The grounds of natural truffle-beds of Tuber magnatum Pico in hilly regions of Central Italy.

The soil color, in the studied truffle-beds, is generally grey, with sensible variations according to the moisture contents, from very light grey or pale yellow in dry samples to brownish grey or olive brown in the moist ones.

In 33.8% of the samples skeleton is completely lacking and in 54,4% it is present in modest quantity (< 10%); only 11,8% of the examined grounds contains more than 10% of > 2 mm fragments, with peaks around 25 %.

The soil structure is in prevalence (82,4%) angular blocky passing to subangular blocky with an increase of the sandy component and/or organic matter.

The content of sand shows the highest variabitity (1 - 61 % ) with constant clear prevalence of the fine fractions compared to the coarse ones ; a slightly smaller variability is showed by silt (24 - 73 %) and a still lower by clay (13 - 45 %).

Soil textures mainly range between loam (35,3%), silty-clay-loam (25%) , silty-loam (16,2%) and clay-loam (13,2%).

Generally lime is present in notable quantity (21% as averag value): it is missing only in the 4.4% of the samples and is present in modest quantity (< 10%) in the 19.1% of them ; 20.6 % of the grounds has a content of 10 - 20%, 30.9% with 20 - 30% and finally 25% has > 30% of lime, with peaks around 50 %.

Accordingly, the reaction show elevated values (mean value 7,85): except the 4.4% of soils with pH 7.3 - 7,5, the 39.7% of the grounds with reaction 7,55-7,95 and finally the 55.9% have an alkaline reaction (pH > 8); the maximum reached value is 8,25.

Organic matter is present in quantity between 0.95% and 5.80% (mean value 2,82%): precisely, in 36.8% of the grounds < 2% O.M. is present, in 32.4% between 2 and 4% and finally, in 30.8% of the soils, more than 4%.

The total nitrogen is present in varying quantity, from 0.068 to 0.278 % (mean value 0,131), and C / N ratio generally presents values between 10 and 15 (mean 12,3) showing a "calcic mull" humus.

According to high contents in clay and lime, soils are observed with a generalized lackin P (11 - 86 Kg/ha of available P2O5 ; mean value 26) and richness in K (270 - 1670 Kg/ha of exchangeble K2O; mean value 565).

Relatively to the different containts in organic matter and clay, oscillations in C.E.C. are observed between 22 and 26 meq/ 100 g of soil.

These soils are at the first evolution phases for a number of concomitant causes like the natural conditions (high erodibility of the materials, climatic factors, slope gradient) and the human factors (bad government of the waters and, in general, unappropriate ground management) that cause erosion.

The profile is reduced to a sequence A (B) C, or even an AC; very often in the alteration horizon the lime removal is not total (“Regosols”, “Alluvial soils” and “Brown calcareous soils”).

As concern the Soil Taxonomy, these soils belong to Typic Xerorthents, Typic Udifluvents and Xerofluvents, Typic and Fluventic Xerochrepts.