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.

No abstract

Organic amendments combined with the sowing of gramineous grasses are effective for the early protection of burnt soils (BS) but cannot restore soil N status to pre-fire level; this has led to interest in combining their use with N₂ fixer legumes. The effectiveness of applying poultry manure (PM; 2 Mg ha^-1) and sowing legumes (<em>Lotus corniculatus, Lupinus polyphyllus </em>and <em>Trifolium repens</em>) for the early protection of BS was compared with that of applying PM + <em>Lolium perenne</em> and growing these four species without PM in a 3-month pot experiment, which also included a control consisting of an unburnt soil (US). In US, the shoot and root biomass increased as follows: <em>Trifolium </em>~<em> Lotus </em>&lt;&lt; <em>Lolium </em>&lt; <em>Lupinus.</em> Compared with those grown in US, plants grown in BS were smaller and weaker in three species (<em>Lupinus, Lolium</em> and <em>Trifolium</em>). The reverse was true for the four species grown in BS+PM, which showed the benefits of PM addition. In all the treatments, plant N uptake, which prevents soil-N losses, increased as follows: <em>Trifolium </em>~ <em>Lotus</em> &lt; <em>Lupinus </em>&lt; <em>Lolium.</em> The lack of nodules observed suggested that none of the legumes fixed atmospheric-N₂.