One of the most practical lectures at the last conference in Cahors was the one about irrigation in black truffle orchards done by Carlos Colinas. For the first time we get some specific data about it. Congrats to the whole team!
They already published a work where they showed as the first years for Quercus ilex to water 50% of potential evapotranspiration increased black truffle mycorrhization in your trees. This 50% equals to a water potential from -1,5 MPa and -o,35 MPa.
In a 22 years old evergreen oak plantation in Teruel they set 3 watering regimes. This is 32 l/m2 every 2-3-5 weeks and they harvested more truffles when watering every 2 weeks.
Results show how it is better to do not leave water potential to drop below -1 MPa for more than one week during the summer.
During the questions and discussion after Colinas speech, Gilberto Bragato made a quite interesting appreciation: he said that water potential is directly related to soil pore sizes, so some water potential made possible to plant roots to absorb water but not to small fungal mycelium or bacteria that may be 3microns diameter…
If anyone interested just found this table with the relations:
Here you can see another unit, the water potential (pF) that was as well used by Le Tacon, who found that when pF3 or pF4 no truffles fruit.
BTW, now that we are in Tuber magnatum season, Gilberto Bragato just made a reiew of soil characteristics for this truffle. See reference at the bottom.
As a conclusion for the mycorrhizae it looks that a dry “window” at mid summer may be good, but for truffle fruiting this research shows that a stress period in summer is no good at all.
Marcos S. Morcillo
Oliach, D., Fischer, C. R., Colinas, C. (2016). Soil water potential relation to truffle productivity. In: Abstract book of The eighth international workshop on edible mycorrhizal mushrooms (IWEMM8). Oral presentation. 10-17 october 2016, Cahors, France.
Le Tacon F, Delmas J, Gleyze R, Bouchard D (1982) Influence du régime hydrique du sol et de la fertilisation sur la fructification de la truffe noire du Perigord (Tuber melanosporum Vitt.) dans le Sud-Est de la France. Acta Oecol-Oec Appl 3:291–306