An investigation of former land-use activity through the physical and chemical analysis of soils from the Isle of Lewis, Outer Hebrides

In this study, the impact of human activity on the pedological environment of an agriculturally marginal site is investigated and the use of soils for analysing the site’s land-use history is discussed. For townships such as Knockaird (Isle of Lewis), for which detailed layout/location prior to crofting is not recoverable through plans, such analyses can offer a prospective approach. The nature of traditional Hebridean farming provides an essential background to this prospective or diagnostic approach using soil analysis. Arable farming, at least by the eighteenth century, was characterized by labour-intensive techniques of husbandry with vast inputs of labour required to help transfer manurial supplements such as manure, seaweed, peat and turf. These practices had a considerable impact on the soil environment. A stratified sampling system was undertaken over the township of Knockaird and 335 topsoil samples were collected along predetermined transect lines. Of the seven soil properties investigated (topsoil depth, pH, loss-on-ignition, K, P, Ca, Mg), enrichments of K and P clearly identify the suspected location of the pre-crofting settlement of Knockaird. Sites enriched only in P are a less reliable indicator of human habitation, possibly because P enrichment may result from additions of animal manure as well as by human habitation of an area. Enrichments of K and Ca respectively, observed running the length of two individual crofts, do not appear related to any pre-crofting use of the land but to recent crofting activity. The Ca anomaly suggests liming, whereas the enhanced K levels suggest additions of K-rich fertilizer. This study highlights the importance of identifying the spatial covariance of elements and the need for several lines of geoarchaeological evidence when interpreting former land-use activity through the prospective analysis of soils. Copyright.