Soil moisture sensor enables precision farming

Researchers have developed a soil moisture sensor based around a metal-organic framework (MOFs) with a very high affinity for water, an advance that could enable farmers to deliver targeted crop watering.


Developed by a team at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, the sensor could help farmers to maximise food production and save water.

“Irrigation management can help improve crop quality, decrease agricultural costs and preserve water,” said Mohamed Eddaoudi, who led the research along with Khaled Salama.

MOFs are highly porous synthetic materials with a cage-like internal structure that can be tailored to host specific small molecules, including water.

“With their modular porous structure and easy functionalisation, MOFs are excellent candidates for sensing applications,” said Osama Shekhah, a research scientist in Eddaoudi’s team. “MOF thin films have already been incorporated into electronic devices, paving the way for their translation to real-world use.”

The MOFs in the study were selected based on their hydrolytic stability, water capacity and water uptake.

“We explored several different MOFs, including the highly porous Cr-soc-MOF-1 developed by our group at KAUST that can capture twice its own weight in water,” said Ph.D. student Norah Alsadun.

The team coated the MOFs onto an inexpensive interdigitated electrode microsensor that can be fabricated by inkjet printing or laser etching. When this sensor was inserted into moist soil, air in the MOF was displaced by water, altering its electrical capacitance, a process that can be detected and measured.

Each MOF device was tested in clayey and in loamy sand soil types, which can show significant differences in texture and water-holding capacity.

“Notably, the Cr-soc-MOF-1-coated soil-moisture sensor showed the highest sensitivity, of about 450 per cent in clayey soil, with a response time of around 500 seconds,” Salama said. The sensor’s response was highly selective for water even when various metal ions were present in the soil.

“We are now designing and developing a portable prototype MOF-based soil moisture sensor that can be easily used for control experiments in real-world, in-field measurements,” Eddaoudi said in a statement.

Salama believes that MOF-based soil-moisture sensors will advance the next-generation soil-moisture sensor technology, offering automated and precise irrigation systems.