The judicious use of irrigation water in the agricultural sector assumes greater importance as pressures mount on securing sufficient food and water supplies worldwide. A sensitive soil moisture sensor has been designed by researchers from Saudi Arabia’s King Abdullah University of Science and Technology (KAUST) and Dhirubhai Ambani Institute of Information and Communication Technology (India) to help farmers tailor water use to the exact needs of crops.

A porous metal-organic framework (MOF) material with a high affinity for water layers the portion of an electrode microsensor that is inserted into soil. This chemically and hydrolytically stable chromium-based MOF — Cr-soc-MOF-1 — has the ability to adsorb nearly twice its weight in water. As the film draws water in from the soil, that water displaces some of the air within the MOF, changing its electrical capacitance proportionally. That change is detected by the microsensor, thus providing an electronic reading on the soil's moisture levels.

Tests conducted in clayey and in loamy sand soil types demonstrated significant differences in texture and water-holding capacity. As reported in ACS Applied Materials & Interfaces, the MOF-coated soil-moisture sensor showed the highest sensitivity of about 450% in clayey soil, with a response time of around 500 seconds.

The inexpensive interdigitated electrode microsensor can be fabricated by inkjet printing or laser etching and can be of value in improving agricultural water management efficiency.