The environment of Truffle

The "Tuber" may be found in the valley bottoms or on not too dry hillsides. The soil, partly rocky, is clayish-calcareous, rather compact, sometimes more compact on the surface, but with a lighter layer underneath. It may consist also of sand, gravel or even pebbles, but the subsoil is compact so that superficial roots can grow easily. The areas where truffles grow may be meadowy or with a thin vegetation cover, but free from brushwood and with a relatively high humidity.
On the other hand, a clayish-calcareous soil (when not too dry) offers a favourable condition to the life of symbiont trees, and namely: common oak (Quercus robur), Turkey oak (Q. cerris), durmast oak (Q. petraea), pubescent oak (Q. pubescens), black poplar (Populus nigra), white poplar (P. alba), eastern poplar (P. deltoides cv. carolinensis), tremulous poplar (P. tremula), pussy-willow (Salix caprea), osier willow (S. viminalis), white willow (S. alba), linden (Tilia platyphyllos), hop hornbeam (Ostrya carpinifolia), and hazel nut (Corylus avellana).
The sun exposure is not particularly important, but the grounds with a North, North-West exposure seem to be the best. The tree vegetation should be 50%, shrubs should be scarce or absent, grass should be 20-70%. Inland areas are better since the soil hydrography is kept constant by rainfalls which are more abundant on the hills than on the coast.
A prolonged drought in summer is not favourable to the growth of the T. magnatum and its symbionts which belong to the continental flora, i.e. the climate they grow in is characterized by a more remarkable seasonal temperature range. On the other hand, like all the mushrooms, truffles enjoy summer rains.
The most suitable areas are valleys sheltered from wind, where the soil is prevented from a quick drainage, as well as a temperature drop. The white truffle can grow at no more than 700 m above sea level. 
The soil pH may range from a minimum of 6,8 to a maximum of 8,5. The organic matter is better to be scarce.
Therefore, it is required to have a precise relation among environmental conditions, chemical composition and humidity of the soil, and climate conditions. In conclusion, the soil should preferably be marly-calcareous, at a height lower than 700 m, moderately windy but not too permeable, with a decent humidity in the upper layers even in the driest months, rather rich in limestone, poor in phosphorous and nitrogen, rich in potassium, with a 6,8-8,5 pH, poor in organic matter, soaked by spring and summer rains, possibly with rivers flowing nearby but no ponds, with a modest inclination (about 15%).
The Tuber melano-sporum grows well in a soil featuring a calcareous and/or calcareous-clayish substratum. The soil consists of rather thin grains and calcareous rubble cemented by marly matter, sand, sandstone and other filling materials.
These areas are often hilly, dotted with trees spaced out from six to twelve metres (depending on the age and the growth of the tree), thus making up thin woods with spots of wild vegetation.
Irregular cracks in the ground, typical insects of fruiting bodies and some traces of previous digging – all signs of the presence of truffles.
The T. melanosporum needs calcareous-gravelly (permeable) soil with a compact subsoil which favours the growth of roots on the surface. The percentage of clay shouldn’t be higher than 40%, otherwise the soil becomes too permeable to water and causes asphyxia. This kind of soil is very rich in calcium carbonate, and poor in organic remains. In the black truffle grounds, humus is almost abscent. It can also grow in soils richer in organic matter, but with little phosphorus and nitrogen.
The T. melanosporum lives in symbiosis mainly with pubescent oak (Quercus pubescens), German oak (Q. ilex), Turkey oak (Q. cerris), linden (Tilia platyphyllos), hazel nut (Corylus avellana), hop hornbeam (Ostrya carpinifolia), rockrose (Cistus spp.).
The most fruitful truffle grounds (according to the quantity and size of truffles) have a South or South-East exposure. The tree cover should be about 30%, shrubs are scarce or almost absent, grass is almost absent. 
A good light penetration is required, and therefore a good heating of the soil. Despite its xerophilia, long periods of drought – especially in summer – are not advisable. Both the inland hilly areas and the seashores are suitable. 
More rustic than the rare white truffle, this variety can be found up to 1.100 m above sea level. The soil pH is the most important parameter and may range from 7 to 8,5.
In conclusion, the soil must be permeable, ventilated, rather stony, rich in limestone, with a 7-8,5 pH, under 1.100 m, with a small amount of clay, poor in organic matter, having no ponds, being exposed to the sun (no North exposure except for some very hot and dry places), poor in phosphorous and nitrogen, rich in potassium. Iron may be useful as well. Recent studies carried out by the Experimental Institute of Study and Protection of the soil of Florence, have pointed out that the soils which are best in developing truffles (both black and white) are those featuring a quite unordered system, because the disorganization of materials favours the interconnection of empty spaces.
Therefore, the macro and micro porosity of the soil are fundamental.