Currently we’re depending on a translated/transposed Spanish text. Please add your regional experience.
The concept of Virtual water for truffle growing has yet to be tackled. This is a measure of the total water used in production of a good or service. Recycling washing water is a big issue in Spain (during drought years). The Virtual Water concept “was initially used to illustrate the advantages to water scarce nations of trade with other nations, rather than attempting to produce all goods locally. In recent times the concept has been applied to argue against production of commodities with high embodied water content, or to argue against their export on the basis that these activities waste scarce water resources. Virtual water estimates have also been used as an indicator of environmental damage of certain production activities”.
Because truffles are a luxury or non-essential produce, this has implications when we’re diverting irrigation water away from food crops.
Author: Marcos Morcillo from his trufflefarming blog
Watering for Black Truffle
The truffle is a fungus suited to low water conditions, as shown by its tolerance to dry spells. In the summer in can tolerate 25-28 days without rain, depending on the soil type. Poor soil that is dry and porous facilitates the development of the long, 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 January and February. They also show that each stage of the truffle’s development has its own water needs.
In the Southern hemisphere, between November and December, 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 November are beneficial.
January 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 February do not appear to be decisive in limiting truffle growth. A month of February without rain, and even up to the middle of March does not seem to be harmful. If it rains in January mulching may be sufficient. Conversely, abundant watering (30-50 millimetres) is necessary after a dry January.
From mid- March to mid-April 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-April 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, (Micofora and IRTA) we quantified the amount of mycelium of black truffle in the soil with molecular techniques. Measured at 40cm and 100cm out 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! (Mycelium also grows slowly.)
Marcos also has some suggestion for drip irrigation systems in the early years.
Using a drip system in the early years makes more efficient the use of water, favouring the truffle mycelium to remain in the area of moisture under the drip and not to expand. A practical application of this would be to install micro sprinklers in the first years (1- 3) using a variable flow rate and diameter, aimed at helping the truffle mycelium to expand rapidly in the soil. Over the years we can move to other sprinklers with a rate of 35 l/h, with a throw diameter of 4m ( in high density plantations ), at sessions of 6 hours every 10 days. The water and soil receives is about 16 l/sq.m. After 5-7 days look at the soil moisture physically and if it is dry below 8 cm of the surface, water again. You are trying to have water at least 20cm deep where you want the truffles to form. In established orchards that are re-innoculating it’s a little different, see this video.
See our Tools section for help in choosing the right Moisture probe.
How do you find out if you are watering properly?
While we’ve advanced our knowledge of much of the cycle of truffle production, how much to water and when to add it remains maddeningly untested.
Ian Hall et al in their book Taming the Truffle which has been regularly reprinted since its publication in 2007 and which has set many of the ‘growing’ ground rules both here and in New Zealand, say …
One might have thought that our lack of knowledge of what triggers the fruiting of edible ectomycorrihizal mushrooms and the factors controlling the size of harvest would have spawned a rash of field-based research, at least for the species that can be cultivated. However, publications on this topic are rare, so it remains a fertile area of research for someone with 20 years to spare – and the research funding to go with it. Hopefully, with irrigation becoming more popular in European truffières based on some spectacular experimental results and with irrigation being almost mandatory in the drier parts of of Australia and New Zealand, more reliable information on how much water should be applied and when will become available over the next decade.
Sorry Ian, but ten years on we still haven’t done more than confirm that we need to make sure the trees are watered in spring and summer when the truffles are forming. The Truffle and Wine Company in WA shared their extensive experiments in watering, driven by the concern that they were causing truffle rot by over watering (Harry Eslick author 2012 RIRDC report PDF). Their yields were mostly reporting the quantity of unusable truffle. I’m sure they are keeping on going data. Many individual growers have been keeping records for their own use, but the idea of sharing those or taking part in wide field-based research, for whatever reasons hasn’t happened.
What could this research be like?
Perhaps it starts with something like this.
Before the 2015 Conference in Queanbeyan, Wayne Haslam approached MEA (Measurement Engineering Australia) an Adelaide-based company, to demonstrate their soil moisture monitoring products at the field day. There’s a video of Sonia van Wegen’s presentation “Getting truffle irrigation right” in the media page from the 2015 Conference.
In a generous contribution to the ATGA members and to further the industry knowledge, MEA agreed to leave the sensors at Blue Frog Truffles for a year, and Wayne Haslam agreed to make the web interface open to members, so they could see in real time what soil moisture and soil temperature was like for the Sutton truffière. Details of how to access that data on the Green Brain website is here.
Wayne explains the method used and the feedback that he’s been getting (and after winter, he’ll share the details of any production increases based on the changed watering regime.)
“On the Greenbrain, the irrigation applied is shown in green lines as mm and the blue lines are rainfall in mm. I have been entering both of these. You can also alter period of the graph shown by going to the green stripe on the right hand menu and adjusting the duration shown. You see more of a pattern with longer periods (options are 1, 3 and 6 months).
As well as the remote probes, there is also a Gdot placed at 200mm depth in the gully, which shows 7 yellow dots for the wettest condition (soil suction <10Kpa) and one yellow dot (soil suction 60-100Kpa) This is visual and I usually don’t water until the Gdot gets down to two dots (soil suction 20-40Kpa).
(Wayne explains the Gdot operation in the video below).
I have no idea what is the ideal moisture content for mycelium, and everyone I have asked doesn’t seem to know, and I realise the best moisture content will vary with the soil type. That is why there are two probes in the Back Block section, with the North probe one being in gravelly light clay and the South probe in light sandy loam. If you do a screen print of each and compare them you will see the difference. They are over 20 metres apart across the soil change boundary.
I irrigate at night and can only do 2 stations over 8 hours and I have 8 stations, so that’s 4 day cycles at the driest time. Electricity is expensive (off peak rates cheaper at night) and I don’t want to over water. I know from last year’s experience that I didn’t irrigate nearly enough (given the poor truffle result and their depth) and this year the climate has been similarly dry and I have watered a lot, but still left it a little on the dry side, I think. Experience in WA showed huge rot levels resulting form over watering, as you probably know. I water the Back Block 10mm per session as there is more runoff and the trees are bigger and the Gully at 7.5mm due to smaller trees and the contour structure holds the moisture better.
Finally the 100 mm temperatures are interesting (just click on the temperature) and you can see that on the three probes, 2 in the Back Block and 1 in the Gully. It is now dropping on all the sites with daily fluctuations of 5 degrees, summer had a daily temperature up to 26C. The end of April usually sees a marked weather change so we can expect colder weather from here on.”
Feedback from other growers. Colin Carter has installed an MEA system and will be taking part in monitoring data collection. Timeless Hill Estate in WA has an installation as well. Andres Haas (Black Cat Truffles) also shared this comment.
Hi Wayne,
I bought one of the Gdot systems as an easy reckoner after seeing it in action on your truffière. It has been of some use, but marginal. It was quite a dry summer in Vic and after watering for 90 mins it would register 1 or 2 dots most of the time. This would go down to 0 dots over 5 days and I would water a day later. As the summer extended, it was drier still and no dots showed even after watering. It would be great if it was more sensitive still.
Thinking that it wasn’t working, I poured water on the sensor spot – cranked right up very quickly.
FYI – top of sensor block buried at around 10cm, 30cm in from sprinkler radius. 45 l/ph sprinklers, tabs still on. We can’t water much more than that.
Cheers,
Andres
A seal of approval from Marcos Morcillo
Hi Wayne and Fred,
I apologize for the delay, I just wanted to have enough time to see it calmly.
Thanks a lot Wayne for sharing me your link for your data loggers. We have been using them for some researches here but not really on commercial orchards. They give lots of good information on how effective waterings and rains are, how deep they arrive, so to manage “watering windows” more efficiently, depending on how deep you want your truffles to fruit.
The correlation of all these data during different seasons, in different areas with different soil textures and finally yields will show amazing new information.
I remember Wayne you send me a few years ago lots of data of your 2 different blocks, that I will recheck again, where I´ve seen you put a sensor in each one.
I do think this should be the future, not just eye observation a few days after each irrigation…
Marcos Morcillo Serra
Director – Micologia Forestal & Aplicada
micofora.com
http://trufflefarming.wordpress.com/
http://micofora.blogspot.com.es/
Background on watering
As we’ve moved to farmed production of truffles, we brought along the knowledge of how truffles (especially black) grow in the wild in the Mediterranean Basin regions of Italy, France and Spain (and beyond). That has, until now, dictated where we’ve chosen to plant in Australia. Regions with warm summers with late spring and autumn rain (or irrigation) and cold winters. In Europe areas with summer thunderstorms also seemed more productive.
In recent years, when spring and summers were hot and dry, and where the soil dried up to 20 cm deep, (which is where they find truffle in deep open soils), wild truffle production almost ceased. Areas however that had summer rain had only a slightly reduced output of truffle production. This has been a pattern that has continued up to the last winter season 2015-16 when in Spain, wild truffle was not available in commercial quantities and their harvesting period was shortened dramatically. It is clearly the lack of water, as irrigated truffiéres in the same regions who were watering to 30 cm deep (mostly because their re-innoculating trenches and ‘wells’ were at that depth), produced good crops.
Auxins (plant hormones) produced in the twig’s terminal buds stimulate root growth. Gibberellins (plant hormones) produced in the root tip stimulate canopy growth.
The tree balances root growth versus canopy growth by these hormones.
Soil factors that limit root growth will in turn influence canopy growth.
Storm damage or excessive pruning may reduce auxins, slowing root growth. Following storm damage, trees often put on heavy growth of water sprouts due to a low auxins/high gibberellins ratio (coupled with unobserved, limited root growth). This is followed by a decline in the canopy caused by the reduced root growth.
Author: David Whiting Colorado State University Extension
Results/key findings of 2012 ATGA, RIRDC and Truffle & Wine Co survey (PDF)
Results showed that truffle rot was more prevalent in truffles which had formed at the soil surface and
become exposed during the course of development. In addition, at the study site over 98% of all
truffles were found in the top 5 cm of the soil profile. To combat this growers commonly import soils
and re-cover exposed truffles, which is a labour intensive task. Results presented in this report show
that this practice is not effective at reducing the level of truffle rot or the incidence of insect damage
even when conducted at weekly intervals.
Of the four field experiments conducted, the only one to show promise as a method to reduce the
incidence of truffle rot was irrigation management. When irrigation was withheld over the summer,
until early February, the amount of rot observed at harvest declined dramatically from 29% in the
control down to 8% (p= 0.066). However this result can only be regarded as preliminary because of
the low level of statistical significance and low level of replication used. While the experiment
demonstrated a dramatic decline in the level of rot, there was no associated change in the depth at
which truffles were found, potentially indicating that multiple factors contribute to rot development.
Further work is urgently required to confirm these findings and identify the mechanism for this effect.
Bacterial isolation from three of the rotten truffles tested in May gave 95 isolates which were used for
further analysis. Inoculation of healthy truffles with groups of pure bacterial strains as well as a rotten
truffle extract failed to result in rot development. These preliminary data suggest that rot may not
solely be triggered by biotic agents. However, further work is required before this should be regarded
as fact, as experimental conditions can greatly influence the outcomes of this type of pathogenicity
trial. In addition, these early observations require confirmation more broadly across Australia because
of the implications for movement of infested material if rot were to be caused by biotic agents.
This initial study took a broad approach, considering all the variables potentially involved in the
problem and has identified several key contributing factors. More focused research is now required to
confirm these finding and further elucidate the mechanisms involved before firm management
techniques can be confidently prescribed to growers. In the mean time growers experiencing truffle rot
are advised to look at their irrigation regime and test the effects of reducing their water application.
Author Harry Eslick (now) Truffle and Wine Company.
Wonderful stuff