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Adoption of appropriate conservation practices and cropping systems can result in increased soil organic carbon (SOC) sequestration in many agricultural production regions. The use of notill, other conservation practices, and complex crop rotations has greatly expanded over the past three decades in the Planalto region of the state of Rio Grande de Sul in southern Brazil, which covers nearly 8 million ha and is a major corn, soybean, and wheat production region. These crop production trends have resulted in increased SOC levels across much of the Planalto region as verified in field measurements. A modeling system has been constructed using Century 4.0, the interactive Century (i_Century) interface, and ArcGIS data layers to simulate the long-term SOC trends in the municipality of Ibirub, an 83,500 ha area in the central part of the Planalto region that is representative of agriculture throughout Rio Grande de Sul. The system is capable of accounting for cropping and management system trends from 1900 to the present, capturing periods of both decreasing and increasing SOC trends, as well as simulating projections out to the year 2050. Long-term simulations performed with the modeling system show that Ibirub SOC stocks declined 33% by 1980, increased 26% by 2005 in response to conservation tillage and other SOC enhancing practices, and that SOC could increase by 4 to 26% beyond original levels by 2050 depending on agricultural system production trends.