SSSAJ: Volume 74: Number 6 • November–December 2010 1847 Soil Sci. Soc. Am. J. 74:1847–1860 Published online 30 Sept. 2010 doi:10.2136/sssaj2009.0412 Received 3 Nov. 2009. *Corresponding author (valerie.viaud@rennes.inra.fr). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Toward Landscape-Scale Modeling of Soil Organic Matter Dynamics in Agroecosystems Review & Analysis T he relevance of a landscape-scale approach to addressing environmental con- cerns in agricultural areas is being increasingly recognized. Many issues relat- ed to climate change, air quality, water quality, and soil conservation involve energy and matter luxes across space and time, and therefore require impact assessment and management options at integrated spatial scales. From that perspective, plan- ning activities and public policies (environmental assessment and management practices) are increasingly targeting integrated spatial scales rather than individual ields or farms, to account for interactions between sources and sinks through ei- ther natural or anthropogenic (mainly farm-scale) processes. For instance, the wa- tershed approach is widely used for implementing water-quality monitoring and planning programs in Europe (Gerrits and Edelenbos, 2004; Merot et al., 2008) as well as in North America (Maxted et al., 2009). his scale is also receiving increas- ing attention from soil scientists, especially for estimation of soil C stocks (Garten and Ashwood, 2002; Kravchenko et al., 2006). Soil organic matter is key to soil functioning in (agro)ecosystems, both inlu- encing and being inluenced by environmental conditions and luxes of matter and energy. First, SOM is a key component of soil quality because it directly afects soil chemical, physical, and biological properties and plays a crucial role in sustaining soil fertility (Tiessen et al., 1994) and environmental quality (Lal, 2009). Changes Valérie Viaud* INRA UMR 1069 SAS F-35000 Rennes, France Denis A. Angers Soils and Crops Research and Development Centre Agriculture and Agri-Food Canada Quebec City, Quebec, G1V 2J3 Canada Christian Walter Agrocampus Ouest UMR 1069 SAS F-35000 Rennes, France Because of its role in soil functioning, our ability to predict soil organic matter (SOM) dynamics, as inluenced by natural and anthropogenic processes, is essential to mitigating soil degradation, ensuring food security, and improving the global environment. Numerous mathematical models have been developed to predict the response of SOM to agricultural practices at the soil-proile or small-plot scales. he same models, coupled with spatial databases, have been applied to larger spatial extents, especially in response to the demand for national inventories of soil C sequestration potential. Modeling SOM dynamics must also be developed at an intermediate integrative level to better investigate the relative importance of transfer and transformation processes in SOM dynamics in agricultural landscapes. Predictive models at the landscape scale will facilitate the assessment of the impact of SOM dynamics on the environment and provide management guidelines at the farm and watershed levels. We review the existing approaches and outline the various needs toward an integrated modeling of SOM at the landscape scale. Landscape-scale modeling involves speciic land area representation and model requirements, which include: modeling SOM dynamics in the uncultivated elements of a landscape; simulating SOM distribution and diferen- tial dynamics along the soil proile; modeling SOM vertical and lateral luxes linked to erosion, dissolved organic matter luxes, and litter transfer; and modeling the spatial distribution of organic matter input and management practices. Even though progress is being made toward all of these aspects, a fully integrated framework for SOM modeling at the landscape level has still to be developed. his will only be possible with the design of a lexible, three-dimensional, spatially explicit representation of the landscape system and with the integration of functional interactions and organic matter transfer functions into the classical SOM modeling frameworks. Abbreviations: DOC, dissolved organic carbon; DOM, dissolved organic matter; OM, organic matter; SOM, soil organic matter. Published November, 2010