IoT Sensors

Sensors
Nature is in effect a real time sensor with constant flux changes from various inputs. Trees do this by regulating the amount of water that moves from the soil solution into the roots, up through the xylem, and out to the atmosphere by opening or closing of stomatal pores. This cannot be achieved without the energy from the sun which is driving photosynthesis. With this relationship the cumulative use of water over a season and the resulting photosynthetic activity provides the plant sugars that move through the tree increasing total dry matter and or yield.

Although should the nutrients not be available in the soil solution, which is dependent on soil moisture, then yields can be reduced. If the paddocks are being over irrigated leaching can occur removing fertiliser from the rootzone resulting in reduced efficiency. Soil moisture sensors placed at a 15, 30 and 90cm intervals, common soil profile measurements, to monitor where the moisture levels are can help prevent deep drainage losses, and over or under irrigating which could lead to ineffective energy use. The recent energy audits have included soil sensors as part of the energy water nexus with some sites witnessing a reduction of up to 30% in water use.

Soil moisture sensors alone are not without issues. The contact with the soil is in comparison a very small sample of what may be occurring across a larger area (hectares) which can have varying soil properties (spatial variability). Further, it can get complex when two trees of the same species are close to one another, as they undertake Hydraulic Coupling, transferring water and nutrient through the root systems and between them.
Typically, pump and flow meter data is used to estimate the volume of water applied from an irrigation event. To improve the efficiency in tree crops it is becoming increasingly common to measure the volume of water moving through tree stems using sap flow meters. Water stress can also be measured using stem psychrometers. This allows growers to see when their trees are active (day or night), and to closely match the total applied irrigation water to tree water use at exactly the right time.
To achieve greater efficiencies, increase production while minimising resource use such as energy and water a suite of available sensors are available, these include;

• Energy- uses current transformers to measure the energy consumed at your circuit board, and also that generated from a renewable energy system
• Sap flow- uses a heater and two temperature sensing needles logging very low and reverse sap flow and data logging in litres per hour of water used by the plant. The water used is completely independent of evaporative losses in the soil, run off or through drainage.
• Plant Psychrometer- measures plant water potential considering environmental parameters such as solar radiation, temperature, humidity, wind speed and soil water. It can continuously log changes in plant water status/potential, which directly reflect the energy required to access water or the stress the plant is under. Useful for most crops including sugar cane, wheat, rice, maize, almond, grape, citrus, mango, coffee, avocado, greenhouse crops capsicum, cucumber, tomato.
• Soil moisture sensor- measures soil moisture with recommended install depths at 15,30 and 90cm. Useful to determine if the moisture is at root depth or being leached out through deep drainage losses.
• Stem diameter (Dendrometer) - measures the diameter of fruits, plants, and trees. Monitors the swelling and shrinkage of stems during the day and night. The maximum Daily Shrinkage (MDS), is the calculated difference in daily minimum and maximum stem diameter, is a commonly used for irrigation scheduling.  

• Light, photosynthetically active radiation (PAR)- light can be absorbed, reflected, or transmitted. The light wavelengths of 400-700 nm utilised by plants for photosynthesis. Lighting for plants is different from lighting for humans. Light energy for humans is measured in lumens, with light falling onto a surface measured as illuminance with units of lux (lumens per square meter) or foot candles (lumens per square foot). Light energy for plants, on the other hand, is measured as photosynthetic active radiation (PAR), with light falling onto a surface measured as photosynthetic photon flux density (PPFD) with units of μmol/s-m2. If PAR levels are low plant growth and carbon assimilation is reduced, while too much may damage the photosynthetic apparatus.

• Plant light interception efficiency- is a key determinant of carbon uptake by plants; plant productivity over seasonal timescales is approximately proportional to intercepted light. The measurement of fraction of intercepted PAR (f) is an indicator of a plant’s light use efficiency or its ability to convert sunlight into biomass.
• Infrared canopy temperature- accurate measurements of plant canopy temperature, which, along with other environmental variables, allows estimation of canopy transpiration and crop stress using a calculation such as Crop Water Stress Index (CWSI).
• Leaf wetness measures water on the canopy caused by rainfall, dew, or guttation. Leaf wetness duration (LWD) is a concern for the development of disease.
• Normalised Differentiation Vegetative Index (NDVI)- measures plant health. Leaf chlorophyll absorbs red light (FR- 680nm), and the cellular structure of the leaves strongly reflect near-infrared light (NIR- 730nm). When the plant is water stressed or diseased plant tend to absorb more of the NIR. Observing this change provides an indication of the presence of chlorophyll and therefore plant health.

​Along with the mentioned sensors there are many more which cover many other factors. Dam and tank water levels can also be monitored along with the ability to auto start pumps according to rules set by the software that displays the incoming data. Armed with this data improvements in efficiency can be made. ​