EVOLUTION OF SOILS ON SANDY FORMATIONS UNDER THE IMPACT OF CHESTNUT ORCHARD RECONVERSION

Within the framework of a research project entitled "Recovery and Exploitation of Abandoned Chestnut Groves in the Province of Bologna" an experimental station was set up by Pro Sementi S.p.A in the municipality of Granaglione (Bologna), where an abandoned chestnut grove is being reconverted to use as a source of both wood and chestnut fruit. In parallel with the strictly forestry-related activities, a soil monitoring program was started up with the aim of assessing soil evolution and changes in relation to the grove's reconversion. The monitoring was conducted over a two-year period on the same representative soil profiles in the area designated for reconversion to timber production (zone 1) and over a one-year period in the area reconverted to chestnut fruit production (zone 2). The typical soil in this Apennine region developed on a sandy substrate, is generally shallow in depth, and displays dystric characteristics and an acid reaction. Where the slope is greatest (>35%) it appears to have evolved little (zone 1), its thickness being limited by a layer of continuous hard rock (Endoleptic Regosols); in more gently sloping areas (zone 2) the thickness and degree of evolution increase (Dystric Cambisols). The profiles sampled in zone 1 showed a rapid physical deterioration of the already exiguous epipedon, induced by diffuse laminar erosion and further accentuated by the lack of tree cover, which by the end of the first year led to the nearly complete disappearance of litter and of the surface organic horizon. The chemical parameters that testify most clearly to this deterioration are linked to changes in organic carbon and the base saturation percentage. Over time it was possible to note a gradual and constant loss of total organic carbon (TOC) from the epipedon, with TOC falling from 76 to 70 g/kg after one week of heavy precipitation and to 42 g/kg after one year of clear-cutting; the humification index (HI), which was initially in line with the typical values for woods and meadowland, where humification processes prevail over mineralisation, showed values after one year indicating that the soil was deteriorating toward situations of intense mineralisation. The other humification indexes calculated reveal the same negative trend. Base saturation fell from 86 to 82% after the first week, eventually arriving at a value of 6% after one year of clear-cutting, with lixiviation of alkaline cations and a progressive increase in acidic cations. During the first year of monitoring an increase was also observed in the levels of Fe and Al in soil, with the values of Alox + ½ Feox (spodicity index) rising from 0.59 to 1.99. After two years of clear-cutting, the resumption of plant growth and non-clearing of underbrush permitted the formation of a new cover of turf, such as to favour a distinct countertrend both from a physical (reconstitution of the epipedon) and a chemical (accumulation of total organic carbon) standpoint. The humification indexes reveal a more marked trend toward humification processes as opposed to mineralisation. The conversion of the chestnut grove in the less sloping area did not show such a markedly negative trend from a physiochemical viewpoint.