Environmental Modelling & Software 16 (2001) 361–375 www.elsevier.com/locate/envsoft Modelling long-term C dynamics in croplands in the context of climate change: a case study from Ohio Fatih Evrendilek a,* , Mohan K. Wali b a Department of Landscape Architecture, Faculty of Agricultural Engineering, Mustafa Kernal University, 31034 Antakya-Hatay, Turkey b Environmental Science Graduate Program and School of Natural Resources, The Ohio State University, 2021 Coffey Road, Columbus, OH 43210-1085, USA Received 16 March 2000; received in revised form 18 August 2000; accepted 19 November 2000 Abstract A simple dynamic model (CBUDGET) was developed to quantify long-term carbon (C) dynamics in croplands. By using inde- pendent datasets (on continuous wheat) from the Waite Permanent Rotation Trial (Australia) and from Northwest Ohio, the tests of its performance resulted in R 2 values of 0.85 and 0.80, respectively, between observed and simulated values. Our model suggests that the rate of residual C addition into the soil is the primary factor that controls soil organic carbon (SOC) storage for Ohio croplands under continuous corn, wheat and oats for the period 1866–1996 and continuous soybean for the period of 1924–1996. The interaction of CO 2 -fertilization and a temperature increase of 0.5°C decreased mean SOC levels for the selected crops over the same periods. A multiple linear regression model (MLR) relating carbon dioxide (CO 2 ) emissions to population growth, affluence and energy intensity with an R 2 of 0.99 indicates the significance of underlying causes of anticipated climate change. The MLR model thus serves to capture a more complete picture of anthropogenic sources of global climate change than considering agricultural activities only in exploring locally and regionally mitigative and preventive measures towards global climatic stability.  2001 Elsevier Science Ltd. All rights reserved. Keywords: Cropland sustainability; Ecosystem modelling; Carbon dynamics Software availability Name of software: CBUDGET Developers: F. Evrendilek and M.K. Wali Hardware required: IBM compatible personal computer 486 or higher (4 MB RAM) Software required: Windows 95 or later and STELLA 4.0 or higher Program language: STELLA graphic language Availability: available from first author at no charge 1. Introduction Ecosystems are open interacting systems of biotic (autotrophs and heterotrophs), abiotic (climate, geomor- * Corresponding author. Tel.: +90-326-245-5844 ext. 1031. E-mail address: fevrendilek@mku.edu.tr (F. Evrendilek). 1364-8152/01/$ - see front matter  2001 Elsevier Science Ltd. All rights reserved. PII:S1364-8152(00)00089-X phology, geology, soil, relief, hydrology), and natural and human-induced disturbance components in given spatial-temporal scales (Tansley, 1935; Lindeman, 1942; Odum, 1969). Biogeochemical cycles (atmospheric, hydrologic and sedimentary cycles) connect ecosystems to one another by enabling a continuous exchange of energy and matter among the atmosphere, hydrosphere, lithosphere and biosphere. The carbon (C) budget is glo- bally-closed and stoichiometrically-coupled with the cycling of nutrients across the ecosystems, thus, mani- festing a dynamic balance between dissipative processes (e.g., respiration, decomposition and mineralization) and ordering processes (e.g., growth, development, regener- ation, and formation of humus). The magnitude of deficit or surplus in the C budget of any ecosystem in a given time and space, therefore, can serve as a significant ecos- ystem-level indicator because it reveals deviations from sustainability under current patterns of human-induced disturbances (Wali et al., 1999). Fossil fuel combustion, and ecologically-destructive changes in land use and cover such as deforestation,