THE GLOBALSOILMAP PROJECT : PAST , PRESENT , FUTURE , AND NATIONAL EXAMPLES FROM FRANCE © 2018

© 2018 D. Arrouays, A. C. Richer-de-Forges, A. B. McBratney, A. E. Hartemink, B. Minasny, I. Savin, M. Grundy, J. G. B. Leenaars, L. Poggio, P. Roudier, Z. Libohova, N. J. McKenzie, H. van den Bosch, B. Kempen, V. L. Mulder, M. Lacoste, S. Chen , N. P. A. Saby, M. P. Martin, M. Román Dobarco, I. Cousin, T. Loiseau, S. Lehmann, M. Caubet, B. Lemercier, C. Walter, E. Vaudour, C. Gomez, G. Martelet, P. Krasilnikov, P. Lagacherie 13


INTRODUCTION
Soils have critical relevance to global issues, such as food and water security, climate regulation, sustainable energy, desertification and biodiversity protection (Montanarella et al., 2016).As a consequence, soil is becoming one of the top priorities for the global environmental policy agenda (Hartemink and McBratney, 2008;McBratney et al., 2014;Amundson et al., 2015).Although sustainable soil management is a global issue, appropriate actions from soil users (land use planners, farmers) require high-resolution data about soil properties.Conventional soil maps suffer from large limitations, i.e. most of them are static and often obsolete (Rossiter, 2018), are often generated at coarse scale, and can be uneasy to handle.Also, they are most often non quantitative, based upon very simplified level of soil classification, and most of them lack any quantitative estimates of soil properties.Digital Soil Mapping (DSM) (McBratney et al., 2003;Lagacherie et al., 2006;Arrouays et al., 2017a, Rossiter, 2018) has been developed as a solution to generate highresolution maps of soil properties over large areas.Two projects, Glob-alSoilMap (Arrouays et al., 2014b) and SoilGrids (Hengl et al., 2014(Hengl et al., , 2017)), presently aim at delivering the first generation of global, highresolution soil property fine grids.The former relies in a bottom-up approach (from country to globe), while the latter uses a top-down approach (a global model that predicts properties for every country).As acquiring new soil data is laborious and expensive, both projects promote the use of existing legacy and heritage soil survey data available across the world.These data are being rescued, compiled and processed into a common, consistent and harmonized dataset of relevant soil properties covering the planet's land surface (Arrouays et al., 2017b).The resulting data are then used for spatial prediction of soil attributes using ancillary spatial information.
The resulting maps are essential for scientific communities from climate and environmental modeling to decision making and sustainable resources management at a scale that is relevant to soil management.From a global policy point of view, these initiatives could bring a major contribution to the implementation of the priorities of the United Nations' Global Soil Partnership, Pillar 4, one objective of which is to deliver fine grids of soil properties all over the planet.The GlobalSoilMap initiative brings together some world scientific leaders involved in both projects.We believe that the full utilization potential of can only be realized by creating a strong link to a public policy framework to ensure meeting quality, reliability, continuity, coherence and usability requirements.In this paper, we briefly describe the GlobalSoilMap history, its present status and present achievements, and illustrate some of these with (mainly) French examples.We cite some other examples of achievements and finally discuss the future and prospects of this project, including the scientific issues still to be solved and the necessary collaboration between projects aiming at delivering similar products.

OBJECTIVES OF GLOBALSOILMAP
The GlobalSoilMap initiative aims at developing and transferring methods to improve the prediction accuracy of soil properties and their associated uncertainty, by using legacy soil data and ancillary spatial information.The objective of the GlobalSoilMap project is to provide a scientific framework to deliver fine grids of soil attributes as a consistent, spatially explicit and continuous database freely available for all.The fine grids of soil attributes will be delivered at high spatial resolution, thus applicable to both global and local applications.The specifications of the GlobalSoilMap products have been discussed collegially by a scientific consortium, and written into a detailed document based on peer-review.The specified product includes predicted values of selected key soil properties at 6 standard depth intervals (0-5, 5-15, 15-30, 30-60, 60-100 and 100-200 cm), at a global scale on a 3 arc-second support grid (approximately 90 × 90 m) along with their uncertainties.The key primary soil properties include the clay, silt and sand contents, coarse fragments, pH in water, soil organic carbon (SOC) content, effective cation exchange capacity (ECEC), soil depth to bedrock and effective root zone depth.Additional key properties, mainly derived using pedotransfer functions (PTF, see a review from, Minasny and Hartemink, 2011), include bulk density and plant-available water holding capacity.This minimal dataset may be supplemented by other soil attributes on an ad-hoc basis (e.g., P, N and S contents, electric conductivity, soil type, presence of diagnosis horizons, trace elements contents).Predictions are generated using state-of-the-art Digital Soil Mapping (DSM) techniques (McBratney et al., 2003;Grunwald et al., 2001;Minasny and McBratney, 2016;Arrouays et al., 2017a;Rossiter, 2018).The final GlobalSoilMap product aims to be outcome soil information product that can be updated iteratively, i.e. when new or additional soil profile data or environmental co-variates are available either at a countrybased or a world-based scale, updated soil maps can be quickly produced thus continuously improving the accuracy of this collaborative product.Hereby, we support data science for informed policy making by providing up to date, high-resolution soil information for practical support of planning and environmental policy frameworks.

GLOBALSOILMAP BRIEF HISTORY
A brief history of the GlobalSoilMap initiative is summarized in table 1.The initial idea came from a meeting of the International Union of Soil Sciences (IUSS) DSM Working Group in Rio de Janeiro, Brazil, 2006.Further meetings and conferences led to the publication of the first version of the specifications in 2008.In continuation, a great impulse to the project was provided by a 18 M$ grant from the Bill&Melinda Gates foundation (mainly dedicated to actions to undertake in Africa), and by the publication of a highly cited seminal paper in Science (Sanchez et al., 2009).In 2012, some changes of governance were decided during a business meeting on the occasion of another IUSS DSM Working Group in Sydney, Australia.Later that same year, a dedicated GlobalSoilMap workshop on uncertainty assessment was held in Lincoln, USA.Indeed, there are many ways to assess uncertainty, and even uncertainty on uncertainty, and this workshop led to refining the ways of assessing uncertainties of predicted values and to define four tiers level for GlobalSoil-Map products.These four tiers, and other refinements of the specifications, were discussed in detail in 2013 during the first GlobalSoilMap conference held in Orléans, France and then incorporated into the 2 nd version of the specifications.
One of the most productive years was 2014; with the organization of a dedicated symposium and a business meeting during the IUSS World Congress of Soil Sciences (WCSS) in Jeju, Korea; the publication of the book of the first GlobalSoilMap conference (Arrouays et al., 2014a), and of a very detailed and highly cited paper (Arrouays et al., 2014b); and finally an invited keynote talk in a dedicated session and open discussion organized during the IUSS DSM WG conference in Nanjing, China.This year was also characterized by the beginning of countrywide releases of products (table 1).Indeed, from 2013 to 2018, the number of national or sub-national products progressively increased, including e.g. products from Denmark, Nigeria, Scotland, continental USA, Chile and France.).The product line for sub-Saharan Africa is complete in terms of targeted soil properties.Although, these were often delivering different attributes or layer depths and a bit coarser resolution (1 km to 250 m).In 2015, the complete product for Australia was released (Grundy et al., 2015;Viscarra Rossel et al., 2015) and a new business meeting was organized in Ottawa, Canada.This business meeting showed the willingness of some new countries to join the project.
The next GlobalSoilMap business meeting took place during the IUSS DSM Working Group Conference in Aarhus, Denmark, 2016.During this meeting, it was decided that a core group (D.Arrouays, P. Roudier, A. McBratney, Z. Libohova) would prepare a motion to propose the creation of a new IUSS WG 'GlobalSoilMap', under Division 1 and Commission 1.5 of the IUSS.D. Arrouays defended this motion during the IUSS inter-congress council meeting in Rio de Janeiro (Brazil, November, 2016) and it was unanimously accepted and endorsed by the IUSS Council.In 2016, the GlobalSoilMap initiative officially received the 'honorable mention' for the international data rescue award in geosciences delivered by the Interdisciplinary Earth Data Alliance (IEDA) and Elsevier.This award was followed by an international review publication about soil data rescuing efforts in the world, involving 89 co-authors from all continents (Arrouays et al., 2017b).
In July 2017, the GlobalSoilMap international conference was organized by the V.V. Dokuchaev Soil Science Institute (Moscow, Russian Federation) and the Agrarian Technological Institute of RUDN University (Moscow, Russian Federation) under the umbrella of the IUSS, and the Soil Science Society named after V.V. Dokuchaev, with financial support from the Russian Science Foundation (Grant N°15-16-30007).This conference was very well organized and successful and stimulated the development of the project and the delivery of products in all parts of the world, especially in the former USSR republics where scientific activity in DSM is rapidly emerging.During this conference, the IUSS GlobalSoilMap WG was officially launched and had its first formal business meeting.The second book on GlobalSoilMap 'GlobalSoilMap.
Digital Soil Mapping from Country to Globe' was rapidly published (Arrouays et al., 2018).
During 2018, GlobalSoilMap was presented at various invited conferences around the world (e.g.Bahrein, Philippines, Thailand, India, Belgium, France, Korea, Brazil).A first joint business meeting of the DSM and GlobalSoilMap IUSS Working Groups was held during the WCSS in Rio de Janeiro, Brazil.During this business meeting, we decided to organize a next joint DSM and GlobalsoilMap WG conference in Chile, in March 2019.We had also sound discussions about the need to consolidate relations between the IUSS GlobalSoilMap WG and more policy-related initiatives that have a common aim, including the activities carried out under the Pillar 4 of the Global Soil Partnership (GSP) that was created under the auspices of the Food and Agricultural Organization (FAO) of the United Nations.In 2018, a large number of countries aggregated their 90-m GlobalSoilMap SOC predictions to a 1 km grid in order to give a country bottom-up input to the Global Soil Organic Carbon map initiative of the GSP.

EXAMPLES FROM FRANCE
Here, we briefly describe the development and delivery of Glob-alSoilMap products for mainland France and in some specific French regions.
The years 2013 and 2014 were mainly dedicated to rescuing and harmonizing all soil point data available for the country, and to gathering and resampling all the co-variates that were meaningful and exhaustively available over the territory to the 90-m resolution needed for the final products.Then, the soil profile properties were harmonized according to the GlobalSoilMap specifications (e.g., by using spline functions, Bishop et al., 1999)), and various prediction models were evaluated.The first available products were SOC (Mulder el al., 2016a) and total soil depth (Lacoste et al., 2016).A much more complete set of 'primary' data was then produced leading to a 2 nd version of GlobalSoilMap France (Mulder et al., 2016b).We also assessed how the relief (and mainly the slope) could affect the assessment of stocks on a regular square grid (Chen, Arrouays, 2018).As many secondary data (e.g., bulk density, available water capacity) had very scarce in situ georeferenced measurements, we then focused on developing pedo-transfer functions to predict them using more easily available data (e.g., for bulk density, Chen et al., 2018a; for available water capacity, Román Dobarco et al., 2019) We also used the GlobalSoilMap products to derive new products (e.g., Chen et al, 2018b; Román Dobarco et al. submitted) which are more directly usable by end users.We are now finalizing the AWC and BD products, and we are beginning to test new approaches for prediction of censored soil properties such e.g.soil depth.At more regional or even local scales, we tested if the use of other methods could also be used to predict other soil attributes, such as, for instance, the presence of diagnosis horizons (Richer-de-Forges et al., 2017).The use of DSMART (Odgers et al., 2014) as a tool for disaggregating/downscaling soil maps was tested in Brittany (Vincent et al., 2016), and new methods, such as Quantile Random Forest (QRF) were tested to use point data for GlobalSoilMap products in the south of France (Vaysse and Lagacherie, 2017).In the western Paris croplands, a bootstrap resampling procedure provided estimations for the uncertainty regionally and for each sample location, using a criterion of pointwise RMSE (Zaouche et al. 2017).We also explored the potential of new airborne gamma-ray measurements in some regions, and the potential of a large range of spatial and spectral resolutions of Visible and Near Infrared (400-2500 nm) imagery data (Vaudour et al., 2016;Gomez et al., 2012Gomez et al., , 2018)).Finally, we are also convinced that extending the list of GlobalSoilMap attributes will be a future necessity, and thus we have been exploring the possibility to predict new ones (e.g.soil type, phosphorus (Delmas et al., 2015), soil contaminants (Villanneau et al., 2013;Orton et al., 2013;Marchant et al., 2017), and inorganic carbon (Marchant et al., 2015)).
The French teams that are active in producing DSM methods have been grouped since 2016 into a federative project (CES Theia "Digital Soil mapping", https://www.sol-theia.org) for producing methodological advances on critical aspects of DSM (e.g. the use remote sensing data in DSM, calibration and validation procedures), promoting and diffusing DSM approaches and, in the near future, accompanying the users of GSM products.

FUTURE AND PROSPECTS
In this final section, we recap the main prospects we see for the development of GlobalSoilMap products.
From a 'technical and scientific' point of view: -There is still an enormous potential for forthcoming research and for delivering products more helpful for end users.Key here is the continuous progress in available co-variates, in their spatial, spectral and temporal coverage and resolution through remote sensing products.
-All over the world, there is still a very large amount of point soil data still to be rescued and this effort should be pursued and encouraged.
-Statistically advances are expected by exploring and implementing new models.Especially relevant are spatial-temporal models and contemporary Artificial Intelligence for handling the complex big data.
-Advances should be made and research efforts are needed on estimating the uncertainties, and even on estimating uncertainties on uncertainties (Lagacherie et al., 2019).
-Attempts to merge different model strategies and products (for instance deriving from different covariates, spatial extents, soil data sources, and models) should be made in order to get the most useful information from each of these predictions, and to identify how controlling factors may change depending on scales (Román Dobarco et al., 2017Dobarco et al., , 2019;;Caubet et al., 2019).
From a 'policy and scientific' point of view: We are now in the situation where there is a global consensus about the specifications for gridded soil information products.We have a very advanced science and technology.The technology to support the development of high resolution grids, such as IT solutions to deal with large datasets and to support fast calculation, is quickly increasing.Glob-alSoilMap is now institutionalized as the IUSS WG on GlobalSoilMap supporting considerable progress on DSM methodology and on improving the specifications.At the same time, the Global Soil Partnership which has been endorsed by the FAO member countries, provides an efficient policy mechanism to engage countries to deliver products.We believe that the full utilization potential can only be realized by creating a strong link to a public policy framework to ensure meeting quality, reliability, continuity, coherence and usability requirements.Hereby, we can support data science for informed policy making by providing up to Бюллетень Почвенного института им.В.В.Докучаева.2018.Вып.95.Dokuchaev Soil Bulletin, 2018, 95 date, high-resolution soil information for practical support of planning and environmental policy frameworks from the national to global scale.The IUSS GlobalSoilMap Working Group, and the Global Soil Partnership Pillar 4 should collaborate intimately for improving the specifications and make scientific advances, but also for capacity development for the less advanced countries.
This provides a unique opportunity to deliver sound and standardized national and global soil information products We should not miss this unique opportunity; it would be a terrible error for the future of our soils and for the world safety.