the agronomic and environmental factors that determine these strategies. Strategies were identified by analyzing survey results on: (1) the type and degree of use of conservation agriculture practices by farmers, and (2) the effects it produces in terms of soil disturbance and soil cover (low, medium and high). We carried out a survey of 159 European organic farmers and collected 125 data sets on management of winter-sown crops. Among the conservation agriculture practices, reduced tillage was used by 89%, no-tillage by 27% and green manure by 74% of the 159 interviewed farmers. Green manures were more frequently used in northern Europe than in the south (below 45°N). Most of the farmers used crop rotations, with a mean duration of 6 years. A wide diversity of conservation agriculture practices were used, with farmers rarely using all three techniques (no-till, reduced till and green manures) within one system. The range of practices was grouped into five strategies ranging from intensive non-inversion tillage without soil cover to very innovative techniques with no-tillage and intercrops. The five strategies for conservation agriculture could be grouped into two larger categories based on weed control approach: (1) intensification of the mechanical work without soil inversion or (2) biological regulation of weeds with cover crops. The diversity of strategies identified in this study shows that organic farmers use innovative approaches to implement conservation agriculture without herbicides. This study's findings will help organic farmers to experiment with innovative practices based on conservation agriculture principles and also benefit conventional farmers who use conservation agriculture practices and would like to reduce or eliminate the use of herbicides.

In organic agriculture, weeds and nitrogen deficiency are the main factors that limit crop production. The use of relay-intercropped forage legumes may be a way of providing ecological services such as weed control, increasing N availability in the cropping system thanks to N fixation, reducing N leaching and supplying nitrogen to the following crop. However, these ecological services can vary considerably depending on the growing conditions. The aim of this study was to identify early indicators to assess these two ecological services, thereby giving farmers time to adjust the management of both the cover crop and of the following crop. Nine field experiments were conducted over a period of three years. In each experiment, winter wheat was grown as sole crop or intercropped with one of two species of forage legumes; Trifolium repens L. or Trifolium pratense L Two levels of fertilization were also tested (0 and 100 kg N ha(-1)). After the intercropping stage, the cover crop was maintained until the end of winter and then destroyed by plowing before maize was sown. Legume and weed biomass, nitrogen content and accumulation were monitored from legume sowing to cover destruction. Our results showed that a minimum threshold of about 2 t ha(-1) biomass in the aboveground parts of the cover crop was needed to decrease weed infestation by 90% in early September and to ensure weed control up to December. The increase in nitrogen in the following maize crop was also correlated with the legume biomass in early September. The gain in nitrogen in maize (the following crop) was correlated with legume biomass in early September, with a minimum gain of 60 kg N ha(-1) as soon as legume biomass reached more than 2 t ha(-1). Legume biomass in early September thus appears to be a good indicator to predict weed control in December as well as the nitrogen released to the following crop. The indicator can be used by farmers as a management tool for both the cover crop and following cash crop. Early estimation of available nitrogen after the destruction of the forage legume can be used to adjust the supply of nitrogen fertilizer to the following crop.

International audience; AbstractReduced tillage is increasingly promoted to improve sustainability and productivity of agricultural systems. Nonetheless, adoption of reduced tillage by organic farmers has been slow due to concerns about nutrient supply, soil structure, and weeds that may limit yields. Here, we compiled the results from both published and unpublished research comparing deep or shallow inversion tillage, with various categories of reduced tillage under organic management. Shallow refers to less than 25 cm. We found that (1) division of reduced tillage practices into different classes with varying degrees of intensity allowed us to assess the trade-offs between reductions in tillage intensity, crop yields, weed incidence, and soil C stocks. (2) Reducing tillage intensity in organic systems reduced crop yields by an average of 7.6 % relative to deep inversion tillage with no significant reduction in yield relative to shallow inversion tillage. (3) Among the different classes of reduced tillage practice, shallow non-inversion tillage resulted in non-significant reductions in yield relative to deep inversion; whereas deep non-inversion tillage resulted in the largest yield reduction, of 11.6 %. (4) Using inversion tillage to only a shallow depth resulted in minimal reductions in yield, of 5.5 %, but significantly higher soil C stocks and better weed control. This finding suggests that this is a good option for organic farmers wanting to improve soil quality while minimizing impacts on yields. (5) Weeds were consistently higher, by about 50 %, when tillage intensity was reduced, although this did not always result in reduced yields.

Conservation agriculture and organic farming are considered as promising sustainable agricultural system for producing food, while minimizing environmental impacts. Despite an increasing number of experimental data on organic conservation practices and various studies dealing with the adoption of conservation agriculture by farmers, none of those studies have specifically addressed conservation agriculture adoption under organic conditions in Europe. We carried out a survey with 159 farmers located in 10 European countries. These farmers had applied at least two of the following conservation practices: (i) no-tillage, (ii) reduced tillage and (iii) green manures. Each farmer assessed socio-economic, agronomic and environmental motivations and problems for each conservation practice, using a Likert scale. For each conservation practice, we ranked motivations and problems and carried out a principal component analysis, followed by clustering to identify groups of farmers. Independent of the conservation practices, the most important motivations were related to soil fertility preservation and challenges were mainly linked to crop management, machinery and yield performances. For all conservation practices, we identify three groups of farmers that shared the same type of motivations and challenges across Europe: “soil conservationists,” “agro-technically challenged farmers,” and “indifferent farmers.” Soil conservationist farmers were strongly motivated by soil preservation and minimizing environmental impacts. Agro-technically challenged farmers mainly expressed agronomic problems and challenges. There were no clear effects of location or farm characteristics explaining these attitudes, but they depended on farmers’ environmental concerns and beliefs. The study demonstrated that research priorities should address agronomic problems caused by the adoption of conservation practices in organic farming, weed control in particular.

In organic wheat, nitrogen is one of the key limiting factors responsible for irregular productivity and low quality. On arable farms, the decreasing use of N-organic sources such as forage legumes, manures and composts relative to mixed-farms requires the development of suitable fertility strategies based on the use of off-farm organic fertilizers. The Azodyn crop model was previously adapted to organic fertilization and evaluated on various field trials in order to predict grain yield, grain protein content and soil mineral N at harvest. This paper analyses the value of Azodyn-Org as a decision-tool for managing N fertilization by (1) evaluating the economic benefits of an organic N application and (2) selecting optimal fertilization strategies according to farmers’ constraints and conditions. It appears that Azodyn-Org is relevant for selecting appropriate strategies in various conditions only if the multiple limiting factors (e.g. weeds, diseases, soil compaction) effect on yield was well predicted. In these conditions, its use could allow to identify the fields where an organic N application is profitable, through rule-based simulations. The development of an early risk-assessment method to predict the effect of major limiting factors is required before providing this tool to users. Other methodological elements of model-based explorations are addressed in the discussion.

In agriculture, differences between the kinetics of crop requirements and the rate of soil mineralization are known to affect wheat yield and quality. The high cost of organic nitrogen fertilizer may result in nitrogen availability being a limiting factor during the crop cycle. It is therefore necessary to improve fertilizer application conditions, to limit losses, to ensure that grain quality exceeds a certain threshold, and to optimize economic efficiency. The aim of this study was to improve nitrogen management in organic winter wheat crops by optimizing spring fertilization. We validated and used the Azodyn model [Eur. J. Agron. 10 (1999) 129] to determine the effect of various fertilization strategies on winter wheat production under N constraints. We first adapted the Azodyn model by constructing an organic fertilizer submodel. The resulting Azodyn–Org model was tested under several sets of conditions for the rate and timing of organic fertilizer applications, in three experiments. Preliminary results confirmed that the Azodyn model accurately predicted N soil availability in a wide range of conditions. We assessed the performance of the Azodyn–Org model for predicting grain yield, grain protein content and mineral N in the soil. We found that grain yield was correctly predicted whereas grain protein content was slightly overestimated. Thus, the Azodyn–Org model has potential for use as a decision-making tool for managing spring N fertilization in organic wheat crops.

International audience; Many authors have focused on the contribution of inner farm nutrient recycling to closed nutrient cycles, but little is known about the contribution of exchanges among farms to nutrient cycling. By using a network approach, we assessed the structure of farm mass flows networks and their consequences for nitrogen (N), phosphorus (P) and potassium (K) recycling in organic farming at the local scale. Organic farming was considered as a prototype of farming systems that aims at better closing nutrient cycles. Inflows and outflows were collected for two cropping years on 63 organic farms. The farms were located in three French agricultural districts with areas ranging from 520 to 1021 km2 and differentiated by their degree of specialization (specialized in crop production, animal production, or mixed). Local nutrient recycling was assessed at the district scale through: (i) the local supply, defined as the ratio of the amount of nutrients from exchanges among farms plus the amount of nitrogen from atmospheric sources, to the sum of inputs to organic farms; and (ii) the cycling index, defined as the fraction of nutrients flowing at least twice through the same farms. Results showed that exchanges among farms were mainly short-distance exchanges (

Organic farmers are interested in soil conservation by reduced tillage, techniques well known in conventional agriculture to protect soil quality and limit labor time and energy costs. However, organic farming and reduced tillage can modify weeds, soil structure, and thus soil nitrogen (N) mineralization which strongly influences wheat yield and quality. The main objectives of this study were to analyze how reduced tillage applied to organic wheat influenced (1) grain yield, protein concentration, and weed infestation; (2) deoxynivalenol (DON) contamination on grain; (3) technological quality parameters such as dry gluten, zeleny index, falling number, and gluten index; (4) protein composition (F1, F2, F3, F4, and F5 fractions, and UPP, gliadin/glutenin ratio); and (5) baking test. For this purpose, we analyzed five site-years of data from winter wheat crops where mouldboard ploughing and reduced tillage were compared in three experimental trials (two in France and one in Switzerland). Main results concern wheat yields: the effect of reduced tillage on wheat yield was influenced by several factors such as weed competition. No significant increase in mycotoxin content (DON) due to reduced tillage was detected. Contamination with DON was always below the European threshold for human consumption. The technological quality parameters were less affected by the tillage treatments than grain yield: protein content, gluten index, zeleny index, and falling number showed on average no significant difference between treatments although the protein composition was slightly different. The main results of this study are that the effect of reduced tillage on grain yield depends very much on soil type, weather conditions, and time after conversion, whereas there is only minor impact on wheat quality. This is in contrast to the hypothesis that reduced tillage under organic farming will cause problems in baking quality.

Nitrogen (N) management is a key issue in livestock-free organic grain systems. Relay intercropping with a legume cover crop can be a useful technique for improving N availability when two cash crops are grown successively. We evaluated the benefits of four relay intercropped legumes (Medicago lupulina, Medicago sativa, Trifolium pratense and Trifolium repens) on N dynamics and their contribution to the associated and subsequent cash crops in six fields of organic farms located in South-East France. None of the relay intercropped legumes affected the N uptake of the associated winter wheat but all significantly increased the N uptake of the succeeding spring crop, either maize or spring wheat. The improvement of the N nutrition of the subsequent maize crop induced a 30 % increase in grain yield. All relay intercropped legumes enriched the soil-plant system in N through symbiotic fixation. From 71 to 96 % of the N contained in the shoots of the legumes in late autumn was derived from the atmosphere (Ndfa) and varied between 38 and 67 kg Ndfa ha(-1). Even if the cover crop is expected to limit N leaching during wintertime, the presence of relay intercropped legumes had no significant effect on N leaching during winter compared to the control.

Fusarium head blight caused by different varieties of Fusarium species is one of the major serious worldwide diseases found in wheat production. It is therefore important to be able to quantify the deoxynivalenol concentration in wheat. Unfortunately, in mycotoxin quantification, due to the uneven distribution of mycotoxins within the initial lot, it is difficult, or even impossible, to obtain a truly representative analytical sample. In previous work we showed that the sampling step most responsible for variability was grain sampling. In this paper, it is more particularly the step scaling down from a laboratory sample of some kilograms to an analytical sample of a few grams that is investigated. The naturally contaminated wheat lot was obtained from an organic field located in the southeast of France (Rhône-Alpes) from the year 2008-2009 cropping season. The deoxynivalenol level was found to be 50.6 ± 2.3 ng g⁻¹. Deoxynivalenol was extracted with a acetonitrile-water mix and quantified by gas chromatography-electron capture detection (GC-ECD). Three different grain sampling techniques were tested to obtain analytical samples: a technique based on manually homogenisation and division, a second technique based on the use of a rotating shaker and a third on the use of compressed air. Both the rotating shaker and the compressed air techniques enabled a homogeneous laboratory sample to be obtained, from which representative analytical samples could be taken. Moreover, the techniques did away with many repetitions and grinding. This study, therefore, contributes to sampling variability reduction in the evaluation of deoxynivalenol contamination of organic wheat grain, and then, at a reasonable cost.

International audience; Organic farming systems are often nutrient-limited. Moreover, even if organic guidelines emphasize the reliance on ecological processes and recycling, the trend towards farm specialisation induces an increased reliance on off-farm fertilising materials in arable areas. There is, therefore, a need to better understand the drivers of nutrient inflows on organic farms. Our objectives were to assess the nitrogen (N,) phosphorus (P) and potassium (K) farm-gate inflows through fertilising materials, and the nutrient budget and use efficiency over a large range of organic farming systems. To do this, 56 interviews with organic farmers concerning their nutrient management for the years 2010 and 2011 were carried out in 2012 in three French agricultural districts distributed over a gradient of farming activity. The results showed that the farm-gate fertilising material inflows were strongly related to both the ratio of land under cereal and oilseed crops (proxy of nutrient ‘demand’) and the stocking rate (proxy of nutrient ‘supply’). However, other inflows (biological N fixation, feed use, fodders and straws) increased with the stocking rate, leading to low farm-gate N and K use efficiency (0.2 and 0.7, respectively) on livestock farms compared to arable, stockless farms (1.4 and 3.5, respectively). Such results helped to disentangle the drivers of nutrient use in organic farms compared to previous analyses based solely on farm production typology.

ESSN: 1879-4246; International audience; Organic agriculture is a production system which relies on ecosystem management and ecological processes rather than on the external flow of agricultural inputs. The development of the organic sector has incluced a spatial decoupling of livestock and crop production. This has increased the flow of nutrients that occurs between farms compared to what happens within individual farms. Organic systems have replaced synthetic inputs with site-specific management practices to balance input and output nutrients to ensure short-term productivity and long-term sustainability. This paper addresses the nutrient management of mixed and specialized farming systems, with a special emphasis on the reliance on livestock production for the nutrient management of arable farmland. We assessed the nutrient budgets of nitrogen (N), phosphorus (P), and potassium (K) of 28 organic farms selected according to livestock density from three French countries. The farms were classified as stockless, mixed, and cattle farming systems. A soil surface nutrient budget was calculated for each farm based on inputs (N fixation, excreta, and manure) and outputs (grazing, offtake, harvests) on annual crops and grasslands. Inputs due to N atmospheric deposition and seeds and losses due to leaching and volatization were not considered in this study. Nutrient budgets of the 28 farms revealed N, P and K deficits, although disparities between farming systems and their geographical location were also observed. Stockless farms presented high N deficit whereas mixed and livestock farming systems presented lower deficits (close to equilibrium) or even surpluses in a county with a high density of livestock farms. Differences between farming systems in terms of P and K budgets followed the same trend, but regional specificities appreared significant in stockless and livestock systems (related to the size of farms and the stocking rate). None of the farms purchased off-farm organic fertilizers when exchanges of manures and straw were observed at the regional scale. When livestock is present on the farm, the nutrient resources came mainly from recycling internal resources (manures, excreta, and N fixation), whereas stockless farming systems purchased organic manure from neighboring farms ( 14 to 58 % of total N inputs, 10 to 100 % of total P and K inputs). The sustainability of stockless organic farming systems is questioned, noticeably those that were located in regions where resources of organic matter are scarce. Only farming systems producing large quantities of manure or which purchased feed showed balanced nutrient budgets.

Wheat yields and grain protein content are lower and more variable in organic conditions than in conventional agriculture, mainly due to nitrogen (N) deficiency and weed competition. The undersowing of legume cover crops in growing winter wheat, also known as relay intercropping, is assumed to be a proficient way of enriching the soil-crop system with N and improving weed control. However, competition for resources may impair wheat performance. Relay intercropping in springtime in growing winter wheat is expected to limit competition for resources from the legume. The aim of our study was to analyze wheat performance and resource competition in relay intercropping systems with legume cover crops under various environmental conditions. Eight field experiments were conducted on organic grain-oriented farms located in southeast France. Black medic (Medicago lupulina), alfalfa (Medicago sativa), red clover (Trifolium pratense) and white clover (Trifolium repens), undersown at wheat tillering stage, were compared with a sole crop of winter wheat (Triticum aestivum cv. Lona). The aerial biomass of wheat and legumes and total N content of wheat were determined at both the flowering stage and harvest time of the wheat. The main trophic resources (water, N and light) were monitored at similar stages. Wheat grain yield and grain protein content were also measured. Sites were classified according to wheat sole crop performance at harvest to evaluate the effect of relay intercropping in the various conditions tested. In all but one of the thirty-two treatments, wheat grain yield was not significantly disturbed by relay intercropping whatever the aerial development of legumes. Abundant aerial development of legumes after flowering (>20% of the aerial biomass of wheat at harvest) was associated with a mean significant decrease in wheat grain protein content of 8.5% of the control treatment value, this occurring in one third of the situations. These ratios of aerial biomasses of legumes compared to wheat were also associated with reductions in soil moisture and wheat N uptake. The effect on the availability of trophic resources for wheat may have led to a decrease in grain protein content without having any effect on grain yield. Sites which registered a low performance for wheat sole crops were less negatively impacted by the presence and aerial development of legumes. The performance of the four legume species and the mechanisms of induced disturbance of resource availability are then discussed. Finally, we try to define ranges of legumes' development and resource availability in which wheat performance was maintained or limited. (C) 2013 Elsevier B.V. All rights reserved.

This chapter is a first attempt to analyse bottlenecks and challenges of European organic bread wheat sector involving technical, political and market issues. From 2000, the organic grain market has largely increased in Western Europe. To balance higher consumer demand there is a need to increase organic production by a new transition and technical improvement. Bread wheat is grown in a variety of crop rotations and farming systems where four basic organic crop production systems have been defined. Weeds and nitrogen deficiency are considered to be the most serious threat inducing lowest grain yield under organic production. The choice of cultivar, green manure, fertilization and intercropping legumes – grain or forage – are efficient ways to obtain high grain quality and quantity. The economic viability of wheat production in Europe is also affected by subsidies from European Union agri-environmental programs. Support has been granted to organic farming since the beginning of the 1990s. Direct payments from European regulation combined with premium prices paid by consumers had compensated the lowest crop production. In the European Union, the current cycle of the Common Agricultural Policy (CAP) is due to end in 2013. Discussions are now under way to support the policy for the period 2014–2020. With the increasing consumer awareness of their food, the growth of the organic sector may continue in the near future. However, financial crisis in some countries may lead to stagnation or even decline of consumer demand. The development of the organic grain sector is actually confronted to others challenges as quality and safety value. Technological ways of milling and baking may also improve baking quality and nutritional value of organic flour, as well as it prevents mycotoxin contamination. For instance, milling process strongly influences flour characteristics. Stone milling improves nutritive value when characteristics remain very stable independently of the milling yield while flour characteristics from roller milling appear very susceptible to the milling yield. The economic efficiency of the bread wheat sector is also influences by the existence of an adequate marketing structure answering consumers’ requirements. This paper is a contribution of a multidisciplinary group of researchers involved in AGTEC-Org project using peer review, statistical data and interviews of key actors: farmers, advisers or experts (coreorganic.org/research/projects/agtec-org/index.html).

International audience; The present major agricultural issues are to feed the world and reduce negative environmental impacts. To this end, organic farming appears as a promising solution. However organic farming has several drawbacks such as difficult weed management. Indeed weeds can reduce crop yields. Therefore there is a need for improved decision support tools for weed management in organic farming. An existing weed competition model actually predicts the effect of early multispecies weed density, both on organic wheat yield loss and on the weed density at flowering stage. However main existing models do not take into account the activity of end-users, e.g. farmers, during model design. Therefore we analysed weed information acquisition by farmers using the dynamic environment theory to design a decision support system that takes into account end-users. We interviewed eight French organic farmers. We analysed interview data using a coding scheme inspired by dynamic environment theory. Our results show that weed quantity was the information most frequently collected by organic farmers both for short- and long-term crop management. This information was compatible with early weed density, the main input of the previously developed models. Findings also show that procedures for gathering information and processing depended on farmer profiles. We also show that a conceptual model based on dynamic situations and a coding structure were appropriate for taking into account the information elaborated by end-users. Finally we propose further design of a decision support system for tactical organic weed management using a participatory approach.

International audience; Organic agriculture could achieve the objectives of sustainable agriculture by banning the use of synthetic fertilizers and pesticides. However, organic crops generally show lower performances than conventional ones. In France, organic winter wheat production is characterized by low grain protein content. There is a crucial need for better understanding the variability of grain protein content, because millers require batches with values over 10.5% of dry matter. Here, a regional agronomic diagnosis was carried out to identify the limiting factors and crop management practices explaining the variability of grain protein content. The studied field network was a set of 51 organic winter wheat plots in south-eastern France. The mixed-model method was used for identifying and ranking the limiting factors and the crop management practices responsible for variation in limiting factors. Our results show that the grain protein content variation was mostly explained by the baking quality grade of the cultivar, crop nitrogen status and weed density at flowering. There was a positive correlation between grain protein content and both crop nitrogen status and weed density. To a lesser extent, climatic factors also explained grain protein content variability. A lower water stress increased grain protein content, whereas an increase in the photothermal quotient and daily temperature over 25 °C reduced grain protein content. In south-eastern France, grain protein content of organic winter wheat could be increased by improving fertilization management, using an improved baking quality grade cultivar, choosing a legume fodder crop as preceding crop, or by avoiding late sowing dates.

Conservation tillage covers a range of tillage practices, mostly non-inversion, which aim to conserve soil moisture and reduce soil erosion by leaving more than one-third of the soil surface covered by crop residues. Organic farmers are encouraged to adopt conservation tillage to preserve soil quality and fertility and to prevent soil degradation – mainly erosion and compaction. The potential advantages of conservation tillage in organic farming are reduced erosion, greater macroporosity in the soil surface due to larger number of earthworms, more microbial activity and carbon storage, less run-off and leaching of nutrients, reduced fuel use and faster tillage. The disadvantages of conservation tillage in organic farming are greater pressure from grass weeds, less suitable than ploughing for poorly drained, unstable soils or high rainfall areas, restricted N availability and restricted crop choice. The success of conservation tillage in organic farming hinges on the choice of crop rotation to ensure weed and disease control and nitrogen availability. Rotation of tillage depth according to crop type, in conjunction with compaction control measures is also required. A high standard of management is required, tailored to local soil and site conditions. Innovative approaches for the application of conservation tillage, such as perennial mulches, mechanical control of cover crops, rotational tillage and controlled traffic, require further practical assessment.

International audience; A diagnostic method for assessing regional variations in yield was implemented for a network of 24 organic wheat fields located in two neighboring regions, Diois and Val de Drôme (France). We studied: yield and its components; field environmental conditions of the fields; relations between indicators of potential limiting factors and yield components; and linkages between crop management and yield-limiting factors. The yield performances were low and variable (3.5 ± 1.4 t*ha-1). The relative kernel number (RKN) was significantly related to nitrogen nutrition and weed density at flowering. The nitrogen nutrition index (NNIf) had a strong and positive effect on relative kernel number, while weed density (1/WF) had a negative effect. The percentage of kernel number variation explained by the regression model (RKN = 0.112 + 0.609 × NNIf + 0.2 × 1/WF) was adequate (Adj. R2 = 0.53) with a RMSE of 0.09. The duration of the period of grain filling, reflected in the temperature sum, had a strong and positive effect on relative kernel weight (RTKW), while soil compaction and high temperature had a negative influence. Adjusted R2 for the model was 0.42 with a RMSE of 0.16. The results confirm that legumes preceding crops improve nitrogen nutrition on subsequent winter wheat, e.g. the Nitrogen Nutrition Index at flowering (NNIf) = 0.51 ± 0.12 for a crop rotation with a rate of legumes over 37% vs. 0.41 ± 0.11 for a crop rotation with a rate of legumes under 25%. Alfalfa preceding crops significantly limited the weed density at harvest while stony soils and early sowing (before November 1st) enhanced weed density.

International audience; Organic farming is increasingly recognized as a prototype for sustainable agriculture. Its guidelines ban the use of artificial fertilizers. However, organic farms may import nutrients from conventional farming through material exchanges. In this study, we aimed at estimating the magnitude of these flows through the quantification of nitrogen, phosphorus and potassium inflows from conventional farming to organic farming. Material inflows and outflows were collected for two cropping years on 63 farms. The farms were located in three French agricultural districts distributed over a gradient of farming activity defined by both the stocking rate and the ratio of the farm area under arable crops. Our results showed that on average, inflows from conventional farming were 23%, 73% and 53% for nitrogen, phosphorus and potassium, respectively. These inflows were strongly determined by the farm production systems. However, for farms similar in terms of production systems, the inflows also depended on the local context, such as the proximity of organic livestock farms: the reliance of organic farming on conventional farming was lower in mixed than in specialized districts. These results highlight the necessity to quantify the contribution of nutrient inflows from conventional farming when assessing organic farming and development scenarios.

Cover crop-based no-tillage (NT) techniques appear as an innovative solution to manage weeds while limiting soil disturbance and facing economic, sociologic and agro ecologic challenges of the 21st century (Mäeder et Berner, 2012). This technic consists of sowing a cash crop without tillage either under living or terminated cover crop with a roller crimper (Mirsky et al., 2012). This innovation has been developed in North America and NT is emerging in France. Especially, farmers are motivated by NT adoption to improve soil fertility, reduce fuel and herbicides consumption and decrease labor (Soane et al., 2012 ; Casagrande et al., 2015). Cover crop-based NT practice represents a major challenge both in organic farming and conventional farming to reduce tillage and limit and/or replace the use of the Glyphosate causing discussions in Europe (Johnsen et al., 2016). However, high number of difficulties are often reported (cover crop control, weeds management, nitrogen availability etc.) and a system rethinking is required to limit them. In addition, only few references are available on this subject and most of the studies have been conducted in North America (Moyer, 2011). Consequently, concerns reminds on means to adopt the innovation in current farms (equipment, skills, knowledge, technical and organizational choices etc.) and on economic and agronomic benefits provided by cover crop-based NT techniques. This thesis relies on these three major issues and proposes to design viable solutions in current farms integrating cover crop-based NT techniques under European conditions. This thesis project aims especially to consider the farmer’s objectives and constraints at three organizational level (plot, cropping systems, farm) combining both a systemic and an analytic approach.; Le semis direct sous couvert végétal (SDSC) apparaît comme une solution innovante pour gérer les adventices tout en limitant les dégradations des sols et en répondant aux enjeux économiques, sociologiques et agroécologiques du XXIème siècle (Mäeder et Berner, 2012). Cette technique culturale sans labour consiste à implanter une culture, sans travail du sol, soit sous un couvert végétal vivant soit sous un couvert détruit mécaniquement à partir d’un rouleau cranteur (Mirsky et al., 2012). Cette innovation se développe en Amérique du Nord et commence à émerger en France. Elle suscite en effet beaucoup d’intérêts auprès des agriculteurs qui souhaitent améliorer la fertilité des sols, réduire la consommation de carburant et d’herbicides ou encore limiter le temps de travail (Soane et al., 2012 ; Casagrande et al., 2015). Cette technique constitue un enjeu majeur à la fois en agriculture biologique et en agriculture conventionnelle pour diminuer le recours au travail du sol et limiter ou remplacer l’utilisation du glyphosate à l’origine de nombreux débats en Europe (Johnsen et al., 2016). Toutefois, d’importantes difficultés sont souvent relevées lors de l’adoption du SDSC (maîtrise du couvert et des adventices, disponibilité de l’azote etc.) et une reconsidération de l’ensemble du système serait nécessaire pour les limiter. De plus, peu de références existent sur cette thématique et la majorité des études a été menée dans un contexte nord-américain (Moyer, 2011). Ainsi, des questions persistent sur les moyens de mise en œuvre de cette innovation dans les exploitations agricoles actuelles (machinisme, compétences, connaissances, choix techniques et organisationnels etc.) ainsi que sur les performances économiques et agronomiques du SDSC. Cette thèse s’axe donc autour de ces trois grandes problématiques et propose de développer des solutions viables chez les agriculteurs pour intégrer cette technique dans un contexte européen. Ce projet vise notamment à prendre en compte les objectifs et les contraintes des producteurs à plusieurs niveaux d’organisation (parcelle, systèmes de culture, exploitation agricole) en alliant une approche à la fois systémique et analytique.

Cover crop-based no-tillage (NT) techniques appear as an innovative solution to manage weeds while limiting soil disturbance and facing economic, sociologic and agro ecologic challenges of the 21st century (Mäeder et Berner, 2012). This technic consists of sowing a cash crop without tillage either under living or terminated cover crop with a roller crimper (Mirsky et al., 2012). This innovation has been developed in North America and NT is emerging in France. Especially, farmers are motivated by NT adoption to improve soil fertility, reduce fuel and herbicides consumption and decrease labor (Soane et al., 2012 ; Casagrande et al., 2015). Cover crop-based NT practice represents a major challenge both in organic farming and conventional farming to reduce tillage and limit and/or replace the use of the Glyphosate causing discussions in Europe (Johnsen et al., 2016). However, high number of difficulties are often reported (cover crop control, weeds management, nitrogen availability etc.) and a system rethinking is required to limit them. In addition, only few references are available on this subject and most of the studies have been conducted in North America (Moyer, 2011). Consequently, concerns reminds on means to adopt the innovation in current farms (equipment, skills, knowledge, technical and organizational choices etc.) and on economic and agronomic benefits provided by cover crop-based NT techniques. This thesis relies on these three major issues and proposes to design viable solutions in current farms integrating cover crop-based NT techniques under European conditions. This thesis project aims especially to consider the farmer’s objectives and constraints at three organizational level (plot, cropping systems, farm) combining both a systemic and an analytic approach.; Le semis direct sous couvert végétal (SDSC) apparaît comme une solution innovante pour gérer les adventices tout en limitant les dégradations des sols et en répondant aux enjeux économiques, sociologiques et agroécologiques du XXIème siècle (Mäeder et Berner, 2012). Cette technique culturale sans labour consiste à implanter une culture, sans travail du sol, soit sous un couvert végétal vivant soit sous un couvert détruit mécaniquement à partir d’un rouleau cranteur (Mirsky et al., 2012). Cette innovation se développe en Amérique du Nord et commence à émerger en France. Elle suscite en effet beaucoup d’intérêts auprès des agriculteurs qui souhaitent améliorer la fertilité des sols, réduire la consommation de carburant et d’herbicides ou encore limiter le temps de travail (Soane et al., 2012 ; Casagrande et al., 2015). Cette technique constitue un enjeu majeur à la fois en agriculture biologique et en agriculture conventionnelle pour diminuer le recours au travail du sol et limiter ou remplacer l’utilisation du glyphosate à l’origine de nombreux débats en Europe (Johnsen et al., 2016). Toutefois, d’importantes difficultés sont souvent relevées lors de l’adoption du SDSC (maîtrise du couvert et des adventices, disponibilité de l’azote etc.) et une reconsidération de l’ensemble du système serait nécessaire pour les limiter. De plus, peu de références existent sur cette thématique et la majorité des études a été menée dans un contexte nord-américain (Moyer, 2011). Ainsi, des questions persistent sur les moyens de mise en œuvre de cette innovation dans les exploitations agricoles actuelles (machinisme, compétences, connaissances, choix techniques et organisationnels etc.) ainsi que sur les performances économiques et agronomiques du SDSC. Cette thèse s’axe donc autour de ces trois grandes problématiques et propose de développer des solutions viables chez les agriculteurs pour intégrer cette technique dans un contexte européen. Ce projet vise notamment à prendre en compte les objectifs et les contraintes des producteurs à plusieurs niveaux d’organisation (parcelle, systèmes de culture, exploitation agricole) en alliant une approche à la fois systémique et analytique.