Accounting for systemic effects of anaerobic digestion development on farmers’ practices: implications for environmental assessment

doi:10.21203/rs.3.rs-5219576/v1

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Accounting for systemic effects of anaerobic digestion development on farmers’ practices: implications for environmental assessment

https://doi.org/10.21203/rs.3.rs-5219576/v1

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On-farm biogas production has been increasingly developing in Europe since the beginning of the twentieth century, mainly supported by energy policies. However, biogas production brings new challenges in agriculture, and it is difficult to draw clear conclusions on its agri-environmental effects from the current scientific literature. Current studies focus on one or more of the agri-environmental effects of on-farm biogas development (mainly greenhouse gas balance, carbon storage, and nitrogen losses), assuming that the farming system as a whole remains unchanged, but they rarely investigate how the performance of biogas relates to indirect changes in farm practices and activities.

To better understand the changes in farm practices linked to biogas production, we surveyed 23 biogas farmers corresponding to 19 different on-farm biogas units in two areas of northeast France. We aimed to cover a diversity of configurations (e.g., of farm activities, installed biogas capacity, number of biogas farmers per project, and energy recovery methods) to capture a diversity of farm functioning. We analyzed these qualitative data by looking for recurring examples of changes in practices (or lack thereof) and drivers of the identified changes.

Our results show various changes in practices and drivers of change resulting in a much more diverse range of environmental impacts than those generally assessed in the literature. This diversity of impacts depends on both the farm characteristics and the different organizations of farm activities that biogas farmers can develop. Here we show that the necessary conditions to attain the best environmental balance are not always met, contrary to the common assumptions in the biogas assessment literature. On-farm biogas sustainability research must better consider the dynamics of farming systems and the agency of farmers in on-farm biogas development.

Biogas

sustainability

practices’ change

anaerobic digestion

systemic effects

diversity

farming system

Since the beginning of the 21st century, biogas produced from anaerobic digestion (AD) has developed around the world. Biogas production is mainly supported for its contribution to the energy transition, as a renewable decarbonized gas.

The environmental impacts of AD vary greatly from one country to another, according to the feedstock digested (crops, manure, agricultural residues, biowaste), the technical options (AD unit technology, digestate management practices) and the magnitude of its development. In Europe, Germany is an example of high AD development: it has facilitated an increased in decarbonized electricity production, but at the same time, has seen negative impacts on biodiversity (Vergara and Lakes 2019) and food prices (Britz and Delzeit 2013). In France, AD was developed in agriculture (Fig. 1) with the aim of avoiding the negative agri-environmental impacts observed in Germany. French biogas policy has even supported biogas production for its contribution to sustainable agriculture.

The current environmental balance of biogas in France is under debate, and the scientific literature has failed to draw clear conclusions on its agri-environmental impacts (Moinard 2021; Malet 2022; Cadiou et al. 2023). In this paper, we identify two main categories of studies that address this issue. The first category, which is the larger of the two, focuses on one or more of the agri-environmental effects of on-farm biogas development (mainly greenhouse gas balance, biodiversity, carbon storage, and nitrogen losses), assuming that the farming system as a whole remains unchanged. The literature in this category tends to assess direct changes limited to a few agricultural practices (Quakernack et al. 2012; Möller 2015; Bacenetti et al. 2016; Nicholson et al. 2017; Paolini et al. 2018; Greenberg et al. 2019; Launay et al. 2020; Esnouf et al. 2021), such as new methods of digestate fertilization, the introduction of energy cover crops, and manure digestion. Although these assessments analyse a range of different practices, they do not consider the systemic interactions between them. In general, the literature in this category assumes that farmers adopt the “best practices” recommended by agronomists (Cadiou et al. 2023) and that certain agri-environmental effects are rather consensual. For example, the view may be expressed that adopting best practices will improve the greenhouse gas (GHG) balance, which can bring climate benefits (Hijazi et al. 2016; Bacenetti et al. 2016; Ingrao et al. 2019; Malet 2022); or that increased use of digestate fertilizer decreases the need for synthetic nitrogen, if the best spreading practices are adopted (Clements et al. 2012; Nkoa 2014; Koszel and Lorencowicz 2015; Guilayn et al. 2019). Without the adoption of best practices, increased use of digestate could increase the risk of air (Nkoa 2014; Carton and Bulcke 2021; Moinard 2021) and water pollution (Möller 2015; Nicholson et al. 2017, 2018; Räbiger et al. 2020; Purswani and Llorente 2021). Other issues lack consensus or are even the subject of contradictory conclusions, such as the effects of digestate on soil carbon, which depends considerably on return-to-soil practices (Moinard 2021). Finally, the literature in this category contains much uncertainty on some issues, because the long-term perspective remains poorly documented, such as the impacts of digestate spreading on soil biology (Sadet-Bourgeteau et al. 2020; van Midden et al. 2023) and the impacts of AD on soil compaction and regional biodiversity.

The second category of literature, which is much smaller, identifies indirect mechanisms that can influence the adoption of practices, highlighting that, as well as direct change, the development of AD on farms sometimes triggers changes in practices in other farm activities. Thus Beausang et al. (2021) show that the sustainability of grass silage used as an AD feedstock, depends on whether it indirectly displaces feed for livestock elsewhere. Carton & Levavasseur (2022) show that soil carbon storage and biodiversity vary from one farm to another, on the introduction of energy cover crops to supply the AD unit. In Germany, Blumenstein et al. (2018) and Siegmeier et al. (2015) show, through qualitative modelling, that in some AD farms, higher crop yields and improved nitrogen management are coupled with a reducing labor and less energy costs. This body of research shows that the environmental performance of biogas can be related to other changes in the functioning of the farm or of the territory, even though few works really explore these links. Other papers show unexpected social, economic, and ecological outcomes. In Italy, an increase in a farm’s bioenergy crop production (Carrosio 2014; Cavicchi 2016) or a territorial-level increase in the need for biomass as an AD feedstock can lead to increases in farmland rent, which in turn can influence agricultural systems. In Germany, in the 2010s, AD development led to a huge increase in maize production, increased land prices, and increased food prices (Lüker-Jans et al. 2017; Vergara and Lakes 2019). Based on these two categories of literature, it is difficult to draw clear conclusions on the environmental impacts of on-farm biogas development. Very few studies empirically assess the impacts of AD looking at systemic mechanisms and their influence on several agri-environmental aspects. This article aims to contribute to the understanding of the real effects of AD on farming practices and therefore on the sustainability pathways of farms by answering the following two questions: how does on-farm AD development change farm practices?; and what are the related agri-environmental impacts?

To this end, we mobilize the “farming system studies” framework, which assumes that a system approach is necessary to capture the reasoning that underlies practices and their evolution (Sebillotte 1974; Biggs 1985). It considers the agricultural system through the interaction between three scales: technical systems (field scale), production systems (farm scale) and agricultural territory (landscape scale) (Darnhofer et al. 2012; Cochet 2012). Technical systems include highly interconnected cropping, livestock and forage systems: changing a practice in one technical system often affects other practices within the system, and other systems (Meynard et al. 2001). This approach also enables us to understand the trade-offs between production factors (labour, land, expertise) on a farm, and how this influences technical systems. AD is a new farm technical system that can modify the existing links between and within other technical systems (cropping, livestock…). Beyond the consideration of AD as a technical system, its development necessarily requires the allocation of production factors. This, in turn, has consequences on the overall functioning of the farming system (Cochet et al. 2007). Such changes must be understood through “the meaning that actors give to [them]” (Darnhofer et al. 2012). The concept of “situated rationality” puts farmer strategies at the heart of the evolution of farming systems, viewing them as stakeholders and drivers of the emergence of new forms of sociotechnical organization (Osty et al. 1998). This framework moves us away from an analysis of biogas development based on “rational modernization” and towards an understanding of the underlying “logic” of farmers, knowing that they may have conflicting goals. Finally, this article puts forward the following hypothesis: changes in practices associated with the management of AD units can be linked to indirect mechanisms involving other practices, other farm activities, and even regional dynamics, resulting in a much more diverse range of environmental impacts than the effects generally documented in the literature.

We surveyed 23 AD farmers in two French areas, Vosges and Bas-Rhin (northeast France) corresponding to 19 different on-farm AD units. The two areas differed in terms of (i) AD type (mostly combined heat and power (CHP) in Vosges, compared to biomethane injection in Bas-Rhin) and (ii) agricultural context (predominantly mixed farming in Vosges compared to more diversified production in Bas-Rhin, with field crops, mixed farming, market gardening, pigs and poultry). The aim was to cover a diversity of configurations based on the following criteria:

Activity of the farm contacted (suckler, dairy, mixed farming, pig farming, cereals)
Number of AD unit project owners (individual, small or medium-sized collective)
Installed capacity of the unit
Energy recovery method (CHP or injection, and on-farm energy recovery activity)

We tried to select the surveyed unit based on the digested feedstocks insofar as we were able to gather information on this criterion before the survey. We also selected biogas plants with a start-up date preferably before 2018, to gain perspective on farming systems changes.

The choice of respondents therefore followed the “snowball sampling” method, to enable evolution in our field of investigation (Biernacki and Waldorf 1981; Handcock and Gile 2011): this approach involves making contact with an initial farmer, who then refers us to other farmers, from whom we get further referrals, and so on. In parallel, we gathered information on AD units and farms from technical publications, from AD unit websites, and from interviews with local stakeholders, to better select the farms surveyed according to our criteria. We stopped snowball sampling once we had covered a diverse range: in Vosges we surveyed 25% of the AD units in operation in 2021, and 50% in Bas-Rhin. Each farmer was interviewed for two to three hours, in two stages: a semi-structured interview in 2021, including a visit to the AD site, except for three farmers for whom the interview was conducted by phone; followed by a complementary semi-structured phone interview between January and June 2022. The author transcribed the interviews. Each farmer is designated by a letter.

Interviews began by gathering data on (i) current farming systems and the technical AD system; and (ii) the origin and history of the AD project. The interview then moved to a discussion of the ways in which AD had modified the farm, focusing on the following points:

Whether or not the farming system, technical systems and practices had changed following the start of the AD project;
The interactions between farming system components, and potentially the interactions between other regional variables/components (other farms, food industry);
The rationale behind these changes, or the maintenance of previous practices.

Table 1

*Characteristics of farms and AD units surveyed (from* (Cadiou 2023)*). * It includes arable land and permanent grassland.*
Region		Vosges	Bas-Rhin
Number of farms for each agricultural activity	Multi-crop dairy	3	2
	Mixed crop-livestock	6	4
	Grass-fed meat farming (sheep and cattle)	1	1
	Cereal	1	2
	Monogastric livestock	0	3
Farm area characteristics: average and [range of variation]	Average total cultivated area* (ha)	330 [80–680]	146 [40–370]
Farm area characteristics: average and [range of variation]	Average area of permanent grassland (ha)	134 [25–360]	47 [0-150]
Number of farmers having invested in the AD unit	Individual unit (N = 1)	6	5
	Small collective unit (N = 2)	1	2
	Medium collective unit N = [4–7]	3	2
Total number of AD units surveyed		10	9
Total number of AD farmers surveyed		11	12
Year of unit start-up	Interval between the oldest unit and the most recent unit	[2013–2019]	[2012–2020]
Average installed capacity of units surveyed	Cogeneration of heat and power (kW)	404	542
Average installed capacity of units surveyed	Biomethane injection (Nm3)	140	218
Biogas recovery method (cogeneration or injection)	Number of cogeneration units out of total number of units	9 out of 10	5 out of 9

We analysed the data by looking for recurring examples of changes in practices (or lack of change) and of the drivers of the changes identified. In this way we have identified three main areas of technical change: crop rotations, fertilization, and forage and permanent grassland management. Data collected in the interviews on the description of practices were mainly qualitative and based on the observations of farmers. During the initial interviews, there was a back and forth with the literature to identify variables accessible to farmers, which enabled us to describe practices and to link them with agri-environmental effects based on the scientific literature. To characterize the sustainability of fertilization practices, we collected data on the digestate doses applied, the application calendar, application equipment, changes in mineral nitrogen fertilization, constraints, and levers for implementing good practices, and estimated nitrogen fertilizer savings on farms. Regarding the evolution of cropping systems, we collected data on crop succession, technical interventions (treatments, tillage), and the links between AD supply and crop rotation planning. Regarding forage management, we collected data on the evolution of forage cultivation (surface area, species, technical interventions) as well as on the established links between anaerobic digestion and livestock farming.

3.1. Changes in crop rotations

In the two areas studied, AD is developing by valorizing livestock manure, supplemented by more methanogenic feedstock such as energy crops, cover crops, crop residues, biowaste and by-products (see Table 2). Manure digestate is supported by French law, with a “manure” prime which gets to its maximum for a 60% manure supply or more.

Table 2

Supply of surveyed AD plants (average percentage by volume of raw material according to feedstock category and ranges of variation in our sample).

Source: farmers.
Average percentage [variation range] per area	10 Vosges units	9 Bas-Rhin units
Average percentage of livestock manure	71% [35–83%]	66% [30–90%]
Average percentage of by-product (agricultural or agro-industrial) and biowaste	8% [0–16%]	22% [5–60%]
Average percentage of energy crops	12% [5–45%]	4% [3–17%]
Average percentage of energy cover crops	6% [4–18%]	7% [0–42%]

These differentiated supplies depend on the available feedstock in the area, which in turn influences strategies for changing cropping systems. We have identified four different patterns of change:

Pattern 1: Maintaining previous crops and marginal changes to the cropping system (two farmers). The initial rotation changed little, the introduction of new energy cover crops (ECC) for the AD plant remaining marginal. Q and R farmers have only modified their summer ECC for biogas production (maize, sorghum, or mixed crops), as they didn’t want to affect the yields of their spring crops. But they did not rely on these summer ECC crops to supply the biogas plant, because of their low yields, due to summer drought. These farmers feed their AD unit with a diversified mix of feedstock harvested in the area: agricultural co-products (maize stover (R), livestock effluents (Q, R)), bio-waste (R), agro-industrial by-products (Q).

Pattern 2: Maintaining previous crops and developing ECC (3 farmers). The farmers (J, O, T) have chosen to produce more biomass via winter or summer ECC, for biogas production, without however modifying the succession of main crops: T and J cover their soils extensively in winter with rye and ryegrass (80ha and 40ha respectively at J), while farmer O has introduced around 20 ha of winter CIVE, and has increased his summer ECC area further - even though it is not very productive. The most methanogenic feedstocks come in part from off-farm purchases, such as bio-waste (O) and agro-industrial co-products (J, O, T), which are supplemented by winter CIVE.

Pattern 3: Modification of the cropping system to contribute to biogas production by introducing energy crops and ECC (12 farmers). Most farmers have modified their rotations to introduce energy and ECC to supply the AD units. Eleven farmers have increased their area under maize silage, and two farmers have introduced a triticale and rye mix intercrop. These crops replace cash crops, mostly cereals (A, C, E, H, I, V), but also rapeseed (B, G), and grain maize (K, L, M, S, V) (see Table 3). As in pattern 2, farmers have introduced ECC either between their main crops or following energy crops. Most farmers chose winter ECC (rye, triticale, meslin) or temporary ryegrass-type meadows (A, B, C, E, G, H, I, M, S, V, W), which are methanogenic, and whose production per hectare is regarded as good (A, B, E, G, H, M, S, V, W). Compared with pattern 2, some farmers have accepted that double cropping affects maize yield (main crop) because the average net margin per hectare is better from their point of view (B, C, G, H, I, S, V, W). Others have preferred not to grow a double crop including maize, as the double crop affects the maize yield too much (A, E, L), so they have switched to an energy winter crop that is maintained on the field for longer: therefore, growing a winter rye followed by a temporary grassland or a summer ECC (A, E). Growing these crops on their own ensures autonomy in supplying the AD unit and means that they are not dependent on the availability and price of feedstocks purchased locally.

Table 3

Changes in crop rotation for Pattern 3 farmers with the development of AD
Farmer	Stopped cultivation…	Replaced by…	Double cropping (if concerned)
A	5–6 ha of cereals 7–8 ha of permanent grassland	12–14 ha of rye Few ha of maize	Double cropping possible depending on the year and the plot
B	15–20 ha of rapeseed	15–20 ha of maize 10–15 ha of ryegrass (ECC) 50ha of summer ECC (mix of grasses and legumes)	Double cropping before maize
C	20 ha of barley	20 ha of maize Partial reintroduction of temporary grassland (alfalfa, clover)	Double cropping with yield loss on the following maize crop
E	30–40 ha of cereals	40 ha of rye, followed by a three-year ryegrass	No double cropping because of the maize yield loss
G	15 ha of rapeseed	15 ha of maize 65 ha of winter cover crops (15ha of rye, 50 ha of ryegrass) Few ha of summer ECC	Double cropping before maize
H	x ha of permanent grassland (25-x) ha of triticale and clover	25 ha of maize/sorghum 25 ha of rye (ECC)	Double cropping with yield loss on the following maize crop
I	4–5 ha of permanent grassland 2ha of barley	6–7 ha of maize Few ha of temporary grassland cover
K	25 ha of permanent grassland 10ha of maize	10–15 ha of alfalfa + 10 ha of cash crops 10 ha of rye followed by clover temporary grassland Increase in summer ECC
L	15 ha of grain maize	15 ha of silage maize Adaptation of summer ECC species for biogas production
M	20 ha of grain maize	20 ha of silage maize 15ha of rye (ECC) Few ha of ryegrass
S	10 ha of grain maize	10 ha of silage maize 20-30ha of rye or ryegrass	Double cropping with yield loss on the following maize crop
V	Varies from year to year: a few ha of irrigated grain maize	Variable from year to year: a few ha of irrigated silage maize or sorghum, or other irrigated summer ECC Various surface of winter ECC	Double cropping only on conventional crops
W	12 ha of wheat and barley	12 ha of triticale-rye	Double cropping with yield loss on the following maize crop

Pattern 4: A major transformation of the cropping system linked to the dynamics of the agricultural activity in which AD takes place (four farmers). For some farmers, the development of AD is associated with major changes in their production activities. Three farms converted to organic farming in connection with AD. By fertilizing their organic crops with digestate, these farmers have significantly increased their yields (close to conventional farming yields), enabling them to make significant economic gains.

“We wondered about going organic at the same time. The Chamber of Agriculture told us that we were crazy, that we would never grow enough to feed the AD plant, but then after a year of operation (...) we said to ourselves, why not go organic, especially because the digestate solves the fertilizer problem. And we also said to ourselves, if a crop fails in organic farming, we'll still be able to make the AD plant work, we won't have any dry losses. So finally, the conversion went more smoothly" (Farmer D)

Farmer U chose to remain in conventional production but saw that AD opened an opportunity to transform his whole farming activity: he diversified by introducing new activities (AD unit, milk processing workshop) and changed his cropping system to supply AD and make his dairy farm more resilient.

As part of these structural transformations, farmers have developed ECC cultivation in different ways. In organic arable farming, D opted for ECC followed by temporary grassland, as double cropping reduced maize yields too much (Table 3, line 2). He also buys conventional maize silage to supply his AD unit. Farmer N has integrated ECC into his rotation, he is due to supply the collective unit (Table 3, line 3). To do so, he has diversified his rotation from maize//wheat and green manure crop//beet; to wheat/rye (ECC)//buckwheat/triticale (ECC)//temporary grassland with clover (one year) (where “/” denotes intra-annual succession and “//” is inter-annual succession). For F and U, the evolution of the rotation is more closely linked to changes in their livestock farming. Both farmers switched from maize-based animal feed to a grass-based diet (F, U) combined with a cessation of maize in the crop rotation. Farmer F did not introduce energy crops or ECC as he was already supplying his AD unit without difficulty: he has links with a biowaste processing company through which he has access to the biowaste and agro-industrial co-products market. Farmer U, on the other hand, has introduced meslin energy crops into his rotation. To increase his crop production (AD and cows), he ploughed up 10 ha of permanent grassland.

Beyond the individual characteristics of farmers, we can identify three drivers that influence the patterns of change:

Access and/or dependence on a market for methanogenic feedstocks. The farmers with the oldest AD units [beginning in 2012–2016] stress the fact that the price of co-products and bio-waste has risen considerably in recent years. Eleven farmers mention that, eight years ago, they were able to obtain these products at low cost or even free of charge, whereas now they face ever-increasing prices. For example, in 2021 farmer E bought mustard by-products for €56/tonne, compared to €28/tonne in 2013. The calculation of the biogas generated from a feedstock is at the heart of the construction of the supply of biogas plants: faced with the rising price of by-products, farmers adopted various strategies and decided whether to buy by-products, and whether to produce crops on their farms. Farmer T, for example, explained that to keep costs under control, he shifted his AD supply away from co-products and towards CIVE and energy crops (corn) – which equates to a recent change from pattern 2 to pattern 3. Conversely, farmer R, who does not want to produce more crops on his farm, has tried to diversify his supply with biowaste, which is less expensive than co-products (pattern 1). These dynamics show the importance of the structuring of the territorial biomass market in the development of crop successions. We show that, depending on a farmer’s objectives and the market for feedstocks, this quest for feedstock autonomy opens up different rotation patterns - within the regulatory limit of a maximum of 15% energy crops in the supply.
The profitability requirement of the biogas plant. For farmers heavily dependent on ECC, the management of ECC is guided by the objective to produce as much biogas as possible. Since cultivating ECC requires more work than buying feedstock from outside the farm, it must be profitable. Farmers therefore often choose cereal (rye, triticale, meslin) for winter ECC and corn for summer ECC: which produces a lot of biomass. Among the farmers surveyed, two introduced legumes, marginally, via their summer (B) or winter (I) ECC. Reintroducing legumes does not serve their main objective, which is to produce as much biomass as possible.
Synergy between organic farming and AD: a driver towards more diversified cropping systems. We observed synergies between AD and organic farming, involving the use of digestate as fertilizer. Among AD farmers who were converting to organic, this process leads to systemic changes in production systems, such as the lengthening and diversification of cropping systems. However, as two farmers demonstrated, the joint economic optimization of food and biogas production may rely on the purchase of non-organic crops from neighboring farmers (via biowaste for F, or via the purchase of manure and maize silage for D).

3.2. Changes in fertilization practices

Fertilization practices have evolved with the start of AD for almost every farmer surveyed, since there is a need to manage digestate on their farms. P is the exception: as a mountain sheep farmer, it would not be feasible to spread digestate on his grassland. The way each farmer uses digestate influences to a greater or lesser extent his consumption of synthetic mineral nitrogen, depending on whether he replaces his mineral fertilizer applications with digestate.

A first group of six farmers do not reduce their use of synthetic fertilizer, or make only marginal reductions. They adopt the following practices: spreading digestate on crops before sowing corn, or when sowing cereals in autumn (E, H, Q, I), the remaining digestate is spread on grassland in autumn (C, E, K, I). There are three main reasons for the limited application of digestate to cereals in spring: (i) soils often have a low carrying capacity in spring, whereas spreading equipment is heavy (C, E, H, I, K, Q) and large volumes are needed to reach the necessary nitrogen supply for cereals; (ii) spreading takes a long time in spring (large volumes) (E, H, K); and (iii) farmers are concerned that spreading could damage seedlings that have just emerged (I). In autumn, on the other hand, there is a need to empty the slurry pit before winter, which leads to spreading at this time (E, K, H, I). New requirements for mineral nitrogen have also arisen on these farms, with the use of mineral nitrogen on crops destined for AD (E, H, I, K).

"We don't want to spread at all in winter, so in October the tank has to be empty (...) because in spring we're not sure we'll be able to spread, and then in spring I do all the fields that have a sufficient soil bearing capacity" (Farmer C).

Nine other farmers identify similar constraints influencing their practices (B, G, J, M, O, R, S, T, U). However, they are able to make bigger reductions in synthetic nitrogen use because of their willingness to spread digestate on winter wheat or barley in spring, whenever possible. Their success in this regard is linked to manpower, work schedules and spreading techniques (see below). Farmer U has been able to make even greater reductions in synthetic fertilizer use as a result of decreasing his milk production, and therefore adopting a spreading system that is sufficient for his low production objectives.

The other four farmers (D, F, N, V) face similar spreading constraints but have significantly reduced their consumption of mineral nitrogen as they have partially or fully converted to organic farming.

These different levels of reductions in nitrogen consumption are linked to the equipment and organization of spreading, that influence the speed of the spreading (characterized notably by the flow rate of the spreader and by the complexity to use the spreader) and the weight of the spreader, associated with risks of compaction.

Equipment and practices adopted due to “low resources” - Farmer I (Table 5, column 2) decided to invest in a small slurry spreader (11 m3), because he could not afford a larger one, and its output is sufficient to spread on his small, grouped fields. Even though the spreader is light, nitrogen savings are limited because nozzle spreading can increase digestate nitrogen volatilization.
Equipment and practices adopted to achieve “weight-rate compromise" - farmers (B, C, E, F, H, K, L, M, N, Q, S, T, U, W) have sought a compromise between flow rate (hence working time and spreading efficiency) and equipment weight (risk of compaction). This choice is associated with a diversity of practices linked to personal objectives and resources: B, C, K, M, S and W spread in spring when they consider compaction risk to be limited; H and U practice minimum tillage to improve carrying capacity; B, C, H, K and L have invested in technical solutions to limit compaction (polypropylene tank, 3-axle tank, "low-pressure" tyres, decompaction tools); S increased site efficiency by transporting digestate to the field with a larger slurry tank (24 m³), and then spreading with a 18 m³ tank. Farmer T has a self-propelled machine that enters the field without a tank, but which has storage for digestate that he fills up off the field. Farmers E and Q have opted for high throughput spreading (21 m³- 28 m³ tank), with the aim of spreading large volumes of digestate and limiting spreading time. However, this practice limits the areas that can be spread in spring, and therefore also limits potential reductions in mineral fertilizer use. For these farmers, such practices result in a range of reductions in nitrogen fertilizer use (Table 5, column 3). Other farmers, such as M, N and F consider that it is in their economic interest to spread at the optimum time for the crop, which is spring, even if this increases the risk of compaction. Overall, these practices can reduce mineral nitrogen use considerably (Table 5, column 3, lines 3–4).
“Optimization of valorization" practices - farmers D, G, J, O, R and V have sought to extend their spreading window by investing in slurry tanks of different sizes, and/or by combining slurry tank spreading with "tank free" spreading. Such tank-free equipment transports the digestate to the spreader via hoses, thus greatly reducing the weight in the field. This enables the extension of the spreading window, with less risk of compaction and plant mortality compared to spreading with a tank. As a result, these farmers save more on mineral fertilizers (Table 5, column 5). Most use service providers (A, G, J, O), as these operations are more complex and require more manpower and equipment than most farmers have. Over a certain field size, such equipment has a better throughput than equipment with a tank, but it is expensive. This system and equipment enable significant reductions in nitrogen fertilizer use, to a greater or lesser extent depending on the farm (last column of Table 5).

The different objectives of farmers, and their resources and constraints are therefore translated into a diversity of spreading practices, with various consequences in terms of reducing mineral nitrogen consumption.

Table 5

Diversity of relationships between fertilization practices and choice of spreading equipment and strategy. Farmer A is excluded from the classification as his fertilization system is too unstable to be analysed. Farmers L and W are included in the analysis, even though the recent and still incomplete implementation of certain practices suggests that these practices are likely to evolve in time. P is not included as he does not spread digestate on his farm.
Savings /spreading practices	“Low resource”	“Weight-rate compromise"	“Optimization of valorization"
0% or slight diminution	I	C, E, H, K, L, Q, W
Significant decrease (between 30% and 60%)		B, M, S	G, J, O, R
Strong decrease (Between 70% and 100%)		F, N, U, T	D, V

The choice of spreading equipment also includes the choice of techniques for depositing and/or burying digestate. In our surveys, all but one farmer used a dribble bar to limit ammonia volatilization; most bought this equipment when the AD was installed. The farmer (I) who did not invest in a dribble bar did so because he prefers smaller, less expensive equipment, even if it means losing nitrogen through volatilization. Two farmers spoke about problems with clogged pipes (W, H): H prefers to use splash plate spreading in winter, which avoids the risk of frozen digestate clogging the pipes. Eighteen out of 21 farmers, however, have no specific digestate burying equipment, because: (i) it is too expensive (nine farmers); (ii) it requires too much power, so would require reinvestment in a new tractor (ten farmers); (iii) it spreads over a smaller width, so would require more passes over the field (ten farmers); or (iv) it is not practical for spreading on grassland (S). Seven of these 18 farmers plough the digestate into the land quickly (just after or on the same day) when spreading before sowing by tilling (stubble cultivator, disc or harrow), to limit nitrogen losses. The work schedule may delay soil preparation, as in the case of farmer M, who harrows when he has available manpower. The last three farmers (C, Q, T) have invested in equipment that can tow a burying ramp and has a high work rate, with the goal of reducing nitrogen losses. All three had sufficient manpower to manage spreading and the economic capacity to invest in this equipment.

3.3. Changes in forage and permanent grasslands management

With the development of AD, six farmers (A, B, E, G, K, J) have decided to produce more fodder crops (maize, temporary meadows) and to stockpile more in anticipation of potential drought: these farmers report that if stockpiles are not used in livestock farming a last-resort economic outlet exists in AD. By guaranteeing a way to valorize plant biomass, AD gives these farmers greater flexibility in forage management.

"This year we made a rye-clover mixture to make a second-cut clover. Depending on forage stocks, the rye may or may not be used for AD" (Farmer K).

Conversely, other farmers (B, C, H, J, M) used the crops planned for AD as animal feed. While other farmers (A, K, B, J, Q, R) considered that they could afford to buy external maize or other products for AD - which is less the case for livestock farming. They therefore prioritize the use of their own farm-grown crops for livestock production. Other farmers (K, O), due to repeated droughts and low ECC and corn production, buy corn silage to supplement their AD crops.

"Initially intended for AD, the rye has been partly conserved for cows (5ha). The sorghum produced in 2022 will also be used primarily for cows, depending on needs. AD still requires the purchase of silage maize" (Farmer M)

More broadly, the arrival of AD is bringing about changes on farms that are influencing the management of permanent grasslands. In the Vosges and Bas-Rhin areas, farmers say that they fertilize permanent grasslands more than before AD. The farmers who significantly increased their grassland fertilization were those who had previously fertilized little (A, E, J, K, T, W) with slurry/manure, and had now started to fertilize with digestate. Other farmers who used to fertilize with mineral nitrogen (between 15 and 65kgN/ha) have also increased their fertilization (B, C, H, M, S). They fertilize more because the meadows are easily spreadable before winter, when the digestate pit must be emptied (see 3.2). This change in fertilization has resulted in an increase in grass yields, noted by 12 farmers, and consequently a change in grassland management and grass consumption strategies for some of these farmers:

C and J now sell more grass.
A, H, I and K have ploughed grassland areas to produce more cash crops, for livestock and for AD.
A, B, C, D, I and K use their surplus grass from permanent grassland for AD, generally the 2nd and 3rd cuts, which are of poorer quality for cows.
Some farmers (E, G, H, J) also use temporary grassland for AD.

Behind these different changes in practices, we can identify two important drivers:

Competition or synergy between AD and livestock farming: The economic attractiveness of anaerobic digestion is a key factor in encouraging farmers to adopt AD. Seven farmers said that for the same amount of work, an AD unit is more profitable than livestock. Changes in forage management practices depend on the economic choices made by farmers around the adoption of these activities, and on the economic benefits delivered by AD. Some farmers have made livestock farming a priority: they emphasize their attachment to the livestock profession and a desire to maintain these activities, even if there would be greater economic benefit in prioritizing AD feeding (J, B, O). Some farmers were initially reluctant to use corn or other crops for AD, but ultimately decided to do so. Other farmers plan to prioritize AD over livestock farming or the production of cash crops (I, K), because of economic considerations. Other farmers have also made the financial decision to invest in AD instead of livestock: C and E have disposed of beef finishing units to devote more resources (fodder and labour) to AD.
Digestate that can be used to intensify permanent grassland: AD introduces a new organic fertilizer to the farm that can easily be used on permanent grassland. As discussed in section 3.2, spring spreading constraints mean that autumn spreading on grassland is sometimes favoured by farmers, enabling them to intensify forage production. AD is therefore indirectly changing grassland management practices, the composition of animal feed and land use.

4.1 Understanding changes in practices involves considering the agency of farmers and the dynamics of farming systems.

As discussed in the introduction, there has been little research into the influence of AD on farming practices that also consider the mechanisms of systemic changes at the farm level.

First, we showed that the evolution of the organization of farm activities plays a role in the development of a diversity of practices. These results are in line with the few studies that have highlighted that the creation of AD on a farm has a major influence on its socio-economic organization (Emmann et al. 2013; Carrosio 2014; Grouiez et al. 2020). The synergies or competition between livestock rearing and AD on forage management illustrate the importance of considering interactions between farm activities to assess AD impacts. Some mechanisms have been identified, such as the increase or loss of forage autonomy (Solagro 2018), and the increase in animal husbandry (Carrosio 2014), while structural synergies between AD and organic farming have already been studied in Germany (Siegmeier et al. 2015). Our empirical work also shows that digestate production on AD farms can facilitate the transition to organic farming. However, AD raises the question of closing the nitrogen cycle, an issue that is not tackled in the scientific literature. If an AD unit on an organic farm is fed at least in part by products from conventional farms, then the synergy between organic farming and AD depends indirectly on the use of mineral fertilizers on these conventional farms. These circumstances may not encourage the closing of the nitrogen cycle with the development of legume crops (as a main or cover crop). At the territorial level, to our knowledge there has been no research into the regional dynamics of AD development, and how this can influence farm practices. We show that the availability of methanogenic feedstock on the territory can influence the evolution of cropping systems. This result is in line with (Cadiou 2023), who showed that a rapid increase in the number of AD units in a territory could create competition among farmers for access to feedstock (agro-industrial by-products, manure from surrounding farms, maize).

Secondly, regarding digestate spreading, we have shown that farm characteristics (field size, economic resources, farmer knowledge, manpower) make certain technical solutions either beneficial or feasible: the choice of spreading equipment and techniques depends on a multiplicity of factors linked to the farm, which are independent of the AD system. On this subject, our results converge with those of (Carton and Levavasseur 2022) and (Markard et al. 2016), and with the literature on farming system research (Ingram 2008; Toffolini et al. 2017), which show that choices of practices depend very much on a farmer’s previous knowledge and practices, and not only on the best available or recommended technical solutions. Farmers may also pursue diverse farm management objectives (maintenance of livestock, increased income, better allocation of work time etc.) that open up additional digestate management options. For example, some farmers view digestate as a cumbersome by-product that requires a lot of work, while for others (such as organic farmers), digestate is a new fertilization opportunity that offers economic gains and greater autonomy. As a result, the nitrogen in digestate would be used inefficiently by the former, while the latter would opt for practices that optimize nitrogen use. In this way, a better understanding of the agency of AD farmers can help identify the obstacles and levers to good practices. In fact, our results take issue with the hypotheses of economic rationality and technique optimization - which are established in the technology development literature

(Geels and Smith 2000; Wangel 2011) – by highlighting the importance of the diversity of situations faced by farmers and their motivations. Thus, considering the diversity of farms and the agency of farmers, we show that actual practices can be more varied than previously documented. These indirect mechanisms are little anticipated in assessment studies (Cadiou et al. 2023) while they appear to influence the agri-environmental effects of AD to varying degrees.

These results suggest that AD sustainable development needs to involve more specific support for agricultural situations, and for the territorial context in which anaerobic digestion is being developed. By understanding the farmer's rationality, farming advisory services could play a major role in the sustainable development of biogas plants.

4.2. The environmental impacts on the farms surveyed vary considerably.

Assessed against the scientific literature, this diversity of practices shows that the agri-environmental balance of AD can vary greatly from farm to farm. There is a large volume of literature on energy cover crops and their benefits and risks for the agri-environment (Beillouin et al. 2021; Launay 2023). Cover cropping can have positive impacts on plot biodiversity, soil fertility, soil carbon storage and diseases, as well as weed and pest management. It can also lead to negatives such as reduced groundwater recharge and the need for increased nitrogen inputs. First, we have shown that although ECC was a common option for supplying the AD units, not all farmers decided to develop this crop on their farms. Among the farmers that cultivate ECC, they have adopted a diversity of practices (fertilization, species choice, acreage). We have identified two trends in crop rotation evolution, which have already been described in some empirical studies. The first trend is the development of winter energy crops in double cropping systems as observed in other French region (Carton and Levavasseur 2022), and as promoted in other countries like Austria (Szerencsits et al. 2015). These cropping systems have advantages in terms of soil cover and can help store more carbon in the soil (Launay et al. 2020; Carton and Levavasseur 2022; Malet 2022). However, the choice of ECC species can lead to a reduction in the diversity of crops with an increase in the proportion of grasses (Carton and Levavasseur 2022). In addition, ECC require additional water, which for some farmers means a drop in the yield of the main crop that follows (Launay et al. 2022). Ultimately, the magnitude of these effects will depend on a farmer’s technical management skills, the acreage concerned (see Table 3) and production objectives. The second trend is the development of maize, which is an excellent crop in terms of energy produced per hectare, whose area is frequently increasing in regions where biogas plants are being developed (Herrmann 2013; Lüker-Jans et al. 2017; Vergara and Lakes 2019; Ruf et al. 2021; Levavasseur et al. 2023). According to our 2021 surveys, maize is an economically attractive crop for AD in France, however, the increase in maize acreage is much less than that observed in Germany. In any case, conventional maize growing in the studied regions has no major agri-environmental benefit and tends to perpetuate conventional cultivation practices with synthetic input use, as also shown in the Ile-de-France region by Carton and Levavasseur (2022). However, we have also shown that some farmers make major changes to their crop rotations in relation to their conversion to organic farming. In this case, AD is a driver of legume reintroduction, it reduces the use of pesticides and brings diversification to the rotation. Outside of organic farming, on the surveyed farms, AD does not appear to be a direct lever of legume reintroduction through cover crops. Some technical and scientific literature on (energy) cover crops assess the value of choosing legumes to improve farm GHG balance (Stinner 2015) and nitrogen management (Stinner et al. 2018). (Marsac et al. 2019) have also shown that a legume association (up to 40%) with cereal is possible with no yield loss for the cover crop. But we have not observed the drivers for the development of these practices. The cultivation practices and evolution pathways of the farms studied are related to diverse environmental impacts and benefits. The “best practices” with regard to the cultivation of cover crops, which allow crop diversification and the reintroduction of legumes, are not often implemented, as a farmer’s strategy may involve the selection of other practices.

The literature on digestate documents the benefits and technical conditions of optimized fertilization. Optimized nitrogen fertilization means optimizing chemical and physical fertility and minimizing nutrient losses to water and air. Therefore, in addition to the substitution of synthetic nitrogen, good spreading practices include: application according to the needs of the crop (at the end of winter and in spring for cereals and oilseed rape, before planting or during the first six to eight weeks for maize); equipment that limits nitrogen volatilization (using a dribble bar and burying digestate immediately after spreading); limiting compaction (monitoring the weight of the tank, using remote inflation, “tank-free” spreading) (Lukehurst et al. 2010; Severin et al. 2016; Nicholson et al. 2017, 2018; Carton and Bulcke 2021). In the literature, agri-environmental assessments of biogas plants are often carried out on the assumption that these conditions are met (Vaneeckhaute et al. 2018; Grillo et al. 2021; Moinard 2021; Esnouf et al. 2021; Cadiou et al. 2023; Caquet et al. 2024). However, we have shown that these conditions are not always met, and sometimes cannot be met by farmers. Varying responses to spreading constraints lead to a diversity of fertilization practices and different ways of implementing recommended practices to optimize the use of digestate. The obstacles mentioned by the farmers (insufficient soil bearing capacity, cost of spreading equipment, work schedule burden) lead to varying degrees of substitutions of mineral nitrogen with digestate, ranging from very low substitution to total replacement of the mineral nitrogen consumed. These results testify to the possible discrepancies between practical implementation and theoretical "optimized" projections.

From an environmental perspective, if digestate feedstocks are not used to replace synthetic nitrogen, then a farm will develop a nitrogen surplus, which increases the pollution risk (group 1). Conversely, reductions in the purchase of mineral N, being replaced by digestate fertilization for crops (group 2: farms with reductions of between 30% and 60%), improve the agri-environmental balance of farms. On these farms, the digestion of agro-industrial feedstocks and bio-waste offers an opportunity to establish a circular economy. However, easy access to external feedstocks rich in organic nitrogen could hinder the reintroduction of nitrogen-fixing plants into rotations.

The combination of organic farming and anaerobic digestion (farms with savings between − 70% et -100%) may help to promote nitrogen circularity if the farm manages to complete its nitrogen cycle. Organic conversion appears to be a strong driver for the reintroduction of legumes, to lengthen the rotation and manage weed populations. However, the farms we surveyed also show that two out of three organic farmers base their production on the import of external nitrogen. As (Dumont et al. 2020) and (Nowak et al. 2015) have shown, assessing the sustainability of these systems requires quantifying the dependence of organic farming on conventional farming. Regarding soil fertility, spreading digestate in spring can increase the risk of soil compaction, as it tends to increase machinery traffic on crops and grasslands, as well as the weight of this machinery. Soil compaction affects the ecological functioning of soil (Keller and Or 2022), reduces fertilizer efficiency and yield (Meynard et al. 1981) and increases denitrification processes and N₂O emissions (Sitaula et al. 2000). The issue of soil compaction is still poorly addressed empirically in the literature, but our qualitative results are consistent with the few modelling works on the subject (Ruf et al. 2021). In addition, we show that these compaction risks can vary greatly from one farmer to another, depending on whether they are able to invest in certain technical solutions (tank-free spreader, "low-pressure" tyres, decompaction tools) recommended in the literature (Carton and Bulcke 2021).

The literature on the impacts of AD on permanent grassland is poor in France and in Europe. In Germany, Lupp et al. (2014) showed that under AD development - and under the policy framework of the time - the need for biomass and increased grassland yields can lead farmers to plough permanent grasslands. The ploughing of permanent grassland in connection with AD has not been shown to be a significant phenomenon in France at the national level (Levavasseur et al. 2023), but our results show that this situation does occur, driven by the same reasons as in Germany. Since 2013, grassland ploughing has been subject to regulation at the European level (European Parliament and Council 2013). This regulation is linked to unfavourable consequences resulting from land conversions for biodiversity and soil carbon storage (Tang et al. 2020).

In France, one argument for developing AD is that it could support the maintenance of permanent grassland (and all of its environmental benefits on biodiversity and carbon storage): in a context of decreasing livestock, the digestion of grass could economically justify grassland conservation (Couturier et al. 2016). However, this mechanism has not been empirically assessed and should be the subject of further study.

We have also observed an intensification in the management of permanent grasslands on most livestock farms. The increase in digestate fertilization can stimulate grass production. This grassland intensification, by promoting farm protein autonomy, can lower the consumption of animal concentrates. Indirectly it can also improve the GHG balance of feed since animal concentrates have a poor carbon footprint (Boerema et al. 2016). But this intensification in fertilization can also lead to a reduction of species biodiversity (Plantureux et al. 2005; Pärtel et al. 2015). Here again, we can see that AD development on farms can stimulate a variety of impacts, most of which are poorly documented.

Our sample is not representative of the diversity of French farms that have adopted AD, but it shows that the environmental impacts of AD can be far more diverse than has been documented and assessed to date. According to the scientific literature, technically speaking, AD can be compatible with sustainable agriculture in terms of a range of issues (sustainable nitrogen management, greenhouse gases, soil carbon storage), however, as we have shown, the necessary conditions to attain the best environmental balance are not always met. These results converge with other empirical studies in France (SOLAGRO et al. 2018; Carton and Levavasseur 2022).

So we can assume that the environmental impact of AD depends more on the pre-existing practices, production factors and the norms of the farming systems in which AD is developed, rather than on the AD technology itself (Markard et al. 2016; Cadiou 2023). AD thus appears to be an innovation compatible with the intensive farming regime that dominates in France for arable crops. This regime is characterized by the pursuit of high yields, is specialized in a small number of species, and relies heavily on synthetic inputs (Guichard et al. 2017; Meynard et al. 2018). But AD also appears compatible with organic farming, which represents a form of sustainable agriculture. This raises the question of the right socio-technical and socio-political conditions for the sustainable development of AD.

4.3 Assessing the sustainability of practices must consider the dynamics of farming systems and the agency of farmers.

We have therefore shown that AD can induce a diversity of mechanisms on farms, leading to a range of agri-environmental impacts. The Farming system research framework is a good way of grasping the effects of AD on farming practices, moving away from a technical approach that focuses on the direct benefits and risks of AD technology. This research framework takes into consideration the interactions between practices, and therefore enables us to highlight issues that have been little addressed, such as the impacts of digestate fertilization on grassland biodiversity. It also accounts for different AD management strategies that lead to different impacts, which can be developed depending on the agency of the farmer.

Conducting an impact assessment approach therefore requires 1/ documenting the actual practices of farmers in terms of managing AD feedstock and digestate; 2/ documenting the impacts of AD on other farm activities, and even on neighboring farms; and 3/ assessing their agri-environmental implications based on a battery of indicators chosen according to the evaluators' expectations, as for example the IDEA (Zahm et al. 2018). These sustainability indicators must be adapted to the new practices developed by farmers. During these three phases, particular attention must be paid to systemic changes, which may involve more virtuous or less virtuous practices overall (Byerlee et al. 1982; Doré et al. 1997). To make this kind of assessment more actionable, for example to support public policy making or farming advisory services, then such assessments could be supplemented by an analysis of the underlying logic behind farm changes.

This approach can be developed by mobilizing the tools of agronomic diagnosis that aim to reconstruct the complex direct and indirect links between practices and performance. Indicators can be used to identify agronomic, environmental, and economic benefits and risks, but they do not tell us how practices should evolve (Meynard and David 1992; Doré et al. 1997). Thus, an agronomic diagnosis would provide a better understanding of the role of biogas in maintaining or changing certain practices and the need to think about the transition of the farm to optimize the impacts associated with biogas.

These principles could be the basis for new research on the AD sustainability, but could also support the assessment studies conducted by R&D organisms, such as Chambers of Agriculture or technical institutes. This would help to improve understanding of the levers and constraints that influence the way that AD can lead to sustainable changes in practices.

Our results validate the hypothesis presented at the beginning of the article: the agri-environmental sustainability of AD depends on complex systemic effects farm-level effects, that influence changes in practices in different ways. Consequently, AD induces a diversity of impacts depending on the management strategies and characteristics of each farm. Agri-environmental impacts related to these indirect mechanisms remain insufficiently documented in the literature even though they can significantly modify the agri-environmental balance of AD. To better assess the impact of biogas on agriculture, our results should be complemented by empirical studies in other regions, which would enable us to better document this diversity and identify the most representative practices and impacts.

We have identified the following three avenues for further research. First, farm dynamics are themselves caught up in territorial dynamics. AD farmer can establish links with regional stakeholders during the development of an AD project, as well as when managing the AD supply and digestate spreading. Documenting these interactions and how they influence the farmers’ practices would help us to better grasp the indirect determinants of anaerobic digestion's impacts. Second, several agri-environmental issues are still very poorly empirically documented such as soil biodiversity and soil compaction. Researching these dimensions would elucidate how to protect the fertility of soils in the future. Third, systemic assessments of the impacts of AD could form the basis for a renewal of biogas public policy. Considering these mechanisms will lead to a better understanding of the factors driving or hampering sustainable biogas in both energy and agri-environmental terms. Our results orient public action toward establishing the conditions for adopting best practices and developing more sustainable AD systems on farms.

Conflicts of interest/Competing interests

(include appropriate disclosures): All authors have no conflicts of interest to declare that are relevant to the content of this article, and disclose financial or non-financial interests that are directly or indirectly related to this study. Dr. Jean-Marc Meynard serves as an Editor for Agronomy for Sustainable Development, but was never involved in the assessment of this article. In accordance with indexing service guidelines, he is permitted to submit manuscripts to the journal.

Ethics approval

(include appropriate approvals or waivers): The study was performed in accordance with the ethical standards as laid down in the 1964 Declaration of Helsinki.

Consent to participate

(include appropriate statements): Informed consent has been obtained from all human participants involved in this study

Consent for publication

(include appropriate statements): Consent for publication has been obtained from all individuals whose data is included in this study.

Funding:

This work was supported by ADEME (French Agency for Ecological Transition); ANR (French National Agency for Research) [grant number ANR-10-LABX-14–01]; INRAE (France's National Research Institute for Agriculture, Food, and the Environment); IDDRI (Institute for Sustainable Development and International Relations) and the IdEx Université de Paris [ANR-18-IDEX-0001].

Authors' contributions

(include appropriate statements): JC designed the research study, conducted investigation and data analysis and wrote the first draft of the manuscript. JMM contributed to the study design, provided guidance throughout the research process, supervised the study and analysis and revised the manuscript for important intellectual content. PMA contributed to the study design, supervised the study and critically reviewed the manuscript. All authors read and approved the final manuscript.

Acknowledgments:

The authors would like to thank the 23 farmers who devoted their time to our surveys. The authors would also like to thank all the people in the Grand Est region who helped facilitate our fieldwork and the conduct of the interviews.

Declarations:

Availability of data and material

(see in section 13 below what is expected here): The datasets generated during and/or analyzed during the current study are not publicly available due to anonymization needs.

Code availability

(software application or custom code): Not applicable.

Bacenetti J, Sala C, Fusi A, Fiala M (2016) Agricultural anaerobic digestion plants: What LCA studies pointed out and what can be done to make them more environmentally sustainable. Appl Energy 179:669–686. https://doi.org/10.1016/j.apenergy.2016.07.029
Beausang C, McDonnell K, Murphy F (2021) Assessing the environmental sustainability of grass silage and cattle slurry for biogas production. J Clean Prod 298:126838. https://doi.org/10.1016/j.jclepro.2021.126838
Beillouin D, Pelzer E, Baranger E et al (2021) Diversifying cropping sequence reduces nitrogen leaching risks. Field Crops Res 272. https://doi.org/10.1016/j.fcr.2021.108268
Biernacki P, Waldorf D (1981) Snowball Sampling: Problems and Techniques of Chain Referral Sampling. Sociol Methods Res 10:141–163. https://doi.org/10.1177/004912418101000205
Biggs SD (1985) A farming systems approach: Some unanswered questions. Agric Adm 18:1–12. https://doi.org/10.1016/0309-586X(85)90037-8
Blumenstein B, Siegmeier T, Selsam F, Möller D (2018) A case of sustainable intensification: Stochastic farm budget optimization considering internal economic benefits of biogas production in organic agriculture. Agric Syst 159:78–92. https://doi.org/10.1016/j.agsy.2017.10.016
Boerema A, Peeters A, Swolfs S et al (2016) Soybean Trade: Balancing Environmental and Socio-Economic Impacts of an Intercontinental Market. PLoS ONE 11:e0155222. https://doi.org/10.1371/journal.pone.0155222
Britz W, Delzeit R (2013) The impact of German biogas production on European and global agricultural markets, land use and the environment. Energy Policy 62:1268–1275. https://doi.org/10.1016/j.enpol.2013.06.123
Byerlee D, Harrington L, Winkelmann DL (1982) Farming Systems Research: Issues in Research Strategy and Technology Design. Am J Agric Econ 64:897–904. https://doi.org/10.2307/1240753
Cadiou J (2023) Le déploiement de la politique de méthanisation agricole en France. implications pour la transition agroécologique
Cadiou J, Aubert P-M, Meynard J-M (2023) The importance of considering agricultural dynamics when discussing agro-environmental sustainability in futures studies of biogas. Futures 153:103218. https://doi.org/10.1016/j.futures.2023.103218
Caquet T, Axelos M, Soussana J-F et al (2024) Enjeux agronomiques, techniques et économiques d’une mobilisation accrue des différents gisements de biomasse et de leur transformation en bioénergies. https://doi.org/10.17180/CVM4-AK69
Carrosio G (2014) Energy production from biogas in the Italian countryside: Modernization vs. repeasantization. Biomass Bioenergy 70:141–148. https://doi.org/10.1016/j.biombioe.2014.09.002
Carton S, Bulcke Q (2021) L’utilisation des digestats en agriculture: Les bonnes pratiques à mettre en oeuvre. https://methasynergie.fr/guide-lutilisation-des-digestats-en-agriculture-les-bonnes-pratiques-a-mettre-en-oeuvre/. Accessed 7 Jan 2022
Carton S, Levavasseur F (2022) Performances agronomiques et environnementales de la méthanisation agricole dans un contexte de grandes cultures céréalières (sans élevage) et recommandations de bonnes pratiques. Rapp Étude Command Par Ministère L’Agriculture. L’Alimentation 84
Cavicchi B (2016) Sustainability that backfires: the case of biogas in Emilia Romagna. Environ Innov Soc Transit 21:13–27. https://doi.org/10.1016/j.eist.2016.02.001
Clements LJ, Salter AM, Banks CJ, Poppy GM (2012) The usability of digestate in organic farming. Water Sci Technol 66:1864–1870. https://doi.org/10.2166/wst.2012.389
Cochet H (2012) The systeme agraire concept in francophone peasant studies. Geoforum 43:128–136. https://doi.org/10.1016/j.geoforum.2011.04.002
Cochet H, Devienne S, Dufumier M (2007) L’agriculture comparée, une discipline de synthèse ? Économie Rurale 99–112. https://doi.org/10.4000/economierurale.2043
Couturier C, Charru M, Doublet S, Pointereau P (2016) Scénario Afterres 2050. https://afterres2050.solagro.org/wp-content/uploads/2015/11/Solagro_afterres2050-v2-web.pdf. Accessed 9 Sep 2023
Darnhofer I, Gibbon D, Dedieu B (eds) (2012) Farming Systems Research into the 21st Century: The New Dynamic. Springer Netherlands, Dordrecht
Doré T, Sebillotte M, Meynard JM (1997) A diagnostic method for assessing regional variations in crop yield. Agric Syst 54:169–188. https://doi.org/10.1016/S0308-521X(96)00084-4
Dumont AM, Gasselin P, Baret PV (2020) Transitions in agriculture: Three frameworks highlighting coexistence between a new agroecological configuration and an old, organic and conventional configuration of vegetable production in Wallonia (Belgium). Geoforum 108:98–109. https://doi.org/10.1016/j.geoforum.2019.11.018
Emmann CH, Guenther-Lübbers W, Theuvsen L (2013) Impacts of Biogas Production on the Production Factors Land and Labour – Current Effects, Possible Consequences and Further Research Needs. 13. https://doi.org/10.22004/ag.econ.164768
Esnouf A, Brockmann D, Cresson R (2021) Analyse du Cycle de Vie du BIOMETHANE issu de ressources agricoles - Rapport d’ACV. https://www.inrae.fr/sites/default/files/pdf/Rapport%20ACV_Biomethane%20issu%20de%20ressources%20agricoles_INRAE%20Transfert_GRDF.pdf. Accessed 9 Sep 2023
European Parliament and Council (2013) Regulation (EU) No 1307/2013 of the European Parliament and of the Council of 17 December 2013 establishing rules for direct payments to farmers under support schemes within the framework of the common agricultural policy and repealing Council Regulation (EC) No 637/2008 and Council Regulation (EC) No 73/2009
Geels FW, Smith A (2000) Lessons and pitfalls from Failed Technology Futures: Potholes in the Road to the Future. In: Contested Futures: A sociology of prospective techno-science, Ashgate Publishing. Burlington. Singapore, Sydney, pp 129–155
Greenberg I, Kaiser M, Gunina A et al (2019) Substitution of mineral fertilizers with biogas digestate plus biochar increases physically stabilized soil carbon but not crop biomass in a field trial. Sci Total Environ S 0048969719320625. https://doi.org/10.1016/j.scitotenv.2019.05.051
Grillo F, Piccoli I, Furlanetto I et al (2021) Agro-environmental sustainability of anaerobic digestate fractions in intensive cropping systems: Insights regarding the nitrogen use efficiency and crop performance. https://doi.org/10.3390/agronomy11040745. Agronomy 11:
Grouiez P, Berthe A, Fautras M, Issehnane S (2020) Déterminants et mesure des revenus agricoles de la méthanisation et positionnement des agriculteurs dans la chaîne de valeur « biomasse-énergie » - Scientific report. https://halshs.archives-ouvertes.fr/halshs-02886217/document. Accessed 9 Sep 2023
Guichard L, Dedieu F, Jeuffroy M-H et al (2017) Le plan Ecophyto de réduction d’usage des pesticides en France: décryptage d’un échec et raisons d’espérer. Cah Agric 26:14002. https://doi.org/10.1051/cagri/2017004
Guilayn F, Jimenez J, Martel J-L et al (2019) First fertilizing-value typology of digestates: A decision-making tool for regulation. Waste Manag 86:67–79. https://doi.org/10.1016/j.wasman.2019.01.032
Handcock MS, Gile KJ (2011) COMMENT: ON THE CONCEPT OF SNOWBALL SAMPLING. Sociol Methodol 41:367–371
Herrmann A (2013) Biogas Production from Maize: Current State, Challenges and Prospects. 2. Agronomic and Environmental Aspects. BioEnergy Res 6:372–387. https://doi.org/10.1007/s12155-012-9227-x
Hijazi O, Munro S, Zerhusen B, Effenberger M (2016) Review of life cycle assessment for biogas production in Europe. Renew Sustain Energy Rev 54:1291–1300. https://doi.org/10.1016/j.rser.2015.10.013
Ingram J (2008) Are farmers in England equipped to meet the knowledge challenge of sustainable soil management? An analysis of farmer and advisor views. J Environ Manage 86:214–228. https://doi.org/10.1016/j.jenvman.2006.12.036
Ingrao C, Bacenetti J, Ioppolo G, Messineo A (2019) Energy and Environmental Assessments of Agro-biogas Supply Chains for Energy Generation: A Comprehensive Review. In: Basosi R, Cellura M, Longo S, Parisi ML (eds) Life Cycle Assessment of Energy Systems and Sustainable Energy Technologies: The Italian Experience. Springer International Publishing, Cham, pp 99–117
Keller T, Or D (2022) Farm vehicles approaching weights of sauropods exceed safe mechanical limits for soil functioning. Proc Natl Acad Sci 119:e2117699119. https://doi.org/10.1073/pnas.2117699119
Koszel M, Lorencowicz E (2015) Agricultural Use of Biogas Digestate as a Replacement Fertilizers. Agric Agric Sci Procedia 7:119–124. https://doi.org/10.1016/j.aaspro.2015.12.004
Launay C (2023) Insertion of energy cover crops in cropping systems in France: multi-scale assessment of potential production and water-nitrogen-carbon impacts
Launay C, Crépeau M, Girault R et al (2020) MéthaPolSol, impacts de l’introduction de méthaniseurs dans un territoire sur les stratégies de fertilisation des cultures et leurs conséquences sur les dynamiques du carbone et de l’azote dans les sols: cas de la plaine de Versailles. In: JRI2020 ATEE Toulouse Fr. https://hal.inrae.fr/hal-02951996. Accessed 9 Sep 2023
Launay C, Houot S, Frédéric S et al (2022) Incorporating energy cover crops for biogas production into agricultural systems: benefits and environmental impacts. A review. Agron Sustain Dev 42:57. https://doi.org/10.1007/s13593-022-00790-8
Levavasseur F, Martin L, Boros L et al (2023) Land cover changes with the development of anaerobic digestion for biogas production in France. GCB Bioenergy 15:630–641. https://doi.org/10.1111/gcbb.13042
Lukehurst CT, Frost P, Seadi TA (2010) Utilization of digestate from biogas plants as biofertiliser. https://task37.ieabioenergy.com/wp-content/uploads/sites/32/2022/02/Digestate_Brochure_Revised_12-2010.pdf. Accessed 9 Sep 2022
Lüker-Jans N, Simmering D, Otte A (2017) The impact of biogas plants on regional dynamics of permanent grassland and maize area—The example of Hesse, Germany (2005–2010). Agric Ecosyst Environ 241:24–38. https://doi.org/10.1016/j.agee.2017.02.023
Lupp G, Steinhäußer R, Starick A et al (2014) Forcing Germany’s renewable energy targets by increased energy crop production: A challenge for regulation to secure sustainable land use practices. Land Use Policy 36:296–306. https://doi.org/10.1016/j.landusepol.2013.08.012
Malet N (2022) Retour au sol ou méthanisation agricole: quelle est la stratégie de gestion de la biomasse la plus efficace pour atténuer les émissions de CO2 ?
Markard J, Wirth S, Truffer B (2016) Institutional dynamics and technology legitimacy – A framework and a case study on biogas technology. Res Policy 45:330–344. https://doi.org/10.1016/j.respol.2015.10.009
Marsac S, Heredia M, Bazet M et al (2019) Optimisation de la mobilisation de CIVE pour la méthanisation dans les systèmes d’exploitation. Nicolas Delaye, Robert Trochard, Hélène Lagrange, Caroline Quod, Eve-Anna Sanner. https://librairie.ademe.fr/cadic/4557/opticive_optimisation_methanisation__cive_rapport.pdf. Accessed 9 Sep 2022
Meynard J-M, Boiffin J, Caneill J, Sebillotte M (1981) Elaboration du rendement et fertilisation azotée du blé d’hiver en Champagne crayeuse II. - Types de réponse à la fumure azotée et application de la méthode du bilan prévisionnel. Agronomie 1:795–806. https://doi.org/10.1051/agro:19810912
Meynard J-M, Charrier F, Fares M et al (2018) Socio-technical lock-in hinders crop diversification in France. Agron Sustain Dev 38. https://doi.org/10.1007/s13593-018-0535-1
Meynard J-M, David G (1992) Diagnostic de l’élaboration du rendement des cultures. Cah Agric 1(1):9–19
Meynard J-M, Doré T, Habib R (2001) L’évaluation et la conception de systèmes de culture pour une agriculture durable. Comptes Rendus Académie Agric Fr 87:223–236
Moinard V (2021) Conséquences de l’introduction de la méthanisation dans une exploitation de polyculture-élevage sur les cycles du carbone et de l’azote. Combinaison de l’expérimentation et de la modélisation à l’échelle de la ferme
Möller K (2015) Effects of anaerobic digestion on soil carbon and nitrogen turnover, N emissions, and soil biological activity. A review. Agron Sustain Dev 35:1021–1041. https://doi.org/10.1007/s13593-015-0284-3
Nicholson F, Bhogal A, Cardenas L et al (2017) Nitrogen losses to the environment following food based digestate and compost applications to agricultural land. Environ Pollut 228:504–516. https://doi.org/10.1016/j.envpol.2017.05.023
Nicholson F, Bhogal A, Rollett A et al (2018) Precision application techniques reduce ammonia emissions following food based digestate applications to grassland. Nutr Cycl Agroecosystems 110:151–159. https://doi.org/10.1007/s10705-017-9884-4
Nkoa R (2014) Agricultural benefits and environmental risks of soil fertilization with anaerobic digestates: a review. Agron Sustain Dev 34:473–492. https://doi.org/10.1007/s13593-013-0196-z
Nowak B, Nesme T, David C, Pellerin S (2015) Nutrient recycling in organic farming is related to diversity in farm types at the local level. Agric Ecosyst Environ 204:17–26. https://doi.org/10.1016/j.agee.2015.02.010
Osty P-L, Lardon S, de Sainte-Marie C (1998) Comment analyser les transformations de l’activité productrice des agriculteurs ? Propositions à partir des systèmes techniques de production. Études Rech Sur Systèmes Agraires Dév 397–413
Paolini V, Petracchini F, Segreto M et al (2018) Environmental impact of biogas: A short review of current knowledge. J Environ Sci Health Part A 53:899–906. https://doi.org/10.1080/10934529.2018.1459076
Pärtel B, Sammul (2015) Biodiversity in temperate European grasslands: origin and conservation. Grasslande Sciences in Europe
Plantureux S, Peeters A, McCracken D (2005) Biodiversity in intensive grasslands: Effect of management, improvement and challenges. Agron Res 3:153–164
Purswani J, Llorente CP (2021) Nitrification and Denitrification Processes: Environmental Impacts. In: Nitrogen Cycle. CRC
Quakernack R, Pacholski A, Techow A et al (2012) Ammonia volatilization and yield response of energy crops after fertilization with biogas residues in a coastal marsh of Northern Germany. Agric Ecosyst Environ 160:66–74. https://doi.org/10.1016/j.agee.2011.05.030
Räbiger T, Andres M, Hegewald H et al (2020) Indirect nitrous oxide emissions from oilseed rape cropping systems by NH3 volatilization and nitrate leaching as affected by nitrogen source, N rate and site conditions. Eur J Agron 116:126039. https://doi.org/10.1016/j.eja.2020.126039
Ruf T, Gilcher M, Udelhoven T, Emmerling C (2021) Implications of Bioenergy Cropping for Soil: Remote Sensing Identification of Silage Maize Cultivation and Risk Assessment Concerning Soil Erosion and Compaction. Land 10:128. https://doi.org/10.3390/land10020128
Sadet-Bourgeteau S, Maron P-A, Dijon A, Rev (2020) AES 10 – 1 Agronomie et méthanisation:4
Sebillotte M (1974) Agronomie et agriculture: essai d’analyse des tâches de l’agronome. Série Biol 24:3–25
Severin M, Fuß R, Well R et al (2016) Greenhouse gas emissions after application of digestate: short-term effects of nitrification inhibitor and application technique effects. Arch Agron Soil Sci 62:1007–1020. https://doi.org/10.1080/03650340.2015.1110575
Siegmeier T, Blumenstein B, Möller D (2015) Farm biogas production in organic agriculture: System implications. Agric Syst 139:196–209. https://doi.org/10.1016/j.agsy.2015.07.006
Sitaula BK, Hansen S, Sitaula JIB, Bakken LR (2000) Effects of soil compaction on N2O emission in agricultural soil. Chemosphere - Glob Change Sci 2:367–371. https://doi.org/10.1016/S1465-9972(00)00040-4
Solagro (2018) Expertise Agronomique: Résultats de MethaLAE. https://solagro.org/travaux-et-productions/references/methalae-comment-la-methanisation-peut-etre-un-levier-pour-lagroecologie. Accessed 9 Oct 2023
– SOLAGRO et al (2018) AILE, TRAME, La méthanisation, levier de l’agroécologie ? In: Solagro. https://solagro.org/travaux-et-productions/references/methalae-comment-la-methanisation-peut-etre-un-levier-pour-lagroecologie. Accessed 18 Sep 2023
Stinner PW (2015) The use of legumes as a biogas substrate - potentials for saving energy and reducing greenhouse gas emissions through symbiotic nitrogen fixation. Energy Sustain Soc 5:4. https://doi.org/10.1186/s13705-015-0034-z
Stinner PW, Deuker A, Schmalfuß T et al (2018) Perennial and Intercrop Legumes as Energy Crops for Biogas Production. In: Meena RS, Das A, Yadav GS, Lal R (eds) Legumes for Soil Health and Sustainable Management. Springer, Singapore, pp 139–171
Szerencsits M, Weinberger C, Kuderna M et al (2015) Biogas from Cover Crops and Field Residues: Effects on Soil, Water, Climate and Ecological Footprint. Int J Environ Ecol Eng 9:4. https://doi.org/10.5281/zenodo.1126493
Tang Y, Luo L, Carswell A et al (2020) Changes in soil organic carbon status and microbial community structure following biogas slurry application in a wheat-rice rotation. Sci Total Environ. https://doi.org/10.1016/j.scitotenv.2020.143786
Toffolini Q, Jeuffroy M-H, Mischler P et al (2017) Farmers’ use of fundamental knowledge to re-design their cropping systems: situated contextualisation processes. NJAS Wagening J Life Sci 80:37–47. https://doi.org/10.1016/j.njas.2016.11.004
van Midden C, Harris J, Shaw L et al (2023) The impact of anaerobic digestate on soil life: A review. Appl Soil Ecol 191:105066. https://doi.org/10.1016/j.apsoil.2023.105066
Vaneeckhaute C, Styles D, Prade T et al (2018) Closing nutrient loops through decentralized anaerobic digestion of organic residues in agricultural regions: A multi-dimensional sustainability assessment. Resour Conserv Recycl 136:110–117. https://doi.org/10.1016/j.resconrec.2018.03.027
Vergara F, Lakes T (2019) Maizification of the Landscape for Biogas Production? Humboldt. https://doi.org/10.18452/20977. -Univ Zu Berl
Wangel J (2011) Exploring social structures and agency in backcasting studies for sustainable development. Technol Forecast Soc Change 78:872–882. https://doi.org/10.1016/j.techfore.2011.03.007
Zahm F, Ugaglia AA, Barbier J-M, Boureau H (2018) Evaluating sustainability of farms: introducing a new conceptual framework based on three dimensions and five key properties relating to the sustainability of agriculture. The IDEA method version 4. 13th Eur IFSA Symp Farming Syst Facing Uncertainties Enhancing Oppor 20

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Accounting for systemic effects of anaerobic digestion development on farmers’ practices: implications for environmental assessment

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Abstract

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1. Introduction

2. Material and Methods

3. Results

3.1. Changes in crop rotations

3.2. Changes in fertilization practices

3.3. Changes in forage and permanent grasslands management

4. Discussion

4.1 Understanding changes in practices involves considering the agency of farmers and the dynamics of farming systems.

4.2. The environmental impacts on the farms surveyed vary considerably.

4.3 Assessing the sustainability of practices must consider the dynamics of farming systems and the agency of farmers.

5. Conclusion

Declarations

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