Author: Marco Ferrazzani, NaanDanJain Italy 

Introduction

Truffles are fruit bodies produced by hypogenous fungi of the genus Tuber (Ascomycetes) that in nature are spontaneously formed in certain environments, in association (mycorrhizal symbiosis) with some forest plants such as oaks, hornbeams, hazelnut trees, linden trees, cedar trees, pines, poplars and willows, in well-drained soils.

They bear fruit throughout the year and can be found buried between the leaf litter and the soil. The most important factors in truffle production are the correct humidity levels of young trees, combined with the permeability of the soil.

Among the numerous truffle species present in Europe, only a few show a commercial interest: the white truffle (Tuber magnatum Pico), the black truffle (Tuber melanosporum Vitt.), and black summer truffles (Tuber aestivum). They are consumed mainly in Europe, and grown in France, Spain, Italy, Slovenia and Croatia. They are sold at prices as high as 3,000 Euro per kilo.

Truffle Cultivation in Italy

Truffles are grown in Italy, mainly in Piemonte, Toscana, Umbria, Abruzzo and other mountainous areas. Since 1980, an estimated 9,000 ha of orchards have been planted for truffle growth. An additional 120,000 additional trees are planted each year, supporting the cultivation of black truffles (80%), black summer truffles (15%), and white truffles (5%).

Truffle Irrigation

When irrigation of truffles started, a lot of attention was given to the symbiotic, occasionally weak, association between the fungi and the tree roots. This was followed by studies that concentrated on the ecological requirements, namely optimal weather and soil conditions. Irrigation was introduced to simulate the weather conditions that occurred in particularly productive years with outstanding truffle yields (70-150 kg/ha).

Drip irrigation or sub-surface irrigation methods have not proven viable for truffles, since the water completely saturates a given soil area for a certain period of time, removing all the oxygen. As a result, the fungi rot.

Micro-sprinkler irrigation is the best method for truffles. NaanDanJain has installed the 2002 AquaSmart flow-regulated micro-sprinkler in wide truffle-growing areas with by variable topography. The 2002 AquaSmart is equipped with the two-stage wetted diameter control: the first stage is used for small trees, and the second for the phase of major tree growth. Flow rates range from 20-95 l/h, simulating adequate rainfall without overstressing infiltration rate into the soil. Wetted area radius varies from 2.5 to 8 m.

Irrigation simulates the soil level humidity prevalent in years of favorable truffle yield, and enables us to stabilize the truffle production at 70-150 kg/ha, year after year.

Criteria for proper micro-sprinkler irrigation:

Make sure an analysis of water quality is conducted (acid pH may influence production).
Do not allow for soil saturation.
Irrigate only during early morning or evening hours, and avoid irrigating during the hottest hours.
Adapt irrigation to the type of soil to always ensure the right level of humidity into the soil. It should simulate ideal rainfall conditions.
Do not use drip irrigation.

Conclusion

Truffle irrigation, in addition to promoting the growth of young trees, helps to maintain the mycorrhizal fungi and aids the development of truffles. There is a close correlation between seasonal rainfalls and the production of truffles: if there is no rain in summer, there are no truffles the following winter.

Irrigation in truffle cultivation has changed from a 'rescue' practice to a 'farming' practice in order to increase and stabilize the production of fruiting bodies.

We express our thanks to the following people for contributing of this paper:

Dr. Gabriella Di Massimo, Professor in the Agricultural Faculty, University of Perugia

Mr. Moreno Moraldi, Director of Umbraflor

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