In the framework of the project "Study of the hazelnut agro-food chain in the Cimino-Sabatini productive district" (founded by the Italian Ministry of agricultural, food, and forestry policies), a survey on plant nutritional conditions and soil biological fertility was carried out, since soil and plant nutritional status are strictly interdependent. In particular, the typical pedo-climatic conditions of such an area suggested a possible vulnerability of these soils to hazelnut cultivation with consequences on both soil quality and plant nutritional conditions. The objective was to verify the ecological equilibrium of soil microbiota functionality together with the corresponding plant nutritional status, as detected by foliar analysis. The study was carried out on five representative hazelnut farms, chosen according to the cultivar (the main cv. is 'Tonda Gentile Romana'), the orchard management, the eventual occurrence of diseases and the planting age. Soil and leaf sampling were carried out according to standardised protocols, in order to minimise environmental variability. The main results did not show in general a direct relationship between the content of elemental nutrients in soil and plants, nor significant differences between soil quality indicators under healthy and sick trees. As a general trend, poor organic carbon stocks were stored in soils, both as total and as a microbial pool, comprising one organically-managed farm. However, no stress condition for soil microbial biomass activity was detected, probably due to adapting phenomena of soil micro-organism activity. Indication for a possible change in soil microbiota metabolism was deduced from data obtained in a young plantation with different cover crops under trees. Finally, foliar analysis showed values close to those established as provisional standard values of the cultivar 'Tonda Gentile' in the Province of Viterbo.
