The historic man-made soils of the Generalife garden (La Alhambra, Granada, Spain)

We studied the soils of the Patio de la Acequia garden of the Generalife, a palatial villa forming part of La Alhambra, a World Heritage Site in Granada, Spain. This garden, which is estimated to be around 700 years old, is the oldest historical garden in the Western World. The soils are man-made cumulimollihumic-calcaric (hypereutric, anthric) Regosols. Noteworthy amongst the main pedogenic processes, in relation to the human activities of cultivation, irrigation and tillage, are horizonation, melanization (the contents of organic carbon varied between 0.59% and 8.87%, and those of P₂0₅ extracted with citric acid between 723 mg kg⁻¹ and 7333 mg kg⁻¹, with maximae in the Ap horizons) and structure formation. The soil fabric, studied at the ultramicroscopic level using scanning electron microscopy, is of laminar and partition-walls' type in the lower horizons, depending on the microped zones. The partition-walls' fabrics found are different to those of the possible pre-existing sedimentary fabrics. These are numerous lithological discontinuities and at least two burials, leading us to deduce that there have been two main stages of filling with materials in the formation of these soils. The first is Arabic-Medieval (13th century), when the garden was created, its surface being some 50 cm below the level of the paved area of the present patio. In the deeper parts, the materials employed in the fill are similar to the in situ soils of the zone, unaffected by the buildings. The second stage is Christian (15th century to the present day). During this period the Medieval garden was gradually buried under a layer of materials from the nearby soils and/or sediments mixed with manure until the surface was only just below the level of the paved area of the patio. In this work we discuss the difficult classification of these relatively little studied soils. In spite of their being clearly related to human activity, they are not classified as Anthrosols in the FAO system (1998) because soil materials cannot be classified as anthropopedogenic or as anthropogeomorphic.