Canopy temperature sensors improve irrigation scheduling

A new sensor will allow growers to refine irrigation scheduling, saving water while maintaining yields.

Developed by a team of CSIRO researchers based out of the Australian Cotton Research Institute at Narrabri and funded through the Cotton Research Development Corporation, the new canopy sensor technology will be commercially available through Goanna Ag.

CSIRO Agriculture and Food research scientist Dr Michael Bange said while current tools that are used to help time irrigation focused on moisture status of the soil, new methodologies essentially asked how the plants were fairing.

"We are using the plants to tell us how stressed they are," he said.

"Soil based instruments and weather based approaches to irrigation scheduling are like getting an opinion.

We are using the plants to tell us how stressed they are

- Dr Michael Bange

"While opinions are valuable, we are using the canopy temperature system to inform us of the plants stress."

Dr Bange said the system worked by identifying and using different stress thresholds depending on the crop.

"The analogy is when you go to the doctor's surgery and they measure your temperature," he said.

"We use the underpinning biochemistry of the species to inform us whether it is stressed or not.

"As plants can't control their temperature, as their environment has less water they exhibit more signs of stress."

Dr Bange said while scientists have been aware for almost 100 years that canopy temperature indicated stress in plants, the key to practically applying this knowledge was constant monitoring combined with smart analytics and algorithms, which allowed for high stress events, such as a heatwave.

"If it is a really hot, or humid, day we can tell the reason the plant is stressed is the weather and not a lack of available water in the ground," he said.

"The key to this technology is we are monitoring the crop all the time."

Dr Bange said the sensor, which is commercially available through Goanna Ag, was recommended to be used in conjunction with a capacitance probe and weather station.

"It means you are measuring what is going on under the ground as well as in terms of the crop," he said.

"A common problem with using capacitance probes on their own is that often you will see stress effects too late.

"This system allows you to pick up the stress earlier and confirm you need to irrigate by looking at your soil moisture probe."

CSIRO Agriculture and Food research scientist Dr Hizbullah Jamali said the sensors monitored the plants in real time, allowing growers to make decisions in real time regarding irrigation scheduling before the stress levels affected yield.

"You can see the plant approaching a trigger point, where it needs the irrigation," he said.

"One of the things with a capacitance probe is growers will often follow a fixed water deficit, say 50 millimetres and I'm going to open the siphons.

"But sometimes what we have found is on a normal 35 degree day that 50mm might be fine, but to cope with a 40 degree day you might need to time your irrigation a bit earlier.

"We are no longer using a fixed approach, we are using what the plants need."

Dr Jamali said having both temperature and moisture sensors meant growers could manage risk better, particularly around whether they could delay an irrigation a few days if a rainfall forecast looked promising.

"Working with growers what we have noticed is that when there is rain predicted they may delay irrigation beyond their set moisture deficit," he said.

"With our system we have had feedback from growers that they can now look at the plant stress and decide whether the delay will affect the plant yield."

Dr Bange said growers could loose one to three per cent of their yield within a day of hitting the moisture stress thresholds.

"This system allows growers to avoid losses, while stretching irrigation and saving water by not irrigating too frequently," he said.

Dr Jamali said from a research perspective the technology was now being used to investigate managing crops with partial irrigation through the season.

"If you only have one irrigation you want to get the best out of it," he said.

Dr Bange said work was also being conducted to apply the technology to other high value irrigated crops.