Assessment of soil health in orchards of “Rosa Romana” apple of different ages in the Northern Apennines (Italy)

Soil health is fundamental in maintaining and promoting overall ecosystem health and is defined as the continued capacity of soil to function as a vital living system, sustaining biological productivity as well as maintaining or enhancing the quality of air and water.

The aim of this study was to assess the health of soils under orchards where the cultivation of Rosa Romana, a local apple cultivar, is taking place. These orchards were located in the Bologna Apennine farms, ranged in age between 5 and 30 years and were implanted on former cropland. They were all grassed and cultivated following the principles of organic farming.

In this context, a comparison between the soils which belonged to orchards of at least 5 years in six farms with loamy texture was made. In each orchard, a morphological study of soils was carried out through the core of soil until 120 cm; then three mini pits were dug and sampled at a depth of 0-15 and 15-30 cm for physicochemical and biological analyses.

Soil health assessment was carried out via physicochemical and biological analyses and the calculation of two indexes: Dilly’s index (metabolic quotient to soil organic carbon ratio) that highlights the carbon use efficiency of soil microorganisms and the Index of Biological Fertility (IBF), obtained through the sum of scores assigned to significant parameters such as organic matter, microbial biomass C content and its activity.

Soil sampling and analyses were part of the Rural Development 2014-2020 of Emilia Romagna Region Project named “Rosa Romana apple of the Bolognese Apennines: organization of a quality organic supply chain”, which addresses to promote the sustainable management of agricultural areas in the Bologna Apennine by bringing together all actors involved in the cultivation, processing, and commercialization of this local apple cultivar.

The indicators related to soil health showed a difference between the orchards of less than ten years compared to the older ones, the latter displaying better overall health. Dilly’s index showed a growing microbial efficiency from the young orchards to the old ones and the same pattern is present in the IBF. This is due to the older orchards having a higher microbial C content and lower metabolic quotient in both soil layers, and higher SOM in the topsoil layer. These differences, which indicate a lower microbial stress and higher efficiency in the old orchards, may be due to the effect of reduced or null disturbance inflicted to the soil after the conversion of cropland into orchard, as they were no longer tilled and have a permanent grass cover. Moreover, in the topsoil the mineralization quotient and the nitrogen isotope ratio are lower in the older orchards, which may indicate respectively a tendency toward carbon accumulation and a higher fresh organic matter input to the soil of orchards of more than ten years.

These results may suggest that the promotion of the cultivation of the local Apennine apple variety “Rosa Romana” on former cropland in hill and mountain areas could promote the restoration of soil health.