The Very Grounds Underlying Twentieth-Century Authoritarian Regimes: Building Soil Fertility in Italian Libya and the Brazilian CerradoAbstract: This article analyzes the role of soil in the making of authoritarian regimes and illustrates twentieth-century practices and discourses related to fertility across the globe. It compares two different approaches to and understandings of soil fertility: the first emerged in North Libya under Italian Fascist rule (1922–1943), the second in Central Brazil during the civil-military dictatorship (1964–1985). We compare two soil-forming processes that changed physical and chemical properties of the original matter and were embedded within specific ideologies of modernization. In both cases, state agendas of agrarian production played a paramount role not only in socioeconomic projects but also as an instrument to suppress opposition. Technocratic and political aspects of building and maintaining fertility were interwoven, although in different patterns in the two countries. We show how the rejuvenation of land bled into the regeneration of communities through processes that anchored the self-definition and development of these authoritarian regimes, and argue that attempts at landscape transformations through agricultural activity and strategies of fertilization are inescapable features of dictatorships. In so doing, we elaborate the concept of “authoritarian soil.” The juxtaposition of these non-synchronous cases reveals how agricultural modernization developed throughout the twentieth century. Our study is rooted in environmental history and contributes to the ongoing dialogue between that field and science and technology studies. Its cross-temporal, comparative methodology draws upon sources and historiographical debates in English, Italian, and Portuguese.