From Marl to Rock Powder: On the History of Soil Fertility Management by Rock Materials.
Verena Winiwarter, Institute for Soil Science, Univ of Natural Resources and Applied Life Sciences, Peter Jordan-Strasse 82, Vienna, Austria and Winfried E.H. Blum, Institute for Soil Science, Univ of Natural Resources and Applied Life Sciences, Peter Jordan-Strasse. 82, Vienna, Austria.
Unlike organic fertilizers such as manure, which intervene into the solar energy budget of soils, marl, lime, rock phosphate and other rock powders intervene into the orogenic energy cycles of soils, thus on a more profound level. The materials all exhibit slow or retarded effects, making it difficult to set exact dosages and determine cause-effect-relations. Nevertheless their potential at rejuvenating soils has made them interesting agents of intervention over the course of human history. We will look into their history to situate them in the larger context of the changes in social metabolism their use is connected to and as a contribution to understand the history of knowledge about soils and the management of their fertility, in which the fertilizing effect of inorganic substances has constituted one of the great puzzles. The role of marl as fertilizer has not received due attention in soil science and its history. In the historical overview in Russell's Soil conditions and plant growth, no reference to marl is made, and other works treat marl only in passing. Yet, rock materials have been used to increase soil fertility at least since the 1st century CE. Pliny the Elder wrote in his natural history (Book 17, 44), that marl had been introduced to Roman agriculture by Germanic people, from whom the material also got its name. Pliny was aware of the long-term effect of marling, a procedure which was recommended on a decadal scale only. In this contribution, we will pick up the history of marl and other rock materials in the 18th century. We will look at the descriptions of marling (and liming) in agricultural and horticultural manuals, at the first attempts to analyze marls and at the few references we have on peasants actually using marl, who even rediscovered the practice for themselves. In this reconstruction of the history of knowledge we aim to show how at first sight unrelated discourses such as Alchemical theory (e.g. Johann Glauber), practical expertise by agricultural pioneers (e.g. Phillip Miller, 1776; Christoph Bernhard, 1764; Balthasar Ehrhart, 1753 and other relatively unknown writers), the first chemical analyses (Johann Gerhard Andreae, 1769) and the mounting pressure to increase harvests in the 18th century all contributed in various ways to the development of integrated theories of soil fertility, which took account of the fertilizing power of marl and lime. The proven effect of marl challenged those who held that fertility was an all-organic phenomenon, and thus made way for the agricultural knowledge revolution of the 19th century. It reverberates in the work of Albrecht Thaer, who devoted ample room to discuss their role and function. Rock materials also allow to show how agricultural fertility management is connected to the technical possibilities of a society on a larger scale: The practical limit to the use of marl in pre-industrial times was transportation. Rock powder became available as a by-product of the fossil-fuel driven mineral sector of modern economies, technical and energetical limits to fertilization become apparent in this example. Rock materials continue to be used for fertility management. Their complex interactions with the biology of soils still pose several questions. Also, the parent material of the soil and the acidity at time of application are to be taken into account when applying rock powder, a fact that is seldom mentioned in their marketing. Using Austria as an example, the paper will question the marketing of rock powder and show, how misleading information is still used in material directed to farmers. Marl was known in the 18th century as a agent to make fathers rich and grandsons poor. Interventions into the long-term orogenic energy budget of soils, despite being a part of sustainable, integrated management of fertility, need to be undertaken with care. The long history of knowledge allows access to a reservoir of information which could and should be tapped for the development of sustainable soil management.