Afforestation of overexploited agricultural soils: preliminary results on soil quality after 18 years from plantation

The issue of soil exhaustion or soil sickness, referring to the progressive loss of soil quality and decrease in fertility, has increased considerably in the last decades. Recent models predicted that around 200,000 km2 of degraded agricultural land in Europe will be abandoned between 2000 and 2040. Accordingly, this research aims at identifying an adequate forest management that might recover low fertility soils through an increase of soil organic matter (SOM) and soil quality, improving the ecosystem services of those areas. Thus, a former agricultural site was identified in Brusciana (FI) where, for the past 18 years, various forest associations for wood production have been established, namely white poplar and common walnut (K), which were also planted intercropped with other species such as hazelnut (C), Italian alder (A), and autumn olive (E). These forest stands were compared also to an adjacent agricultural field (X). Preliminary analyses on the topsoil (0-10 cm) showed a general low concentration of SOM (10-70 mg/g), although lowest values were found in X and highest in A, while the others were intermediate. The same trend was followed by soil urease enzyme, while β-glucosidase was lower in the agricultural field in comparison to the other stands, where no significance difference were reported Regarding the acid phosphomonoesterase, significant differences were found between A and X, while the remaining stands showed similar values. We have computed the AI3 index as a reference for soil quality, which showed a better values in A compared to X, indicating that soil quality increased up to 4 times compared to the beginning of the experiment, while the other values were comparable. In conclusion, our preliminary results showed that afforestation of tired agricultural soils improved soil organic matter and soil quality, in particular in the stands where Italian alder were planted.