The grounds of the natural truffle-beds of Tuber melanosporum Vitt.

The soil color is generally brown (from light yellowish brown to dark reddish brown) with weak variations according to the moisture contents. The soil structure is usually subangular blocky, granular with increase of sandy fraction or organic matter content.

The percentage of skeleton varied from 9 to 92% (general average 52,8%) with most values next to the average.

The percentages of sand, silt and clay result more heterogeneous. The sand has a mean value of 33.5% but the sand content changes much from a sample to another: the least value is 0.8% and the maximum one overcomes 80%.

The silt is the more abundant fraction (mean value 41,8%) and varied from 8% to more than 80%.

Generally, clay is less represented (general average 24,8%) with a least value of 6% and a maximum of 68,5%.

As concern the physical parameters, most grounds are rich in skeleton, with a silty-loam or sandy-loam texture.

This character is more accented in Abruzzo region where higher amounts of silt and the lower ones of clay are recorded.

In this region the truffle-bed soils are very loose and usually deep; probably for these reasons the fructification of the truffles takes place at bigger depth as regards to the Umbrian ones.

The pH is the more uniform parameter among those examined, presenting a mean value of 8.00 (from 7.05 to 8,25).

Most part of the pH value is next to 8 (the least one of 7.05 is an exception referring to a sample beside a chestnut wood).

The lime presents fairly elevated average values (29,6%) with peaks at 83 %. Rarely it is contained in small quantity. The active lime represents on average 1/ 3 of the total.

The content of organic matter is also very varying but relatively high. In the Abruzzo truffle-beds the average content is 3,85%, a lower value compared to the other Regions, where it is present from a minimum of 1.1 to a maximum of 17.4% with a mean value of 4,58 that represents fairly elevated quantities as regards to the agrarian grounds situated in the same environments.

The total nitrogen presents normally low and enough varying values (general average 0,23%).

The content of available P2O5 is from low to medium for most samples. K2O is present in medium-high quantity.

The exchangeble Ca++ value has resulted low only in those samples with notable presence of Mg++ and Na+.

Mg++ is always well represented except for any rare situation of absence.

Sulphur, determined like soluble sulfates, is contained in good quantity in each sample (beyond 100 ppm) while in others, considered poorly gifted, it has values < 50 ppm.

Mo and Cu are always present with values considered sufficient; Zn and Mn were low (< 1 ppm) only in some soils.

Bo shows high variability ; Fe often presents average contents.

Generally, the natural soils situated in proximity of the "beds" belong to thick "brown" or "brown calcareous soils", developped from decarbonation clays of the underlying limestones and have a A1 Bw C R profile.It is not infrequent a secondary enrichment in lime.

Less frequent A1 C and A1 R profiles, referable to "Regosols", "Lithosols", and "Rendzina soils".

As concern the Soil Taxonomy, these particular ground belong to Orthents or Arents. There is also a presence of Typic, Lithic and Dystric Xerochrepts and Eutrochrepts , Typic and Lithic Xerorthents, Typic and Entic Rendolls , and sporadic Lithic Rhodoxeralfs and Typic Palexeralfs.

The greater changements suffered by soils triggered by the truffle harvesting, concern the profile (homogenize), the increase of skeleton and lime in the superficial horizons, raising of the pH, reduction of the content in organic matter, a light lowering of C/N ratio, increase of macroporosity and the inside drain.