Modeling traditional manuring practice: Soil organic matter sustainabilityof an early Shetland community?

Modeling of soil systems is an essential approach to discussions of the his torical dimensions of soil sustainability, but as yet there has been no for mal 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 Pap a Stour. Observations suggest that the model makes accurate predictions and can be used to develop and test hypothetical land management scenarios. Re sults suggest that within historic time the arable areas of Papa Stour were manured at a level above that required to maintain soil organic carbon lev els, and consequently the hill-land source of organic material was overexpl oited 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. Suc cessful rise of the CENTURY model in this historic context suggests that it may be applicable to questions of soil sustainability in other areas of th e North Atlantic region.