Grasslands contribute greatly to increasing soil organic carbon (SOC) storage in cropland. Models can be used to predict effects of grasslands under different soil, weather, and management conditions. We calibrated the STICS soil-crop model to simulate the grassland yield and SOC dynamics of productive-grassland systems, taking into account the contribution of roots to soil carbon (C) inputs. We used observations from three contrasted long-term (13-27 years) French experiments that included different grassland durations and management practices (i.e. temporary/permanent, mown/grazed, fertilised/unfertilised). We optimised some root parameters using a subset of treatments from one of the three sites and then evaluated STICS using the remaining treatments. STICS accurately predicted the observed dynamics of grassland root carbon and nitrogen at one site, and the predicted ranges of root variables (e.g. root:shoot ratio and root C:N ratio) at the three sites were consistent with the literature. STICS satisfactorily predicted SOC dynamics for all three sites and treatments, with low relative error (nRMSE) and bias, ranging from 2.5 to 5.9% and -2.5 to 0.6 t C ha-1, respectively. It also reproduced the observed positive effect of grasslands on SOC stocks. Although STICS slightly underpredicted effects of the sites and treatments on grassland yield and nitrogen content, these predictions were considered satisfactory. Therefore, STICS could be used to predict net C footprints of cattle farms based on productive grasslands or to develop predictive metamodels of SOM dynamics, which would support implementation of better practices in livestock farming.

Soil organic carbon (SOC) models need independent evaluation against field measurements, but those latter are rarely publicly available and harmonized. In this study, we collected and shared data from 167 agronomic treatments in 34 agronomic long-term experiments (LTEs) located in temperate croplands, allowing the evaluation of several soil organic C models such as RothC, Century, AMG, MIMICS, ICBM, Millenial, and CTOOL. The dataset includes climate data, soil properties, C inputs from crops (n = 4588 records) and organic amendments, irrigation data, monthly soil cover, as well as SOC stock measurements in the topsoil layer (n = 1328 records). Climate, soil moisture, and soil temperature data were extracted from daily climate databases. Carbon inputs from crops were calculated from observed yields and harvest index, with some harvest index values estimated, combined with crop allometric coefficients from the literature. Descriptions of LTE, agronomic treatments, methodological metadata, and a part of the code, accompanies the dataset. The dataset can be reused to evaluate single SOC models, or to evaluate an ensemble of models.

Forage crop rotations including grasslands, common in dairy systems, are known to ensure good productivity and limit the decrease of soil organic matter frequently observed in permanent arable land. A dataset was built to compile data from the Kerbernez long-term experiment, conducted in Brittany(France) from 1978 to 2005. This experiment compared the effect of different forage crop rotations fertilized with ammonium nitrate and/or slurry, with or without grassland, on forage production (quantity, quality) and changes in soil physio-chemical characteristics. These forage crop rotations were based on silage maize and cut monospecific grasslands of Italian ryegrass (Lolium multiflorum L.) or perennial ryegrass (Lolium perenne L.). More precisely, the experiment compared silage maize monocultures, rotations with silage maize and Italian ryegrass established for 6 to 18 months, and rotations with silage maize and perennial ryegrass established for three to more than 10 years. They are representative of the forage crop rotations and permanent grasslands that were at the heart of Brittany's forage revolution in the 1970s. The dataset includes information about the climate and soil conditions, the management of crops and grasslands, the evolution of topsoil organic carbon and nitrogen stocks, the inter-annual variations in crop and grassland dry matter yields and nitrogen contents. The dataset also includes characterisation of soil structural stability, particle-size soil organic matter fractions and potential soil carbon and nitrogen mineralisation at the end of the trial. It consists of fourteen csv files. This dataset can be used for a variety of purposes, namely for assessing the ability of mechanistic models to simulate soil organic matter dynamics and associated fluxes, and to estimate the influence of grassland presence and duration in forage crop rotations on such fluxes.

CONTEXT: Pollution of water resources by substances emitted by agriculture, such as nitrate, pesticides, pharmaceutical residues, fecal microorganisms and microplastics, remains a crucial issue. To assess the effectiveness of pollution-mitigation projects, water quality is usually monitored at the watershed scale. In parallel, farmers and agricultural advisors use mainly means-based indicators to assess farm sustainability. In Brittany, France, the Terres de Sources project addresses the following issues: (i) individual farmers cannot assess effects of changes in their practices using result-based water-quality indicators at the watershed outlet and (ii) means-based indicators provide little information about local water quality. OBJECTIVE: The aim of this project was to gather together researchers, farmers and advisors to build operational result-based indicators that would allow farmers to estimate on-farm emissions of pollutants to water. This article highlights the implementation and outputs of a collective design process to create such indicators. METHODS: The Knowledge-Concepts-Proposals design method was implemented to explore ideas around the initial concept of "result-based water-quality indicators at the farm scale". The method's design process has four steps, from initiation to outputs. Emerging ideas of indicators were classified in four categories and we finally selected scientifically relevant and achievable indicators. The methods for measuring these indicators were worked during the final phase of the design process. RESULTS AND CONCLUSIONS: The main results of the design process were (i) a set of result-based indicators focused on nitrate and pesticides and related to chemical measurements and bioindicators, (ii) the development of phases of "farm characterization" and "on-farm monitoring strategy" to understand water circulation, the relevant "types of water" to sample and suitable on-farm monitoring locations. In addition, breakthrough ideas have emerged but not exploited in this project; they were related to indicators based on senses and on exposure of livestock to pollutants. Despite fixation effects, the group was actively involved in the design process and in the proposal of subsequent prototype testing on farms. SIGNIFICANCE: Most of the indicators selected had already been developed at the watershed scale, but attempting to adapt them to the farm scale was an originality. Farm-scale studies help understand sources of pollutant emissions that decrease water quality. Farmers' use of comprehensive assessment tools would help encourage them to pursue their efforts in agroecological transition.

Among the many ecosystem services attributed to grasslands, that of preserving water quality figures prominently, thanks in part to the permanence of the nutrient-uptaking vegetation, the scarcity of phytosanitary treatments and the soil structuring that favor infiltration. Areas dominated by grasslands have proved to provide very good quality water, at least as long as the management practices enable most of the minerals involved to be recycled, while landscape structures associated to livestock farming (e.g hedges) are present to intercept the run-off flows. The aim of this article is to summarise the main works dealing with the role of grasslands and their soils on water quality, in order to identify the conditions under which benefits and risks are expressed. This will enable us to recall the good management practices that help maintain, or even regain, satisfactory water quality for aquatic environments and human needs.

In 2018, a participatory national workshop was organized by ITAB (Organic Food and Farming Technical Institute) and INRA (National Institute for Agricultural Research) in order to highlight issues on soils in Organic Farming (OF) systems. The objectives were: i) to identify the key research questions to be addressed on soils in OF, ii) to make it possible to facilitate network and project building from interactions between academics and stakeholders.Over 150 participants from academic and professional origins attended the workshop which was designed according to The Town Hall Meeting (THM) methodology.High level discussions among participants and panel experts ended up with a list of 20 research questions which confirmed the important lack of knowledge on that topic and the needs for research on the following issues: soils functioning with a focus on biogeochemical cycling and biological interactions; long term effects of agricultural practices, more or less specific to OF; soils protection; tools for soils diagnosis and management.

The physical, chemical and biological properties of the soil will affect plant growth and condition the sustainability of the grasslands. Thus, soil compaction due to grazing or machine traffic will result in a loss of yield, the effects being variable according to texture (more pronounced on more clayey soils) and season. On the other hand, the preservation of soil organisms and associated functions will contribute to increasing yields. On the other hand, grassland management will also impact soil properties. Thus, the introduction of grassland in the crop rotation will quickly allow, from the second year, to favor soil biodiversity (fauna, microorganisms) and their activities. More broadly, the introduction of grassland into an annual crop rotation positively influences the maintenance of soil structure and the conservation of biodiversity, without modifying water regulation. The positive effect inherited from grasslands in the rotation can be observed even three years after recultivation. The sustainability of the grasslands will be conditioned by several factors: the duration of the grassland in the rotation, grazing management (load, period), fertilization and plant diversity. Levers exist to ensure the sustainability of these temporary or permanent grassland systems.

Often, the destruction of sown grasslands is linked to a decrease in productivity and/or a change in flora over time. These evolutions are rarely objectified and are the subject of two recent research-action projects in the Great West, in which observatories of young, well-established plots were monitored for 4 years (PERPeT project) and 5 years (PTD project). The monitoring focused on the annual biomass harvested and botanical composition, in order to determine how the grasslands age according to the initial sowing, the pedoclimate and the use practices of the plots. The synthesis of the main results allows us to conclude that "it is possible to age grasslands well", that their evolution is multifactorial with climatic factors (water supply), among the main determinants, then linked to practices and soils. Several types of grasslands and evolutionary trajectories were characterized, with certain species playing an important role in these dynamics. The flora diversifies and the prairie bottom becomes balanced after 5-6 years, with a root development making the soils more resistant to trampling. Finally, these evolutions, more or less favorable in terms of quantity and quality of harvestable grass, can lead to reconsider the function of each plot in the forage system.

Grasslands, whether sown or permanent, grazed or mowed, are the basis of herbivore production systems aiming at economy and autonomy. With the uncertainties linked to climate change, to the socio-economic context, but also with regard to society's expectations in terms of ecosystem services, the sustainability of grasslands is becoming an important concern for farmers and land managers. However, the very notion of sustainability of grasslands is not explicit and needs to be clarified. Are we looking for the fact that temporary cover allows for quantitative and qualitative biomass production, or for the fact that a grassland cover can meet the farmer's objectives in the long term? This article presents some elements of reflection to better understand the objectives and expectations of the different actors, the biological components of grassland sustainability at different scales (plants, plant communities, farms), in order to better understand the keys to improving this sustainability. This panorama is an introduction to the theme "Valuing, Maintaining and Ensuring the Sustainability of Grasslands" that the papers that will be presented during these AFPF 2022 days will allow to develop, illustrate and deepen.

How can we get fanners to make grasslands a subject of technical exchanges by re -appropriate knowledge and know-how? What support would be useful for them to develop a management strategy of theirgrasslands that is consistent with their environmental conditions, their forage system and their expectations? In order to answer these questions, partners of the PEI 4ageprod SP3 PERPETproject are co-constructing a facilitation tool that will allow participants to collectively carry out a grassland diagnosis and to discuss the levers in place or to be put in place to age their grasslands well. This tool, started in response to field expectations, is being built by directly experimenting its use in grasslands with future users and beneficiaries. With a game board and support cards, it will propose 3 steps to think collectively about practices adapted to the state of the grassland, its environmental conditions and the farmer's expectations.