Spatial dynamics of agricultural practices on a basin territory: a retrospective study to implement models simulating nitrate flow. The case of the Seine basin

Abstract

-Within an interdisciplinary research programme which has aimed at modelling the nitrate flow evolution in the whole Seine basin since the seventies, we propose a methodological process in order to reconstitute and spatialise cropping systems' dynamics, whose characteristics are used to implement the STICS agronomic model. This process makes use of both expert opinions and departmental or national agricultural statistics that are compared, step by step, in order to build the most reliable database in relation to the time and space scales considered. Data mining and statistical cartography methods are, respectively used to model the crop sequences' temporal evolution and to spatialise them over the spatial pattern of the agricultural districts. The results show an important spatial and temporal differentiation of the cropping systems, both in the cropping sequences developed and in the cultivation techniques employed. Crossing several information sources allows the identification of historical trends, but with a decreasing precision as we go back in time.cropping system / statistical cartography / data mining / inquiry / agricultural statistics

Typical features of particulate phosphorus in the Seine estuary (France)

“…The isotopic dilution method has been chosen to investigate exchangeable P at the scale of the estuary to improve coherence with other interdisciplinary studies that have been carried out on the Seine river, from the head waters to the mouth of its estuary. Such studies, for example Piren-Seine and Seine-Aval programmes, involve agronomists, who take into account the human activity within the agricultural basin (Mignolet et al, 2004), and hydro-biogeochemists, who study water quality and eutrophication at the scale of the whole hydrographic network Garnier et al, 2004aGarnier et al, , 2005Né mery et al, 2005). The isotopic dilution method, developed for soils (Fardeau, 1993;Morel et al, 2002), already applied to study exchangeable P in freshwater sediments (Capblancq et al, 1986;Vaas et al, 1987;Dorioz et al, 1998), has never been used before in estuaries.…”

Integrating expert knowledge and quantitative information for mapping cropping systems

“…Water management units convey some hydromorphic and topographic conditions and some constraints regarding access to water. Small agricultural regions, although defined in 1946, are still used as a spatial basis for statistics regarding agricultural activities and well represent uniform farming zones (Mignolet et al, 2004). The mapping was done using GIS software, and resulted in 67 SUs, with a mean area of 10,000 ha.…”

“…The kind of information depends on the person who provides it, his own perception of the study area, his memory and his capacity for synthesis (Mignolet et al, 2004;Becu, 2006). The information given is often a simplified perception of the study area: it allows objects or categories to be identified that are a representative but approximate view of the reality (Clavel et al, 2008).…”

“…This task often consists in establishing statistical correlations between variables of geo-referenced databases available on the study area. These databases can cover the entire study area, like digitized aerial photographs (Claessens et al, 2009), but they can cover it partially, like the TerUti land use database used by Mignolet et al (2004). In some cases, the task is made harder because data are semi-distributed (Bürgi et al, 2004).…”

“…To overcome this lack of data, one solution is to turn to experts for specifying such relationships to complement existing data (e.g. Mignolet et al, 2004). Another solution is to assume that relations between characteristics of cropping systems and location factors (soil and climate) are due to farmers' attempts to maximise profit.…”