Because of tensions on fossil energy and phosphorus markets, the rise in fertilizer prices observed during the last decades may continue in the future, putting into question production pathways relying heavily on crop intensification. To evaluate how, in this context, economic choices may alter crop yields, we first construct different fertilizer price scenarios to 2050 based on an econometric relation with oil and gas prices. Other possible scenarios, such as the continuation of historical trends, are also considered. The resulting changes in fertilizer price range between +0.8% and +3.6% per year over the 2005–2050 period. These scenarios are tested in a global land-use model incorporating an endogenous representation of the land–fertilizer substitution. We find that the supply-side response to rising fertilizer prices could lower crop yields in 2050 from −6% to −13%, with a corresponding increase in global cropland area ranging between 100 and 240 Mha if the demand for food and nonfood products has to be met. The sensitivity of these results is tested with regard to assumptions on food consumption, change in potential yield and nutrient use efficiency. (Résumé d'auteur

Abstract.Interactions between food demand, biomass energy and forest preservation are driving both food prices and land-use changes, regionally and globally. This study presents a new model called Nexus Land-Use version 1.0 which describes these interactions through a generic representation of agricultural intensification mechanisms within agricultural lands. The Nexus Land-Use model equations combine biophysics and economics into a single coherent framework to calculate crop yields, food prices, and resulting pasture and cropland areas within 12 regions inter-connected with each other by international trade. The representation of cropland and livestock production systems in each region relies on three components: (i) a biomass production function derived from the crop yield response function to inputs such as industrial fertilisers; (ii) a detailed representation of the livestock production system subdivided into an intensive and an extensive component, and (iii) a spatially explicit distribution of potential (maximal) crop yields prescribed from the Lund-Postdam-Jena global vegetation model for managed Land (LPJmL). The economic principles governing decisions about land-use and intensification are adapted from the Ricardian rent theory, assuming cost minimisation for farmers. In contrast to the other land-use models linking economy and biophysics, crops are aggregated as a representative product in calories and intensification for the representative crop is a non-linear function of chemical inputs. The model equations and parameter values are first described in details. Then, idealised scenarios exploring the impact of forest preservation policies or rising energy price on agricultural intensification are described, and their impacts on pasture and cropland areas are investigated.

Interactions between food demand, biomass energy and forest preservation are driving both food prices and land-use changes, regionally and globally. This study presents a new model called Nexus Land-Use version 1.0 which describes these interactions through a generic representation of agricultural intensification mechanisms. The Nexus Land-Use model equations combine biophysics and economics into a single coherent framework to calculate crop yields, food prices, and resulting pasture and cropland areas within 12 regions inter-connected with each other by international trade. The representation of cropland and livestock production systems in each region relies on three components: (i) a biomass production function derived from the crop yield response function to inputs such as industrial fertilisers; (ii) a detailed representation of the livestock production system subdivided into an intensive and an extensive component, and (iii) a spatially explicit distribution of potential (maximal) crop yields prescribed from the Lund-Postdam-Jena global vegetation model for managed Land (LPJmL). The economic principles governing decisions about land-use and intensification are adapted from the Ricardian rent theory, assuming cost minimisation for farmers. The land-use modelling approach described in this paper entails several advantages. Firstly, it makes it possible to explore interactions among different types of biomass demand for food and animal feed, in a consistent approach, including indirect effects on land-use change resulting from international trade. Secondly, yield variations induced by the possible expansion of croplands on less suitable marginal lands are modelled by using regional land area distributions of potential yields, and a calculated boundary between intensive and extensive production. The model equations and parameter values are first described in details. Then, idealised scenarios exploring the impact of forest preservation policies or rising energy price on agricultural intensification are described, and their impacts on pasture and cropland areas are investigated

International audienceGlobalization drives a process of diet convergence among developing and developed countries that challenges the predictions about future patterns of food consumption. To address this issue, the objective of this article is to map the range of the possible future diet changes and to explore their impact on agriculture using the Nexus Land-Use model. This model computes agricultural intensification in the crop and livestock sectors at the global scale, based on an architecture accounting for the different types of food calories. By considering four scenarios built on distinct assumptions regarding diet convergence, this article sheds light on the pivotal role of diet changes as drivers of tensions on agriculture and land use and shows the uncertainty associated with processes of diet convergence for foresight exercises on food and agriculture. Finally, the interactions between food production and the other land-use patterns are explored by testing the sensitivity of our results to assumptions regarding biofuel production, deforestation, potential crop yields, and nutrient-use efficiency

Abstract. The central role of land-use change in the Earth System and its implications for food security, biodiversity and climate has spurred the development of global models that combine economical and agro-ecological drivers and constraints. With such a development of integrated approaches, evaluating the performance of global models of land-use against observed historical changes recorded by agricultural data becomes increasingly challenging. The Nexus Land-Use model is an example of land-use model integrating both biophysical and economical processes and constraints. This paper is an attempt to evaluate its ability to simulate historical agricultural land-use changes over 12 large but economically coherent regions of the world since 1961. The evaluation focuses on the intensification vs. extensification response of crop and livestock production in response to changes of socio-economic drivers over time, such as fertiliser price, population and diet. We examine how well the Nexus model can reproduce annual observation-based estimates of cropland vs. pasture areas from 1961 to 2006. Food trade, consumption of fertilisers and food price are also evaluated against historical data. Over the 12 regions considered, the total relative error on simulated cropland area is 2% yr−1 over 1980–2006. During the period 1961–2006, the error is larger (4% yr−1) due to an overestimation of the cropland area in China and Former Soviet Union over 1961–1980. Food prices tend to be underestimated while the performances of the trade module vary widely among regions (net imports are underestimated in Western countries at the expense of Brazil and Asia). Finally, a sensitivity analysis over a sample of input datasets provides some insights on the robustness of this evaluation.

In the XVIIIth century, Surinam had become a major subject of interest for Enlighted scholars as well as brokers, owing to agricultural successes and wealth. Its fame led to the writing of important and fairly reliable studies which can now be used as starting points for new analyses. During the same century the political situation had been rulled by conflictual relationships between the Colony and its Mother-country, which generated deep social unrest and troubles (slave revolts, plantocracy opposition to local government, confessionnal tensions between christians and jews...). From the end of the XVIIth century down to the 1750s, economic circumstances were clearly governed by sugar production, with a regular growth of peak exports in the period. In point of fact, Surinam plantation economy underwent deep transfers giving way to strong land merging trends. Such capitalization underlined the settlers' dependancy and debtor position upon metropolitan financial centers (Amsterdam and Rotterdam), and finally caused the development of an absented Landlordism in Dutch Surinam. As a matter of fact, this Dutch practice of colonial credit played a major role upon the sugar production trend : when compared to the financial structure of the plantations and prices evolution, a relatively low loan interest rate of 6% considerably increased the planters' debt. Hence, from 1750 on, a relative slow down of export peaks and even stagnation of production can be shown closely related to serious demonstrations within the Colony (slave revolts), due to such an increase of colonial loans and their ultimate negative effect. Finally, the Surinam example of sugar plantage is a remarkable indicator to measure these transfers of the proto-industrial era in what would become the «Thirld World».

«Dans l'univers mental « euraméricain » , l'Eldorado a été identifié à une véritable Terre Promise située quelque part aux confins de la Guyane. Cette identification emprunte les voies d'un processus cumulatif irrationnel évoluant dans le cadre normatif de l'histoire coloniale de l'Amérique méridionale du début du XVIe siècle, pour ne retrouver une certaine rationalité qu'au milieu du XIXe siècle. A ce titre, le processus en cause participe pleinement de l'opposition des rationalités et irrationalités déterminant fondamentalement l'agir humain, dans la définition intemporelle la plus large. Au fil de cette évolution mythologique, les formes de représentation et de savoir humains les plus variés interviendront pour consolider ou aider à la diffusion du mythe lui-même : géographie « expérimentale » de la découverte, droit des gens devenu aujourd'hui droit international, histoire, théologie, philosphie et même économie élémentaire. Ces représentations seront en outre les fruits, mûris au cours de plusieurs siècles, d'élaborations partagées ou disputées par des acteurs issus autant de la péninsule ibérique que de la France ou des États riverains de la mer du Nord (Grande-Bretagne, Pays-Bas, Confédération germanique élargie aux marches de l'Autriche...). Ce partage géographique a d'ailleurs indéniablement contribué à la mondialisation du mythe d'El Dorado. Au terme de multiples investigations, cette étude présente les circonstances à partir desquelles il est devenu possible, en cette fin de XXe siècle, d'élucider et d'expliquer les mécanismes de transfert et d'errance dans l'imaginaire humain d'un rite et d'une croyance fondés sur une pratique religieuse autochtone. Ainsi, la croyance en un royaume aux richesses fabuleuses, qui s'est fondée sur une réelle pratique religieuse née sur les bords de la région du lac de Guatavita (région de l'actuelle capitale de la Colombie, Bogota), s'est déplacée jusqu'à la Côte Noyée de la Guyane en passant par les contreforts de la cordillère des Andes et- la forêt amazonienne. De même, il est observé comment cet itinéraire du mythe représente, par-delà quantité d'entrelacs idéologiques, politiques ou économiques, une contribution essentielle à la formation de l'histoire culturelle guyanaise et plus largement latino-américaine. Et l'un des moindres paradoxes ainsi mis en évidence réside sans doute dans le fait qu'en dépit d'une notoriété rendue universelle grâce à une médiatisation des plus précoces de l'Histoire, la légende d'El Dorado est demeurée l'une des plus diffuses de celles conservées à ce jour par le souvenir humain.

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