Modeling Traditional Manuring Practice: Soil Organic Matter Sustainability of an Early Shetland Community?

Modeling of soil systems is an essential approach to discussions of the historical dimensions of soil sustainability, but as yet there has been no formal testing and application of such models. In this paper we first test the ability of the CENTURY agroecosystem model to predict soil organic carbon levels in anthropogenic plaggen soils from ethnographic and historical land management information of manuring practices on the Shetland island of Papa Stour. Observations suggest that the model makes accurate predictions and can be used to develop and test hypothetical land management scenarios. Results suggest that within historic time the arable areas of Papa Stour were manured at a level above that required to maintain soil organic carbon levels, and consequently the hill-land source of organic material was overexploited with no real apparent gain. Modeled evidence suggests that short-term observations of soil organic carbon levels would indicate a greater degree of manure application than was actually required over the longer term. Successful use of the CENTURY model in this historic context suggests that it may be applicable to questions of soil sustainability in other areas of the North Atlantic region.