Abstract

We analyzed the isotopic (13C and 15N) composition of a polycyclic terraced soil located in Santiago de Compostela (NW Spain) and compared it with previous results on total aluminum, iron and silicon and their fractionation by selective dissolution techniques. The aim was to recognize the imprints of land management changes, with particular attention to fertilization techniques applied during the use history of the terrace (~1600 y). The buried paleosol, found below the terraced layers, is considered to preserve the soil properties prior to the terrace construction. The isotopic composition (13C, 15N) provided evidence of extensive land use previous to the construction of the terrace, with the utilization of fire as liming and clearance tool. In the Late Antiquity and Early Medieval Ages the soil use was more intense and amendments with vegetal remains from nitrogen fixing shrubs were likely applied. Since the Early Middle Ages, animal wastes were used as a way to maintain or increase soil fertility because of an intensification of the agrarian use.
 Descifrando la evolución de las tecnologías agrarias durante los últimos ~1.600 años utilizando la huella isotópica (δ13C, δ15N) en un suelo aterrazado policíclico - Hemos analizado la composición isotópica (13C y 15N) de un suelo policíclico aterrazado situado en Santiago de Compostela (NO de España) y la hemos comparado con resultados geoquímicos previamente obtenidos de aluminio, hierro y silicio totales, así como las fracciones en las que se distribuyen estos elementos, mediante técnicas de disolución selectiva. El objetivo era reconocer las señales de los cambios de manejo del suelo agrícola, con especial atención a la aplicación de técnicas de fertilización, durante la historia de uso de la terraza (~1600 años). Se asume que el paleosuelo enterrado, que se conserva bajo los niveles de aterrazamiento, preserva las propiedades del suelo previas a la construcción de la terraza. La composición isotópica (13C y 15N) proporcionó evidencias de un uso extensivo del suelo con anterioridad a la construcción de la terraza, con la utilización del fuego como principal herramienta para el encalado y el clareo del terreno. Durante la Antigüedad tardía y la Alta Edad Media el uso del suelo se intensificó y se introdujeron técnicas de fertilización basadas en la adición de restos de vegetales de arbustos fijadores de nitrógeno. A partir de la Alta Edad Media se detecta el uso de abonos de origen animal, como medio para mantener o aumentar la fertilidad del suelo, ante una creciente intensificación del uso.

Highlights

  • The agricultural landscape of NW Spain is mainly inherited from ancient agricultural practices

  • In this traditional agricultural system, the land is divided between that used for intensive agriculture and plow and land used for growing slash and complementary activities, configuring what some authors called “concave landscape” (BALLESTEROS-ARIAS et al 2011)

  • Other noteworthy research on this issue was developed by Ballesteros-Arias et al (2006a, 2006b, 2010) from an archaeological point of view, drawing conclusions about the land division systems, the constructed landscape and the spatial distribution of the agrarian activity that greatly improved the comprehension of the current landscape and the history of its evolution

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Summary

INTRODUCTION

The agricultural landscape of NW Spain is mainly inherited from ancient agricultural practices. Previous research has successfully used colluvial soils for reconstructing deforestation, pollution and fire use history and past climatic or vegetation changes (KAAL et al 2008, 2011, 2013; MARTÍNEZ CORTIZAS et al 2009; LÓPEZ-MERINO et al 2012) We applied this capability of colluvial soils for the reconstruction of land-use evolution by the analysis of a polycyclic soil sequence in an agricultural terraced system in Monte Gaiás (Santiago de Compostela, NW Spain). A dual isotope approach with carbon (δ13C) and nitrogen (δ15N) is useful in studying SOM sources (PETERSON & FRY 1987) This investigation attempts to provide information on the evolution of the fertilization practices in Monte Gaiás terraced soils by studying the changes in the δ13C and δ15N isotopic fingerprint, together with the chemical properties and the previous knowledge about paleoclimatic conditions and archaeological information

MATERIALS AND METHODOLOGY
Isotopic measurements
Dating
Data Handling
RESULTS AND DISCUSSION
Inferred implications for the evolution of soil management
CONCLUDING REMARKS
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