Physical and chemical properties of soils from different geological formations affecting Tuber melanosporum plantations: a case study in Acqualagna area (central Italy)

Soil properties play a pivotal role in the fructification of the Périgord black truffle (Tuber melanosporum Vittad.). However, the precise manner in which soil composition influences truffle production remains unclear. This study considered three plantation sites located in Acqualagna (central Italy), an important area for the cultivation of black truffles. The sites differed in terms of productivity and geological terrains. Site 1, which produced 4 kg yr−1, was on Schlier sediments (marls and clayey marls; Miocene age), site 2, which yielded 12 kg yr−1, was on alluvial deposits (heterogeneous, mainly sandy gravels and gravels; Holocene age), and site 3 produced 40 kg yr−1 was on Scaglia variegata (alternating marly limestones, calcareous marls, and marls; Eocene age). A total of 62 soil samples were collected and analyzed for their physical, chemical, organic, and mineralogical composition. Among the samples a control area without the presence of truffle was included. The soils composition differed for the content in phyllosilicates and calcite which ranged from 124 to 398 g kg−1 and 98 to 450 g kg−1, respectively. Principal component analysis extracted three factors, accounting for 82% of the total variance. Factor 1 (46.2% of the variance) was strongly and positively correlated with sheet silicates, smectite, clay and negatively with skeleton (fraction > 2 mm). The soils from Scaglia variegata and Schlier clustered around the active carbonate content which was 266 g kg−1 in Scaglia and 250 g kg−1 in Schlier. These soils clustered also for the clay fraction (389 g kg−1 and 428 g kg−1, respectively) as well as for the smectite (268 g kg−1 and 307 g kg−1, respectively). In spite, the soils from alluvial deposits clustered per skeleton (638 g kg−1). In terms of soil productivity, it can be posited that the contribution of the skeleton was always dominant. The carbonate contents allow for the differentiation between intermediate soils (alluvial deposits) and low-productivity soils (Schlier). Additionally, the clay component was found to be high in both low (428 g kg−1) and high productivity soils (389 g kg−1). Conversely, it was low in medium productivity soils (125 g kg−1). The automatic linear modelling (ALM) indicated that among all of the variables considered in this study, six of them were included in the equation and explained 94.3% of the variation in soil classified as suitable for black truffle production. In particular, calcite was identified as the most important predictor variable, followed by available P and K. Regarding the influence of functional groups of humic substances, amide I (1641 cm−1) exerted a positive effect while lignin residues (1510 cm−1) had a negative one. The findings of this study may assist in the selection of optimal soils for black truffle cultivation.