Managing Irrigation in Truffle Farms During Summer
The art of truffle cultivation requires precision, particularly during Australia’s increasingly challenging summers. For truffle growers, managing irrigation is not just about keeping trees alive; it is about maintaining the delicate underground ecosystem to support truffle production.
This summer presents unique challenges…
The Bureau of Meteorology’s long-range forecast for January to April highlights that:
What does this mean for Australian Truffle Growers?
Higher Daytime Temperatures
Soil Moisture Effects
Increased temperatures cause more rapid evaporation from soil surfaces, creating several cascading effects:
Soil Biology Impacts
Temperature changes significantly affect soil microorganisms and biochemical processes:
Importance of Lower Overnight Temperatures
Lower overnight temperatures play several crucial roles in the lifecycle and development of Tuber melanosporum.
The temperature differential between day and night acts as a vital physiological signal for the fungus.
Cooler night temperatures create temperature gradients in the soil that promote gas exchange. As the surface soil cools, it increases air circulation within the soil pores, which is essential for:
Night cooling also provides crucial moisture management benefits:
The cooler night period allows both the host tree and fungal partner to recover from daytime heat stress. Energy reserves are replenished.
Potential Effect on Yield
When overnight temperatures remain too high, it can disrupt these natural cycles and potentially reduce truffle quality or yield. This is why traditional (natural) truffle-growing regions are characterised by significant diurnal temperature variations, particularly during the critical summer and autumn periods.
These changes can persist even after temperatures return to normal, as rebuilding soil biological communities and their functions takes time.
Know your soil type
The quantity of water needed will vary based on soil type. Clay-rich soils retain moisture better, but require careful management to prevent waterlogging, while sandy soils need more frequent irrigation.
Depending on soil type (assuming loam in this case), a ‘typical’ mature truffle farm may require a basis of between 15-20 litres per square metre (in and around the brûlé area), per week during summer.
View our guide on how to test your own soil’s texture and where it lands on the soil texture triangle by clicking on the image.
Soil Moisture Management
In an average summer, truffle farmers tend to irrigate deeply and less frequently, typically every 8-14 days depending on rainfall, heat etc. The amount of irrigation applied depends on indicators from soil moisture monitors. Some growers use the technique of replacing 50% of the evapotranspiration (ET) deficit for a period.
Only replacing 50% of ET is called deficient irrigation. This is ok in average summers with intermittent rainfall but doing it for long periods in more extreme summers will gradually deplete the soil profile of moisture. Growers using deficient irrigation must monitor the soil moisture down through the root profile to determine when longer and deeper watering is required.
Summer Extremes
During very hot summers, when temperatures exceed or are sustained above 35°C (95°F) for even a few days, the soil moisture should be carefully regulated to prevent both drought stress and oversaturation, either of which can damage the fungal network.
This will invariably mean irrigating more frequently.
Modern truffle farms employ sophisticated irrigation systems that typically utilise soil moisture and temperature sensors. These sensors, placed at various points throughout the truffle beds, provide real-time data about soil water content and temperature. The most critical zone is between 50–300 mm deep, where the majority of tree root activity, mycorrhizal activity and truffle formation occurs.
Visual Inspection
Even if you have soil moisture monitors, I recommend also doing regular visual soil inspections with a shovel so that you can learn about the variable soil characteristics of the plantation. If the soil surface is looking dry, open it up with a shovel and assess the soil moisture. Check the soil at the periphery of the brûlé area.
Slice straight down into the soil to approx. 300 mm deep. Make another cut approx. 30 mm behind the first slice, then extract the slice from the soil. Lay the soil slice on the grassed area and check the dark areas of the soil. The top area will likely be light in colour and become darker with visual signs of moisture down through the profile if there is water held in the sample. You could also use a ruler to measure just how far down the moist layer reaches. Feel the soil. The soil should feel damp.
Two days after an irrigation, when the soil has drained excess water, you should see, and feel, moisture in the soil down to 250 mm depth.
Micro Sprays
When using micro sprays, it is important to understand the ‘litres per hour’ (L/h) delivered by the emitter type, and the ‘diameter’ of the wetted area. You can measure this when the system is operating if it’s not too windy.
Younger farms may have emitters with a ‘restrictor’ tab still in place, to lessen the diameter of the wetted area. This conserves water and allows for irrigation of the critical zone around the young root system. When removed however, the wetted diameter is likely to be somewhere between 4 and 6 metres.
Measure It Accurately, Manage It Well
Measure the wetted area in square metres (m2) and divide the litres per hour delivered by the square metres. This will give you the amount of water you are applying to each square metre of soil. E.g. A 40 L/h emitter delivering over 4 square metres equals 10 L/m2 (equivalent to 10 mm). To deliver the equivalent of 20 mm per square metre, you will need to irrigate for 2 hours in this case.
If the restrictor tabs are removed (year 6-7, as the brûlé areas increase), you may now be delivering the same 40 L/h over 12-14 square metres, depending on emitter type. In this case, to deliver the same 20 mm per square metre, you would need to irrigate for 6-7 hours per section, each time.
If you are unsure about this, take a shovel and check the soil moisture depth after 3 hours of irrigation.
In my capacity as an industry consultant, I speak to many growers and have found that this concept is not clearly understood, leading to underwatering and stress on the mycorrhizae.
Drip Irrigation
For truffles, modern drip irrigation systems typically use 1 L/h or 1.6 L/h high tech drippers built into the pipe at 400 mm intervals.
Initially, one drip line either side of the tree is installed. The lines are incrementally moved away from the tree at 100 mm per year as the root area expands. A further two lines outside of these are installed in year 6 after planting. This system allows for the efficient and focused use of water, less evaporation, and in particular, the ability to irrigate in windy conditions without water loss.
In a typical 3 m x 7 m farm layout, the system will deliver approx. 14 L/h per tree (with two lines) and 28 L/h per tree when the second set of lines are installed.
In a loamy soil type, a drip irrigation system (employing 4 lines of 1 L/h emitters every 400 mm) would need to run for approx. 3 hours to wet a zone of 400 mm wide and 250 mm depth.
What If You Do Not Have Moisture Monitors?
Firstly, I would encourage you to purchase and retro fit a suitable soil moisture monitoring model to your irrigation system. This will not only ensure you have the correct information but also save water.
The system we use in our farm designs is the Toro Tempus® Ag. Download their info brochure here.
There are also a range of ‘portable’ soil moisture probes available on the market. These probes are designed for spot checking. Quality is sometimes an issue with these products, so it is essential to purchase a reputable brand.
Mulch mats and Natural Shading
For the first three years of the young tree’s life, a weed mat system protects the soil from drying out easily and most importantly, from competition from weed growth. We are also currently testing forms of natural shading systems and companion planting to reduce soil temperature and water loss.
Ground covers like native grasses can help retain soil moisture, though they must be carefully selected to avoid competing with the truffle mycorrhizae.
Spring and Autumn Irrigation
Contrary to a more consistent water application required in the heat of summer; when irrigating in spring and autumn, research suggests that controlled ‘water stress’ for short periods can stimulate truffle primordia formation, though the timing must be precise. This has led farmers to adopt deficit irrigation techniques, deliberately reducing water supply during specific growth phases to enhance truffle production.
Changing Climate
The success of summer irrigation in truffle farms depends on careful monitoring and quick response to changing conditions. As climate patterns continue to shift, the ability to adapt irrigation strategies becomes increasingly crucial for maintaining productive truffle harvests.
The agricultural/horticultural industries have been advised that each season is likely to present vastly different scenarios than we’ve seen in the past.