Edited by: Ngonidzashe Chirinda, International Center for Tropical Agriculture (CIAT), Colombia
Reviewed by: Justice Nyamangara, Marondera University of Agricultural Sciences and Technology (MUAST), Zimbabwe; Jessica Davies, Lancaster Environment Centre, Lancaster University, United Kingdom
This article was submitted to Climate-Smart Food Systems, a section of the journal Frontiers in Sustainable Food Systems
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France is a major agricultural power, characterized by a high degree of regional specialization, either in stockless cash crop farming, exporting most of its intensive cereal production, or in intensive livestock farming highly dependent on foreign feed imports. This agricultural model is characterized by wide nutrient and carbon cycle opening and severe environmental pollution. Based on the nutrient accounting GRAFS model, two contrasted scenarios for the French agricultural system at the 2050 horizon have recently been designed and evaluated for their capacity to meet both the national population's food demand and environmental standards in terms of water pollution. The first scenario (O/S, for opening and specialization) assumes the continuation of the current trends of intensification, specialization, and opening to international markets. The second one (A/R/D, for autonomy, reconnection, and demitarian diet) assumes a radical change toward organic farming with diversification of crop rotations, reconnection of crop and livestock farming, and reduction of the proportion of animal proteins in the human diet. Herein we calculate the budget of CO2 emissions and C sequestration in soils of these two scenarios compared with the current situation of the French agro-food system, by coupling the GRAFS and AMG models. These simulations reveal that the overall CO2 emissions balance of the O/S scenario is far higher than those of the A/R/D, namely because of the emissions associated with mineral fertilizer manufacture, and imported feed and mechanization of land management requiring a large amount of fossil fuel. As the organic carbon content of the soil is known to be highly path-dependent (in the sense that it is the inheritance of previous land use practices), we tested the effect of two rates of implementation of the two scenarios and evaluated the response time of the C soil store, which is of the order of two decades or more. This reveals that after about two-three decades following the implementation of a scenario, an equilibrium is reached with no more net soil C emission nor sequestration.
The 4% initiative (
The behavior of agricultural soils as a sink or source of C to the atmosphere results from the equilibrium between inputs and mineralization of humified C to the soil (Jenkinson and Rayner,
Whether the agricultural sector can be considered as having a potential for climate change mitigation through C storage in soil also depends on the C emissions generated by the use of fossil-fuel for agricultural production. Gingrich et al. (
Designing prospective scenarios for the future of the agro-food system as a whole makes it possible to consider the effects of a combination of factors on the environmental imprint of the agro-food system. Recently, several studies used this contrasted scenario building approach to investigate their consequences on the ability to feed humans while preserving ecosystems. At the global scale, Billen et al. (
In this context, here we explore the impact of two contrasted prospective scenarios designed by Billen et al. (
The same assumptions as those described by Billen et al. (
These prospective scenarios for French regional agro-food systems can be represented in terms of C fluxes with the nutrient-accounting GRAFS model (Billen et al.,
GRAFS representation of the C fluxes within the French agro-food system for the current (reference) situation in 2004–2014
The O/S scenario uses the projections made by the National Institute for Statistics and Economic Studies (INSEE;
Regarding the cropping system, the O/S scenario hypothesizes a strengthening of the current specialization of agricultural regions (Le Noë et al.,
The A/R/D scenario assumes a generalization of organic farming systems. Cropping systems are estimated based on the current literature on organic farming in different French regions (ITAB,
Similarly, the production of permanent
Ymax values for both crops and grassland in each region are considered constant over the whole period of simulation, thus neglecting possible effects of climate change on agricultural production.
Regarding
All these hypotheses regarding both scenarios bear a series of constraints that are compiled and applied to all regions using a simple Microsoft Excel VBA macro (Billen et al.,
Net emissions of C from cropland and grassland are calculated by coupling the GRAFS approach with the AMG model (Saffih-Hdadi and Mary,
Because of the slow rate of change of soil organic carbon stock (SOC) and its resulting long inertia, it is necessary to know its past dynamics to simulate the trends of the prospective scenarios. Therefore, we used the estimation of SOC trajectories in agricultural soil of French regions from 1852 to 2014 already calculated by Le Noë et al. (
The coupling of the GRAFS description of the two scenarios to the AMG model makes it possible to calculate the dynamics of SOC in cropland and grassland, assuming a gradual implementation of the scenarios starting from 2014 and reaching its final state in 2050, following a linear trajectory. The extension by 10 years of the scenarios originally designed by Billen et al. (
where net C emissions UAA is the annual average net C emissions from agricultural soil over the 2040–2050 period in region
Stock C CL/GL yr
Ha UAA2050
Carbon net emissions from agricultural soils were calculated for both scenarios (average over the 2040–2050 decade) and for the reference situation (average over the 2004–2014 period). Positive net emission indicates that agricultural soils are a source of C, either because soils release C or because of a reduction of agricultural surface leading to a decrease of the total C stock in soil. Negative net emission indicates that agricultural soils are a sink of C, either because soils accumulate C or because of an increase in agricultural surface leading to an increase of the total C stock in agricultural soil.
The details of the calculations are provided in the xls files appended as
The C-CO2 emissions related to energy consumption in agriculture includes mechanical and motorized work, building heating, mineral fertilizer manufacture, production, and transport of imported feed. We calculated these emissions based on the data provided by Doublet (
Major CO2 emissions linked to energy consumption in agriculture.
Fertilizer N manufacture | ton C-CO2 ton N−1 | 1.118 |
Fertilizer P manufacture | ton C-CO2 ton P−1 | 0.460 |
Production and transport. of imported feed | ton C-CO2 ton N imported−1 | 1.339 |
Machinery | ton C-CO2 ha UAA−1 yr−1 | 0.026 |
Energy for cropland land work | ton C-CO2 ha CL−1 yr−1 | 0.077 |
Energy for grassland land work | ton C-CO2 ha GL−1 yr−1 | 0.055 |
Energy for livestock management | ton C-CO2 LU−1 yr−1 | 0.056 |
We used these figures to estimate C-CO2 emissions related to energy consumption in agriculture in both prospective scenarios and for the current situation, assuming that no significant technical evolution would occur in both scenarios so that coefficients remain valid and C-CO2 emissions only depend on the use of mineral fertilizers, importation of feed, and cultivated and grazed surfaces. Note also that emissions related to pesticide products, irrigation, mineral K fertilizer and lime inputs were not accounted here, as they represented <10% of agricultural emissions in 2006.
The budget of net C emissions of each French region was calculated as the sum of net emissions from agricultural soils and the net emissions related to energy consumption by agriculture. A positive budget indicates that the agriculture sector is a net emitter of C-CO2 while a negative budget indicates that it is a net sink for atmospheric C-CO2 through soil sequestration.
Since the organic carbon content of the soil is known to be highly path-dependent (in the sense that it follows the inheritance of previous land use practices), we tested the effect of different rates and timing of implementation of the two scenarios and evaluated the response time of the C soil storage. To that end two alternative pathways to the same final scenarios were calculated: (i) the scenarios follow an early and rapid linear implementation for 10 years from 2014 and the systems then remain in the same configuration from 2024 to 2050; (ii) the current situation remains constant until 2040 and the scenarios are then rapidly implemented following a linear pathway from 2040 to 2050.
Both prospective scenarios and the reference level for the 2004–2014 period reveal positive net C emission budgets in agriculture at the national level. However, the extent to which the agricultural sector is a contributor of net C emissions to the atmosphere varies greatly between the three situations. The carbon budget is the highest in the current reference system, with net emissions amounting to 7.4 MtC yr−1, but is very close to the C emissions budget of the O/S scenario (6.6 MtC yr−1). By contrast, the A/R/D scenario would enable agriculture to reduce its net emissions to 2.7 MtC yr−1, more than 2.5 times lower. These values result from the balance between net emissions from agricultural soil and from energy consumption in agriculture.
In the
Main variables involved in net C emissions of the French agricultural sector (national level) for the current reference situation (2004–2014) and the two contrasted scenarios.
Change in C content in cropland (‰ yr−1) | −1.1 | 0.24 | −1.2 |
Change in C content in grassland (‰ yr−1) | −0.32 | 0.43 | −3.0 |
Change in UAA (% UAA yr−1) | −0.20 | 0 | −0.02 |
Change in cropland area (%UAA yr−1) | −0.01 | −0.04 | 0.3 |
Change in grassland area (%UAA yr−1) | −0.19 | +0.04 | −0.3 |
Net emissions from agricultural soil (MtC yr−1) | +1.4 | −0.03 | −2.4 |
Emissions for energy consumption (MtC yr−1) | +6 | +2.7 | +9 |
Net C emissions budget (MtC yr−1) | +7.4 | +2.67 | +6.6 |
In the
By contrast, in the
Analyzing results only at the national level conceals significant disparities at the regional level, strongly linked to the current specialization of agricultural regions, into either intensive livestock farming (e.g., Brittany), stockless cash crop farming (e.g., Eure) or mixed crop and livestock farming (e.g., Loire Amont), as described by Le Noë et al. (
Relative change in total usable agricultural area
Net C emissions from energy consumption in agriculture for the reference situation (2014–2014)
In the
In the
In the
A sensitivity analysis was carried out to assess the extent to which the design and hypothesis of the modeled scenarios regarding the timing and rate of the change from the current situation to one or the other scenario tested for 2050 affect the above results (
At the national level, our analysis indicates that an early and rapid change starting in 2014 and completed in 2024 would lead to higher SOC stocks in 2050 in agricultural soils in the
As far as the
Overall, this test highlights the temporary nature of C sequestration in agricultural soils: an early rapid 10 year change leads the SOC stock to reach an equilibrium with respect to the rate of humified inputs at the 2050 horizon. This equilibrium means that neither sequestration nor soil net CO2 emissions continues to occur. C sequestration in agricultural soil is therefore only a transient characteristic of a given scenario.
A scenario is by no means a prediction of the future, but simply a representation of what it could be under certain constraints. Even so, representing such a projection of a possible future in an intelligible way requires simplifying the system under study and considering only certain parameters to model, leaving aside other aspects of the system, thus limiting the model.
In the present study, it must be stressed that a major restriction to our hypothesis is the non-inclusion of forest as part of the C budget. Losses or gains of C in cropland and grassland soils represent here the combined effects of changes in SOC content in soils and changes in agricultural land surfaces. When reduction in agricultural surfaces results from extension of urbanized areas, this indeed represents an effective loss of C from the agricultural system. However, if land-use change in agriculture is linked to change in the forest area, then the estimated change in SOC stocks of agricultural soils may not correspond to net emissions of C-CO2 to the atmosphere. Purposedly, in the scenarios tested here, no expansion of cropland or grassland at the expense of forest area and no expansion of forest over agricultural land were taken into account, forest area remaining thus strictly constant in both scenarios. A deeper prospective investigation, not only into the agro-food system, but also into the overall land-use system could articulate a vision of how all land uses are related to one another in a given socio-ecological scenario.
Another restriction of this study is that it is limited to the C emissions budget and does not take into consideration non-CO2 greenhouse gas emissions by agriculture, namely methane and nitrous oxide, which also contribute to global warming. This aspect is taken into account in another paper (Garnier et al.,
Several other aspects have not been taken into account, as for instance the possible effect of soil erosion on the soil C budget. Also, by lack of robust models for predicting climate change in the next 50 years at the scale of the French regions as defined here, we only considered a gradual 1.5°C temperature increase from 2014 to 2050 with respect to the current seasonal temperature variations in each region, as estimated from the mere linear extrapolation of the trend observed in the last 20 year (Le Noë et al.,
In spite of the above limitations, our analysis of the C emissions budget reveals that the current French agricultural sector is by no means a net sink of C, as C sequestration in agricultural soils is far from compensating the CO2 emissions linked to fossil fuel combustion for mechanization, fertilizer manufacture and import of feed. The dependence of modern agriculture on fossil fuels and industrial fertilization, and its openness to distant markets, are the structural causes of this largely CO2-emitting balance.
The O/S scenario depicting a future in which these trends of opening and specialization would be continued and reinforced, even while meeting the current environmental regulation regarding fertilization, would temporarily increase C sequestration in agricultural soil, owing to a larger NPP, hence an increased C input to the soil. It does not result in a very significant decrease of the net emitting CO2 budget of agriculture, however (
The A/R/D scenario, on the other hand, represents a quite different vision of the future, based on the extension of some low-level trends already emerging today toward a more local connection between food consumption and production, and between crop and livestock farming, as well as a more frugal food regime (Billen et al.,
We can therefore conclude that a deep redesign of the structure of the agro-food system, toward more autonomy and local connection and less dependency on fossil fuel would reduce CO2 emissions by the agriculture sector. Our results also show that the role of C sequestration in agricultural soils, although quite desirable in terms of improvement of their agronomical properties, has rather limited effects for mitigating C emissions. Moreover, this effect is limited in time because it accompanies the changing period but would disappear once the SOC pool has reached its equilibrium, as clearly seen in
The present study is based entirely on the biogeochemical analysis of the two contrasted, hypothetical scenarios of the future of the French agro-food system (Billen et al.,
Unless adopting a completely deterministic view of both human and natural history in which the future could be known just as the past as far as we were able to model the systems studied (as in the famous metaphor of the Devil of Laplace, Bergson,
According to Wright (
Following the Weberian vision of the relation between science and politics (Weber,
Therefore, scientists may help advance toward that goal by conceiving transmittable and appropriable knowledge favoring an ascending transition toward more sustainability in agro-food systems and, more generally, in socio-ecological systems (Gonzalez de Molina and Toledo,
JG and GB contributed to data processing and article redaction. JL designed the paper and contributed to data processing and article redaction.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
This work has been carried out within the scope of the PIREN-Seine research projects (CNRS/AESN). Thanks are also due to the Fédération Ile-de-France de Recherche pour l'Environnement (FIRE) for providing an interdisciplinary framework that was beneficial for this work. We are very grateful to Manuel Martin (INRA, Infosol) for his valuable help and assistance in data collection from the RMQS network (
The Supplementary Material for this article can be found online at: