Management of tree crop irrigation using IoT sensors has reduced tree water use (macadamia) and prevented fruit drop (avocado)
New South Wales and Queensland, Australia
To minimise fruit drop (abscission) in avocado, it is necessary to mange the water stress the tree is under at key times in fruit production. Avocado trees are particularly affected by heat (and therefore water stress) at the time of flowering and fruit set. This water stress is caused by a decrease in soil moisture content and an increase in vapour pressure deficit.
Monitoring soil moisture content and vapour pressure deficit, can minimise the the risk of fruit drop by increasing watering events in response to alerts from a LoRaWAN sensor network.
As a result of the new measurement possibilities, when a period of extreme heat occurred during the flowering and fruit set of the avocado tree, the sensors detected events that cause significant plant water stress.
With two events, one of VPD greater than 5 kPA and one of low soil moisture content, the sensor data showed the high VPD and also the low soil moisture content. The soil moisture event was observed in both the soil moisture data and the dendrometer data, as the trees experienced increased daily shrinkage.
These events were observed to coincide with increased fruit drop during the low soil moisture/increased daily shrinkage. With this new knowledge, an irrigation system will be installed to minimise these risks in the future based on the sensor data.
Reducing the quantity of water used for irrigation, but not reducing crop yield is possible. Reductions of between 15-20% in water applied during winter and early spring compared to the same period in the prior year were achieved by using sap flow monitoring (accounting for rainfall pattern difference between years).
A producer can be confident that all the trees’ water requirements are being met with an improved irrigation schedule developed by closely observing the constant feedback from SFM1x Sap Flow Meters.
Macadamia flowering in Southern Queensland, Australia, commences around September 1st and lasts for approximately one month. It is important to maintain high water use and low water stress during flowering to maximise potential yield. To achieve this, the SFM1x Sap Flow Meters were installed late in August. These sensors indicated the commencement of water stress as the sap flow rate steadily dropped from approximately 20 litres to 12 litres per day (per tree). When irrigation started on September 2nd, daily water use (or sap flow) increased from approximately 12 litres to 24 litres.
Not only does improving irrigation management practices result in reduced water use, there are other benefits.
Reducing over irrigation, and the subsequent reduced soil moisture levels, also reduced soil pathogen pressure and resulted in healthier trees, especially on the heavier soils.
The lower operating soil moisture levels created by the improved scheduling have also increased the residual buffering capacity of the soil profile against over-saturation during heavy rainfall events, substantially aiding in erosion control and vigour management.
For these installations the following sensors were used;
The multiple sensors used required LoRaWAN connection to bring the data to a single dashboard in real-time. Connected using IoT Nodes, the sensors utilise a real-time clock to allow for exact measurements
The SFM1x Sap Flow Meter is a powerful tool for irrigation scheduling, being able to measure the daily water use of a tree or plant. With this knowledge, and combined with knowledge on the available water reserves, growers can efficiently allocate their water stock over the crucial events in the growing season.
The SFM1x can be connected to the decision making dashboards using LoRaWAN (SFM1x-L1) or CAT-M1/NB-IoT (SFM1x-C), as well as for local downloading using Bluetooth (SFM1x-UB).
The Vaisala WXT-536 is a rugged and reliable all-in-one weather station that measures rainfall, wind speed and direction, air pressure, and temperature and humidity.
Using multidepth soil moisture sensors, accurate measurement of soil moisture content in the root zone and subsurface areas can be undertaken. This ensures appropriate irrigation schedules are developed and maintained.
Micro-climate sensors are installed both outside and within the avocado tree canopy to measure temperature, relative humidity and subsequently allow the calculation of VPD.
The DBS60 sensor measured the avocado tree trunk diameter. Dendrometers provide an indication of the plant water stress due to the ability to measure the shrinkage and expansion of the tree they are measuring; with a resolution of 0.1 mm, the DBS60 can measure the small changes that show that a tree is entering a stressed period.
Data from the sensors is transmitted over a private LoRaWAN network to a Gateway utilising a fixed-point network connection. Eagle.io is used for data storage / visualisation and alarming of soil moisture, VPD and Maximum Daily trunk Contraction (MDC).
The system notifies operators (via SMS and email) when irrigation is necessary to avoid plant water stress and potential fruit drop, hence crop loss.