Now that black truffles start to being formed and summer is coming, irrigation is a must in most areas.
The truffle is a fungus suited to low water conditions, as shown by its tolerance to dry spells in the summer of 25-28 days without rain, depending on the soil type. Poor soil that is dry and porous facilitates the development of the long, scarcely branching roots beneficial to truffles. This water stress, in turn, promotes the production of lignins and tannins, which can be used later by the truffle mycelium.
A comparison of the statistics of precipitation and truffle production shows there to be a correlation between good production and precipitation rates of the order of 150 millimetres between June and August. They also show that each stage of the truffle’s development has its own water needs:
− in the north hemisphere, between April and May, irrigation to maintain the soil’s water reserves is only necessary if the winter has been very dry. Too much rain in this period seems harmful to the formation of truffle primordia. Some studies note that a few dry weeks at the end of April are beneficial.
− June seems to be the most sensitive month, both in terms of absence and excess of water. If the soil is already damp, a mulch may be sufficient.Water requirements in July do not appear to be decisive in limiting truffle growth. A month of July without rain, and even up to the middle of August, does not seem to be harmful. If it rains in June mulching may be sufficient. Conversely, abundant watering (30-50 millimetres) is necessary after a dry June
− From mid-August to mid- September, statistics show irrigation to be indispensable if it has not rained. In this period there do not appear to be any problems due to excess water, so irrigation of 25-50 millimetres every 10-20 days would be suitable
− As of mid-September excess water does seems to affect the production of truffles. An excessively dry autumn may also delay the start of the season and result in a mediocre gathering season.
In a recent study of our own, in which we quantified the mycelium of black truffle with molecular techniques at 40cm and 100cm from the tree trunk, we found that at 40cm the quantity of mycelium was 8 mg/g of soil, but at 1 meter is was reduced 1000 times to 0,008 mg/g!
A dripping system in the early years, even it makes more efficient the use of water, favor the truffle mycelium to remain in the bag moisture under drip and not to expand. A practical example would be to install in the first years micro sprinklers with variable flow rate and diameter, will aim of favoring the truffle mycelium to expand rapidly in the soil. Over the years we can move to other sprinklers of 35 l / h, with a diameter of 4 m ( in high density plantations ) , at doses of 6 hours every 10 days. The water and soil receives is about 16 l / m2. After 5-7 days looked soil moisture and if it is below 8 cm of the surface, back to water again.
Marcos S. Morcillo